Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2017	Mar. 01, 2018	Jun. 30, 2017
Document and Entity Information
Entity Registrant Name	Onconova Therapeutics, Inc.
Entity Central Index Key	0001130598
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Smaller Reporting Company
Entity Public Float			$ 17.8
Entity Common Stock, Shares Outstanding		18,946,163
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	FY

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 4,024	$ 21,450
Receivables	59	31
Prepaid expenses and other current assets	820	1,588
Total current assets	4,903	23,069
Property and equipment, net	64	152
Other non-current assets	12	12
Total assets	4,979	23,233
Current liabilities:
Accounts payable	6,186	5,323
Accrued expenses and other current liabilities	3,335	4,382
Deferred revenue	455	455
Total current liabilities	9,976	10,160
Warrant liability	1,773	3,401
Deferred revenue, non-current	4,091	4,545
Total liabilities	15,840	18,106
Commitments and contingencies
Stockholders' (deficit) equity:
Preferred stock, $0.01 par value, 5,000,000 authorized at December 31, 2017 and 2016, none issued and outstanding at December 31, 2017 and 2016
Common stock, $0.01 par value, 25,000,000 authorized at December 31, 2017 and 2016, 10,771,163 and 6,759,895 shares issued and outstanding at December 31, 2017 and 2016	108	68
Additional paid in capital	350,514	342,484
Accumulated other comprehensive income	3	(31)
Accumulated deficit	(362,316)	(338,224)
Total Onconova Therapeutics, Inc. stockholders' (deficit) equity	(11,691)	4,297
Non-controlling interest	830	830
Total stockholders' (deficit) equity	(10,861)	5,127
Total liabilities and stockholders' (deficit) equity	$ 4,979	$ 23,233

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Consolidated Balance Sheets
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	25,000,000	25,000,000
Common stock, shares issued	10,771,163	6,759,895
Common stock, shares outstanding	10,771,163	6,759,895

Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Consolidated Statements of Operations
Revenue	$ 787	$ 5,546
Operating expenses:
General and administrative	7,405	9,178
Research and development	19,119	20,071
Total operating expenses	26,524	29,249
Loss from operations	(25,737)	(23,703)
Change in fair value of warrant liability	1,628	3,988
Other income, net	30	62
Net loss before income taxes	(24,079)	(19,653)
Income taxes	13	14
Net loss	(24,092)	(19,667)
Net loss attributable to Onconova Therapeutics, Inc.	$ (24,092)	$ (19,667)
Net loss per share of common stock, basic and diluted (in dollars per share)	$ (2.68)	$ (4.44)
Basic and diluted weighted average shares outstanding (in shares)	9,000,326	4,426,639

Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Consolidated Statements of Comprehensive Loss
Net loss	$ (24,092)	$ (19,667)
Other comprehensive income (loss), before tax:
Foreign currency translation adjustments, net	34	(9)
Other comprehensive income (loss), net of tax	34	(9)
Comprehensive loss	(24,058)	(19,676)
Comprehensive loss attributable to Onconova Therapeutics, Inc	$ (24,058)	$ (19,676)

Consolidated Statements of Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Common Stock	Additional Paid in Capital	Accumulated deficit	Accumulated other comprehensive income (loss)	Non-controlling interest	Total
Balance at Dec. 31, 2015	$ 25	$ 328,564	$ (318,557)	$ (22)	$ 830	$ 10,840
Balance (in shares) at Dec. 31, 2015	2,546,419
Increase (Decrease) in Stockholders' Equity (Deficit)
Net loss			(19,667)			(19,667)
Other comprehensive loss				(9)		(9)
Exercise of stock options		3				3
Exercise of stock options (in shares)	403
Stock-based compensation		3,929				3,929
Shares issued in connection with reverse stock split (in shares)	110
Issuance of common stock and pre-funded warrants, net	$ 37	8,949				8,986
Issuance of common stock and pre-funded warrants, net (in shares)	3,599,786
Issuance of common stock upon exercise of warrants	$ 4					4
Issuance of common stock upon exercise of warrants (in shares)	419,493
Issuance of common stock, net	$ 2	1,039				1,041
Issuance of common stock, net (in shares)	193,684
Balance at Dec. 31, 2016	$ 68	342,484	(338,224)	(31)	830	$ 5,127
Balance (in shares) at Dec. 31, 2016	6,759,895					6,759,895
Increase (Decrease) in Stockholders' Equity (Deficit)
Net loss			(24,092)			$ (24,092)
Other comprehensive loss				34		34
Stock-based compensation		1,710				1,710
Issuance of common stock, net	$ 40	6,320				6,360
Issuance of common stock, net (in shares)	4,011,268
Balance at Dec. 31, 2017	$ 108	$ 350,514	$ (362,316)	$ 3	$ 830	$ (10,861)
Balance (in shares) at Dec. 31, 2017	10,771,163					10,771,163

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Operating activities:
Net loss	$ (24,092)	$ (19,667)
Adjustment to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	88	96
Change in fair value of warrant liabilities	(1,628)	(3,988)
Stock compensation expense	1,710	3,929
Changes in assets and liabilities:
Receivables	(28)	1,473
Prepaid expenses and other current assets	768	244
Accounts payable	863	1,902
Accrued expenses and other current liabilities	(1,047)	653
Deferred revenue	(454)	(455)
Net cash used in operating activities	(23,820)	(15,813)
Financing activities:
Proceeds from the sale of common stock and warrants, net of costs	6,360	17,420
Proceeds from the exercise of stock options		3
Net cash provided by financing activities	6,360	17,423
Effect of foreign currency translation on cash	34	(9)
Net (decrease) increase in cash and cash equivalents	(17,426)	1,601
Cash and cash equivalents at beginning of period	21,450	19,849
Cash and cash equivalents at end of period	$ 4,024	$ 21,450

Nature of Business	12 Months Ended
Nature of Business	Dec. 31, 2017
Nature of Business
Nature of Business	1. Nature of Business Reverse Stock Split All common stock, equity, share and per share amounts in the financial statements and notes have been retroactively adjusted to reflect a one-for-ten reverse stock split which was effective May 31, 2016. The Company Onconova Therapeutics, Inc. (the "Company") was incorporated in the State of Delaware on December 22, 1998 and commenced operations on January 1, 1999. The Company's headquarters are located in Newtown, Pennsylvania. The Company is a clinical-stage biopharmaceutical company focused on discovering and developing novel small molecule product candidates primarily to treat cancer. Using its proprietary chemistry platform, the Company has created an extensive library of targeted anti-cancer agents designed to work against specific cellular pathways that are important to cancer cells. The Company believes that the product candidates in its pipeline have the potential to be efficacious in a variety of cancers. The Company has three clinical-stage product candidates and several preclinical programs. In 2011, the Company entered into a license agreement, as subsequently amended, with SymBio Pharmaceuticals Limited ("SymBio"), which grants SymBio certain rights to commercialize rigosertib in Japan and Korea. In 2012, the Company entered into a development and license agreement with Baxter Healthcare SA, the predecessor in interest to Baxalta GmbH (together with its affiliates, "Baxalta"), pursuant to which the Company granted an exclusive, royalty-bearing license for the research, development, commercialization and manufacture (in specified instances) of rigosertib in all therapeutic indications in Europe. The Baxalta agreement terminated effective August 30, 2016, at which time the rights the Company licensed to Baxalta reverted to the Company at no cost. The Company has retained development and commercialization rights to rigosertib in the rest of the world, including the United States. During 2012, Onconova Europe GmbH was established as a wholly owned subsidiary of the Company for the purpose of further developing business in Europe. In April 2013, GBO, LLC, a Delaware limited liability company, ("GBO") was formed pursuant to an agreement with GVK Biosciences Private Limited, a private limited company located in India, ("GVK") to collaborate and develop two programs using the Company's technology platform. The two preclinical programs sublicensed to GBO have not been developed to clinical stage as initially hoped, and the Company is in discussions with GVK regarding the future of GBO. On May 31, 2016, the Company amended its certificate of incorporation to effect a 1 for 10 reverse stock split of its common stock and to decrease the number of authorized shares of common stock from 75,000,000 to 25,000,000. Liquidity The Company has incurred recurring operating losses since inception. For the year ended December 31, 2017, the Company incurred a net loss of $24,092,000 and as of December 31, 2017 the Company had generated an accumulated deficit of $362,316,000. The Company anticipates operating losses to continue for the foreseeable future due to, among other things, costs related to research, development of its product candidates and its preclinical programs, strategic alliances and its administrative organization. At December 31, 2017, the Company had cash and cash equivalents of $4,024,000. The Company will require substantial additional financing to fund its operations and to continue to execute its strategy. These conditions raise substantial doubt about the Company's ability to continue as a going concern within one year after the date that the financial statements are issued. From its inception through July 2013, the Company raised significant capital through the issuance of ten series of preferred stock. On July 30, 2013, the Company completed its initial public offering (the "IPO") of 594,167 shares of the Company's common stock, par value $0.01 per share ("Common Stock"), at a price of $150.00 per share. The Company received net proceeds of $79,811,000 from the sale, net of underwriting discounts and commissions and other offering expenses. Immediately prior to the consummation of the IPO, all outstanding shares of preferred stock automatically converted into shares of Common Stock at the applicable conversion ratio then in effect. In October 2015 the Company entered into a purchase agreement with Lincoln Park Capital Fund, LLC ("Lincoln Park"). Upon execution of this purchase agreement, Lincoln Park purchased 84,676 shares of the Company's Common Stock for $1,500,000. Subject to the terms and conditions of the purchase agreement, including the effectiveness of a registration statement covering the resale of the shares, the Company may sell additional shares of its Common Stock, having an aggregate offering price of up to $15,000,000 to Lincoln Park from time to time until December 1, 2018. On January 5, 2016, the Company entered into a securities purchase agreement with an institutional investor providing for the issuance and sale by the Company of 193,684 shares of the Company's Common Stock and warrants to purchase 96,842 shares of the Company's Common Stock for aggregate net proceeds of $1.6 million (See Note 18) On July 29, 2016 the Company closed on a rights offering of units of common stock and warrants. The Company issued 3,599,786 shares of common stock, 3,192,022 tradable warrants and 656,400 pre-funded warrants in connection with the rights offering. Net proceeds were approximately $15.8 million. (See Note 18) On April 26, 2017 the Company closed on an underwritten public offering of 2,476,190 shares of Common Stock. On May 17, 2017, the Company sold an additional 363,580 shares as a result of the underwriter's exercise of its over-allotment option. Net proceeds from these transactions were approximately $5.3 million. (See Note 18) On November 14, 2017 the Company closed on a registered direct offering to select accredited investors of 920,000 shares of common stock. Net proceeds were approximately $1.1 million. (See Note 18) On February 12, 2018 the Company closed on an offering of units of common stock and warrants. The Company issued 7,005,000 shares of common stock, pre-funded warrants to purchase 2,942,500 share of common stock, and preferred stock warrants to purchase 1,044,487.5 shares of Series A convertible preferred stock. Each share of Series A convertible preferred stock is convertible into ten shares of common stock. Net proceeds were approximately $8.7 million. (See Note 19) The Company has and may continue to delay, scale-back, or eliminate certain of its research and development activities and other aspects of its operations until such time as the Company is successful in securing additional funding. The Company is exploring various dilutive and non-dilutive sources of funding, including equity financings, strategic alliances, business development and other sources. The future success of the Company is dependent upon its ability to obtain additional funding. There can be no assurance, however, that the Company will be successful in obtaining such funding in sufficient amounts, on terms acceptable to the Company, or at all. The Company currently anticipates that current cash and cash equivalents will be sufficient to meet its anticipated cash requirements into the third quarter of 2018. Accordingly, management has concluded that substantial doubt exists with respect to the Company's ability to continue as a going concern within one year after the date that these financial statements are issued.

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2017

Summary of Significant Accounting Policies

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Basis of Presentation

The consolidated financial statements are prepared in conformity with accounting principles generally accepted in the United States ("GAAP"). The financial statements include the consolidated accounts of the Company, its wholly-owned subsidiary, Onconova Europe GmbH, and GBO. All significant intercompany transactions have been eliminated.

All common stock, equity, share and per share amounts in the financial statements and notes have been retroactively adjusted to reflect a one-for-ten reverse stock split which was effective May 31, 2016.

Segment Information

Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker, or decision-making group, in deciding how to allocate resources and in assessing performance. The Company views its operations and manages its business in one segment, which is the identification and development of oncology therapeutics.

Use of Estimates

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenues, expenses, other comprehensive income and related disclosures. On an ongoing basis, management evaluates its estimates, including estimates related to clinical trial accruals, warrant liability, and allocation of consideration for revenue recognition. The Company bases its estimates on historical experience and other market-specific or other relevant assumptions that it believes to be reasonable under the circumstances. Actual results may differ from those estimates or assumptions.

Concentrations of Credit Risk and Off-Balance Sheet Risk

Financial instruments that potentially subject the Company to concentrations of credit risk are primarily cash and cash equivalents. The Company maintains a portion of its cash and cash equivalent balances in the form of money market accounts with financial institutions that management believes are creditworthy. The Company has no financial instruments with off-balance sheet risk of loss.

Cash and Cash Equivalents

The Company considers all highly liquid investments with original or remaining maturity from the date of purchase of three months or less to be cash equivalents. Cash and cash equivalents include bank demand deposits, marketable securities with maturities of three months or less at purchase, and money market funds that invest primarily in certificates of deposit, commercial paper and U.S. government and U.S. government agency obligations. Cash equivalents are reported at fair value.

Fair Value of Financial Instruments

The carrying amounts reported in the accompanying consolidated financial statements for cash and cash equivalents, accounts payable, and accrued liabilities approximate their respective fair values because of the short-term nature of these accounts. The fair value of the warrant liability is discussed in Note 8, "Fair Value Measurements."

Property and Equipment

Property and equipment are stated at cost, less accumulated depreciation. Property and equipment are depreciated using the straight-line method over the estimated useful lives of the assets. Leasehold improvements are amortized over the useful life of the asset or the lease term, whichever is shorter. Maintenance and repairs are expensed as incurred. The following estimated useful lives were used to depreciate the Company's assets:

		Estimated Useful Life
Lab equipment		5 - 6 years
Software		3 years
Computer and office equipment		5 - 6 years
Leasehold improvements		Shorter of the lease term or estimated useful life

Upon retirement or sale, the cost of the disposed asset and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is recognized.

The Company reviews long-lived assets for impairment when events or changes in circumstances indicate that the carrying value of the assets may not be recoverable. Recoverability is measured by comparison of the assets' book value to future net undiscounted cash flows that the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the book value of the assets exceeds their fair value, which is measured based on the projected discounted future net cash flows generated from the assets. No impairment losses have been recorded through December 31, 2017.

Warrant Accounting

Common stock warrants are accounted for in accordance with applicable accounting guidance provided in ASC Topic 815, Derivatives and Hedging—Contracts in Entity's Own Equity (ASC Topic 815), as either derivative liabilities or as equity instruments depending on the specific terms of the warrant agreement. (See Note 4).

The Company's warrants that are classified as liabilities are recorded at fair value. The warrants are subject to remeasurement at each balance sheet date and any change in fair value is recognized as a component of change in fair value of warrant liability in the consolidated statements of operations. The Company has both tradable and non-tradable warrants. At December 31, 2017, the tradable warrants are classified as level 1 liabilities and the Company uses the Nasdaq quoted market price to estimate the fair value of the related derivative warrant liability. The non-tradable warrants are classified as level 3 liabilities and the Company uses the Black-Scholes pricing model to estimate the fair value of the related derivative warrant liability. (See Note 8 for a discussion of the fair value hierarchy).

Foreign Currency Translation

The reporting currency of the Company and its U.S. subsidiaries is the U.S. dollar. The functional currency of the Company's non-U.S. subsidiary is the local currency. Assets and liabilities of the foreign subsidiary are translated into U.S. dollars based on exchange rates at the end of the period. Revenues and expenses are translated at average exchange rates during the reporting period. Gains and losses arising from the translation of assets and liabilities are included as a component of accumulated other comprehensive income. Gains and losses resulting from foreign currency transactions are reflected within the Company's results of operations. The Company has not utilized any foreign currency hedging strategies to mitigate the effect of its foreign currency exposure.

Revenue Recognition

The Company's revenue is generated primarily through collaborative research and license agreements. The terms of these agreements contain multiple deliverables which may include (i) licenses, (ii) research and development activities, (iii) participation in joint steering committees and (iv) product supply. The terms of these agreements may include nonrefundable upfront license fees, payments for research and development activities, payments based upon the achievement of certain milestones, royalty payments based on product sales derived from the collaboration, and payments for supplying product. In all instances, revenue is recognized only when the price is fixed or determinable, persuasive evidence of an arrangement exists, delivery has occurred or the services have been rendered, collectability of the resulting receivable is reasonably assured, and the Company has fulfilled its performance obligations under the contract.

