Verastem (VSTM) 10-K 13 Mar 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2017	Mar. 07, 2018	Jun. 30, 2017
Document and Entity Information
Entity Registrant Name	Verastem, Inc.
Entity Central Index Key	1,526,119
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	Accelerated Filer
Entity Public Float			$ 79,779,254
Entity Common Stock, Shares Outstanding		50,800,908
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 82,176	$ 32,349
Short-term investments	4,496	48,548
Prepaid expenses and other current assets	1,115	398
Total current assets	87,787	81,295
Property and equipment, net	861	1,417
Restricted cash	162	162
Other assets	981	755
Total assets	89,791	83,629
Current liabilities:
Accounts payable	9,186	4,095
Accrued expenses	7,942	6,896
Total current liabilities	17,128	10,991
Non-current liabilities:
Long-term debt	14,828
Other non-current liabilities	151	341
Total liabilities	32,107	11,332
Stockholders' equity
Preferred stock, $0.0001 par value; 5,000 shares authorized, no shares issued and outstanding at December 31, 2017 and 2016, respectively
Common stock, $0.0001 par value; 100,000 shares authorized, 50,801 and 36,992 shares issued and outstanding at December 31, 2017 and 2016, respectively	5	4
Additional paid-in capital	360,823	307,587
Accumulated other comprehensive (loss) income	(2)	29
Accumulated deficit	(303,142)	(235,323)
Total stockholders' equity	57,684	72,297
Total liabilities and stockholders' equity	$ 89,791	$ 83,629

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
CONSOLIDATED BALANCE SHEETS
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
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)	$ 0.0001	$ 0.0001
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	50,801,000	36,992,000
Common stock, shares outstanding	50,801,000	36,992,000

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating expenses:
Research and development	$ 46,423	$ 19,779	$ 40,565
General and administrative	21,381	17,223	17,634
Total operating expenses	67,804	37,002	58,199
Loss from operations	(67,804)	(37,002)	(58,199)
Interest income	561	562	334
Interest expense	(559)
Net loss	$ (67,802)	$ (36,440)	$ (57,865)
Net loss per share - basic and diluted	$ (1.76)	$ (0.99)	$ (1.61)
Weighted-average number of common shares used in net loss per share-basic and diluted	38,422	36,988	35,932
Net loss	$ (67,802)	$ (36,440)	$ (57,865)
Unrealized (loss) gain on available-for-sale securities	(31)	(14)	32
Comprehensive loss	$ (67,833)	$ (36,454)	$ (57,833)

CONSOLIDATED STATEMENTS OF STOC

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common stockFollow-on offerings	Common stockAt-the-market equity offering program	Common stock	Additional paid-in capitalFollow-on offerings	Additional paid-in capitalAt-the-market equity offering program	Additional paid-in capital	Accumulated other comprehensive (loss) income	Accumulated deficit	Follow-on offerings	At-the-market equity offering program	Total
Balance at Dec. 31, 2014			$ 3			$ 229,770	$ 11	$ (141,018)			$ 88,766
Balance (in shares) at Dec. 31, 2014			27,259,372
Increase (Decrease) in Stockholders' Equity
Net loss								(57,865)			(57,865)
Unrealized gain (loss) on available-for-sale marketable securities							32				32
Issuance of common stock, net of issuance costs	$ 1			$ 50,941	$ 10,911				$ 50,942	$ 10,911
Issuance of common stock, net of issuance costs (in shares)	8,337,500	1,189,479
Vesting of restricted stock						2					2
Vesting of restricted stock (in shares)			7,995
Issuance of common stock resulting from exercise of stock options						13					13
Issuance of common stock resulting from exercise of stock options (in shares)			33,658
Issuance of common stock resulting from vesting of restricted stock units and payment of tax withholdings						(417)					(417)
Issuance of common stock resulting from vesting of restricted stock units and payment of tax withholdings (in shares)			113,257
Stock-based compensation expense						10,085					10,085
Balance at Dec. 31, 2015			$ 4			301,305	43	(198,883)			102,469
Balance (in shares) at Dec. 31, 2015			36,941,261
Increase (Decrease) in Stockholders' Equity
Net loss								(36,440)			(36,440)
Unrealized gain (loss) on available-for-sale marketable securities							(14)				(14)
Issuance of common stock resulting from exercise of stock options (in shares)			1,605
Issuance of common stock resulting from vesting of restricted stock units and payment of tax withholdings						(5)					(5)
Issuance of common stock resulting from vesting of restricted stock units and payment of tax withholdings (in shares)			49,552
Stock-based compensation expense						6,287					6,287
Balance at Dec. 31, 2016			$ 4			307,587	29	(235,323)			$ 72,297
Balance (in shares) at Dec. 31, 2016			36,992,418								36,992,000
Increase (Decrease) in Stockholders' Equity
Net loss								(67,802)			$ (67,802)
Unrealized gain (loss) on available-for-sale marketable securities							(31)				(31)
Issuance of common stock, net of issuance costs	$ 1			$ 24,691	$ 23,053				$ 24,692	$ 23,053
Issuance of common stock, net of issuance costs (in shares)	8,422,877	5,036,879
Issuance of common stock resulting from exercise of stock options						442					442
Issuance of common stock resulting from exercise of stock options (in shares)			348,734
Stock-based compensation expense						5,050		(17)			5,033
Balance at Dec. 31, 2017			$ 5			$ 360,823	$ (2)	$ (303,142)			$ 57,684
Balance (in shares) at Dec. 31, 2017			50,800,908								50,801,000

CONSOLIDATED STATEMENTS OF STO6

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2015
Follow-on offerings
Issuance of common stock, issuance costs	$ 324
At-the-market equity offering program
Issuance of common stock, issuance costs	$ 112	$ 53

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities
Net loss	$ (67,802)	$ (36,440)	$ (57,865)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	556	670	754
Stock-based compensation expense	5,033	6,287	10,085
Amortization of deferred financing costs, debt discounts and premiums and discounts on available-for-sale marketable securities	223	(140)	264
Loss on disposal of fixed assets			46
Changes in operating assets and liabilities:
Prepaid expenses, other current assets and other assets	(943)	(568)	276
Accounts payable	5,046	153	863
Accrued expenses and other liabilities	577	623	418
Liability classified stock-based compensation awards		(69)	(400)
Net cash used in operating activities	(57,310)	(29,484)	(45,559)
Investing activities
Purchases of property and equipment		(39)	(211)
Purchase of investments	(7,957)	(82,101)	(199,851)
Maturities of investments	51,910	119,067	173,005
Decrease in restricted cash		41
Net cash provided by (used in) investing activities	43,953	36,968	(27,057)
Financing activities
Proceeds from long-term debt, net	14,811
Deferred debt financing costs	(138)
Proceeds from the exercise of stock options	442		13
Proceeds from the issuance of common stock, net	48,069		63,989
Cash used to settle restricted stock liability		(5)	(417)
Net cash provided by (used in) financing activities	63,184	(5)	63,585
Increase (decrease) in cash and cash equivalents	49,827	7,479	(9,031)
Cash and cash equivalents at beginning of period	32,349	24,870	33,901
Cash and cash equivalents at end of period	82,176	$ 32,349	$ 24,870
Supplemental disclosure
Cash paid for interest	295
Supplemental disclosure of non-cash investing and financing activities
Common stock issuance costs included in accounts payable and accrued expenses	$ 324

Nature of business

Nature of business	12 Months Ended
	Dec. 31, 2017
Nature of business
Nature of business	1. Nature of business Verastem, Inc. (the Company) is a biopharmaceutical company focused on developing and commercializing drugs to improve outcomes for patients with cancer. The Company’s operations to date have been limited to organizing and staffing the Company, business planning, raising capital, acquiring and developing its technology, identifying potential product candidates and undertaking preclinical and clinical studies of its product candidates. The Company is subject to a number of risks similar to other life science companies, including, but not limited to, the need to obtain adequate additional funding, possible failure of preclinical testing or clinical trials, inability to obtain marketing approval of product candidates, competitors developing new technological innovations, market acceptance of the Company’s products and protection of proprietary technology. If the Company does not successfully commercialize any of its product candidates, it will be unable to generate product revenue or achieve profitability. As of December 31, 2017, the Company had cash, cash equivalents and investments of $86.7 million and accumulated deficit of $303.1 million. The Company has historical losses from operations and anticipates that it will continue to incur losses for the foreseeable future as it continues the research and development and clinical trials of, and seeks marketing approval for, its lead product candidates. Without additional funding, the Company believes that it will not have sufficient funds to meet its obligations within the next twelve months from the date of issuance of these consolidated financial statements. These factors raise substantial doubt about the Company’s ability to continue as a going concern. The Company plans to continue to fund its operations through proceeds from sales of its common stock under its at-the-market equity offering program, public or private equity offerings, its loan and security agreement with Hercules Capital, Inc. (Hercules), or other strategic transactions. However, adequate additional financing may not be available to the Company on acceptable terms, or at all. If the Company is unable to raise capital when needed or on attractive terms, it may be forced to delay, reduce or eliminate its research and development programs or any future commercialization efforts.