For arrangements with multiple elements, the Company recognizes revenue in accordance with the Financial Accounting Standards Board ("FASB") Accounting Standards Update ("ASU") No. 2009-13, Multiple-Deliverable Revenue Arrangements ("ASU 2009-13"), which provides guidance for separating and allocating consideration in a multiple element arrangement. The selling prices of deliverables under an arrangement may be derived using third-party evidence ("TPE"), or a best estimate of selling price ("BESP"), if vendor-specific objective evidence of selling price ("VSOE") is not available. The objective of BESP is to determine the price at which the Company would transact a sale if the element within the license agreement was sold on a standalone basis. Establishing BESP involves management's judgment and considers multiple factors, including market conditions and company-specific factors, including those factors contemplated in negotiating the agreements, as well as internally developed models that include assumptions related to market opportunity, discounted cash flows, estimated development costs, probability of success and the time needed to commercialize a product candidate pursuant to the license. In validating the BESP, management considers whether changes in key assumptions used to determine the BESP will have a significant effect on the allocation of the arrangement consideration between the multiple deliverables. The Company may use third-party valuation specialists to assist it in determining BESP. Deliverables under the arrangement are separate units of accounting if (i) the delivered item has value to the customer on a standalone basis and (ii) if the arrangement includes a general right of return relative to the delivered item, delivery or performance of the undelivered item is considered probable and substantially within the Company's control. The arrangement consideration that is fixed or determinable at the inception of the arrangement is allocated to the separate units of accounting based on their relative selling prices. The appropriate revenue recognition model is applied to each element and revenue is accordingly recognized as each element is delivered. Management exercises significant judgment in determining whether a deliverable is a separate unit of accounting.

In determining the separate units of accounting, the Company evaluates whether the license has standalone value to the collaborator based on consideration of the relevant facts and circumstances for each arrangement. Factors considered in this determination include the research and development capabilities of the collaborator and the availability of relevant research expertise in the marketplace. In addition, the Company considers whether or not (i) the collaborator could use the license for its intended purpose without the receipt of the remaining deliverables, (ii) the value of the license was dependent on the undelivered items and (iii) the collaborator or other vendors could provide the undelivered items.

Under a collaborative research and license agreement, a steering committee is typically responsible for overseeing the general working relationships, determining the protocols to be followed in the research and development performed and evaluating the results from the continued development of the product. The Company evaluates whether its participation in joint steering committees is a substantive obligation or whether the services are considered inconsequential or perfunctory. The factors the Company considers in determining if its participation in a joint steering committee is a substantive obligation include: (i) which party negotiated or requested the steering committee, (ii) how frequently the steering committee meets, (iii) whether or not there are any penalties or other recourse if the Company does not attend the steering committee meetings, (iv) which party has decision making authority on the steering committee and (v) whether or not the collaborator has the requisite experience and expertise associated with the research and development of the licensed intellectual property.

Whenever the Company determines that an element is delivered over a period of time, revenue is recognized using either a proportional performance model, if a pattern of performance can be determined or a straight-line model over the period of performance, which is typically the research and development term. Progress achieved under the Company's various clinical research organization contracts are typically used as the measure of performance when applying the proportional performance method. At the end of each reporting period, the Company reassesses its cumulative measure of performance and makes appropriate adjustments, if necessary. The Company recognizes revenue using the proportional performance model whenever the Company is able to make reasonably reliable estimates of the level of effort required to complete its performance obligations under an arrangement. Revenue recognized under the proportional performance model at each reporting period is determined by multiplying the total expected payments under the contract (excluding royalties and payments contingent upon achievement of milestones) by the ratio of the level of effort incurred to date to the estimated total level of effort required to complete the performance obligations under the arrangement. Revenue is limited to the lesser of the cumulative amount of payments received or the cumulative amount of revenue earned, as determined using the proportional performance model as of each reporting period. Alternatively, if the Company is not able to make reasonably reliable estimates of the level of effort required to complete its performance obligations under an arrangement, then revenue under the arrangement is recognized on a straight-line basis over the period expected to be required to complete the Company's performance obligations.

Incentive milestone payments may be triggered either by the results of the Company's research efforts or by events external to it, such as regulatory approval to market a product or attaining agreed-upon sales levels. Consideration that is contingent upon achievement of a milestone is recognized in its entirety as revenue in the period in which the milestone is achieved, but only if the consideration earned from the achievement of a milestone meets all the criteria for the milestone to be considered substantive at the inception of the arrangement. For a milestone to be considered substantive, the consideration earned by achieving the milestone must (i) be commensurate with either the Company's performance to achieve the milestone or the enhancement of the value of the item delivered as a result of a specific outcome resulting from the Company's performance to achieve the milestone, (ii) relate solely to past performance and (iii) be reasonable relative to all deliverables and payment terms in the collaboration agreement.

For events for which the occurrences are contingent solely upon the passage of time or are the result of performance by a third party, the contingent payments will be recognized as revenue when payments are earned, the amounts are fixed and determinable and collectability is reasonably assured.

Royalties are recorded as earned in accordance with the contract terms when third party sales can be reliably measured and collectability is reasonably assured.

Research and Development Expenses

Research and development costs are charged to expense as incurred. These costs include, but are not limited to, license fees related to the acquisition of in-licensed products; employee-related expenses, including salaries, benefits and travel; expenses incurred under agreements with contract research organizations and investigative sites that conduct clinical trials and preclinical studies; the cost of acquiring, developing and manufacturing clinical trial materials; facilities, depreciation and other expenses, which include direct and allocated expenses for rent and maintenance of facilities, insurance and other supplies; and costs associated with preclinical activities and regulatory operations.

Costs for certain development activities, such as clinical trials, are recognized based on an evaluation of the progress to completion of specific tasks using data such as patient enrollment, clinical site activations, or information provided to the Company by its vendors with respect to their actual costs incurred. Payments for these activities are based on the terms of the individual arrangements, which may differ from the pattern of costs incurred, and are reflected in the consolidated financial statements as prepaid or accrued research and development expense, as the case may be.

Comprehensive Loss

Comprehensive loss is defined as the change in equity of a business enterprise during a period from transactions and other events and circumstances from non-owner sources.

Income Taxes

The Company accounts for income taxes under the asset and liability method. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases using enacted tax rates in effect for the year in which the differences are expected to affect taxable income. The deferred tax asset primarily includes net operating loss and tax credit carry forwards, accrued expenses not currently deductible and the cumulative temporary differences related to certain research and patent costs, which have been charged to expense in the accompanying statements of operations but have been recorded as assets for income tax purposes. The portion of any deferred tax asset for which it is more likely than not that a tax benefit will not be realized must then be offset by recording a valuation allowance. A full valuation allowance has been established against all of the deferred tax assets (see Note 9, "Income Taxes"), as it is more likely than not that these assets will not be realized given the Company's history of operating losses. The Company recognizes the tax benefit from an uncertain tax position only if it is more likely than not to be sustained upon examination based on the technical merits of the position. The amount for which an exposure exists is measured as the largest amount of benefit determined on a cumulative probability basis that the Company believes is more likely than not to be realized upon ultimate settlement of the position.

Stock-Based Compensation Expense

The Company applies the provisions of FASB Accounting Standards Codification ("ASC") Topic 718, Compensation—Stock Compensation ("ASC 718"), which requires the measurement and recognition of compensation expense for all stock-based awards made to employees and non-employees, including employee stock options.

At certain times throughout the Company's history, the chairman of the Company's board of directors, who is also a significant stockholder of the Company (the "Significant Holder"), afforded option holders the opportunity for liquidity in transactions in which options were exercised and the shares of Common Stock issued in connection therewith were simultaneously purchased by the Significant Holder (each, a "Purchase Transaction") (See Note 10). Because the Company had established a pattern of providing cash settlement alternatives for option holders, the Company accounted for its stock-based compensation awards as liability awards. The Company measured liability awards based on the award's intrinsic value on the grant date and then re-measured them at each reporting date until the date of settlement. Compensation expense was recognized on a straight-line basis over the requisite service period for each separately vesting portion of the award. Compensation expense for each period until settlement was based on the change in intrinsic value (or a portion of the change in intrinsic value, depending on the percentage of the requisite service that has been rendered at the reporting date). Changes in the intrinsic value of a liability that occur after the end of the requisite service period were considered compensation expense in the period in which the changes occur. On April 23, 2013, the Company distributed a notification letter to all equity award holders under the 2007 Plan advising them that Purchase Transactions would no longer occur, unless, at the time of a Purchase Transaction, the option holder has held the Common Stock issued upon exercise of options for a period of greater than six months prior to selling such Common Stock to the Significant Holder and that any such sale to the Significant Holder would be at the fair value of the Common Stock on the date of such sale. Based on these new criteria for Purchase Transactions, the Company remeasured options outstanding under the 2007 Plan as of April 23, 2013 to their intrinsic value and reclassified such options from liabilities to stockholders' deficit within the Company's consolidated balance sheets, which amounted to $14,482,000. The remaining expense for these options was recognized on a straight-line basis over the remaining requisite service period. During the year ended December 31, 2016, the remaining $244,000 of expense related to these options was recognized and as of December 31, 2017 and 2016, there was no unrecognized compensation expense related to these unvested awards.

Share-based payment transactions with employees, including grants of employee stock options, are recognized as compensation expense over the requisite service period based on their estimated fair values. ASC 718 also requires significant judgment and the use of estimates, particularly surrounding Black-Scholes assumptions such as stock price volatility over the option term and expected option lives, as well as expected option forfeiture rates, to estimate the grant date fair value of equity-based compensation and requires the recognition of the fair value of stock compensation in the statement of operations.

Clinical Trial Expense Accruals

As part of the process of preparing its financial statements, the Company is required to estimate its expenses resulting from its obligations under contracts with vendors, clinical research organizations and consultants and under clinical site agreements in connection with conducting clinical trials. The financial terms of these contracts are subject to negotiations, which vary from contract to contract and may result in payment flows that do not match the periods over which materials or services are provided under such contracts. The Company's objective is to reflect the appropriate trial expenses in its financial statements by matching those expenses with the period in which services are performed and efforts are expended. The Company accounts for these expenses according to the progress of the trial as measured by patient progression and the timing of various aspects of the trial. The Company determines accrual estimates through financial models taking into account discussion with applicable personnel and outside service providers as to the progress or state of consummation of trials, or the services completed. During the course of a clinical trial, the Company adjusts its clinical expense recognition if actual results differ from its estimates. The Company makes estimates of its accrued expenses as of each balance sheet date based on the facts and circumstances known to it at that time. The Company's clinical trial accruals are dependent upon the timely and accurate reporting of contract research organizations and other third-party vendors. Although the Company does not expect its estimates to be materially different from amounts actually incurred, its understanding of the status and timing of services performed relative to the actual status and timing of services performed may vary and may result in it reporting amounts that are too high or too low for any particular period. For the years ended December 31, 2017 and 2016, there were no material adjustments to the Company's prior period estimates of accrued expenses for clinical trials.

Collaboration Arrangements

A collaboration arrangement is defined as a contractual arrangement that has or may have significant financial milestones associated with success-based development, which include certain arrangements the Company has entered into regarding the research and development, manufacture and/or commercialization of products and product candidates. These collaborations generally provide for non-refundable, upfront license fees, research and development and commercial performance milestone payments, cost sharing and royalty payments. The collaboration agreements with third-parties are performed on a "best efforts" basis with no guarantee of either technological or commercial success. The Company evaluates whether an arrangement is a collaboration arrangement at its inception based on the facts and circumstances specific to the arrangement. The Company reevaluates whether an arrangement qualifies or continues to qualify as a collaboration arrangement whenever there is a change in the anticipated or actual ultimate commercial success of the endeavor. See Note 15, "License and Collaboration Agreements," for a discussion of the Company's arrangements with Baxalta and SymBio.

Basic and Diluted Net Loss Per Share of Common Stock

Basic net loss per share of common stock is computed by dividing net loss applicable to common stockholders by the weighted-average number of shares of Common Stock outstanding during the period, excluding the dilutive effects of stock options and warrants. Diluted net loss per share of common stock is computed by dividing the net loss applicable to common stockholders by the sum of the weighted-average number of shares of Common Stock outstanding during the period plus the potential dilutive effects of stock options and warrants outstanding during the period calculated in accordance with the treasury stock method, but are excluded if their effect is anti-dilutive. Because the impact of these items is anti-dilutive during periods of net loss, there was no difference between basic and diluted net loss per share of Common Stock for the years ended December 31, 2017 and 2016.

Recent Accounting Pronouncements

In May 2014, the FASB issued Accounting Standards Update No. 2014-09, "Revenue from Contracts with Customers" (ASU 2014-09) and has subsequently issued a number of amendments to ASU 2014-09. The new standard, as amended, provides a single comprehensive model to be used in the accounting for revenue arising from contracts with customers and supersedes current revenue recognition guidance, including industry-specific guidance. The underlying principle is that an entity will recognize revenue to depict the transfer of goods or services to customers at an amount that the entity expects to be entitled to in exchange for those goods or services. The guidance permits two methods of adoption: retrospectively to each prior reporting period presented (the full retrospective method), or retrospectively with the cumulative effect of initially applying the guidance recognized at the date of initial application (the modified retrospective method). The guidance was effective for interim and annual periods beginning on or after December 15, 2017. Early adoption was permitted but not before December 15, 2016. The Company adopted the new standard effective January 1, 2018 under the modified retrospective method. During the fourth quarter of 2017, the Company substantially completed its assessment of the impact that this new standard will have on its consolidated financial statements. Preliminarily, the Company does not expect the implementation of ASU 2014-09 to have a material quantitative impact on its consolidated financial statements as the timing of revenue recognition under the Company's current license agreements is not expected to significantly change. The finalization of the Company's assessment may result in significant changes to estimates that may materially impact the preliminary estimate of the cumulative effect. The adoption of the new guidance will also result in some additional disclosures.

In August 2014, the FASB issued guidance on determining when and how to disclose going-concern uncertainties in the financial statements. The new standard requires management to perform interim and annual assessments of an entity's ability to continue as a going concern within one year of the date the financial statements are issued. An entity must provide certain disclosures if conditions or events raise substantial doubt about the entity's ability to continue as a going concern. The guidance applies to all entities and is effective for annual periods ending after December 15, 2016, and interim periods thereafter, with early adoption permitted. The Company adopted the new guidance as of December 31, 2016. Based on its current cash position and an evaluation of expected future net cash outflows the Company has determined there is substantial doubt about its ability to continue as a going concern (See Note 1).

In February 2016, the FASB issued guidance which supersedes much of the current guidance for leases. The new standard requires lessees to recognize a right-of-use asset and a lease liability on their balance sheets for all the leases with terms greater than twelve months. Based on certain criteria, leases will be classified as either financing or operating, with classification affecting the pattern of expense recognition in the income statement. For leases with a term of twelve months or less, a lessee is permitted to make an accounting policy election by class of underlying asset not to recognize lease assets and lease liabilities. If a lessee makes this election, it should recognize lease expense for such leases generally on a straight-line basis over the lease term. The guidance is effective for fiscal years beginning after December 15, 2018, and interim periods within those years, with early adoption permitted. In transition, lessees and lessors are required to recognize and measure leases at the beginning of the earliest period presented using a modified retrospective approach. The modified retrospective approach includes a number of optional practical expedients primarily focused on leases that commenced before the effective date of the new guidance, including continuing to account for leases that commence before the effective date in accordance with previous guidance, unless the lease is modified. The Company is evaluating the impact of the adoption of the standard on its consolidated financial statements.

In March 2016, the FASB issued guidance that addresses the income tax effects of stock-based payments and eliminates the windfall pool concept, as all of the tax effects related to stock-based payments will now be recorded at settlement (or expiration) through the income statement. The new guidance also permits entities to make an accounting policy election for the impact of forfeitures on the recognition of expense for stock-based payment awards. Forfeitures can be estimated or recognized when they occur. The standard was effective for annual periods beginning after December 15, 2016 and interim periods within that reporting period. Early adoption was permitted in any interim or annual period, with any adjustment reflected as of the beginning of the fiscal year of adoption. The Company adopted the new guidance as of January 1, 2017. The adoption did not have a material impact on the Company's consolidated financial statements and related disclosures.

In November 2016, the FASB issued guidance requiring that amounts generally described as restricted cash and restricted cash equivalents be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. The guidance is effective for interim and annual periods beginning in 2018 and should be applied using a retrospective transition method to each period presented. Early adoption is permitted. The Company adopted this guidance effective December 31, 2017. Restricted Cash was $50,000 at December 31 2017, 2016 and 2015. The adoption did not have a material impact on the Company's consolidated financial statements and related disclosures.

Property and Equipment

12 Months Ended

Dec. 31, 2017

Property and Equipment

Property and Equipment

3. Property and Equipment

Property and equipment and related accumulated depreciation are as follows:

	December 31,
	2017			2016
Laboratory equipment	$	1,037,000		$	1,037,000
Software		92,000			92,000
Computer and office equipment		354,000			354,000
Leasehold improvements		745,000			745,000

		2,228,000			2,228,000
Less accumulated depreciation		(2,164,000	)		(2,076,000	)

	$	64,000		$	152,000

Depreciation and amortization expense was $88,000 and $96,000 for the years ended December 31, 2017 and 2016, respectively.

Warrants

12 Months Ended

Dec. 31, 2017

Warrants

Warrants

4. Warrants

Warrants outstanding at December 31, 2016 and 2017, and warrant activity for the year ended December 31, 2017 is as follows:

Description	Classification	Exercise Price		Expiration Date		Balance Decemeber 31, 2016		Warrants Issued		Warrants Exercised			Warrants Expired		Balance December 31, 2017
Non-tradable warrants	Liability	$	11.50		July 2021		96,842		—		—			—		96,842
Tradable warrants	Liability	$	4.92		July 2021		3,192,022		—		—			—		3,192,022
Non-tradable pre-funded warrants	Equity	$	0.01		July 2023		236,907		—		(231,000	)		—		5,907

							3,525,771		—		(231,000	)		—		3,294,771

Net Loss Per Share of Common Stock

12 Months Ended

Dec. 31, 2017

Net Loss Per Share of Common Stock

Net Loss Per Share of Common Stock

5. Net Loss Per Share of Common Stock

The following table sets forth the computation of basic and diluted earnings per share for the years ended December 31, 2017 and 2016:

	Year ended December 31,
	2017			2016
Basic and diluted net loss per share of common stock:
Net loss attributable to Onconova Therapeutics, Inc	$	(24,092,000	)	$	(19,667,000	)


Weighted average shares of common stock outstanding		9,000,326			4,426,639


Net loss per share of common stock—basic and diluted	$	(2.68	)	$	(4.44	)

The following potentially dilutive securities outstanding at December 31, 2017 and 2016 have been excluded from the computation of diluted weighted average shares outstanding, as they would be antidilutive:

	December 31,
	2017		2016
Warrants		3,294,771		3,525,771
Stock options		894,996		746,353

		4,189,767		4,272,124

Revenue

12 Months Ended

Dec. 31, 2017

Revenue

Revenue

6. Revenue

The Company recognized revenue under its funding, license and collaboration agreements with Baxalta and SymBio as follows:

	Year ended December 31,
	2017		2016
Baxalta	$	—	$	4,999,000
SymBio		787,000		547,000

	$	787,000	$	5,546,000

See Note 14, "Research Agreements," and Note 15, "License and Collaboration Agreements," for a further discussion of the agreements with Baxalta and SymBio.

Balance Sheet Detail

12 Months Ended

Dec. 31, 2017

Balance Sheet Detail

Balance Sheet Detail

7. Balance Sheet Detail

Prepaid expenses and other current assets are as follows:

	December 31,
	2017		2016
Research and development	$	514,000	$	1,075,000
Manufacturing		48,000		90,000
Insurance		181,000		350,000
Other		77,000		73,000

	$	820,000	$	1,588,000

Accrued expenses and other current liabilities are as follows:

	December 31,
	2017		2016
Research and development	$	1,912,000	$	2,376,000
Employee compensation		1,258,000		1,573,000
Professional fees		165,000		235,000
Other		—		198,000

	$	3,335,000	$	4,382,000

Fair Value Measurements

12 Months Ended

Dec. 31, 2017

Fair Value Measurements

Fair Value Measurements

8. Fair Value Measurements

Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date.

The Company utilizes a valuation hierarchy for disclosure of the inputs to the valuations used to measure fair value. This hierarchy prioritizes the inputs into three broad levels as follows. Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities. Level 2 inputs are quoted prices for similar assets and liabilities in active markets or inputs that are observable for the asset or liability, either directly or indirectly through market corroboration, for substantially the full term of the financial instrument. Level 3 inputs are unobservable inputs based on the Company's own assumptions used to measure assets and liabilities at fair value. A financial asset or liability's classification within the hierarchy is determined based on the lowest level input that is significant to the fair value measurement.

On January 5, 2016, the Company entered into a securities purchase agreement (the "Securities Purchase Agreement") with an institutional investor providing for the issuance and sale by the Company of 193,684 shares of the Company's Common Stock, at a purchase price of $9.50 per share and warrants to purchase up to 96,842 shares of the Company's Common Stock (the "Warrants") for aggregate gross proceeds of $1,840,000 (see Note 18). The Company has classified the warrants as a liability (see Note 4). The fair value was estimated using the Black-Scholes pricing model.

On July 29, 2016 the Company closed on a Rights Offering, issuing 3,599,786 shares of Common Stock, 3,192,022 Tradable Warrants and 656,400 Pre-Funded Warrants. The Tradable Warrants are exercisable for a period of five years for one share of Common Stock at an exercise price of $4.92 per share. After the one-year anniversary of issuance, the Company may redeem the Tradable Warrants for $0.001 per Tradable Warrant if the volume weighted average price of its Common Stock is above $12.30 for each of 10 consecutive trading days (see Note 18). The Company has classified the Tradable Warrants as a liability (see Note 4). The Tradable Warrants have been listed on the NASDAQ Capital Market since issuance and the Company regularly monitors the trading activity. During the period from issuance on July 29, 2016 through March 31, 2017 the Company determined that trading volume was insufficient to use the NASDAQ Capital Market value to determine the fair value of the warrant liability. The fair value was estimated using the Black-Scholes pricing model. During the quarter ended June 30, 2017, the Company determined that an active and orderly market for the Tradable Warrants had developed and that the NASDAQ Capital Market price was the best indicator of fair value of the warrant liability. Consequently, the Company changed its valuation technique from the Black-Scholes pricing model to the quoted market price, effective April 1, 2017. The change in valuation technique resulted in a reclassification of the liability within the valuation hierarchy form Level 3 to Level 1. The quoted market price was also used to determine the fair value at December 31, 2017.

The Company estimated the fair value of the non-tradable warrant liability at December 31, 2017, using the Black-Scholes option pricing model with the following weighted-average assumptions:

Risk-free interest rate		2.09%
Expected volatility		75.47%
Expected term		3.53 years
Expected dividend yield		0%

Expected volatility is based on the historical volatility of the Company's common stock since its IPO in July 2013.

The following fair value hierarchy table presents information about the Company's financial assets and liabilities measured at fair value on a recurring basis as of December 31, 2017 and 2016:

	Fair Value Measurement as of:
	December 31, 2017								December 31, 2016
	Level 1		Level 2		Level 3		Balance		Level 1		Level 2		Level 3		Balance
Tradable warrants liability	$	1,755,000	$	—	$	—	$	1,755,000	$	—	$	—	$	3,338,000	$	3,338,000
Non-tradable warrants liability		—		—		18,000		18,000		—		—		63,000		63,000

Total	$	1,755,000	$	—	$	18,000	$	1,773,000	$	—	$	—	$	3,401,000	$	3,401,000

The following table presents a reconciliation of the Company's liabilities measured at fair value on a recurring basis using significant unobservable inputs (Level 3) for the years ended December 31, 2017 and 2016:

	Warrant Liability
Balance at December 31, 2015	$	—
Issuance of warrants		7,389,000

Change in fair value upon re-measurement		(3,988,000	)

Balance at December 31, 2016	$	3,401,000


Reclassification of tradable warrants to Level 1	$	(4,857,000	)
Change in fair value upon re-measurement		1,474,000

Balance at December 31, 2017	$	18,000

There were no transfers between Level 1 and Level 2 in any of the periods reported.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Income Taxes

12 Months Ended

Dec. 31, 2017

Income Taxes

Income Taxes

9. Income Taxes

The Company accounts for income taxes under FASB ASC 740 ("ASC 740"). Deferred income tax assets and liabilities are determined based upon differences between financial reporting and tax bases of assets and liabilities, which are measured using the enacted tax rates and laws that will be in effect when the differences are expected to reverse.

Income taxes have been based on the following income (loss) before income tax expense:

	December 31,
	2017			2016
Domestic	$	(24,131,000	)	$	(19,738,000	)
Foreign		52,000			85,000

	$	(24,079,000	)	$	(19,653,000	)

The provision for income taxes consists of the following:

	December 31,
	2017		2016
Current
US Federal	$	—	$	—
State and Local		—		—
Foreign		13,000		14,000

Total Current	$	13,000	$	14,000

Deferred
US Federal	$	—	$	—
State and Local		—		—
Foreign		—		—

Total Deferred	$	—	$	—

Total Expense (Benefit)	$	13,000	$	14,000

As of December 31, 2017, the Company had federal net operating loss ("NOL") carry forwards of $210,529,000, state NOL carry forwards of $169,672,000 and research and development tax credit carry forwards of $79,725,000, which are available to reduce future taxable income. The federal NOL and tax credit carry forwards will begin to expire at various dates starting in 2022. The state NOL carry forwards will begin to expire at various dates starting in 2025. The NOL carry forwards are subject to review and possible adjustment by the Internal Revenue Service and state tax authorities. NOL and tax credit carry forwards may become subject to an annual limitation in the event of certain cumulative changes in the ownership interest of significant stockholders over a three-year period in excess of 50%, as defined under Sections 382 and 383 of the Internal Revenue Code of 1986, as amended, as well as similar state tax provisions. This could limit the amount of NOLs that the Company can utilize annually to offset future taxable income or tax liabilities. The amount of the annual limitation, if any, will be determined based on the value of the Company immediately prior to the ownership change. Subsequent ownership changes may further affect the limitation in future years.

The Company's reserves related to taxes are based on a determination of whether and how much of a tax benefit taken by the Company in its tax filings or positions is more likely than not to be realized. The Company recognized no material adjustment for unrecognized income tax benefits. Through December 31, 2017, the Company had no unrecognized tax benefits or related interest and penalties accrued.

The principal components of the Company's deferred tax assets are as follows:

	December 31,
	2017			2016
Deferred tax assets:
Net operating loss carryovers	$	57,557,000		$	75,829,000
R&D tax credits		79,725,000			71,811,000
Non-qualified stock options		5,355,000			7,413,000
Deferred revenue		1,242,000			2,030,000
Charitable contributions		4,000			6,000
Accrued expenses		407,000			618,000
Fixed assets		85,000			102,000

Deferred tax assets		144,375,000			157,809,000
Less valuation allowance		(144,375,000	)		(157,809,000	)

Net deferred tax assets	$	—		$	—

ASC 740 requires a valuation allowance to reduce the deferred tax assets reported if, based on the weight of available evidence, it is more likely than not that some portion or all of the deferred tax assets will not be realized. After consideration of all the evidence, both positive and negative, the Company has recorded a full valuation allowance against its deferred tax assets at December 31, 2017 and 2016, respectively. The Company experienced a net change in valuation allowance of $(13,434,000) and $8,738,000 for the years ended December 31, 2017 and 2016, respectively.

A reconciliation of income tax (expense) benefit at the statutory federal income tax rate and income taxes as reflected in the financial statements is as follows:

	December 31,
	2017			2016
Federal income tax expense at statutory rate		34.0	%		34.0	%
Permanent items		(8.1	)		(5.9	)
Effect of Tax Act		(116.9	)		—
State income tax, net of federal benefit		5.8			(15.8	)
Tax credits		29.3			33.5
Provision to return		—			(1.5	)
Change in valuation allowance		55.8			(44.5	)
Other		—			0.1

Effective income tax rate		(0.1	)%		(0.1	)%

On December 22, 2017, H.R. 1 (also, known as the Tax Cuts and Jobs Act (the "Act")) was signed into law. Among its numerous changes to the Internal Revenue Code, the Act reduces U.S. federal corporate tax rate from 34% to 21% and imposes a one-time transition tax on unrepatriated earnings of foreign subsidiaries. As a result, the Company believes that the most significant impact on its consolidated financial statements will be reduction of approximately $28.1 million for the deferred tax assets related to net operating losses and other assets. Such reduction is offset by changes to the Company's valuation allowance. The one-time mandatory transition tax on accumulated foreign earnings resulted in a provisional amount of income of $115,000 for the Company, which the company is offsetting with its net operating loss.

Stock-Based Compensation

12 Months Ended

Dec. 31, 2017

Stock-Based Compensation

Stock-Based Compensation

10. Stock-Based Compensation

In January 2008, the board of directors approved the 2007 Equity Compensation Plan (the "2007 Plan"), which amended, restated and renamed the Company's 1999 Stock Based Compensation Plan (the "1999 Plan"), which provided for the granting of incentive and nonqualified stock options and restricted stock to its employees, directors and consultants at the discretion of the board of directors.

Further, in July 2013, the Company's board of directors and stockholders approved the 2013 Equity Compensation Plan (the "2013 Plan"), which amended, restated and renamed the 2007 Plan. Under the 2013 Plan, the Company may grant incentive stock options, non-statutory stock options, stock appreciation rights, restricted stock, restricted stock units, deferred share awards, performance awards and other equity-based awards to employees, directors and consultants. The Company initially reserved 610,783 shares of Common Stock for issuance, subject to adjustment as set forth in the 2013 Plan. The 2013 Plan includes an evergreen provision, pursuant to which the maximum aggregate number of shares that may be issued under the 2013 Plan is increased on the first day of each fiscal year by the lesser of (a) a number of shares equal to four percent (4%) of the issued and outstanding Common Stock of the Company, without duplication, (b) 200,000 shares and (c) such lesser number as determined by the Company's board of directors, subject to specified limitations. At December 31, 2017, there were 57,632 shares available for future issuance.

Stock-based compensation expense includes stock options granted to employees and non-employees and has been reported in the Company's statements of operations and comprehensive loss in either research and development expenses or general and administrative expenses depending on the function performed by the optionee. No net tax benefits related to the stock-based compensation costs have been recognized since the Company's inception. The Company recognized stock-based compensation expense as follows for years ended December 31, 2017 and 2016:

	Year ended December 31,
	2017		2016
General and administrative	$	975,000	$	1,887,000
Research and development		735,000		2,042,000

	$	1,710,000	$	3,929,000

A summary of stock option activity for the year ended December 31, 2017 is as follows:

				Options Outstanding
	Shares Available for Grant			Number of Shares			Weighted- Average Exercise Price		Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value
Balance, December 31, 2016		6,275			746,353		$	53.50		7.70	$	0
Authorized		200,000			—
Granted		(198,811	)		198,811		$	2.57
Exercised		—			—		$	—
Forfeitures		50,168			(50,168	)	$	85.25

Balance, December 31, 2017		57,632			894,996		$	40.41		7.38	$	0

Vested or expected to vest, December 31, 2017					882,972		$	57.02		6.72	$	0

Exercisable at December 31, 2017					604,555		$	57.02		6.72	$	0

The intrinsic value of options exercised during the years ended December 31, 2017 and 2016 was $0. The aggregate intrinsic value is calculated as the difference between the exercise price of the underlying awards and the quoted price of the Company's common stock for those awards that have an exercise price currently below the closing price.

Information with respect to stock options outstanding and exercisable at December 31, 2017 is as follows:

Exercise Price	Shares		Exercisable
$1.51 - $6.50		488,818		233,957
$14.80 - $15.00		37,375		25,326
$23.20 - $39.80		99,029		79,180
$43.40 - $75.30		91,345		87,706
$132.80 - $151.20		173,079		173,036
$277.10 - $291.40		5,350		5,350

		894,996		604,555

Options granted after April 23, 2013

The Company accounts for all stock-based payments made after April 23, 2013 to employees and directors using an option pricing model for estimating fair value. Accordingly, stock-based compensation expense is measured based on the estimated fair value of the awards on the date of grant, net of forfeitures. Compensation expense is recognized for the portion that is ultimately expected to vest over the period during which the recipient renders the required services to the Company using the straight-line single option method. In accordance with authoritative guidance, the fair value of non-employee stock based awards is re-measured as the awards vest, and the resulting increase in fair value, if any, is recognized as expense in the period the related services are rendered.

The Company uses the Black-Scholes option-pricing model to estimate the fair value of stock options at the grant date. The Black-Scholes model requires the Company to make certain estimates and assumptions, including estimating the fair value of the Company's common stock, assumptions related to the expected price volatility of the Company's stock, the period during which the options will be outstanding, the rate of return on risk-free investments and the expected dividend yield for the Company's stock.

As of December 31, 2017, there was $1,065,000 of unrecognized compensation expense related to the unvested stock options issued from April 24, 2013 through December 31, 2017, which is expected to be recognized over a weighted-average period of approximately 1.72 years.