Significant accounting policies

Significant accounting policies	12 Months Ended
	Dec. 31, 2017
Significant accounting policies
Significant accounting policies	2. Significant accounting policies Basis of presentation The accompanying financial statements of the Company have been prepared in accordance with U.S. generally accepted accounting principles (GAAP) under the assumption that the Company will continue as a going concern for the next twelve months. Accordingly, they do not include any adjustments that might result from the uncertainty related to the Company’s ability to continue as a going concern. The consolidated financial statements include the accounts of Verastem Securities Company, a wholly-owned subsidiary of the Company. All financial information presented has been consolidated and includes the accounts of the Company and its wholly-owned subsidiary. All intercompany balances and transactions have been eliminated in consolidation. Use of estimates The preparation of the Company’s financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. On an ongoing basis, management evaluates its estimates, including estimates related to accruals and stock‑based compensation expense. The Company bases its estimates on historical experience and other market‑specific or other relevant assumptions that it believes to be reasonable. Actual results could differ from such estimates. Segment and geographic information Operating segments are defined as components of an enterprise about which separate discrete information is available and regularly reviewed 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 operating segment, which is the business of developing drugs for the treatment of cancer. All material long-lived assets of the Company reside in the United States. Cash and cash equivalents The Company considers all highly liquid investments with an original or remaining maturity of three months or less at the date of purchase to be cash equivalents. Cash equivalents consist of a U.S. Government money market fund, overnight repurchase agreements collateralized by government agency securities or U.S. Treasury securities, corporate bonds and commercial paper of publicly traded companies. Cash equivalents are reported at fair value. Fair value of financial instruments The Company determines the fair value of its financial instruments based upon the fair value hierarchy, which prioritizes valuation inputs based on the observable nature of those inputs. The fair value hierarchy applies only to the valuation inputs used in determining the reported fair value of the investments and is not a measure of the investment credit quality. The hierarchy defines three levels of valuation inputs: Level 1 inputs Quoted prices in active markets for identical assets or liabilities that the Company can access at the measurement date. Level 2 inputs Inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly. Level 3 inputs Unobservable inputs that reflect the Company’s own assumptions about the assumptions market participants would use in pricing the asset or liability. Items Measured at Fair Value on a Recurring Basis The following table presents information about the Company’s financial instruments that are measured at fair value on a recurring basis (in thousands): December 31, 2017 Description Total Level 1 Level 2 Level 3 Financial assets Cash equivalents $ 80,894 $ 75,478 $ 5,416 $ — Short-term investments 4,496 — 4,496 — Total financial assets $ 85,390 $ 75,478 $ 9,912 $ — December 31, 2016 Description Total Level 1 Level 2 Level 3 Financial assets Cash equivalents $ 30,540 $ 20,540 $ 10,000 $ — Short-term investments 48,548 — 48,548 — Total financial assets $ 79,088 $ 20,540 $ 58,548 $ — These investments and cash equivalents have been initially valued at the transaction price and subsequently valued, at the end of each reporting period, utilizing third party pricing services or other market observable data. The pricing services utilize industry standard valuation models, including both income and market based approaches and observable market inputs to determine value. These observable market inputs include reportable trades, benchmark yields, credit spreads, broker/dealer quotes, bids, offers, current spot rates and other industry and economic events. The Company validates the prices provided by third party pricing services by reviewing their pricing methods and matrices, obtaining market values from other pricing sources, analyzing pricing data in certain instances and confirming that the relevant markets are active. After completing its validation procedures, the Company did not adjust or override any fair value measurements provided by the pricing services as of December 31, 2017 and 2016. Fair Value of Financial Instruments The fair value of the Company’s long-term debt is determined using current applicable rates for similar instruments as of the balance sheet dates and an assessment of the credit rating of the Company. The carrying value of the Company’s debt at December 31, 2017 approximates fair value because the Company’s interest rate yield is near current market rates for comparable debt instruments. The fair value of the Company’s long-term debt was determined using Level 3 inputs. Investments Investments and cash equivalents consist of investments in a U.S. Government money market fund, overnight repurchase agreements collateralized by government agency securities or U.S. Treasury securities, corporate bonds and commercial paper of publicly traded companies that are classified as available‑for‑sale pursuant to Accounting Standards Codification (ASC) Topic 320, Investments—Debt and Equity Securities . The Company classifies investments available to fund current operations as current assets on its consolidated balance sheets. Investments are classified as long‑term assets on the consolidated balance sheets if (i) the Company has the intent and ability to hold the investments for a period of at least one year and (ii) the contractual maturity date of the investments is greater than one year. Investments are carried at fair value with unrealized gains and losses included as a component of accumulated other comprehensive income (loss), which is a separate component of stockholders’ equity (deficit), until such gains and losses are realized. The fair value of these securities is based on quoted prices for identical or similar assets. If a decline in the fair value is considered other‑than‑temporary, based on available evidence, the unrealized loss is transferred from other comprehensive loss to the consolidated statements of operations and comprehensive loss. The Company reviews investments for other‑than‑temporary impairment whenever the fair value of an investment is less than the amortized cost and evidence indicates that an investment’s carrying amount is not recoverable within a reasonable period of time. To determine whether an impairment is other‑than‑temporary, the Company considers the intent to sell, or whether it is more likely than not that the Company will be required to sell, the investment before recovery of the investment’s amortized cost basis. Evidence considered in this assessment includes reasons for the impairment, compliance with the Company’s investment policy, the severity and the duration of the impairment and changes in value subsequent to year end. Realized gains and losses are determined using the specific identification method and are included in interest income in the consolidated statements of operations and comprehensive loss. There were no realized gains or losses on investments for the years ended December 31, 2017, 2016 or 2015. There were no investments that had been in an unrealized loss position for more than 12 months as of December 31, 2017 or December 31, 2016. There were 5 debt securities in an unrealized loss position for less than 12 months at December 31, 2017 and there were 14 debt securities that had been in an unrealized loss position for less than 12 months at December 31, 2016. The aggregate unrealized loss on these securities as of December 31, 2017 and December 31, 2016 was approximately $2,000 and $24,000, respectively, and the fair value was $9.9 million and $23.6 million, respectively. The Company considered the decline in the market value for these securities to be primarily attributable to current economic conditions. As it was not more likely than not that the Company would be required to sell these securities before the recovery of their amortized cost basis, which may be at maturity, the Company did not consider these investments to be other-than-temporarily impaired as of December 31, 2017. Cash, cash equivalents and investments consist of the following (in thousands): December 31, 2017 Gross Gross Amortized Unrealized Unrealized Fair Cost Gains Losses Value Cash and cash equivalents: Cash and money market accounts $ 76,760 $ — $ — $ 76,760 Corporate bonds and commercial paper $ 5,418 $ — $ (2) $ 5,416 Total cash and cash equivalents $ 82,178 $ — $ (2) $ 82,176 Investments: Corporate bonds and commercial paper (due within 1 year) $ 4,496 $ — $ — $ 4,496 Total investments $ 4,496 $ — $ — $ 4,496 Total cash, cash equivalents, and investments $ 86,674 $ — $ (2) $ 86,672 December 31, 2016 Gross Gross Amortized Unrealized Unrealized Fair Cost Gains Losses Value Cash and cash equivalents: Cash and money market accounts $ 22,349 $ — $ — $ 22,349 Overnight repurchase agreements 10,000 — — 10,000 Total cash and cash equivalents $ 32,349 $ — $ — $ 32,349 Investments: Corporate bonds and commercial paper (due within 1 year) $ 48,519 $ 53 $ (24) $ 48,548 Total investments $ 48,519 $ 53 $ (24) $ 48,548 Total cash, cash equivalents, and investments $ 80,868 $ 53 $ (24) $ 80,897 Concentrations of credit risk and off‑balance sheet risk Cash and cash equivalents and investments are financial instruments that potentially subject the Company to concentrations of credit risk. The Company mitigates this risk by maintaining its cash and cash equivalents and investments with high quality, accredited financial institutions. The management of the Company’s investments is not discretionary on the part of these financial institutions. As of December 31, 2017, the Company’s cash, cash equivalents and investments were deposited at two financial institutions and it has no significant off‑balance sheet concentrations of credit risk, such as foreign currency exchange contracts, option contracts or other hedging arrangements. Property and equipment Property and equipment consists of laboratory equipment, office furniture, computer equipment and leasehold improvements. Expenditures for repairs and maintenance are recorded to expense as incurred, whereas major betterments are capitalized as additions to property and equipment. Depreciation and amortization is calculated using the straight‑line method over the following estimated useful lives of the assets: Laboratory equipment 5 years Furniture 5 years Computer equipment 3 years Leasehold improvements Lesser of useful life or life of lease 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 its long‑lived assets for impairment whenever events or changes in business circumstances indicate that the carrying value of assets may not be recoverable. Recoverability is measured by comparison of the asset’s 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 exceed their fair value, which is measured based on the projected discounted future net cash flows arising from the assets. No material impairment losses have been recorded through December 31, 2017. Other assets Other assets primarily consists of prepayments made to contract research organizations (CROs). As of December 31, 2017 and 2016, other assets was primarily comprised of approximately $755,000 of prepaid CRO expenses that the Company assumed and paid to Infinity Pharmaceuticals, Inc. (Infinity) pursuant to the license agreement between the Company