The weighted-average assumptions underlying the Black-Scholes calculation of grant date fair value include the following:

	Year ended December 31, 2017
	2017	2016
Risk-free interest rate	2.09%	1.49%
Expected volatility	79.02%	78.7%
Expected term	5.98 years	5.68 years
Expected dividend yield	0%	0%
Weighted average grant date fair value	$1.76	$3.75

The weighted-average valuation assumptions were determined as follows:

Risk-free interest rate: The Company based the risk-free interest rate on the interest rate payable on U.S. Treasury securities in effect at the time of grant for a period that is commensurate with the assumed expected option term.

Expected term of options: Due to its lack of sufficient historical data, the Company estimates the expected life of its employee stock options using the "simplified" method, as prescribed in Staff Accounting Bulletin (SAB) No. 107, whereby the expected life equals the arithmetic average of the vesting term and the original contractual term of the option.

Expected stock price volatility: Expected volatility is based on the historical volatility of the Company's common stock since its IPO in July 2013.

Expected annual dividend yield: The Company has never paid, and does not expect to pay dividends in the foreseeable future. Accordingly, the Company assumed an expected dividend yield of 0.0%.

Estimated forfeiture rate: The Company's estimated annual forfeiture rate on stock option grants was 4.14% in 2017 and 2016, based on the historical forfeiture experience.

Options granted on or prior to April 23, 2013

On April 23, 2013, the Company distributed a notification letter to all equity award holders under the Company's 2007 Equity Compensation Plan (the "2007 Plan") advising them that Purchase Transactions would no longer occur, unless, at the time of a Purchase Transaction, the option holder has held the Common Stock issued upon exercise of options for a period of greater than six months prior to selling such Common Stock to the Significant Holder and that any such sale to the Significant Holder would be at the fair value of the Common Stock on the date of such sale. Based on these new criteria for Purchase Transactions, the Company remeasured options outstanding under the 2007 Plan as of April 23, 2013 to their intrinsic value and reclassified such options from liabilities to stockholders' deficit within the Company's consolidated balance sheets, which amounted to $14,482,000. As of December 31, 2017, there was no unrecognized compensation expense related to these awards.

Employee Benefit Plan	12 Months Ended
Employee Benefit Plan	Dec. 31, 2017
Employee Benefit Plan
Employee Benefit Plan	11. Employee Benefit Plan In October 2007, the Company established a 401(k) Retirement Savings Plan. Employees are eligible to participate in the plan as soon as they join the Company if they are at least 21 years of age and work a minimum of 1,000 hours per year. The Company matches $0.75 for every dollar of the first 6% of payroll that employees invest, up to the legal limit. Employer contributions vest immediately. For the years ended December 31, 2017 and 2016, the Company contributed $124,000 and $146,000, respectively.

Commitments and Contingencies

12 Months Ended

Dec. 31, 2017

Commitments and Contingencies

Commitments and Contingencies

12. Commitments and Contingencies

Operating leases

In January 2007, the Company entered into a lease for 8,100 square feet of office and lab space in Newtown, Pennsylvania, and in October 2009, the Company and the landlord amended the lease to add three additional one-year options to extend the lease term. In November 2013 the Company renewed the lease for the period April 1, 2014 to March 31, 2015, for rent of $11,000 per month. In December 2014 the Company renewed the lease for the period April 1, 2015 to March 31, 2016, for rent of $11,500 per month. In November 2015 the Company renewed the lease for the period April 1, 2016 to March 31, 2017, for rent of $11,900 per month. In September 2012, the Company sub-leased an additional 1,356 square feet of office space. The lease was renewed through February 28, 2017 for rent of $1,600 per month. In February 2017, the Company combined the leases and renewed the lease for the combined space for the period March 1, 2017 to February 28, 2018, for rent of $13,800 per month. The Company renewed the lease for the combined space for the period March 1, 2018 to February 28, 2019, for rent of $14,200 per month.

Future minimum lease payments under these non-cancellable leases having terms in excess of one year as of December 31, 2017 are as follows:

	December 31, 2017
2018	$	170,000
2019		28,000

Total minimum lease payments	$	198,000

Net rent expense was $152,000 and $191,000 for the years ended December 31, 2017 and 2016, respectively.

Employment agreements

The Company has entered into employment agreements with certain of its executives. The agreements provide for, among other things, salary, bonus and severance payments.

Restructuring	12 Months Ended
Restructuring	Dec. 31, 2017
Restructuring
Restructuring	13. Restructuring In February 2016, the Company, as part of its ongoing commitment to reduce costs and conserve cash implemented workforce reductions of 6 employees in February 2016 and an additional 6 employees in August 2016. Affected employees were offered severance pay in accordance with Company policy or, if applicable, their employment agreements. As part of the workforce reduction the Company terminated the employment of Ajay Bansal, the Company's Chief Financial Officer, and Thomas McKearn, M.D., Ph.D., the Company's President, Research & Development. Mr. Bansal and Dr. McKearn each departed in good standing with the Company and received severance benefits consistent with a termination "without cause" pursuant to his employment agreement and the Company has agreed to extend the post-termination exercise period of their outstanding option awards until February 12, 2018, in consideration for a customary general release. As a result of the workforce reductions, the Company recorded one-time severance-related charges totaling approximately $3.0 million, which included non-cash charges of approximately $1.4 million related to the accelerated vesting of the outstanding stock options for certain of the affected employees during the year ended December 31, 2016.

Research Agreements	12 Months Ended
Research Agreements	Dec. 31, 2017
Research Agreements
Research Agreements	14. Research Agreements The Company has entered into various licensing and right-to-sublicense agreements with educational institutions for the exclusive use of patents and patent applications, as well as any patents that may develop from research being conducted by such educational institutions in the field of anticancer therapy, genes and proteins. Results from this research have been licensed to the Company pursuant to these agreements. Under one of these agreements with Temple University ("Temple"), the Company is required to make annual maintenance payments to Temple and royalty payments based upon a percentage of sales generated from any products covered by the licensed patents, with minimum specified royalty payments. As no sales had been generated through December 31, 2017 under the licensed patents, the Company has not incurred any royalty expenses related to this agreement. In addition, the Company is required to pay Temple a percentage of any sublicensing fees received by the Company.

License and Collaboration Agreements	12 Months Ended
License and Collaboration Agreements	Dec. 31, 2017
License and Collaboration Agreements
License and Collaboration Agreements	15. License and Collaboration Agreements Baxalta Agreement In September 2012, the Company entered into a development and license agreement with Baxter Healthcare SA, the predecessor in interest to Baxalta GmbH (together with its affiliates, "Baxalta"), pursuant to which the Company granted an exclusive, royalty-bearing license for the research, development, commercialization and manufacture (in specified instances) of rigosertib in all therapeutic indications in Europe. In accordance with this agreement, the Company received an upfront cash payment of $50,000,000 in 2012. On March 3, 2016, the Company received a notification of Baxalta's election to terminate the development and license agreement based on a strategic reprioritization review, effective August 30, 2016, at which time, the rights licensed to Baxalta reverted to the Company at no cost. Additionally, any rights the Company had to funding, pre-commercial milestone payments and royalties from Baxalta terminated in accordance with the agreement. Among other things, the Baxalta agreement contemplated development of rigosertib IV in higher-risk MDS patients, through the Company's ONTIME trial and, potentially, additional Phase 3 clinical trials. The ONTIME trial did not achieve its primary endpoint and the Company is continuing the development of rigosertib IV in higher-risk MDS patients through its INSPIRE trial. In accordance with the agreement, the Company elected to have Baxalta fund fifty percent of the costs of the INSPIRE trial, up to $15.0 million. The Company recorded revenue of $4,999,000 during the year ended December 31, 2016, related to Baxalta's funding of the INSPIRE trial. The funding from Baxalta terminated effective August 30, 2016. The Company has overall responsibility for the trial, including determination of the trial specifications, selection of third party service providers and payment for all services and materials. SymBio Agreement In July 2011, the Company entered into a license agreement with SymBio, as subsequently amended, granting SymBio an exclusive, royalty-bearing license for the development and commercialization of rigosertib in Japan and Korea. Under the SymBio license agreement, SymBio is obligated to use commercially reasonable efforts to develop and obtain market approval for rigosertib inside the licensed territory and the Company has similar obligations outside of the licensed territory. The Company has also entered into an agreement with SymBio providing for it to supply SymBio with development-stage product. Under the SymBio license agreement, the Company also agreed to supply commercial product to SymBio under specified terms that will be included in a commercial supply agreement to be negotiated prior to the first commercial sale of rigosertib. The supply of development-stage product and the supply of commercial product will be at the Company's cost plus a defined profit margin. Sales of development-stage product have been de minimis. The Company has additionally granted SymBio a right of first negotiation to license or obtain the rights to develop and commercialize compounds having a chemical structure similar to rigosertib in the licensed territory. Under the terms of the SymBio license agreement, the Company received an upfront payment of $7,500,000. The Company is eligible to receive milestone payments of up to an aggregate of $22,000,000 from SymBio upon the achievement of specified development and regulatory milestones for specified indications. Of the regulatory milestones, $5,000,000 is due upon receipt of marketing approval in the United States for rigosertib IV in higher-risk MDS patients, $3,000,000 is due upon receipt of marketing approval in Japan for rigosertib IV in higher-risk MDS patients, $5,000,000 is due upon receipt of marketing approval in the United States for rigosertib oral in lower-risk MDS patients, and $5,000,000 is due upon receipt of marketing approval in Japan for rigosertib oral in lower-risk MDS patients. Furthermore, upon receipt of marketing approval in the United States and Japan for an additional specified indication of rigosertib, which the Company is currently not pursuing, an aggregate of $4,000,000 would be due. In addition to these pre-commercial milestones, the Company is eligible to receive tiered milestone payments based upon annual net sales of rigosertib by SymBio of up to an aggregate of $30,000,000. Further, under the terms of the SymBio license agreement, SymBio will make royalty payments to the Company at percentage rates ranging from the mid-teens to 20% based on net sales of rigosertib by SymBio. Royalties will be payable under the SymBio agreement on a country-by-country basis in the licensed territory, until the later of the expiration of marketing exclusivity in those countries, a specified period of time after first commercial sale of rigosertib in such country, or the expiration of all valid claims of the licensed patents covering rigosertib or the manufacture or use of rigosertib in such country. If no valid claim exists covering the composition of matter of rigosertib or the use of or treatment with rigosertib in a particular country before the expiration of the royalty term, and specified competing products achieve a specified market share percentage in such country, SymBio's obligation to pay the Company royalties will continue at a reduced royalty rate until the end of the royalty term. In addition, the applicable royalties payable to the Company may be reduced if SymBio is required to pay royalties to third-parties for licenses to intellectual property rights necessary to develop, use, manufacture or commercialize rigosertib in the licensed territory. The license agreement with SymBio will remain in effect until the expiration of the royalty term. However, the SymBio license agreement may be terminated earlier due to the uncured material breach or bankruptcy of a party, or force majeure. If SymBio terminates the license agreement in these circumstances, its licenses to rigosertib will survive, subject to SymBio's milestone and royalty obligations, which SymBio may elect to defer and offset against any damages that may be determined to be due from the Company. In addition, the Company may terminate the license agreement in the event that SymBio brings a challenge against it in relation to the licensed patents, and SymBio may terminate the license agreement without cause by providing the Company with written notice within a specified period of time in advance of termination. The Company determined that the deliverables under the SymBio agreement include the exclusive, royalty-bearing, sublicensable license to rigosertib, the research and development services to be provided by the Company and its obligation to serve on a joint committee. The Company concluded that the license did not have standalone value to SymBio and was not separable from the research and development services, because of the uncertainty of SymBio's ability to develop rigosertib in the SymBio territory on its own and the uncertainty of SymBio's ability to sublicense rigosertib and recover a substantial portion of the original upfront payment of $7,500,000 paid by SymBio to the Company. The supply of rigosertib for SymBio's commercial requirements is contingent upon the receipt of regulatory approvals to commercialize rigosertib in Japan and Korea. Because the Company's commercial supply obligation was contingent upon the receipt of future regulatory approvals, and there were no binding commitments or firm purchase orders pending for commercial supply at or near the execution of the agreement, the commercial supply obligation is deemed to be contingent and is not valued as a deliverable under the SymBio agreement. If SymBio orders the supplies from the Company, the Company expects the pricing for this supply to equal its third-party manufacturing cost plus a pre-negotiated percentage, which will not result in a significant incremental discount to market rates. Due to the lack of standalone value for the license, research and development services, and joint committee obligation, the upfront payment is being recognized ratably using the straight line method through December 2027, the expected term of the agreement. The Company recognized revenues under this agreement of $454,000 and $455,000, for the years ended December 31, 2017 and 2016, respectively. In addition, the Company recognized revenues related to the supply agreement with Symbio in the amounts of $333,000 and $92,000 for the years ended December 31, 2017 and 2016, respectively.

Preclinical Collaboration	12 Months Ended
Preclinical Collaboration	Dec. 31, 2017
Preclinical Collaboration
Preclinical Collaboration	16. Preclinical Collaboration GVK/GBO Agreement In December 2012, the Company agreed to form GBO, an entity owned by the Company and GVK. The purpose of GBO is to collaborate on and develop two programs through filing of an investigational new drug application and/or conducting proof of concept studies using the Company's technology platform. If a program failure occurs for one or both programs, the Company may contribute additional assets to GBO to establish a replacement program or programs. During 2013, GVK made an initial capital contribution of $500,000 in exchange for a 10% interest in GBO, and the Company made an initial capital contribution of a sublicense to all the intellectual property controlled by the Company related to the two specified programs in exchange for a 90% interest. Under the terms of the agreement, GVK may make additional capital contributions. The GVK percentage interest in GBO may change from the initial 10% to up to 50%, depending on the amount of its total capital contributions. During November 2014, GVK made an additional capital contribution of $500,000 which increased its interest in GBO to 17.5%. The Company evaluates its variable interests in GBO on a quarterly basis and has determined that it is the primary beneficiary. For thirty days following the 15-month anniversary of the commencement of either of the two programs, the Company will have an option to (i) cancel the license and (ii) purchase all rights in and to that program. There are three of these buy-back scenarios depending on the stage of development of the underlying assets. In addition, upon the occurrence of certain events, namely termination of the Company's participation in the programs either with or without a change in control, GVK will be entitled to purchase or obtain the Company's interest in GBO. GVK will have operational control of GBO and the Company will have strategic and scientific control. The two preclinical programs sublicensed to GBO have not been developed to clinical stage as initially hoped, and the Company is in discussions with GVK regarding the future of GBO. There was no activity in GBO during the years ended December 31, 2017 and 2016. HanX Biopharmaceuticals, Inc. In December 2017, the Company entered into a license and collaboration agreement with HanX Biopharmaceuticals, Inc. ("HanX"), a company focused on development of novel oncology products, for the further development, registration and commercialization in China of ON 123300. This compound has the potential to overcome the limitations of current generation CDK 4/6 inhibitors. Under the terms of the agreement, the Company will receive an upfront payment, regulatory and commercial milestone payments, as well as royalties on Chinese sales. The key feature of the collaboration is that HanX will provide all funding required for Chinese IND enabling studies performed for Chinese Food and Drug Administration IND approval. The Company and HanX also intend for these studies to comply with the FDA standards. Accordingly, such studies may be used by the Company for an IND filing with the FDA. The Company and HanX will oversee the IND enabling studies. The Company will maintain global rights outside of China. There was no activity or payments related to this agreement during the year ended December 31, 2017.

Related-Party Transactions	12 Months Ended
Related-Party Transactions	Dec. 31, 2017
Related-Party Transactions
Related-Party Transactions	17. Related-Party Transactions The Company has entered into a research agreement, as subsequently amended, with the Mount Sinai School of Medicine ("Mount Sinai"), with which a member of its board of directors and a significant stockholder is affiliated. Mount Sinai is undertaking research on behalf of the Company on the terms set forth in the agreements. Mount Sinai, in connection with the Company, will prepare applications for patents generated from the research. Results from all projects will belong exclusively to Mount Sinai, but the Company will have an exclusive option to license any inventions. Payments to Mount Sinai under this research agreement for the years ended December 31, 2017 and 2016 were $351,000 and $548,000, respectively. At December 31, 2017 and 2016, the Company had $526,000 and $175,000 payable to Mount Sinai under this agreement. The Company has entered into a consulting agreement with a member of its board of directors, who is also a significant stockholder. The board member provides consulting services to the Company on the terms set forth in the agreement. Payments to this board member under this agreement for the years ended December 31, 2017 and 2016 were $132,000 and $131,000, respectively. At December 31, 2017 and December 31, 2016, the Company had $33,000 and $33,000, respectively, payable under this agreement.

Securities Registrations and Sales Agreements	12 Months Ended
Securities Registrations and Sales Agreements	Dec. 31, 2017
Securities Registrations and Sales Agreements
Securities Registrations and Sales Agreements	18. Securities Registrations and Sales Agreements In October 2014, the Company entered into a sales agreement with Cantor Fitzgerald & Co. ("Cantor") to create an at-the-market equity program under which the Company from time to time was able to offer and sell shares of its Common Stock through Cantor. A registration statement (Form S-3 No. 333-199219), relating to the shares, which was filed with the SEC became effective on November 20, 2014. During the year ended December 31, 2015, 2,715,165 shares were sold under the Cantor sales agreement for net proceeds of $6,018,000. The Cantor sales agreement was terminated on January 5, 2016, and there were no sales of Common Stock under this program during the year ended December 31, 2016. On October 8, 2015, the Company entered into a purchase agreement, and a registration rights agreement (the "Registration Rights Agreement") with Lincoln Park. A registration statement (Form S-1 No. 333-207533), relating to the shares, which was filed with the SEC became effective on November 3, 2015. Subject to the terms and conditions of the purchase agreement, including the effectiveness of a registration statement covering the resale of the shares, the Company may sell additional shares of its Common Stock, having an aggregate offering price of up to $15,000,000 to Lincoln Park from time to time until December 1, 2018. Upon execution of the Lincoln Park purchase agreement, Lincoln Park made an initial purchase of 84,676 shares of the Company's Common Stock for $1,500,000. Subject to the terms and conditions of the purchase agreement, including the effectiveness of a registration statement covering the resale of the shares, the Company has the right to sell to and Lincoln Park is obligated to purchase up to an additional $15,000,000 of shares of Common Stock, subject to certain limitations, from time to time until December 1, 2018. The Company may direct Lincoln Park, at its sole discretion and subject to certain conditions, to purchase up to 10,000 shares of Common Stock on any business day, increasing to up to 25,000 shares depending upon the closing sale price of the Common Stock (such purchases, "Regular Purchases"). However, in no event shall a Regular Purchase be more than $1,000,000. The purchase price of shares of Common Stock related to the future funding will be based on the prevailing market prices of such shares at the time of sales. In addition, the Company may direct Lincoln Park to purchase additional amounts as accelerated purchases if on the date of a Regular Purchase the closing sale price of the Common Stock is not below the threshold price as set forth in the Purchase Agreement. The Company's sales of shares of Common Stock to Lincoln Park under the Purchase Agreement were limited to no more than the number of shares that would result in the beneficial ownership by Lincoln Park and its affiliates, at any single point in time, of more than 4.99% of the then-outstanding shares of the Common Stock, which limit increased to 9.99% on May 1, 2016. Pursuant to the terms of the Lincoln Park purchase agreement and to comply with the listing rules of the Nasdaq Stock Market, the number of shares issued to Lincoln Park thereunder shall not exceed 19.99% of the Company's shares outstanding on October 8, 2015 unless the approval of the Company's stockholders is obtained. This limitation shall not apply if the average price paid for all shares issued and sold under the purchase agreement is equal to or greater than $15.56. The Company is not required or permitted to issue any shares of Common Stock under the Lincoln Park purchase agreement if such issuance would breach the Company's obligations under the listing rules of the Nasdaq Stock Market. As consideration for entering into the purchase agreement, the Company issued to Lincoln Park 20,000 shares of Common Stock. Lincoln Park represented to the Company, among other things, that it was an "accredited investor" (as such term is defined in Rule 501(a) of Regulation D under the Securities Act of 1933, as amended (the "Securities Act"), and the Company sold the securities in reliance upon an exemption from registration contained in Section 4(2) under the Securities Act. The securities sold may not be offered or sold in the United States absent registration or an applicable exemption from registration requirements. The net proceeds to the Company under the Lincoln Park purchase agreement will depend on the frequency and prices at which the Company may sell shares of Common Stock to Lincoln Park. The Company expects that the proceeds received from the initial purchase and any additional proceeds from future sales to Lincoln Park will be used to fund the development of the Company's clinical and preclinical programs, for other research and development activities and for general corporate purposes. On January 5, 2016, the Company entered into the Securities Purchase Agreement with an institutional investor providing for the issuance and sale by the Company of 193,684 shares of the Company's Common Stock, at a purchase price of $9.50 per share and warrants to purchase up to 96,842 shares of the Company's Common Stock for aggregate gross proceeds of $1,840,000. The Warrants will be exercisable from July 11, 2016 through July 11, 2021 at an exercise price of $11.50 per share of Common Stock, subject to customary adjustments. Net proceeds from the sale of the Common Stock and Warrants (not including any future proceeds from the exercise of the Warrants) were approximately $1,609,000 after deducting certain fees due to the placement agent and the Company's estimated transaction expenses. The net proceeds received by the Company from the transactions will be used to fund the development of the Company's clinical and preclinical programs, for other research and development activities and for general corporate purposes. The shares of Common Stock sold by the Company pursuant to the Securities Purchase Agreement were sold pursuant to an effective shelf registration statement on Form S-3, which was initially filed with the SEC on October 8, 2014 and subsequently declared effective on November 20, 2014 (File No. 333-199219). The Warrants were issued and sold without registration under the Securities Act in reliance on the exemptions provided by Section 4(a)(2) of the Securities Act and/or Regulation D promulgated thereunder and in reliance on similar exemptions under applicable state laws. Accordingly, the Warrants and the shares of Common Stock underlying the Warrants may not be offered or sold except pursuant to an effective registration statement under the Securities Act or pursuant to an available exemption from, or in a transaction not subject to, the registration requirements of the Securities Act and in accordance with applicable state securities laws. These warrants are classified as liabilities because under certain specific circumstances the warrants could require cash settlement. On July 8, 2016, the Company distributed to holders of its Common Stock and to holders of certain of outstanding warrants, at no charge, non-transferable subscription rights to purchase units. Each unit consisted of one share of Common Stock and 0.75 of a tradable warrant representing the right to purchase one share of Common Stock ("Tradeable Warrants"). The offering of units pursuant to the subscription rights is referred to as the "Rights Offering." On July 7, 2016, the Company entered into a dealer-manager agreement (the "Dealer-Manager Agreement") with Maxim Group LLC ("Maxim"), to engage Maxim as dealer-manager for the Rights Offering. In the Rights Offering, holders received 1.5 subscription rights for each share of Common Stock, or each share of Common Stock underlying participating warrants owned on the record date, July 7, 2016. Subscribers whose subscriptions otherwise would have resulted in their beneficial ownership of more than 4.99% of the Company's Common Stock could elect to receive, in lieu of shares of Common Stock in excess of that threshold, pre-funded warrants to purchase the same number of shares of Common Stock for $0.01 ("Pre-Funded Warrants"), and the subscription price per unit consisting of a Pre-Funded Warrant in lieu of a share of Common Stock was reduced by the $0.01 exercise price. The Rights Offering closed on July 29, 2016. Gross proceeds from the offering were $17.4 million, which represents the sale of all 4,256,186, units at approximately $4.10 per unit. Net proceeds were approximately $15.8 million. The Company issued 3,599,786 shares of Common Stock, 3,192,022 Tradable Warrants and 656,400 Pre-Funded Warrants in the Rights Offering. The Tradable Warrants are exercisable for a period of five years for one share of Common Stock at an exercise price of $4.92 per share. After the one-year anniversary of issuance, we may redeem the Tradable Warrants for $0.001 per Tradable Warrant if the volume weighted average price of our Common Stock is above $12.30 for each of 10 consecutive trading days. On August 3, 2016, the Tradable Warrants were listed for trading on the Nasdaq Capital Market under the symbol "ONTXW." The tradable warrants are classified as liabilities because under certain specific circumstances the warrants could require cash settlement. The Pre-Funded Warrants are exercisable for one share of Common Stock at an exercise price of $0.01. The exercise period for the Pre-Funded Warrants is seven years, which may be extended if an exercise would result in the holder's beneficial ownership of our Common Stock exceeding 4.99%. In connection with the Rights Offering, the Company paid to Maxim a cash fee equal to (a) 4.5% of the dollar amount of the units sold to any holders of subscription rights who were beneficial owners of shares of the Company's common stock prior to July 30, 2013, and (b) 8.0% of the dollar amount of the units sold to any other holders of subscription rights, plus a non-accountable expense allowance of $100,000 for expenses incurred in connection with the Rights Offering. A registration statement on Form S-1, as amended (File No. 333-211769), relating to the securities being offered and sold in connection with the Rights Offering was declared effective by the SEC on July 7, 2016. A prospectus and prospectus supplement relating to and describing the terms of the Rights Offering has been filed with the SEC as a part of the registration statement and is available on the SEC's web site at http://www.sec.gov. In December 2016, the Company entered into a sales agreement with FBR Capital Markets & Co. ("FBR") to create an at-the-market equity program under which the Company from time to time may offer and sell shares of its Common Stock through FBR. The Shares to be sold under the Sales Agreement, if any, will be issued and sold pursuant to the Company's shelf registration statement on Form S-3 (File No 333-199219), previously filed with the SEC on October 8, 2014 and declared effective by the SEC on November 20, 2014. A prospectus supplement related to the Company's at-the-market equity program was filed with the SEC on December 5, 2016. There were no sales of Common Stock under this program during the year ended December 31, 2016. During the year ended December 31, 2017, sales under the Sales Agreement were 20,499 shares for net proceeds of approximately $64,000. The Sales Agreement was terminated effective April 19, 2017. On November 9, 2017, the Company entered into a placement agency agreement with Laidlaw & Company (UK) Ltd. relating to the Company's registered direct offering, issuance and sale to select accredited investors of 920,000 shares of the Company's common stock at a price of $1.50 per share on a best efforts basis. These shares are registered under the Securities Act on the Company's Registration Statement on Form S-3 (File No. 333-199219). The offering closed on November 14, 2017. The net proceeds to the Company from the offering, after deducting Placement Agent fees and other expenses, were approximately $1,082,000. The Company intends to use the net proceeds from this offering to fund the development of its clinical and preclinical programs, for other research and development activities and for general corporate purposes, which may include capital expenditures and funding its working capital needs.

Subsequent Events	12 Months Ended
Subsequent Events	Dec. 31, 2017
Subsequent Events
Subsequent Events	19. Subsequent Events Securities Offering On February 8, 2018, the Company entered into an underwriting agreement with H.C. Wainwright & Co., LLC ("HCW"), relating to the public offering of 5,707,500 shares of the Company's common stock, pre-funded warrants to purchase an aggregate of 2,942,500 shares of common stock and preferred stock warrants to purchase up to an aggregate of 865,000 shares of the Company's Series A Convertible Preferred Stock, par value $0.01 per share (the "Series A Preferred Stock"). Each share of common stock or Pre-Funded Warrant, as applicable, was sold together with a Preferred Stock Warrant to purchase a 0.1 share of Series A Preferred Stock at a combined public offering price of $1.01 per share of common stock or $1.00 per Pre-Funded Warrant, as applicable, and accompanying Preferred Stock Warrant. The Company also granted HCW a 30-day option to purchase up to 1,297,500 additional shares of Common Stock at a purchase price of $1.00 per share and Preferred Stock Warrants to purchase up to an aggregate of 129,750 shares of Series A Preferred Stock at a purchase price of $0.01 per Preferred Stock Warrant, less the underwriting discounts and commissions. Prior to closing, HCW exercised this option in full to purchase 1,297,500 additional shares of common stock and Preferred Stock Warrants to purchase129,750 shares of Series A convertible preferred stock. The offering closed on February 12, 2018. Net proceeds from the offering were approximately $8.7 million after deducting underwriting discounts and commissions and other estimated offering expenses payable by the Company. The Company intends to use the net proceeds from the offering to fund the development of its clinical and preclinical programs, for other research and development activities and for general corporate purposes, which may include capital expenditures and funding its working capital needs. The Pre-Funded Warrants are exercisable immediately at an exercise price of $0.01 per share, may be exercised until they are exercised in full, and may be exercised on a cashless basis in certain circumstances specified therein. The Preferred Stock Warrants are exercisable immediately at an exercise price of $1.01 per 0.1 share of Series A Preferred Stock and will expire on the later of (i) the one-year anniversary of the date on which the Company publicly announces through the filing of a Current Report on Form 8-K that the Charter Amendment (defined below) has been filed with the Secretary of State of the State of Delaware and (ii) the earlier of (A) the one-month anniversary of the date on which the Company publically releases topline results of the INSPIRE Pivotal phase 3 that compare the overall survival (OS) of patients in the rigosertib group vs the Physician's Choice group, in all patients and in a subgroup of patients with IPSS-R very high risk and (B) December 31, 2019. The Preferred Stock Warrants may be exercised on a cashless basis in certain circumstances specified therein. Each 0.1 share of Series A Preferred Stock will be convertible into one share of common stock. The Company does not currently have a sufficient number of authorized shares of common stock to cover the shares issuable upon the conversion of Series A Preferred Stock. As a result, before any shares of Series A Preferred Stock can be converted, the Company needs to receive stockholder approval of an amendment (the "Charter Amendment") to its Tenth Amended and Restated Certificate of Incorporation, as amended, to sufficiently increase the authorized shares of common stock to cover the conversion of all outstanding shares of Series A Preferred Stock into common stock. The Company intends to seek such approval at a special meeting of stockholders on March 21, 2018. The Series A Preferred Stock is not convertible until the next business day after the Company files the Charter Amendment with the Secretary of State of the State of Delaware. In addition, a holder of Series A Preferred Stock will be prohibited from converting Series A Preferred Stock into shares of common stock if, as a result of such conversion, the holder, together with its affiliates, would own more than 4.99% of the shares of the Company's shares of common stock then issued and outstanding, which may be increased to 9.99% in certain circumstances. Shares of Series A Preferred Stock will generally have no voting rights, except as required by law and except that the consent of holders of a majority of the outstanding Series A Preferred Stock will be required to (i) alter or change adversely the powers, preferences or rights given to the Series A Preferred Stock or alter or amend the Certificate of Designation, (ii) amend any provision of the Company's certificate of incorporation that would have a materially adverse effect on the rights of the holders of the Series A Preferred Stock, (iii) increase the number of authorized shares of Series A Preferred Stock, or (iv) enter into any agreement with respect to the foregoing. Shares of Series A Preferred Stock will not be entitled to receive any dividends, unless and until specifically declared by the Company's board of directors, and will rank (i) on parity with the Company's common stock on an as-converted basis, (ii) senior to any class or series of the Company's capital stock created thereafter specifically ranking by its terms junior to the Series A Preferred Stock, (iii) on parity to any class or series of the Company's capital stock created thereafter specifically, (iv) ranking by its terms on parity with the Series A Preferred Stock; and (v) junior to any class or series of the Company's capital stock created thereafter specifically ranking by its terms senior to the Series A Preferred Stock. The exercise price and number of shares of common stock or Series A Preferred Stock issuable upon exercise of the Pre-Funded Warrants or Preferred Stock Warrants, as the case may be, and the conversion price and number of shares of common stock issuable upon the conversion of Series A Preferred Stock, is subject to adjustment in the event of any stock split, reverse stock split, stock dividend, recapitalization, reorganization or similar transaction, as described in the Pre-Funded Warrants, Preferred Stock Warrants and the Certificate of Designation of the Series A Preferred Stock, as applicable. The shares of common stock or Pre-Funded Warrants, as applicable, and the accompanying Preferred Stock Warrants could only be purchased together in the offering were issued separately. HCW acted as sole book-running manager for the offering, which was a firm commitment underwritten public offering pursuant to a registration statement on Form S-1 (Registration No. 333-222374) that was declared effective by the SEC on February 7, 2018. The offering was made only by means of a prospectus forming a part of the effective registration statement. The Company paid HCW a commission equal to 7.0% of the gross proceeds of the offering, a management fee equal to 1.0% of the gross proceeds of the offering and other expenses. As additional compensation, the Company issued warrants to HCW exercisable for 49,737.5Series A Preferred Stock, which are convertible into 497,375 shares of common stock subject to the terms of the Series A Preferred Stock. These warrants have substantially the same terms as the Preferred Stock Warrants except that the exercise price per share is equal to $1.2625 per 0.1 share of Series A Preferred Stock. Agreements with Pint License, Development and Commercialization Agreement On March 2, 2018, the Company entered into a License, Development and Commercialization Agreement (the "License Agreement") with Pint International SA (which, together with its affiliate Pint Pharma GmbH, are collectively referred to as "Pint"). Under the terms of the License Agreement, the Company granted Pint an exclusive, royalty-bearing license, with the right to sublicense, under certain Company patent rights and know-how to develop and commercialize any pharmaceutical product (the "Product") containing rigosertib in all uses of rigosertib or the Product in humans (the "Field") in Latin America countries (the "Territory," including Argentina, Belize, Bolivia, Brazil, Chile, Colombia, Costa Rica, Cuba, Dominican Republic, Ecuador, El Salvador, French Guiana, British Guiana, Suriname, Guatemala, Haiti, Honduras, Mexico, Nicaragua, Panama, Paraguay, Peru, Uruguay and Venezuela). The Company retains the right to develop and commercialize pharmaceutical products containing rigosertib worldwide except for the sale of the Product in the Field in the Territory. Pint has agreed to make an upfront equity investment and a subsequent equity investment in the Company's common stock as described under "Securities Purchase Agreement" below. In addition, the Company could receive up to $42.75 million in additional regulatory, development and sales-based milestone payments as well as tiered, double digit royalties based on net aggregate net sales in the Territory. Pint also has agreed to purchase rigosertib and the Product exclusively from the Company in accordance with a supply and quality agreement between the parties. Pint may terminate the License Agreement in whole (but not in part) at any time upon 45 days' prior written notice. The License Agreement also contains customary provisions for termination by either party in the event of breach of the License Agreement by the other party, subject to a cure period, or bankruptcy of the other party. Securities Purchase Agreement In connection with the License Agreement, on March 2, 2018, the Company and Pint also entered into a Securities Purchase Agreement (the "Securities Purchase Agreement"), under which Pint has agreed to make an upfront equity investment. Closing of the upfront equity investment (the "Initial Closing") will be the later of April 1, 2018 and the date on which the Company files its charter amendment to increase its authorized shares of common stock with the Delaware Secretary of State. Pursuant to these terms, Pint will purchase shares at a premium to the average of the volume weighted average price of common stock for the ten consecutive trading days ended March 2, 2018 at the Initial Closing. In the event that the Initial Closing does not occur by May 1, 2018, Pint will pay the Company the share purchase premium (the "Initial Closing Premium"), and the Company will sell to Pint shares of common stock when the Company has sufficient authorized shares on or before December 31, 2018. If the Initial Closing does not occur and by the close of business on December 31, 2018, the Company has not filed the charter amendment with the Secretary of State of the State of Delaware, the Securities Purchase Agreement will terminate. So long as Pint has paid the Initial Closing Premium, the License Agreement will not terminate due to Pint's failure to purchase shares in the upfront equity investment. In addition, when the FDA approves a New Drug Application (the "NDA") for the Product, Pint will reimburse the Company for certain research and development expenses. Half of the reimbursement amount will be paid in cash, the other half of the amount will be by an equity investment at a premium to the average of the volume weighted average price of common stock for the ten consecutive trading days ended on the day the FDA approves the NDA. In the event the Securities Purchase Agreement is terminated due to nonoccurrence of the Initial Closing, and the Company not filing the charter amendment by December 31, 2018 as described above, Pint will instead pay the Company a share purchase premium(the "Securities Purchase Half Premium"), based on the average of the daily volume weighted average price of common stock for ten consecutive trading days ending on the date the NDA is approved by the FDA, multiplied by the Securities Purchase Half Number of Shares, subject to certain conditions. So long as Pint has paid the Securities Purchase Half Premium, the License Agreement will not terminate due to Pint's failure to purchase shares in connection with the FDA's approval of the NDA. Pint has agreed that the shares it purchases under the Securities Purchase Agreement will be subject to lock-up restrictions for one year from the date of the Initial Closing or, if Pint pays the Initial Closing Premium, the date of such payment (the "Strategic Lock-Up Period"), and certain additional lock-up provisions as applicable. Pint is entitled to registration rights if it holds Registrable Securities (as defined in the Securities Purchase Agreement) upon the expiration of the Strategic Lock-Up Period, and the Company has agreed to use its reasonable best efforts to register such Registrable Securities on a registration statement on Form S-3 (or another appropriate form of registration statement if the Company is not eligible to use Form S-3), to cause such registration statement be declared effective by the Securities and Exchange Commission, and to maintain the effectiveness of such registration statement until Pint no longer holds any Registrable Securities. Until Pint no longer holds any Registrable Securities, Pint also has the right to participate in any equity issuance by the Company in a private placement to institutional investors which includes at least one institutional investor that is not an affiliate of the Company. Subject to certain notice requirements, if Pint decides to participate, the Company will allow Pint to participate up to Pint's pro rata share of beneficial ownership of the Company's outstanding common stock on the same terms, conditions and price as with other investors. Special Meeting of Stockholders on March 21, 2018 On February 28, 2018, The Company filed with the Securities and Exchange Commission a definitive proxy statement on Schedule 14A relating to the Special Meeting of Stockholders the Company intends to hold on March 21, 2018 to seek stockholders' approval of an amendment to the Company's Tenth Amended and Restated Certificate of Incorporation, as amended, to increase the number of authorized shares of capital stock from 30,000,000 shares to 105,000,000 shares in order to increase the number of authorized shares of common stock from 25,000,000 shares to 100,000,000 shares. Warrant Liability Subsequent to December 31, 2017 there was a decrease in the fair value of the warrant liability calculated using the NASDAQ Capital Market quoted price. The fair value at December 31, 2017 was $1,773,000. The estimated fair value at March 16, 2018 is approximately $1,007,000. The estimated decrease in the warrant liability would decrease the Company's net loss by approximately $766,000.