and Infinity. Research and development costs The Company expenses research and development costs to operations as incurred. Research and development expenses consist of: · employee‑related expenses, including salaries, benefits, travel and stock‑based compensation expense; · external research and development expenses incurred under arrangements with third parties, such as CROs, clinical trial sites, manufacturing organizations and consultants, including the scientific advisory board; · license fees; and · facilities, depreciation and other expenses, which include direct and allocated expenses for rent and maintenance of facilities, depreciation of equipment, and laboratory supplies. The Company accounts for nonrefundable advance payments for goods and services that will be used in future research and development activities as expenses when the services have been performed or when the goods have been received rather than when the payment is made. Stock‑based compensation The Company expenses the fair value of employee stock-based awards on a straight-line basis over the requisite service period, which typically is the vesting period. Compensation expense is measured using the fair value of the award at the grant date, net of estimated forfeitures, and is adjusted to reflect actual forfeitures as they occur. Awards subject to performance based vesting requirements are expensed utilizing an accelerated attribution model if achievement of the performance criteria is determined to be probable. The grant date fair value of employee stock options is estimated using the Black‑Scholes option pricing model that takes into account the fair value of its common stock, the exercise price, the expected life of the option, the expected volatility of its common stock, expected dividends on its common stock, and the risk-free interest rate over the expected life of the option. The Company uses the simplified method described in the Securities and Exchange Commission Staff Accounting Bulletin Topic 14.D.2 to calculate the expected term as it does not have sufficient historical exercise data to provide a reasonable basis upon which to estimate the expected term for options granted to employees. The expected term is applied to the stock option grant group as a whole, as the Company does not expect substantially different exercise or post‑vesting termination behavior among its employee population. The computation of expected volatility is based on the historical volatility of five companies, including the Company and a representative group of four public biotechnology and life sciences companies with similar characteristics to the Company, including similar stage of product development and therapeutic focus. The risk‑free interest rate is based on a treasury instrument whose term is consistent with the expected term of the stock options. Historically, the Company has recognized stock-based compensation net of estimated forfeitures over the vesting period of the respective grant. Effective January 1, 2017, the Company adopted Accounting Standard Updated (ASU) 2016-09, Compensation – Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting , which simplified the accounting for share-based compensation arrangements, including the accounting for forfeitures. Upon adoption, the Company elected to begin accounting for forfeitures as they occur, rather than estimating a forfeiture rate, and recorded an immaterial cumulative-effect adjustment to opening accumulated deficit. Stock‑based awards issued to nonemployees, including directors for non‑board related services, are accounted for based on the fair value of such services received or of the equity instruments issued, whichever is more reliably measured. Stock option awards to non-employees are revalued at each reporting date and upon vesting using the Black‑Scholes option pricing model and are expensed on a straight‑line basis over the vesting period. Stock‑based compensation awards which allowed for greater than the minimum statutory tax withholdings were classified as liabilities. These awards were revalued at each reporting date and were expensed on a straight‑line basis over the vesting period. Upon settlement, the awards were revalued and the amounts were reclassified to additional paid‑in capital. Shares were withheld to cover the tax withholding and amounts paid to settle the tax liability were recorded as a reduction of additional paid‑in capital. 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. Tax benefits are recognized when it is more likely than not that a tax position will be sustained during an audit. Deferred tax assets are reduced by a valuation allowance if current evidence indicates that it is considered more likely than not that these benefits will not be realized. Net loss per share Basic and diluted net loss per common share is calculated by dividing net loss applicable to common stockholders by the weighted‑average number of common shares outstanding during the period, without consideration for common stock equivalents. The Company’s potentially dilutive shares, which include outstanding stock options, restricted stock units, unvested restricted stock and the warrant issued in 2014 are considered to be common stock equivalents and are only included in the calculation of diluted net loss per share when their effect is dilutive. All potentially dilutive securities were excluded from the calculation of diluted net loss per share as the securities were anti‑dilutive for all periods presented. The following potentially dilutive securities were excluded from the calculation of diluted net loss per share due to their anti‑dilutive effect: Year ended December 31, 2017 2016 2015 Outstanding stock options 8,719,978 5,848,470 5,390,130 Outstanding warrants — 142,857 142,857 Unvested restricted stock units — — 53,751 Total potentially dilutive securities 8,719,978 5,991,327 5,586,738 Recently Issued Accounting Standards Updates In May 2017, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2017-09, Compensation – Stock Compensation (Topic 718): Scope of Modification Accounting . ASU 2017-09 provides guidance about which changes to the terms or conditions of a share-based award require an entity to apply modification accounting under Topic 718. Specifically, an entity would not apply modification accounting if the fair value, vesting conditions and classification of the awards are the same immediately before and after a modification. ASU 2017-09 is effective for annual and interim periods beginning after December 15, 2017, with early adoption permitted. The Company has not elected to early adopt this standard and does not expect the adoption to have a material impact on its consolidated financial statements and related disclosures. In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash . ASU 2016-18 requires that a statement of cash flows explain the change during the period in the total of cash, cash equivalents and amounts generally described as restricted cash or restricted cash equivalents. Amounts generally described as restricted cash and restricted cash equivalents should 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. ASU 2016-18 is effective for annual and interim periods beginning after December 15, 2017, with early adoption permitted. The Company has not elected to early adopt this standard and does not expect the adoption to have a material impact on its consolidated financial statements and related disclosures. In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments. ASU 2016-15 adds or clarifies guidance on the classification of certain cash receipts and payments in the statement of cash flows. The standard is effective for annual and interim periods beginning after December 15, 2017, with early adoption permitted. The Company has not elected to early adopt this standard and does not expect the adoption to have a material impact on its consolidated financial statements and related disclosures. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842), which supersedes the guidance under FASB Accounting Standards Codification (ASC) Topic 840, Leases, resulting in the creation of FASB ASC Topic 842, Leases. ASU 2016-02 requires lessees to recognize in the statement of financial position a liability to make lease payments and a right-of-use asset representing its right to use the underlying asset for the lease term for both finance and operating leases. The guidance also eliminates the current real estate-specific provisions for all entities. ASU 2016-02 is effective for fiscal years, and interim periods within those years, beginning after December 15, 2018, with early adoption permitted. The Company has not elected to early adopt this standard and is currently evaluating the impact the adoption of the standard will have on its consolidated financial statements and related disclosures . Recently Adopted Accounting Standards Updates In January 2017, the FASB issued ASU 2017-03, Accounting Changes and Error Corrections (Topic 250) and Investments – Equity Method and Joint Ventures (Topic 323): Amendments to SEC Paragraphs Pursuant to Staff Announcements at the September 22, 2016 and November 17, 2016 EITF Meetings. ASU 2017-03 clarifies the SEC staff’s expectations about the extent of disclosures that a registrant is expected to provide regarding the impact that the adoption of ASUs 2014-09 (Revenue from Contracts with Customers), 2016-02 (Leases) and 2016-13 (Measurement of Credit Losses on Financial Instruments) will have on its financial statements. It also conforms SEC guidance on accounting for tax benefits resulting from investments in affordable housing projects to the guidance in ASU 2014-01, Investments -Equity Method and Joint Ventures (Topic 323) . The guidance under this ASU was effective upon issuance and did not have a material impact on the Company’s disclosures. In October 2016, the FASB issued ASU 2016-17, Consolidation (Topic 810): Interests Held through Related Parties That Are under Common Control . ASU 2016-17 updates ASU 2015-02. Under the amendments, a single decision maker is not required to consider indirect interests held through related parties that are under common control with the single decision maker to be the equivalent of direct interests in their entirety. Instead, a single decision maker is required to include those interests on a proportionate basis consistent with indirect interests held through other related parties. ASU 2016-17 is effective for annual and interim periods beginning after December 15, 2016. The Company adopted this standard effective January 1, 2017. The adoption of this ASU did not have an effect on the Company’s financial statements or disclosures. In March 2016, the FASB issued ASU 2016-09, Compensation – Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting . ASU 2016-09 simplifies the accounting for share-based compensation arrangements, including the accounting for forfeitures, income tax consequences, classification of awards as either equity or liabilities and classification on the statement of cash flows. The standard was effective for annual and interim periods beginning after December 15, 2016, with early adoption permitted. The Company adopted ASU 2016-09 effective January 1, 2017. Upon adoption, the Company elected to begin accounting for forfeitures as they occur, rather than estimating a forfeiture rate, and recorded an immaterial cumulative-effect adjustment to opening accumulated deficit. Also u pon adoption, the Company recognized all previously unrecognized tax benefits, which would have resulted in the recognition of an immaterial cumulative-effect adjustment to opening accumulated deficit; however, these unrecognized tax benefits were recorded as a deferred tax asset, which was fully offset by a valuation allowance. Therefore, the recognition of these benefits had no net cumulative-effect on opening accumulated deficit upon adoption.

Property and equipment, net

Property and equipment, net	12 Months Ended
	Dec. 31, 2017
Property and equipment, net
Property and equipment, net	3. Property and equipment, net Property and equipment and related accumulated depreciation are as follows (in thousands): December 31, December 31, 2017 2016 Leasehold improvements $ 2,104 $ 2,104 Laboratory equipment 908 908 Furniture and fixtures 325 325 Computer equipment 279 279 3,616 3,616 Less: accumulated depreciation (2,755) (2,199) Total property, plant and equipment, net $ 861 $ 1,417 Approximate total depreciation and amortization expenses amounted to $556,000, $670,000, and $754,000 for the years ended December 31, 2017, 2016, and 2015, respectively.

Accrued expenses

Accrued expenses	12 Months Ended
	Dec. 31, 2017
Accrued expenses
Accrued expenses	4. Accrued expenses Accrued expenses consist of the following (in thousands): December 31, December 31, Contract research organization costs $ 3,774 $ 3,258 Compensation and related benefits 2,622 2,505 Professional fees 617 403 Consulting fees 579 527 Deferred rent 190 175 Other 160 28 Total accrued expenses $ 7,942 $ 6,896

Long-term debt

Long-term debt	12 Months Ended
	Dec. 31, 2017
Long-term debt
Long-term debt	5. Long-term debt On March 21, 2017 (Closing Date), Verastem, Inc. (the Borrower) entered into a term loan facility of up to $25.0 million with Hercules, a Maryland corporation, the proceeds of which will be used for its ongoing research and development programs and for general corporate purposes. The term loan facility is governed by a loan and security agreement, dated March 21, 2017 (the Original Loan Agreement), which originally provided for up to four separate advances, of which the first tranche of $2.5 million was drawn on the Closing Date. The second and third tranches of $2.5 million and $5.0 million, respectively were drawn on October 12, 2017 after announcing favorable data from the Company’s Phase III clinical study evaluating the safety and efficacy of duvelisib in patients with relapsed/refractory chronic lymphocytic leukemia or small lymphocytic lymphoma. A total of $6.0 million of the proceeds received from the second and third tranches were used to make a milestone payment pursuant to the Company’s license agreement with Infinity. The fourth tranche of $15.0 million could be drawn, at the Borrower’s option and at the sole discretion of Hercules, on or prior to June 30, 2018. On December 20, 2017, the Borrower drew an additional advance on the fourth tranche of $5.0 million. On January 4, 2018, the Borrower entered into the First Amendment to the Original Loan Agreement (the First Amendment) and on March 6, 2018, the Borrower entered into the Second Amendment to the Original Loan Agreement (the Second Amendment, and the Original Loan Agreement as amended by the First Amendment and the Second Amendment, the Amended Loan Agreement). The First Amendment increased the borrowing limit under the Original Loan Agreement from up to $25.0 million to up to $50.0 million (the Term Loan). As $15.0 million in term loans had already been drawn prior to entering into the First Amendment, there is $35.0 million of borrowing capacity remaining under the Amended Loan Agreement. The remaining $35.0 million of borrowing capacity may be drawn in minimum increments of $5.0 million in multiple tranches comprised of (i) term loans (each a Term E Loan Advance) in an aggregate principal amount of up to $10.0 million and (ii) subject to Hercules’ sole discretion, term loans (each a Term F Loan Advance) in an aggregate principal amount of up to $25.0 million. The Amended Loan Agreement permits the Borrower to draw Term E Loan Advances subject to (i) the U.S. Food and Drug Administration accepting on or prior to September 30, 2018 our New Drug Application for duvelisib and (ii) delivery of the Company’s financial and business projections to Hercules in form and substance reasonably acceptable to Hercules. In addition, the Amended Loan Agreement allows the Borrower to draw Term F Loan Advances subject to the prior drawing of all other tranches and Hercules’ sole discretion. The Term Loan will mature on December 1, 2020 (Loan Maturity Date). Each advance accrues interest at a floating per annum rate equal to the greater of either (a) 10.5% or (b) the lesser of (i) 12.75% and (ii) the sum of (x) 10.5% plus (y) (A) the prime rate minus (B) 4.5%. The Term Loan provided for interest-only payments until November 1, 2018, which was extended to May 1, 2019 pursuant to the Amended Loan Agreement upon the Borrower’s receipt of a minimum of $20.0 million cash proceeds from a sale of equity securities in December 2017. Thereafter, amortization payments will be payable monthly in twenty installments of principal and interest (subject to recalculation upon a change in prime rates). Any advance may be prepaid in whole or in part upon seven business days’ prior written notice to Hercules, subject to a prepayment charge of 3.0%, if such advance is prepaid in any of the first twelve (12) months following the Closing Date, 2.0%, if such advance is prepaid after twelve (12) months following the Closing Date but on or prior to twenty-four (24) months following the Closing Date, and 1.0% thereafter. In addition, a final payment equal to 4.5% of the greater of (a) $5.0 million and (b) the total principal amount of the Term Loan extended by Hercules which is due on the Loan Maturity Date, or such earlier date specified in the Amended Loan Agreement. Amounts outstanding during an event of default shall be payable on demand and shall accrue interest at an additional rate of 5.0% per annum of the past due amount outstanding. The Term Loan is secured by a lien on substantially all of the assets of the Borrower, other than intellectual property and contains customary covenants and representations, including a liquidity covenant, financial reporting covenant and limitations on dividends, indebtedness, collateral, investments, distributions, transfers, mergers or acquisitions, taxes, corporate changes, deposit accounts, and subsidiaries. The events of default under the Amended Loan Agreement include, without limitation, and subject to customary grace periods, (1) the Borrower’s failure to make any payments of principal or interest under the Amended Loan Agreement, promissory notes or other loan documents, (2) the Borrower’s breach or default in the performance of any covenant under the Amended Loan Agreement, (3) the Borrower making a false or misleading representation or warranty in any material respect, (4) the Borrower’s insolvency or bankruptcy, (5) certain attachments or judgments on the Borrower’s assets, or (6) the occurrence of any material default under certain agreements or obligations of the Borrower involving indebtedness, or (7) the occurrence of a material adverse effect. If an event of default occurs, Hercules is entitled to take enforcement action, including acceleration of amounts due under the Amended Loan Agreement. The Company assessed all terms and features of the Original Loan Agreement in order to identify any potential embedded features that would require bifurcation or any beneficial conversion features. As part of this analysis, the Company assessed the economic characteristics and risks of the Original Loan Agreement, including put and call features. The Company determined that all features of the Original Loan Agreement were clearly and closely associated with a debt host and did not require bifurcation as a derivative liability, or the fair value of the feature was immaterial to the Company's financial statements. The Company reassesses the features on a quarterly basis to determine if they require separate accounting. The future principal payments under the Amended Loan Agreement are as follows as of December 31, 2017 (in thousands): 2018 $ — 2019 3,609 2020 11,391 Total principal payments $ 15,000