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2017

Summary of Significant Accounting Policies

Basis of Presentation

Segment Information

Use of Estimates

Concentrations of Credit Risk and Off-Balance Sheet Risk

Cash and Cash Equivalents

Fair Value of Financial Instruments

Property and Equipment

		Estimated Useful Life
Lab equipment		5 - 6 years
Software		3 years
Computer and office equipment		5 - 6 years
Leasehold improvements		Shorter of the lease term or estimated useful life

Upon retirement or sale, the cost of the disposed asset and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is recognized.

Warrant Accounting

Foreign Currency Translation

Revenue Recognition

Royalties are recorded as earned in accordance with the contract terms when third party sales can be reliably measured and collectability is reasonably assured.

Research and Development Expenses

Comprehensive Loss

Comprehensive loss is defined as the change in equity of a business enterprise during a period from transactions and other events and circumstances from non-owner sources.

Income Taxes

Stock-Based Compensation Expense

Clinical Trial Expense Accruals

Collaboration Arrangements

Basic and Diluted Net Loss Per Share of Common Stock

Recent Accounting Pronouncements

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2017

Summary of Significant Accounting Policies

Schedule of estimated useful lives used to depreciate the Company's assets

		Estimated Useful Life
Lab equipment		5 - 6 years
Software		3 years
Computer and office equipment		5 - 6 years
Leasehold improvements		Shorter of the lease term or estimated useful life

Property and Equipment (Tables)

12 Months Ended

Dec. 31, 2017

Property and Equipment

Schedule of property and equipment and related accumulated depreciation

	December 31,
	2017			2016
Laboratory equipment	$	1,037,000		$	1,037,000
Software		92,000			92,000
Computer and office equipment		354,000			354,000
Leasehold improvements		745,000			745,000

		2,228,000			2,228,000
Less accumulated depreciation		(2,164,000	)		(2,076,000	)

	$	64,000		$	152,000

Warrants (Tables)

12 Months Ended

Dec. 31, 2017

Warrants

Schedule of warrants outstanding and warrant activity

Description	Classification	Exercise Price		Expiration Date		Balance Decemeber 31, 2016		Warrants Issued		Warrants Exercised			Warrants Expired		Balance December 31, 2017
Non-tradable warrants	Liability	$	11.50		July 2021		96,842		—		—			—		96,842
Tradable warrants	Liability	$	4.92		July 2021		3,192,022		—		—			—		3,192,022
Non-tradable pre-funded warrants	Equity	$	0.01		July 2023		236,907		—		(231,000	)		—		5,907

							3,525,771		—		(231,000	)		—		3,294,771

- Definition

Tabular disclosure of warrants or rights issued. Warrants and rights outstanding are derivative securities that give the holder the right to purchase securities (usually equity) from the issuer at a specific price within a certain time frame. Warrants are often included in a new debt issue to entice investors by a higher return potential. The main difference between warrants and call options is that warrants are issued and guaranteed by the company, whereas options are exchange instruments and are not issued by the company. Also, the lifetime of a warrant is often measured in years, while the lifetime of a typical option is measured in months. Disclose the title of issue of securities called for by warrants and rights outstanding, the aggregate amount of securities called for by warrants and rights outstanding, the date from which the warrants or rights are exercisable, and the price at which the warrant or right is exercisable.

+ References + Details

Net Loss Per Share of Common Stock (Tables)

12 Months Ended

Dec. 31, 2017

Net Loss Per Share of Common Stock

Schedule of computation of basic and diluted earnings per share

	Year ended December 31,
	2017			2016
Basic and diluted net loss per share of common stock:
Net loss attributable to Onconova Therapeutics, Inc	$	(24,092,000	)	$	(19,667,000	)


Weighted average shares of common stock outstanding		9,000,326			4,426,639


Net loss per share of common stock—basic and diluted	$	(2.68	)	$	(4.44	)

Schedule of antidilutive securities which have been excluded from the computation of diluted weighted average shares outstanding

	December 31,
	2017		2016
Warrants		3,294,771		3,525,771
Stock options		894,996		746,353

		4,189,767		4,272,124

Revenue (Tables)

12 Months Ended

Dec. 31, 2017

Revenue

Schedule of recognized revenue under funding, license and collaboration agreements

	Year ended December 31,
	2017		2016
Baxalta	$	—	$	4,999,000
SymBio		787,000		547,000

	$	787,000	$	5,546,000

Balance Sheet Detail (Tables)

12 Months Ended

Dec. 31, 2017

Balance Sheet Detail

Schedule of prepaid expenses and other current assets

	December 31,
	2017		2016
Research and development	$	514,000	$	1,075,000
Manufacturing		48,000		90,000
Insurance		181,000		350,000
Other		77,000		73,000

	$	820,000	$	1,588,000

Schedule of accrued expenses and other current liabilities

	December 31,
	2017		2016
Research and development	$	1,912,000	$	2,376,000
Employee compensation		1,258,000		1,573,000
Professional fees		165,000		235,000
Other		—		198,000

	$	3,335,000	$	4,382,000

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2017

Fair Value Measurements

Schedule of Black-Scholes option pricing model assumptions

The Company estimated the fair value of the non-tradable warrant liability at December 31, 2017, using the Black-Scholes option pricing model with the following weighted-average assumptions:

Risk-free interest rate		2.09%
Expected volatility		75.47%
Expected term		3.53 years
Expected dividend yield		0%

Schedule of financial assets and liabilities measured at fair value on a recurring basis

	Fair Value Measurement as of:
	December 31, 2017								December 31, 2016
	Level 1		Level 2		Level 3		Balance		Level 1		Level 2		Level 3		Balance
Tradable warrants liability	$	1,755,000	$	—	$	—	$	1,755,000	$	—	$	—	$	3,338,000	$	3,338,000
Non-tradable warrants liability		—		—		18,000		18,000		—		—		63,000		63,000

Total	$	1,755,000	$	—	$	18,000	$	1,773,000	$	—	$	—	$	3,401,000	$	3,401,000

Schedule of reconciliation of liabilities measured at fair value on a recurring basis using significant unobservable inputs (Level 3)

	Warrant Liability
Balance at December 31, 2015	$	—
Issuance of warrants		7,389,000

Change in fair value upon re-measurement		(3,988,000	)

Balance at December 31, 2016	$	3,401,000


Reclassification of tradable warrants to Level 1	$	(4,857,000	)
Change in fair value upon re-measurement		1,474,000

Balance at December 31, 2017	$	18,000

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Income Taxes

Schedule of income taxes based on income (loss) before income tax expense

	December 31,
	2017			2016
Domestic	$	(24,131,000	)	$	(19,738,000	)
Foreign		52,000			85,000

	$	(24,079,000	)	$	(19,653,000	)

Schedule of provision for income taxes

	December 31,
	2017		2016
Current
US Federal	$	—	$	—
State and Local		—		—
Foreign		13,000		14,000

Total Current	$	13,000	$	14,000

Deferred
US Federal	$	—	$	—
State and Local		—		—
Foreign		—		—

Total Deferred	$	—	$	—

Total Expense (Benefit)	$	13,000	$	14,000

Schedule of principal components of the Company's deferred tax assets

	December 31,
	2017			2016
Deferred tax assets:
Net operating loss carryovers	$	57,557,000		$	75,829,000
R&D tax credits		79,725,000			71,811,000
Non-qualified stock options		5,355,000			7,413,000
Deferred revenue		1,242,000			2,030,000
Charitable contributions		4,000			6,000
Accrued expenses		407,000			618,000
Fixed assets		85,000			102,000

Deferred tax assets		144,375,000			157,809,000
Less valuation allowance		(144,375,000	)		(157,809,000	)

Net deferred tax assets	$	—		$	—

Schedule of reconciliation of income tax (expense) benefit at the statutory federal income tax rate and income taxes as reflected in the financial statements

	December 31,
	2017			2016
Federal income tax expense at statutory rate		34.0	%		34.0	%
Permanent items		(8.1	)		(5.9	)
Effect of Tax Act		(116.9	)		—
State income tax, net of federal benefit		5.8			(15.8	)
Tax credits		29.3			33.5
Provision to return		—			(1.5	)
Change in valuation allowance		55.8			(44.5	)
Other		—			0.1

Effective income tax rate		(0.1	)%		(0.1	)%

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

Stock-Based Compensation

Schedule of stock-based compensation expense

	Year ended December 31,
	2017		2016
General and administrative	$	975,000	$	1,887,000
Research and development		735,000		2,042,000

	$	1,710,000	$	3,929,000

Schedule of stock option activity

				Options Outstanding
	Shares Available for Grant			Number of Shares			Weighted- Average Exercise Price		Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value
Balance, December 31, 2016		6,275			746,353		$	53.50		7.70	$	0
Authorized		200,000			—
Granted		(198,811	)		198,811		$	2.57
Exercised		—			—		$	—
Forfeitures		50,168			(50,168	)	$	85.25

Balance, December 31, 2017		57,632			894,996		$	40.41		7.38	$	0

Vested or expected to vest, December 31, 2017					882,972		$	57.02		6.72	$	0

Exercisable at December 31, 2017					604,555		$	57.02		6.72	$	0

Schedule of information with respect to stock options outstanding and exercisable

Information with respect to stock options outstanding and exercisable at December 31, 2017 is as follows:

Exercise Price	Shares		Exercisable
$1.51 - $6.50		488,818		233,957
$14.80 - $15.00		37,375		25,326
$23.20 - $39.80		99,029		79,180
$43.40 - $75.30		91,345		87,706
$132.80 - $151.20		173,079		173,036
$277.10 - $291.40		5,350		5,350

		894,996		604,555

Schedule of weighted-average assumptions used for estimating the fair value of the stock compensation granted

	Year ended December 31, 2017
	2017	2016
Risk-free interest rate	2.09%	1.49%
Expected volatility	79.02%	78.7%
Expected term	5.98 years	5.68 years
Expected dividend yield	0%	0%
Weighted average grant date fair value	$1.76	$3.75

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2017

Commitments and Contingencies

Schedule of future minimum lease payments under non-cancellable leases

	December 31, 2017
2018	$	170,000
2019		28,000

Total minimum lease payments	$	198,000

Nature of Business - The Company - Reverse Stock Split (Details)	May 31, 2016 shares	Dec. 31, 2017 shares	Dec. 31, 2016 shares	May 30, 2016 shares
Nature of Business
Reverse stock split ratio	0.1
Common Stock authorized (in shares)	25,000,000	25,000,000	25,000,000	75,000,000

Nature of Business - Liquidity - Financial Statement Items (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Nature of Business
Net loss	$ (24,092)	$ (19,667)
Accumulated deficit	362,316	338,224
Cash and cash equivalents	$ 4,024	$ 21,450	$ 19,849

Nature of Business - Liquidity - Sale of Stock (Details) $ / shares in Units, $ in Thousands		12 Months Ended
	Jul. 30, 2013 USD ($) $ / shares shares	Dec. 31, 2017 class $ / shares	Dec. 31, 2016 $ / shares
Sale of Securities
Number of series denominated as Series A through Series J preferred stock \| class		10
Common stock, par value (in dollars per share)		$ 0.01	$ 0.01
IPO
Sale of Securities
Issuance of stock (in shares) \| shares	594,167
Common stock, par value (in dollars per share)	$ 0.01
Price per share (in dollars per share)	$ 150.00
Proceeds from initial public offering of common stock, net of issuance costs \| $	$ 79,811

Nature of Business - Liquidity - Sales and Purchase Agreements (Details) - Purchase agreement - Lincoln Park - USD ($) $ in Thousands		1 Months Ended
	Oct. 08, 2015	Oct. 31, 2015
Sale of Securities
Aggregate offering price	$ 15,000	$ 15,000
Net proceeds from sales of common stock	$ 1,500	$ 1,500
Issuance of stock (in shares)	84,676	84,676

Nature of Business - Liquidity - Securities Purchase Agreement (Details) - Securities Purchase Agreement $ in Thousands	Jan. 05, 2016 USD ($) shares
Sale of Securities
Issuance of stock (in shares)	193,684
Aggregate net proceeds \| $	$ 1,609
Common Stock Warrants
Sale of Securities
Shares of common stock warrants will purchase (in shares)	96,842