Common stock

Common stock	12 Months Ended
	Dec. 31, 2017
Common stock.
Common stock	6. Common stock As of December 31, 2017 and 2016, the Company had reserved the following shares of common stock for the issuance of common stock for vested restricted stock units, the exercise of stock options, and an outstanding warrant (in thousands): December 31, December 31, 2017 2016 Shares reserved under equity compensation plans 8,264 7,189 Shares reserved for inducement grants 3,616 1,255 Shares reserved for outstanding warrants — 143 Total shares reserved 11,880 8,587 Each share of common stock is entitled to one vote. The holders of the common stock are also entitled to receive dividends whenever funds are legally available and when declared by the board of directors. At-the-market equity offering programs In December 2013, the Company established an at-the-market equity offering program pursuant to which it was able to offer and sell up to $35.0 million of its common stock at then-current market prices from time to time through Cantor Fitzgerald & Co. (Cantor), as sales agent (the 2013 ATM Program). In November 2014, the Company commenced sales under the 2013 ATM Program. During the year ended December 31, 2015, the Company sold 1,189,479 shares of common stock under the 2013 ATM Program with net proceeds (after deducting commissions and other offering expenses) of $12.9 million. No proceeds were received and no additional sales of the Company’s common stock were made under the 2013 ATM Program and no proceeds were received during the years ended December 31, 2017 and 2016. On March 30, 2017, the Company terminated the 2013 ATM Program and established a new at-the-market equity offering program pursuant to which it was able to offer and sell up to $35.0 million of its common stock at then-current market prices from time to time through Cantor, as sales agent (the 2017 ATM Program). On August 28, 2017, the Company amended its sales agreement with Cantor to increase the maximum aggregate offering price of shares of common stock that can be sold under the 2017 ATM Program to $75.0 million. Through December 31, 2017, the Company sold 5,036,879 shares under the 2017 ATM Program for net proceeds of approximately $23.1 million (after deducting commissions and other offering expenses). As of March 13, 2018, the Company sold an additional 97,078 shares of common stock under the at-the-market equity offering program with net proceeds of approximately $342,000 (after deducting commissions and other offering expenses). Equity offering On December 14, 2017, the Company entered into an Underwriting Agreement with BTIG, LLC relating to the underwritten offering of 8,422,877 shares of its common stock at a price of $2.97 per share, for aggregate proceeds, net of underwriting discounts and offering costs, of approximately $24.7 million.