Nature of Business - Liquidity - Rights Offering (Details) - USD ($) $ in Millions	Feb. 12, 2018	Feb. 07, 2018	Jul. 29, 2016
Dealer-Manager Agreement, rights offering
Sale of Securities
Issuance of stock (in shares)			3,599,786
Aggregate net proceeds			$ 15.8
Tradable warrants \| Dealer-Manager Agreement, rights offering
Sale of Securities
Warrants issued (in shares)			3,192,022
Pre-funded warrants \| Dealer-Manager Agreement, rights offering
Sale of Securities
Warrants issued (in shares)			656,400
Subsequent Events
Sale of Securities
Proceeds from Issuance or Sale of Equity	$ 8.7
Subsequent Events \| Dealer-Manager Agreement, rights offering
Sale of Securities
Issuance of stock (in shares)		7,005,000
Aggregate net proceeds	$ 8.7
Subsequent Events \| Pre-funded warrants \| Series A Convertible Preferred Stock
Sale of Securities
Class of Warrant or Right, Number of Securities Called by Warrants or Rights	1,044,487.5
Subsequent Events \| Pre-funded warrants \| Securities Offering
Sale of Securities
Class of Warrant or Right, Number of Securities Called by Warrants or Rights	2,942,500

Nature of Business - Liquidity - Underwritten Public Offering (Details) - USD ($) $ in Millions	Nov. 14, 2017	May 17, 2017	Apr. 26, 2017
The Offering
Subsidiary, Sale of Stock [Line Items]
Issuance of stock (in shares)	920,000		2,476,190
Net proceeds from sales of common stock	$ 1.1	$ 5.3
Underwriter's option \| Laidlaw \| Maximum
Subsidiary, Sale of Stock [Line Items]
Issuance of stock (in shares)			363,580

Summary of Significant Accounting Policies - Concentrations of Credit Risk and Off-Balance Sheet Risk (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Concentrations of Credit Risk and Off-Balance Sheet Risk
Off-balance sheet risk, asset	$ 0
Off-balance sheet risk, liability	$ 0

Summary of Significant Accounting Policies - Property and Equipment (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)
Property and Equipment
Impairment losses	$ 0
Laboratory equipment \| Minimum
Property and Equipment
Estimated useful lives	P5Y
Laboratory equipment \| Maximum
Property and Equipment
Estimated useful lives	P6Y
Software
Property and Equipment
Estimated useful lives	P3Y
Computer and office equipment \| Minimum
Property and Equipment
Estimated useful lives	P5Y
Computer and office equipment \| Maximum
Property and Equipment
Estimated useful lives	P6Y

Summary of Significant Accounting Policies - Stock Based Compensation Expense (Details) - USD ($)		12 Months Ended
	Apr. 23, 2013	Dec. 31, 2017	Dec. 31, 2016
Stock-Based Compensation Expense
Stock-based compensation expense		$ 1,710,000	$ 3,929,000
Unrecognized compensation expense of unvested liability awards		0
Options granted through April 23, 2013 \| Stock options \| 2007 Plan
Stock-Based Compensation Expense
Reclassification of options from liabilities to stockholders' deficit	$ 14,482,000
Stock-based compensation expense			244,000
Unrecognized compensation expense of unvested liability awards		$ 0	$ 0

Summary of Significant Accounting Policies - Recent Accounting Pronouncements (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
ASU 2016-18
Recent Accounting Pronouncements
Restricted Cash	$ 50	$ 50	$ 50

Property and Equipment - Property and Equipment and Related Accumulated Depreciation (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property and Equipment
Property and equipment, gross	$ 2,228	$ 2,228
Less accumulated depreciation	(2,164)	(2,076)
Property and equipment, net	64	152
Laboratory equipment
Property and Equipment
Property and equipment, gross	1,037	1,037
Software
Property and Equipment
Property and equipment, gross	92	92
Computer and office equipment
Property and Equipment
Property and equipment, gross	354	354
Leasehold improvements
Property and Equipment
Property and equipment, gross	$ 745	$ 745

Warrants (Details)	12 Months Ended
Warrants (Details)	Dec. 31, 2017 $ / shares shares
Warrants outstanding and warrant activity
Balance at beginning of the period (in shares)	3,525,771
Warrants Exercised (in shares)	(231,000)
Balance at end of the period (in shares)	3,294,771
Non-tradable warrants expiring July 2021, liability
Warrants
Warrant exercise price (in dollars per share) \| $ / shares	$ 11.50
Warrants outstanding and warrant activity
Balance at beginning of the period (in shares)	96,842
Balance at end of the period (in shares)	96,842
Tradable warrants expiring July 2021, liability
Warrants
Warrant exercise price (in dollars per share) \| $ / shares	$ 4.92
Warrants outstanding and warrant activity
Balance at beginning of the period (in shares)	3,192,022
Balance at end of the period (in shares)	3,192,022
Non-tradable pre-funded warrants expiring July 2023, equity
Warrants
Warrant exercise price (in dollars per share) \| $ / shares	$ 0.01
Warrants outstanding and warrant activity
Balance at beginning of the period (in shares)	236,907
Warrants Exercised (in shares)	(231,000)
Balance at end of the period (in shares)	5,907

Net Loss Per Share of Common Stock - Computation of Basic and Diluted Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Basic and diluted net loss per share of common stock:
Net loss attributable to Onconova Therapeutics, Inc.	$ (24,092)	$ (19,667)
Weighted average shares of common stock outstanding (in shares)	9,000,326	4,426,639
Net loss per share of common stock, basic and diluted (in dollars per share)	$ (2.68)	$ (4.44)

Net Loss Per Share of Common Stock (Details) - shares	12 Months Ended
Net Loss Per Share of Common Stock (Details) - shares	Dec. 31, 2017	Dec. 31, 2016
Potentially dilutive securities outstanding excluded from the computation of diluted weighted average shares as they would be antidilutive
Potentially dilutive securities outstanding excluded from the computation of diluted weighted average shares	4,189,767	4,272,124
Warrants
Potentially dilutive securities outstanding excluded from the computation of diluted weighted average shares as they would be antidilutive
Potentially dilutive securities outstanding excluded from the computation of diluted weighted average shares	3,294,771	3,525,771
Stock options
Potentially dilutive securities outstanding excluded from the computation of diluted weighted average shares as they would be antidilutive
Potentially dilutive securities outstanding excluded from the computation of diluted weighted average shares	894,996	746,353

Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
Revenue (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Revenue
Revenues	$ 787	$ 5,546
Baxalta \| License and collaboration
Revenue
Revenues		4,999
SymBio \| License and collaboration
Revenue
Revenues	$ 787	$ 547

Balance Sheet Detail - Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Prepaid expenses and other current assets:
Research and development	$ 514	$ 1,075
Manufacturing	48	90
Insurance	181	350
Other	77	73
Total	$ 820	$ 1,588

Balance Sheet Detail - Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accrued expenses and other current liabilities:
Research and development	$ 1,912	$ 2,376
Employee compensation	1,258	1,573
Professional fees	165	235
Other		198
Total	$ 3,335	$ 4,382

Fair Value Measurements - Securities Purchase Agreement (Details) - Securities Purchase Agreement $ / shares in Units, $ in Thousands	Jan. 05, 2016 USD ($) $ / shares shares
Sale of Securities
Issuance of stock (in shares)	193,684
Share price (in dollars per share) \| $ / shares	$ 9.50
Aggregate gross proceeds \| $	$ 1,840
Common Stock Warrants
Sale of Securities
Shares of common stock warrants will purchase (in shares)	96,842

Fair Value Measurements - Rights Offering (Details) - Dealer-Manager Agreement, rights offering - $ / shares	Feb. 07, 2018	Jul. 29, 2016
Sale of Securities
Issuance of stock (in shares)		3,599,786
Subsequent Events
Sale of Securities
Issuance of stock (in shares)	7,005,000
Tradable warrants
Sale of Securities
Rights or warrants issued (in shares)		3,192,022
Exercisable, term (in years)		5 years
Shares into which each warrant can be converted (in shares)		1
Exercise price (in dollars per share)		$ 4.92
Redemption period (in years)		1 year
Redemption price (in dollars per share)		$ 0.001
Volume weighted average price per share of common stock (in dollars per share)		$ 12.30
Threshold consecutive trading days (in days)		10 days
Pre-funded warrants
Sale of Securities
Rights or warrants issued (in shares)		656,400
Shares into which each warrant can be converted (in shares)		1
Exercise price (in dollars per share)		$ 0.01

Fair Value Measurements - Fair Value Assumptions (Details) - Non-tradable Warrants	12 Months Ended
	Dec. 31, 2017
Assumption used to estimate the fair value of warrant liability by utilizing the Black-Scholes option pricing model
Risk-free interest rate (as a percent)	2.09%
Expected volatility (as a percent)	75.47%
Expected term	3 years 6 months 11 days
Expected dividend yield (as a percent)	0.00%

Fair Value Measurements - Fair Value Hierarchy Table (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Liabilities measured at fair value
Warrant liability	$ 1,773
Recurring basis
Liabilities measured at fair value
Total	1,773	$ 3,401
Recurring basis \| Tradable warrants
Liabilities measured at fair value
Warrant liability	1,755	3,338
Recurring basis \| Non-tradable Warrants
Liabilities measured at fair value
Warrant liability	18	63
Recurring basis \| Level 1
Liabilities measured at fair value
Total	1,755
Recurring basis \| Level 1 \| Tradable warrants
Liabilities measured at fair value
Warrant liability	1,755
Recurring basis \| Level 3
Liabilities measured at fair value
Total	18	3,401
Recurring basis \| Level 3 \| Tradable warrants
Liabilities measured at fair value
Warrant liability		3,338
Recurring basis \| Level 3 \| Non-tradable Warrants
Liabilities measured at fair value
Warrant liability	$ 18	$ 63

Fair Value Measurements - Reconciliation of Level 3 Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of the warrant liability measured at fair value
Balance at the beginning of the period	$ 3,401
Issuance of warrants		$ 7,389
Change in fair value upon re-measurement	1,474	(3,988)
Balance at the end of the period	18	$ 3,401
Tradable warrants
Reconciliation of the warrant liability measured at fair value
Reclassification of tradable warrants to Level 1	$ (4,857)

Fair Value Measurements - Transfers (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Fair Value Measurements
Amount of transfers of assets out of Level 1 into Level 2	$ 0
Amount of transfers of assets out of Level 2 into Level 1	0
Amount of transfers of liabilities out of Level 1 into Level 2	0
Amount of transfers of liabilities out of Level 2 into Level 1	$ 0

Income Taxes - Income (Loss) before Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Income taxes based on income (loss) before income tax expense
Domestic	$ (24,131)	$ (19,738)
Foreign	52	85
Net loss before income taxes	$ (24,079)	$ (19,653)

Income Taxes - Provision for Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Current
Foreign	$ 13	$ 14
Total Current	13	14
Total Expense	$ 13	$ 14

Income Taxes - Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Net operating loss carryovers	$ 57,557	$ 75,829
R&D tax credits	79,725	71,811
Non-qualified stock options	5,355	7,413
Deferred revenue	1,242	2,030
Charitable contributions	4	6
Accrued expenses	407	618
Fixed assets	85	102
Deferred tax assets	144,375	157,809
Less valuation allowance	(144,375)	(157,809)
Net deferred tax assets	$ 0	$ 0

Income Taxes - Reconciliation of Income Tax (Expense) Benefit at the Statutory Federal Income Tax Rate and Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of income tax (expense) benefit at the statutory federal income tax rate and income taxes
Federal income tax expense at statutory rate (as a percent)		34.00%	34.00%
Permanent items (as a percent)		(8.10%)	(5.90%)
Effect of Tax Act (as a percent)		(116.90%)
State income tax, net of federal benefit (as a percent)		5.80%	(15.80%)
Tax credits (as a percent)		29.30%	33.50%
Provision to return (as a percent)			(1.50%)
Change in valuation allowance (as a percent)		55.80%	(44.50%)
Other (as a percent)			0.10%
Effective income tax rate (as a percent)		(0.10%)	(0.10%)
Deferred tax assets		$ 28,100
Accumulated foreign earnings provisional income tax expense		$ 115
Forecast
Reconciliation of income tax (expense) benefit at the statutory federal income tax rate and income taxes
Federal income tax expense at statutory rate (as a percent)	21.00%

Stock-Based Compensation - Common Stock Reserved for Issuance and Shares Available for Future Issuance (Details) - Stock options - shares	Dec. 31, 2017	Dec. 31, 2016	Jul. 31, 2013
Stock-Based Compensation
Common Stock reserved for issuance (in shares)			610,783
Evergreen provision, percentage of issued and outstanding common stock (as a percent)			4.00%
Evergreen provision, shares (in shares)			200,000
Common Stock available for future issuance (in shares)	57,632	6,275

Stock-Based Compensation - Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Stock-Based Compensation
Net tax benefits related to the stock-based compensation costs	$ 0
Total stock-based compensation	1,710	$ 3,929
General and administrative
Stock-Based Compensation
Total stock-based compensation	975	1,887
Research and development
Stock-Based Compensation
Total stock-based compensation	$ 735	$ 2,042

Stock-Based Compensation - Summary of Stock Option Activity (Details) - Stock options - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Shares Available for Grant
Balance at the beginning of the period (in shares)	6,275
Authorized (in shares)	200,000
Granted (in shares)	(198,811)
Forfeitures (in shares)	(50,168)
Balance at the end of the period (in shares)	57,632	6,275
Number of Shares
Balance at the beginning of the period (in shares)	746,353
Granted (in shares)	(198,811)
Forfeitures (in shares)	(50,168)
Balance at the end of the period (in shares)	894,996	746,353
Vested or expected to vest at the end of the period (in shares)	882,972
Exercisable at the end of the period (in shares)	604,555
Weighted-Average Exercise Price
Balance at the beginning of the period (in dollars per share)	$ 53.50
Granted (in dollars per share)	2.57
Forfeitures (in dollars per share)	85.25
Balance at the end of the period (in dollars per share)	40.41	$ 53.50
Vested or expected to vest at the end of the period (in dollars per share)	57.02
Exercisable at the end of the period (in dollars per share)	$ 57.02
Additional Disclosures
Weighted average remaining contractual term	7 years 4 months 17 days	7 years 8 months 12 days
Weighted average remaining contractual term of options vested or expected to vest	6 years 8 months 19 days
Weighted average remaining contractual term of options exercisable	6 years 8 months 19 days
Aggregate intrinsic value of options outstanding	$ 0	$ 0
Aggregate intrinsic value of options vested or expected to vest	0
Aggregate intrinsic value of options exercisable	$ 0

Stock-Based Compensation - Stock Options Outstanding and Exercisable (Details) - Stock options	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Share-Based Compensation
Shares (in shares)	894,996
Exercisable (in shares)	604,555
Exercise Price Range $1.51 - $6.50
Share-Based Compensation
Exercise price, lower range limit (in dollars per share) \| $ / shares	$ 1.51
Exercise price, upper range limit (in dollars per share) \| $ / shares	$ 6.50
Shares (in shares)	488,818
Exercisable (in shares)	233,957
Exercise Price Range $14.80 - $15.00
Share-Based Compensation
Exercise price, lower range limit (in dollars per share) \| $ / shares	$ 14.80
Exercise price, upper range limit (in dollars per share) \| $ / shares	$ 15.00
Shares (in shares)	37,375
Exercisable (in shares)	25,326
Exercise Price Range $23.20 - $39.80
Share-Based Compensation
Exercise price, lower range limit (in dollars per share) \| $ / shares	$ 23.20
Exercise price, upper range limit (in dollars per share) \| $ / shares	$ 39.80
Shares (in shares)	99,029
Exercisable (in shares)	79,180
Exercise Price Range $43.40 - $75.30
Share-Based Compensation
Exercise price, lower range limit (in dollars per share) \| $ / shares	$ 43.40
Exercise price, upper range limit (in dollars per share) \| $ / shares	$ 75.30
Shares (in shares)	91,345
Exercisable (in shares)	87,706
Exercise Price Range $132.80 - $151.20
Share-Based Compensation
Exercise price, lower range limit (in dollars per share) \| $ / shares	$ 132.80
Exercise price, upper range limit (in dollars per share) \| $ / shares	$ 151.20
Shares (in shares)	173,079
Exercisable (in shares)	173,036
Exercise Price Range $277.10 - $291.40
Share-Based Compensation
Exercise price, lower range limit (in dollars per share) \| $ / shares	$ 277.10
Exercise price, upper range limit (in dollars per share) \| $ / shares	$ 291.40
Shares (in shares)	5,350
Exercisable (in shares)	5,350

Stock-Based Compensation - Options Granted after April 23, 2013 - Unrecognized Compensation Expense (Details) - Options granted after April 23, 2013 - Stock options $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)
Stock-Based Compensation
Unrecognized compensation expense related to unvested stock options	$ 1,065
Weighted-average period for recognizing unrecognized compensation expense related to unvested stock options (in years)	1 year 8 months 19 days

Stock-Based Compensation - Options Granted after April 23, 2013 - Fair Value Assumptions (Details) - Options granted after April 23, 2013 - Stock options - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Assumptions used
Risk-free interest rate (as a percent)	2.09%	1.49%
Expected volatility (as a percent)	79.02%	78.70%
Expected term (in years)	5 years 11 months 23 days	5 years 8 months 5 days
Expected dividend yield (as a percent)	0.00%	0.00%
Weighted average grant fair value (in dollars per share)	$ 1.76	$ 3.75
Annualized forfeiture rate (as a percent)	4.14%	4.14%

Stock-Based Compensation - Options Granted through April 23, 2013 (Details) - USD ($)	Apr. 23, 2013	Dec. 31, 2017	Dec. 31, 2016
Stock-Based Compensation
Unrecognized compensation expense of unvested liability awards		$ 0
Stock options \| 2007 Plan \| Options granted through April 23, 2013
Stock-Based Compensation
Reclassification to stockholders' deficit	$ 14,482,000
Unrecognized compensation expense of unvested liability awards		$ 0	$ 0

Employee Benefit Plan (Details) - Retirement Savings Plan - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Minimum age of employees required to be eligible for participation	21 years
Minimum working hours per year required to be eligible for participation	1000 hours
Employer's match for every dollar of the first specified percentage of payroll that employees invest	$ 0.75
Employer's matching contribution percentage	6.00%
Contributions	$ 124,000	$ 146,000

Commitments and Contingencies - Office and Lab Space in Newton, Pennsylvania (Details)	1 Months Ended	12 Months Ended					19 Months Ended
	Oct. 31, 2009 Option	Feb. 28, 2019 USD ($)	Feb. 28, 2018 USD ($)	Mar. 31, 2017 USD ($)	Mar. 31, 2016 USD ($)	Mar. 31, 2015 USD ($)	Feb. 28, 2017 USD ($)	Sep. 30, 2012 ft²	Jan. 31, 2007 ft²
Operating leases
Lease rent per month		$ 14,200	$ 13,800
Office and lab space of 8,100 square feet area in Newtown, Pennsylvania
Operating leases
Area of space leased (in square feet) \| ft²									8,100
Number of options available for lease extensions \| Option	3
Additional lease term under option	1 year
Lease rent per month				$ 11,900	$ 11,500	$ 11,000
Additional office space of 1,356 square feet area in Newtown, Pennsylvania
Operating leases
Area of space leased (in square feet) \| ft²								1,356
Sub-lease rent per month							$ 1,600

Commitments and Contingencies - Future Minimum Lease Payments (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Future minimum lease payments under non-cancellable leases
2018	$ 170
2019	28
Total minimum lease payments	$ 198

Restructuring (Details) - Employee severance $ in Millions	1 Months Ended		12 Months Ended
Restructuring (Details) - Employee severance $ in Millions	Aug. 31, 2016 employee	Feb. 29, 2016 employee	Dec. 31, 2016 USD ($)
Restructuring
Workforce reduction, number of employees \| employee	6	6
Severance-related charge			$ 3.0
Accelerated vesting of the outstanding stock options for certain of the affected employees			$ 1.4

License and Collaboration Agreements - Baxalta Agreement (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2017	Dec. 31, 2016
License and collaboration agreements
Revenue		$ 787	$ 5,546
License agreement \| Rigosertib \| Baxalta
License and collaboration agreements
Upfront payment	$ 50,000
Revenue			$ 4,999
License agreement \| Rigosertib \| Baxalta \| Rigosertib IV in higher risk MDS patients
License and collaboration agreements
Funding percentage to the entity (as a percent)	50.00%
Cost funded to the entity	$ 15,000

License and Collaboration Agreements - SymBio Agreement (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Jul. 31, 2011	Dec. 31, 2017	Dec. 31, 2016
License and collaboration agreements
Revenues		$ 787	$ 5,546
License agreement \| Rigosertib \| SymBio
License and collaboration agreements
Upfront payment	$ 7,500
Aggregate milestone payments	22,000
Aggregate potential milestone payments based on annual net sales of rigosertib	$ 30,000
Percentage of royalty payments based on net sales of rigosertib (as a percent)	20.00%
Revenues		454	455
Supply commitment agreement \| Rigosertib \| SymBio
License and collaboration agreements
Binding commitments	$ 0
Revenues		$ 333	$ 92
United States and Japan \| License agreement \| Rigosertib \| SymBio
License and collaboration agreements
Aggregate milestone payments due upon receipt of marketing approval for an additional indication	4,000
United States \| License agreement \| Rigosertib \| SymBio \| MDS IV indication
License and collaboration agreements
Regulatory milestones payments due upon receipt of marketing approval for indication	5,000
United States \| License agreement \| Rigosertib \| SymBio \| Rigosertib oral in lower risk MDS patients
License and collaboration agreements
Regulatory milestones payments due upon receipt of marketing approval for indication	5,000
Japan \| License agreement \| Rigosertib \| SymBio \| MDS IV indication
License and collaboration agreements
Regulatory milestones payments due upon receipt of marketing approval for indication	3,000
Japan \| License agreement \| Rigosertib \| SymBio \| Rigosertib oral in lower risk MDS patients
License and collaboration agreements
Regulatory milestones payments due upon receipt of marketing approval for indication	$ 5,000

Preclinical Collaboration (Details) - GBO $ in Thousands	1 Months Ended	12 Months Ended
Preclinical Collaboration (Details) - GBO $ in Thousands	Nov. 30, 2014 USD ($)	Dec. 31, 2017 Program item	Dec. 31, 2013 USD ($)	Dec. 31, 2012 Program
Preclinical Collaboration
Number of new programs to be collaborated and developed \| Program		2		2
Ownership interest in the joint venture (as a percent)			90.00%
Period for which option available to cancel the license and purchase all rights following 15-month anniversary of commencement of program		30 days
Period of anniversary following which option available to cancel the license and purchase all rights for thirty days		15 months
Number of buy-back scenarios \| item		3
GVK BIO
Preclinical Collaboration
Initial capital contribution			$ 500
Ownership interest in the joint venture (as a percent)	17.50%		10.00%
Additional capital contributions	$ 500
GVK BIO \| Minimum
Preclinical Collaboration
Ownership interest in the joint venture (as a percent)			10.00%
GVK BIO \| Maximum
Preclinical Collaboration
Ownership interest in the joint venture (as a percent)			50.00%

Related-Party Transactions (Details) - USD ($)	12 Months Ended
Related-Party Transactions (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Mount Sinai
Related-Party Transactions
Payments to related party	$ 351,000	$ 548,000
Amounts due to related party	526,000	175,000
Member of board of directors
Related-Party Transactions
Payments to related party	132,000	131,000
Amounts due to related party	$ 33,000	$ 33,000

Securities Registrations and Sales Agreements - Sales and Purchase Agreements (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended	12 Months Ended
	Oct. 08, 2015	Oct. 31, 2015	Dec. 31, 2016	Dec. 31, 2015
At-the-market equity program
Securities Registrations and Sales Agreement
Issuance of stock (in shares)			0	2,715,165
Net proceeds from sales of common stock				$ 6,018
Lincoln Park \| Purchase agreement
Securities Registrations and Sales Agreement
Issuance of stock (in shares)	84,676	84,676
Aggregate offering price	$ 15,000	$ 15,000
Net proceeds from sales of common stock	$ 1,500	$ 1,500
Business day limit (in shares)	10,000
Business day limit contingent upon the closing price of the stock (in shares)	25,000
Regular purchase, one day limit	$ 1,000
Beneficial ownership percentage (as a percent)	4.99%
Beneficial ownership percentage after 180 days (as a percent)	9.99%
Maximum shares issued as a percentage of shares outstanding (as a percent)	19.99%
Minimum average price per share (in dollars per share)	$ 15.56
Stock issued as consideration (in shares)	20,000

Securities Registrations and Sales Agreements - Securities Purchase Agreement (Details) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
	Jan. 05, 2016	Dec. 31, 2017	Dec. 31, 2016
Sale of Securities
Value of stock issued		$ 6,360	$ 1,041
Securities Purchase Agreement
Sale of Securities
Issuance of stock (in shares)	193,684
Share price (in dollars per share)	$ 9.50
Aggregate net proceeds	$ 1,609
Securities Purchase Agreement \| Common Stock Warrants
Sale of Securities
Shares of common stock warrants will purchase (in shares)	96,842
Value of stock issued	$ 1,840
Exercise price (in dollars per share)	$ 11.50

Securities Registrations and Sales Agreements - Warrants and Rights Offering (Details) - USD ($) $ / shares in Units, $ in Thousands				12 Months Ended
	Nov. 14, 2017	Nov. 09, 2017	Jul. 29, 2016	Dec. 31, 2017	Dec. 31, 2016
Sale of Securities
Gross proceeds				$ 6,360	$ 17,420
Dealer-Manager Agreement, rights offering
Sale of Securities
Beneficial ownership percentage threshold, elect to receive, in lieu of shares of common stock, certain pre-funded warrants to purchase the same amount of shares of common stock (as a percent)			4.99%
Gross proceeds			$ 17,400
Aggregate net proceeds			$ 15,800
Issuance of stock (in shares)			3,599,786
Percentage of value of units sold to holders of subscription rights (as a percent)			4.50%
Percentage of value of units sold to other holders of subscription rights (as a percent)			8.00%
Non-accountable expense allowance paid			$ 100
FBR Capital Markets and Co. \| ATM Program
Sale of Securities
Issuance of stock (in shares)				20,499	0
Net proceeds from sales of common stock				$ 64
Laidlaw \| Placement Agency Agreement
Sale of Securities
Issuance of stock (in shares)		920,000
Price per share (in dollars per share)		$ 1.50
Net proceeds from sales of common stock	$ 1,082
Non-transferrable Subscription Rights \| Dealer-Manager Agreement, rights offering
Sale of Securities
Shares of common stock per unit (in shares)			1
Tradable warrants per unit (in shares)			0.75
Number of rights issued per share of common stock (in shares)			1.5
Sale price per unit (in dollars per share)			$ 4.10
Rights or warrants issued (in shares)			4,256,186
Tradable warrants \| Dealer-Manager Agreement, rights offering
Sale of Securities
Shares into which each warrant can be converted (in shares)			1
Exercise price (in dollars per share)			$ 4.92
Rights or warrants issued (in shares)			3,192,022
Exercisable, term (in years)			5 years
Redemption period (in years)			1 year
Redemption price (in dollars per share)			$ 0.001
Volume weighted average price per share of common stock (in dollars per share)			$ 12.30
Threshold consecutive trading days (in days)			10 days
Pre-funded warrants \| Dealer-Manager Agreement, rights offering
Sale of Securities
Shares into which each warrant can be converted (in shares)			1
Beneficial ownership percentage threshold, extend exercise period (as a percent)			4.99%
Exercise price (in dollars per share)			$ 0.01
Rights or warrants issued (in shares)			656,400
Exercise, term (in years)			7 years

Subsequent Events (Details) - USD ($) $ / shares in Units, $ in Thousands							12 Months Ended
	Mar. 16, 2018	Mar. 02, 2018	Feb. 12, 2018	Feb. 08, 2018	Nov. 14, 2017	Apr. 26, 2017	Dec. 31, 2017	Dec. 31, 2016	Feb. 28, 2018	Feb. 27, 2018	May 31, 2016	May 30, 2016
Subsequent Events
Preferred stock, par value per share (in dollars per share)							$ 0.01	$ 0.01
Common stock, shares authorized							25,000,000	25,000,000			25,000,000	75,000,000
Fair value of warrant liability							$ 1,773
Change in fair value of warrant liabilities							$ (1,628)	$ (3,988)
Common Stock
Subsequent Events
Issuance of stock (in shares)							4,011,268	193,684
The Offering
Subsequent Events
Issuance of stock (in shares)					920,000	2,476,190
Subsequent Events
Subsequent Events
Net proceeds from stock offering			$ 8,700
Capital stock, shares authorized									105,000,000	30,000,000
Common stock, shares authorized									100,000,000	25,000,000
Fair value of warrant liability	$ 1,007
Change in fair value of warrant liabilities	$ 766
Subsequent Events \| Minimum
Subsequent Events
Maximum percentage of shareholding for conversion (in percentage)				4.99%
Subsequent Events \| Maximum
Subsequent Events
Maximum percentage of shareholding for conversion (in percentage)				9.99%
Subsequent Events \| Common Stock
Subsequent Events
Number of common stock for each 0.1 share of preferred stock				1
Subsequent Events \| Pre-funded warrants
Subsequent Events
Warrant exercise price (in dollars per share)				$ 0.01
Subsequent Events \| Preferred stock warrants \| Series A Convertible Preferred Stock
Subsequent Events
Warrant exercise price (in dollars per share)				$ 1.01
Subsequent Events \| HCW
Subsequent Events
Underwriters commission (in percentage)				7.00%
Management fee (in percentage)				1.00%
Subsequent Events \| HCW \| Series A Convertible Preferred Stock
Subsequent Events
Number of securities converted from warrants as compensation				49,737.5
Subsequent Events \| HCW \| Common Stock
Subsequent Events
Number of common stock shares for conversion preferred stock received as compensation				497,375
Subsequent Events \| HCW \| Preferred stock warrants \| Series A Convertible Preferred Stock
Subsequent Events
Warrants exercise price received as compensation (in dollars per share)				$ 1.2625
Number of securities converted from each warrant as compensation				0.1
Subsequent Events \| Pint \| License agreement \| Rigosertib
Subsequent Events
Maximum proceeds for additional regulatory, development and sales-based milestone payments		$ 42,750
Prior written notice period for termination (in days)		45 days
Subsequent Events \| Pint \| Securities Purchase Agreement
Subsequent Events
Number consecutive trading days to purchase shares		10 days
Lock-up period for purchased shares by counterparty (in years)		1 year
Subsequent Events \| The Offering \| Common Stock
Subsequent Events
Issuance of stock (in shares)				5,707,500
Share price (in dollars per share)				$ 1.01
Subsequent Events \| The Offering \| Pre-funded warrants
Subsequent Events
Warrant purchase price (in dollars per share)				$ 1.00
Subsequent Events \| The Offering \| Pre-funded warrants \| Common Stock
Subsequent Events
Number of securities to each class of warrant (in shares)				2,942,500
Subsequent Events \| The Offering \| Preferred stock warrants \| Series A Convertible Preferred Stock
Subsequent Events
Number of securities to each class of warrant (in shares)				865,000
Preferred stock, par value per share (in dollars per share)				$ 0.01
Portion of preferred stock for each warrant (in share)				0.1
Subsequent Events \| Underwriter's option \| HCW
Subsequent Events
Period available to underwriters to purchase additional shares under the offering				30 days
Subsequent Events \| Underwriter's option \| HCW \| Common Stock
Subsequent Events
Issuance of stock (in shares)				1,297,500
Share price (in dollars per share)				$ 1.00
Subsequent Events \| Underwriter's option \| HCW \| Preferred stock warrants \| Common Stock
Subsequent Events
Number of securities to each class of warrant (in shares)				129,750
Warrant purchase price (in dollars per share)				$ 0.01

Nature of Business - The Company - Clinical-stage Product Candidates (Details)	Dec. 31, 2017 item
Nature of Business
Number of clinical-stage product candidates	3

Summary of Significant Accounting Policies - Segment Information (Details)	12 Months Ended
	Dec. 31, 2017 segment
Segment Information
Number of operating segments	1

Income Taxes - Tax Credit Carry Forwards (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Research and Development Tax Credit Carry Forwards \| IRS
Income Taxes
Tax credit carry forwards	$ 79,725

Income Taxes - Net Operating Loss Carryforwards (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Federal
Income Taxes
Net operating loss (NOL) carry forwards	$ 210,529
State
Income Taxes
Net operating loss (NOL) carry forwards	$ 169,672

Income Taxes - Unrecognized Tax Benefits (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Unrecognized tax benefits
Unrecognized tax benefits	$ 0
Interest and penalties accrued	$ 0

Income Taxes - Valuation Allowance (Details) - USD ($)	12 Months Ended
Income Taxes - Valuation Allowance (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Income Taxes
Net change in valuation allowance	$ (13,434,000)	$ 8,738,000

Commitments and Contingencies - Office Space in Munich, Germany (Details) - USD ($)	12 Months Ended
	Feb. 28, 2019	Feb. 28, 2018
Operating leases
Lease rent per month	$ 14,200	$ 13,800

Research Agreements (Details) $ in Thousands	12 Months Ended
Research Agreements (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Temple
Research Agreements
Sales generated from products covered by the licensed patents	$ 0