Stock-based compensation

Stock-based compensation	12 Months Ended
	Dec. 31, 2017
Stock-based compensation
Stock-based compensation	7. Stock‑based compensation Stock‑based compensation expense as reflected in the Company’s consolidated statements of operations and comprehensive loss was as follows (in thousands): Year ended December 31, 2017 2016 2015 Research and development $ 1,381 $ 1,073 $ 2,411 General and administrative 3,652 5,145 7,273 Total stock-based compensation expense $ 5,033 $ 6,218 $ 9,684 All of the $5.0 million of stock-based compensation expense recorded during the year ended December 31, 2017 was recorded to additional paid-in capital. Of the $6.2 million of stock-based compensation expense recorded during the year ended December 31, 2016, $6.3 million was recorded to additional paid-in capital and approximately $69,000 was recorded as a decrease in liability classified awards. Of the $9.7 million of stock-based compensation expense recorded during the year ended December 31, 2015, $10.1 million was recorded to additional paid-in capital and approximately $400,000 was recorded as a decrease in liability classified awards. The Company has awards outstanding under two equity compensation plans, the 2012 Incentive Plan (the 2012 Plan) and the 2010 Equity Incentive Plan (the 2010 Plan), as well as the inducement award program. Terms of stock award agreements, including vesting requirements, are determined by the board of directors, subject to the provisions of the individual plans. To date, most options granted by the Company vest twenty-five percent (25%) one year from vesting start date and six and a quarter percent (6.25%) for each successive three-month period, thereafter (subject to acceleration of vesting in the event of certain change of control transactions) and are exercisable for a period of ten years from the date of grant. 2012 Incentive Plan The 2012 Plan became effective immediately upon the closing of the Company’s IPO in February 2012. Upon effectiveness of the 2012 Plan, the Company ceased making awards under the 2010 Plan. The 2012 Plan initially allowed the Company to grant awards for up to 3,428,571 shares of common stock, plus the number of shares of common stock available for grant under the 2010 Plan as of the effectiveness of the 2012 Plan (which was an additional 30,101 shares), plus that number of shares of common stock related to awards outstanding under the 2010 Plan which terminate by expiration, forfeiture, cancellation or otherwise. The 2012 Plan includes an “evergreen provision” that allows for an annual increase in the number of shares of common stock available for issuance under the 2012 Plan. The annual increase is added on the first day of each year beginning in 2013 and each subsequent anniversary until the expiration of the 2012 Plan, and is equal to the lower of 1,285,714 shares of common stock, 4.0% of the number of shares of common stock outstanding and an amount determined by the board of directors. On January 1, 2017 and 2016, the number of shares available for issuance under the 2012 Plan increased by 1,285,714 under this provision. Subsequently, on January 1, 2018, the number of shares available for issuance under the 2012 Plan increased by 1,285,714 under this provision. Awards under the 2012 Plan may include the following award types: incentive stock options, nonqualified stock options, stock appreciation rights, restricted stock awards, restricted stock units (RSUs), other stock‑based or cash‑based awards and any combination of the foregoing. As of December 31, 2017, under the 2012 Plan, the Company has granted stock options for 10,684,203 shares of common stock, of which 3,005,939 have been forfeited and 137,127 have been exercised, and restricted stock units for 909,918 shares of common stock, of which 150,101 have been forfeited. The exercise price of each option has been equal to the closing price of a share of our common stock on the grant date. Inducement Award Program In December 2014, the Company established an inducement award program (in accordance with Nasdaq Listing Rule 5635(c)(4)) under which it may grant non-statutory stock options to purchase up to an aggregate of 750,000 shares of common stock to new or prospective employees as inducement to enter into employment with the Company. In December 2016, the Board of Directors authorized and reserved 580,000 additional shares of common stock under this program. In December 2017, the Board of Directors authorized and reserved 2,500,000 additional shares of common stock under this program. The program is governed by the terms of the 2012 Plan but does not fall under the 2012 Plan. As of December 31, 2017, the Company had granted options for 1,324,000 shares of common stock under the program, of which 75,000 have been forfeited and 138,750 have been exercised. As of December 31, 2017, 2,506,000 remain available for future issuance. Stock Options A summary of the Company’s stock option activity and related information for the year ended December 31, 2017 is as follows: Weighted-average Weighted-average remaining Aggregate exercise price per contractual term intrinsic value Shares share (years) (in thousands) Outstanding at December 31, 2016 5,848,470 $ 6.35 8.0 $ 62 Granted 3,553,430 $ 2.60 Exercised (348,734) $ 1.27 Forfeited/cancelled (333,188) $ 2.04 Outstanding at December 31, 2017 8,719,978 $ 5.19 7.9 $ 6,150 Vested at December 31, 2017 4,795,186 $ 7.04 6.9 $ 2,562 Vested and expected to vest at December 31, 2017(1) 8,649,978 $ 5.20 7.9 $ 6,150 (1) This represents the number of vested options as of December 31, 2017, plus the number of unvested options expected to vest as of December 31, 2017. The fair value of each stock option was estimated using a Black‑Scholes option‑pricing model with the following assumptions: Year ended December 31, 2017 2016 2015 Risk-free interest rate 2.02 % 1.48 % 1.75 % Volatility 78 % 75 % 73 % Dividend yield — — — Expected term (years) The Company recorded stock‑based compensation expense associated with employee stock options of $4.5 million, $6.1 million, and $7.9 million for the years ended December 31, 2017, 2016 and 2015, respectively. The weighted‑average grant date fair value of options granted in the years ended December 31, 2017, 2016 and 2015 was $1.83, $0.99, and $3.80 per share, respectively. The fair value of options that vested during the years ended December 31, 2017, 2016 and 2015 was $4.8 million, $6.9 million, and $9.5 million, respectively. The aggregate intrinsic value of options exercised (i.e., the difference between the market price at exercise and the price paid by employees to exercise the option) during the years ended December 31, 2017 and 2016 was $1.1 million and $0, respectively. In June 2016, the Company granted stock options to purchase a total of 500,000 shares of common stock to certain employees that vest only upon the achievement of specified performance conditions. The Company determined that 50% of performance conditions had been achieved during the year ended December 31, 2016. As a result, 250,000 shares vested in October 2016 and the Company recognized stock-based compensation expense related to these awards of approximately $222,000 for the year ended December 31, 2016. In September 2017, the Company determined that the remaining performance conditions had been achieved and as a result the remaining 250,000 shares vested and the Company recognized stock-based compensation expense of approximately $379,000 during the year ended December 31, 2017. The increase in stock-based compensation expense recognized for the awards which vested during the year ended December 31, 2017, as compared to the awards which vested during the year ended December 31, 2016, is a result of the revaluation of an award held by a non-employee to fair value on the vesting date. At December 31, 2017, there was $6.8 million of total unrecognized compensation cost related to unvested stock options and the Company expects to recognize this cost over a remaining weighted-average period of 2.9 years. Restricted Stock Units No restricted stock units were granted during the years ended December 31, 2017, 2016 and 2015. The total fair value of restricted stock units vested during the years ended December 31, 2017, 2016 and 2015 was approximately $0, $65,000 and $1.6 million, respectively. As of December 31, 2016, all RSUs granted under the 2012 plan had vested. During the first quarter of 2013, the Company amended the terms of certain RSUs related to a total of 697,060 shares of common stock to allow for tax withholdings greater than the minimum required statutory withholding amount. As a result of this change in the terms of the awards, the outstanding RSUs were considered to be liability instruments until vested. As a result of this modification, the Company recorded a liability for the fair value of the awards as of each reporting date with the change in fair value recorded through the consolidated statements of operations and comprehensive loss. The Company recorded stock‑based compensation expense equal to the greater of the original grant date fair value of the awards or the settlement date fair value. All RSUs were fully vested as of February 1, 2016. During the year ended December 31, 2017, 2016 and 2015, the Company deposited approximately $0, $5,000, and $417,000, respectively, with tax authorities to settle the tax liability for awards that settled during the respective periods. There was no liability related to these awards as of December 31, 2017 and 2016.

Income taxes

Income taxes	12 Months Ended
	Dec. 31, 2017
Income taxes
Income taxes	8. Income Taxes As of December 31, 2017, the Company had federal and state net operating loss carryforwards of approximately $237.0 million and $235.9 million, respectively, which are available to reduce future taxable income. The Company also had federal and state tax credits of $14.1 million and $1.7 million, respectively, which may be used to offset future tax liabilities. The net operating loss (NOL) and tax credit carryforwards will expire at various dates through 2037. NOL and tax credit carryforwards are subject to review and possible adjustment by the Internal Revenue Service and state tax authorities and 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, as well as similar state provisions. This could limit the amount of tax attributes that can be utilized annually to offset future taxable income or tax liabilities. The amount of the annual limitation is 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. A reconciliation of income taxes computed using the U.S. federal statutory rate to that reflected in operations follows: December 31, 2017 2016 Income tax benefit using U.S. federal statutory rate 34.00 % 34.00 % State tax benefit, net of federal benefit 5.00 % 3.43 % Research and development tax credits 7.04 % 4.42 % Permanent items (1.24) % (3.88) % Effect of U.S. Tax Cuts and Jobs Act (45.19) % — % Change in the valuation allowance 0.19 % (36.71) % Other 0.20 % (1.26) % — % — % The principal components of the Company’s deferred tax assets are as follows (in thousands): December 31, 2017 2016 Deferred tax assets: Net operating loss carryforwards $ 64,677 $ 72,285 Capitalized research and development 2,780 1,836 Research and development credits 15,406 8,298 Stock-based compensation 2,560 3,083 Other 379 429 Gross deferred tax assets 85,802 85,931 Valuation allowance (85,802) (85,931) Net deferred tax asset $ — $ — The Company has recorded a valuation allowance against its deferred tax assets at December 31, 2017 and 2016 because the Company’s management believes that it is more likely than not that these assets will not be fully realized. The decrease in the valuation allowance of approximately $129,000 in the year ended December 31, 2017 primarily relates to the reduction in the federal rate for corporations under the Tax Cuts and Jobs Act of 2017. 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 following resolution of any potential contingencies present related to the tax benefit. From inception and through December 31, 2017, the Company had no unrecognized tax benefits or related interest and penalties accrued. The Company has not conducted a study of research and development (R&D) credit carryforwards. This study may result in an adjustment to the Company’s R&D credit carryforwards; however, until a study is completed and any adjustment is known, no amounts are being presented as an uncertain tax position. A full valuation allowance has been provided against the Company’s R&D credits and, if an adjustment is required, this adjustment would be offset by an adjustment to the valuation allowance. Thus, there would be no impact to the consolidated balance sheet or statement of operations if an adjustment were required. The Company would recognize both accrued interest and penalties related to unrecognized benefits in income tax expense. The Company’s uncertain tax positions are related to years that remain subject to examination by relevant tax authorities. Since the Company is in a loss carryforward position, the Company is generally subject to examination by the U.S. federal, state and local income tax authorities for all tax years in which a loss carryforward is available. On December 22, 2017, the Tax Cuts and Jobs Act (TCJA) was enacted. This law substantially amended the Internal Revenue Code and among other things, effective January 1, 2018, permanently reduced the U.S. corporate income tax rate from 35% to 21% and repealed the performance exception permitting certain executive officer compensation greater than $1.0 million to be deducted. On December 22, 2017, the SEC staff issued Staff Accounting Bulletin No. 118, Income Tax Accounting Implications of the Tax Cuts and Jobs Act (SAB 118), which allows the recording of provisional amounts during a measurement period not to extend beyond one year of the enactment date. In accordance with SAB 118, the Company has determined that its deferred tax asset value and associated valuation allowance reduction of $30.6 million is a provisional amount and a reasonable estimate at December 31, 2017. The final impact may differ from this provisional amount due to, among other things, changes in interpretations and assumptions the Company has made thus far and the issuance of additional regulatory or other guidance. The Company expects to determine the final impact within the measurement period.

Commitments and contingencies

Commitments and contingencies	12 Months Ended
	Dec. 31, 2017
Commitments and contingencies
Commitments and contingencies	9. Commitments and contingencies On April 15, 2014, the Company entered into a lease agreement for approximately 15,197 square feet of office and laboratory space in Needham, Massachusetts. The lease term commenced on April 15, 2014 and expires on September 30, 2019. The Company began using the leased premises as its corporate headquarters and commenced rent payments effective September 22, 2014. The Company agreed to pay an initial annual base rent of approximately $493,000, which base rent increases after every twelve-month period during the lease term to approximately $554,000 for the last twelve-month period. The Company is recording rent expense on a straight-line basis, beginning in April 2014. The Company also received a tenant improvement allowance of approximately $684,000 in connection with the lease. The Company has accounted for the allowance as a lease incentive, which is being recorded as a reduction to rent expense over the lease term. Deferred rent and the lease incentive obligation are included in accrued expenses (current portion) and other liabilities (noncurrent portion) in the consolidated balance sheets. The Company has also agreed to pay its proportionate share of increases in operating expenses and property taxes for the building in which the leased space is located. The Company has provided a security deposit in the form of a letter of credit in the amount of approximately $203,000, which was reduced to approximately $162,000 on April 15, 2016. The amount is included in long term restricted cash on the consolidated balance sheets as of December 31, 2017 and 2016. The minimum aggregate future lease commitments as of December 31, 2017 are as follows (in thousands): 2018 $ 2019 2020 — 2021 — 2022 — Thereafter — Total $ The Company recorded rent expense of approximately $352,000, $352,000 and $352,000 for the years ended December 31, 2017, 2016 and 2015, respectively. Pursuant to the terms of various agreements, the Company may be required to pay various development, regulatory and commercial milestones. In addition, if any products related to these agreements are approved for sale, the Company may be required to pay significant royalties on future sales. The payment of these amounts, however, is contingent upon the occurrence of various future events, which have a high degree of uncertainty of occurring.

License agreements

License agreements	12 Months Ended
	Dec. 31, 2017
License agreements.
License agreements	10. License agreements In November 2016, the Company entered into an amended and restated license agreement with Infinity, under which it acquired an exclusive worldwide license for the research, development, commercialization, and manufacture of products in oncology indications containing duvelisib. In connection with the license agreement, the Company assumed operational and financial responsibility for certain activities that were part of Infinity’s duvelisib program, including the DUO study for patients with relapsed/refractory CLL, and Infinity assumed financial responsibility for the shutdown of certain other clinical studies up to a maximum of $4.5 million. The Company is obligated to use diligent efforts to develop and commercialize a product in an oncology indication containing duvelisib. During the term of the license agreement, Infinity has agreed not to research, develop, manufacture or commercialize duvelisib in any other indication in humans or animals. Pursuant to the terms of the license agreement, the Company is required to make the following payments to Infinity in cash or, at our election, in whole or in part, in shares of our common stock: (i) $6.0 million upon the completion of the DUO study if the results of the DUO study meet certain pre-specified criteria, which milestone was paid in cash by the Company to Infinity in October 2017 and recorded as research and development expense in the consolidated statement of operations, and (ii) $22.0 million upon the approval of a New Drug Application in the United States or an application for marketing authorization with a regulatory authority outside of the United States for a product in an oncology indication containing duvelisib. For any portion of any of the foregoing payments that it elects to issue in shares of our common stock in lieu of cash, the number of shares of common stock to be issued will be determined by multiplying (1) 1.025 by (2) the number of shares of common stock equal to (a) the amount of the payment to be paid in shares of common stock divided by (b) the average closing price of a share of common stock as quoted on Nasdaq for a twenty day period following the public announcement of the applicable milestone event. The shares of common stock will be issued as unregistered securities, and the Company will have an obligation to promptly file a registration statement with the SEC to register such shares for resale. Any issuance of shares will be subject to the satisfaction of closing conditions, including that all material authorizations, consents, approvals and the like necessary for such issuance shall have been obtained. The Company is also obligated to pay Infinity royalties on worldwide net sales of any products in an oncology indication containing duvelisib ranging from the mid-single digits to the high single-digits. The royalties will expire on a product-by-product and country-by-country basis until the latest to occur of (i) the last-to-expire patent right covering the applicable product in the applicable country, (ii) the last-to-expire patent right covering the manufacture of the applicable product in the country of manufacture of such product, (iii) the expiration of non-patent regulatory exclusivity in such country and (iv) ten years following the first commercial sale of a product in a country, provided that if royalties on net sales for a product in the United States are payable solely on the basis of non-patent regulatory exclusivity, the applicable royalty on net sales for such product in the United States will be reduced by 50%. The royalties are also subject to reduction by 50% of certain third-party royalty payments or patent litigation damages or settlements which might be required to be paid by us if litigation were to arise, with any such reductions capped at 50% of the amounts otherwise payable during the applicable royalty payment period. In addition to the foregoing, the Company is obligated to pay Infinity an additional royalty of 4% on worldwide net sales of any products in an oncology indication containing duvelisib to cover the reimbursement of research and development costs owed by Infinity to Mundipharma International Corporation Limited (MICL) and Purdue Pharmaceutical Products L.P. (Purdue). Once Infinity has fully reimbursed MICL and Purdue, the royalty obligations will be reduced to 1% of net sales in the United States. These trailing MICL royalties are payable until the later to occur of the last-to-expire of specified patent rights and the expiration of non-patent regulatory exclusivities in a country. Each of the above royalty rates is reduced by 50% on a product-by-product and country-by-country basis if the applicable royalty is payable solely on the basis of non-patent regulatory exclusivity. In addition, the trailing MICL royalties are subject to reduction by 50% of certain third-party royalty payments or patent litigation damages or settlements which might be required to be paid by the us if litigation were to arise, with any such reductions capped at 50% of the amounts otherwise payable during the applicable royalty payment period. The Company evaluated the license agreement with Infinity under ASC Topic 805 , Business Combinations, and ASU 2017-01 and concluded that as substantially all of the fair value of the gross assets acquired is concentrated in a single identifiable asset or group of similar assets, the transaction did not meet the requirements to be accounted for as a business combination and therefore was accounted for as an asset acquisition. All consideration to be paid under the License Agreement is contingent in nature and will be recognized when the respective contingency is resolved. On July 11, 2012, the Company entered into a license agreement with Pfizer Inc. (Pfizer), under which Pfizer granted the Company worldwide, exclusive rights to research, develop, manufacture and commercialize products containing certain of Pfizer’s inhibitors of focal adhesion kinase (the FAK Products) for all therapeutic, diagnostic and prophylactic uses in humans. The Company is solely responsible, at its expense, for the clinical development of the FAK Products, which is to be conducted in accordance with an agreed upon development plan. The Company is also responsible for all manufacturing and commercialization activities at its own expense. Pfizer is required to provide the Company with an initial quantity of clinical supply of one of the FAK Products for an agreed upon price. Under the agreement, the Company made a one-time cash payment to Pfizer in the amount of $1.5 million and issued 192,012 shares of its common stock. Pfizer is also eligible to receive up to $2.0 million in developmental milestones and up to an additional $125.0 million based on the successful attainment of regulatory and commercial sales milestones. Pfizer is also eligible to receive high single to mid-double digit royalties on future net sales of the FAK Products. The Company’s royalty obligations with respect to each FAK Product in each country begin on the date of first commercial sale of the FAK Product in that country, and end on the later of 10 years after the date of first commercial sale of the FAK Product in that country or the date of expiration or abandonment of the last claim contained in any issued patent or patent application licensed by Pfizer to the Company that covers the FAK Product in that country. The Company accounted for the license agreement as the licensing of in process research and development with no alternative future use.

Employee benefit plan

Employee benefit plan	12 Months Ended
	Dec. 31, 2017
Employee benefit plan
Employee benefit plan	11. Employee benefit plan In June 2011, the Company adopted a 401(k) retirement and savings plan (the 401(k) Plan) covering all employees. The 401(k) Plan allows employees to make pre‑tax or post‑tax contributions up to the maximum allowable amount set by the Internal Revenue Service. Under the 401(k) Plan, the Company may make discretionary contributions as approved by the board of directors. The Company made approximate contributions to the 401(k) Plan of $273,000, $162,000, and $295,000 for the years ended December 31, 2017, 2016, and 2015, respectively.

Reduction in force

Reduction in force	12 Months Ended
	Dec. 31, 2017
Reduction in force
Reduction in force	12. Reduction in force In October 2015, the Company announced a reduction of workforce by approximately 50% to 20 full time employees. All affected employees received severance pay and outplacement assistance. As a result of the reduction in force and associated costs, the Company paid one-time severance and related costs of $1.1 million. Of these one-time severance and related costs, approximately $713,000 and approximately $349,000 was paid during the years ended December 31, 2016 and 2015, respectively.

Quarterly financial information

Quarterly financial information (unaudited, in thousands, except per share data)	12 Months Ended
	Dec. 31, 2017
Quarterly financial information (unaudited, in thousands, except per share data)
Quarterly financial information	13. Quarterly financial information (unaudited, in thousands, except per share data) First Quarter Second Quarter Third Quarter Fourth Quarter Ended Ended Ended Ended March 31, June 30, September 30, December 31, 2017 2017 2017 2017 Operating expenses: Research and development $ $ $ $ General and administrative Total operating expenses Loss from operations Interest income Interest expense Net loss $ $ $ $ Net loss per share —basic and diluted $ $ $ $ Weighted-average number of common shares used in net loss per share —basic and diluted (a) (a)(b) First Quarter Second Quarter Third Quarter Fourth Quarter Ended Ended Ended Ended March 31, June 30, September 30, December 31, 2016 2016 2016 2016 Operating expenses: Research and development $ $ $ $ General and administrative Total operating expenses Loss from operations Interest income Net loss $ $ $ $ Net loss per share —basic and diluted $ $ $ $ Weighted-average number of common shares used in net loss per share —basic and diluted (a) In the third and fourth quarters of 2017, the Company sold 2,853,753 and 2,183,126 shares of its common stock under the Company’s at-the-market equity offering program, which resulted in net proceeds of $14.1 million and $9.0 million, respectively. (b) In December 2017, the Company closed an underwritten offering in which it sold 8,422,877 shares of its common stock at a price of $2.97 per share, for aggregate proceeds, net of underwriting discounts and offering costs of $24.7 million.

Subsequent events

Subsequent events	12 Months Ended
	Dec. 31, 2017
Subsequent events.
Subsequent events	14. Subsequent events The Company reviews all activity subsequent to year end but prior to the issuance of the consolidated financial statements for events that could require disclosure or that could impact the carrying value of assets or liabilities as of the consolidated balance sheets date. The Company is not aware of any material subsequent events other than those disclosed above.

Significant accounting polici22

Significant accounting policies (Policies)	12 Months Ended
	Dec. 31, 2017
Significant accounting policies
Basis of presentation	Basis of presentation The accompanying financial statements of the Company have been prepared in accordance with U.S. generally accepted accounting principles (GAAP) under the assumption that the Company will continue as a going concern for the next twelve months. Accordingly, they do not include any adjustments that might result from the uncertainty related to the Company’s ability to continue as a going concern. The consolidated financial statements include the accounts of Verastem Securities Company, a wholly-owned subsidiary of the Company. All financial information presented has been consolidated and includes the accounts of the Company and its wholly-owned subsidiary. All intercompany balances and transactions have been eliminated in consolidation.
Use of estimates	Use of estimates The preparation of the Company’s financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. On an ongoing basis, management evaluates its estimates, including estimates related to accruals and stock‑based compensation expense. The Company bases its estimates on historical experience and other market‑specific or other relevant assumptions that it believes to be reasonable. Actual results could differ from such estimates.
Segment and geographic information	Segment and geographic information Operating segments are defined as components of an enterprise about which separate discrete information is available and regularly reviewed 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 operating segment, which is the business of developing drugs for the treatment of cancer. All material long-lived assets of the Company reside in the United States.
Cash and cash equivalents	Cash and cash equivalents The Company considers all highly liquid investments with an original or remaining maturity of three months or less at the date of purchase to be cash equivalents. Cash equivalents consist of a U.S. Government money market fund, overnight repurchase agreements collateralized by government agency securities or U.S. Treasury securities, corporate bonds and commercial paper of publicly traded companies. Cash equivalents are reported at fair value.
Fair value of financial instruments	Fair value of financial instruments The Company determines the fair value of its financial instruments based upon the fair value hierarchy, which prioritizes valuation inputs based on the observable nature of those inputs. The fair value hierarchy applies only to the valuation inputs used in determining the reported fair value of the investments and is not a measure of the investment credit quality. The hierarchy defines three levels of valuation inputs: Level 1 inputs Quoted prices in active markets for identical assets or liabilities that the Company can access at the measurement date. Level 2 inputs Inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly. Level 3 inputs Unobservable inputs that reflect the Company’s own assumptions about the assumptions market participants would use in pricing the asset or liability. Items Measured at Fair Value on a Recurring Basis The following table presents information about the Company’s financial instruments that are measured at fair value on a recurring basis (in thousands): December 31, 2017 Description Total Level 1 Level 2 Level 3 Financial assets Cash equivalents $ 80,894 $ 75,478 $ 5,416 $ — Short-term investments 4,496 — 4,496 — Total financial assets $ 85,390 $ 75,478 $ 9,912 $ — December 31, 2016 Description Total Level 1 Level 2 Level 3 Financial assets Cash equivalents $ 30,540 $ 20,540 $ 10,000 $ — Short-term investments 48,548 — 48,548 — Total financial assets $ 79,088 $ 20,540 $ 58,548 $ — These investments and cash equivalents have been initially valued at the transaction price and subsequently valued, at the end of each reporting period, utilizing third party pricing services or other market observable data. The pricing services utilize industry standard valuation models, including both income and market based approaches and observable market inputs to determine value. These observable market inputs include reportable trades, benchmark yields, credit spreads, broker/dealer quotes, bids, offers, current spot rates and other industry and economic events. The Company validates the prices provided by third party pricing services by reviewing their pricing methods and matrices, obtaining market values from other pricing sources, analyzing pricing data in certain instances and confirming that the relevant markets are active. After completing its validation procedures, the Company did not adjust or override any fair value measurements provided by the pricing services as of December 31, 2017 and 2016. Fair Value of Financial Instruments The fair value of the Company’s long-term debt is determined using current applicable rates for similar instruments as of the balance sheet dates and an assessment of the credit rating of the Company. The carrying value of the Company’s debt at December 31, 2017 approximates fair value because the Company’s interest rate yield is near current market rates for comparable debt instruments. The fair value of the Company’s long-term debt was determined using Level 3 inputs.
Investments	Investments Investments and cash equivalents consist of investments in a U.S. Government money market fund, overnight repurchase agreements collateralized by government agency securities or U.S. Treasury securities, corporate bonds and commercial paper of publicly traded companies that are classified as available‑for‑sale pursuant to Accounting Standards Codification (ASC) Topic 320, Investments—Debt and Equity Securities . The Company classifies investments available to fund current operations as current assets on its consolidated balance sheets. Investments are classified as long‑term assets on the consolidated balance sheets if (i) the Company has the intent and ability to hold the investments for a period of at least one year and (ii) the contractual maturity date of the investments is greater than one year. Investments are carried at fair value with unrealized gains and losses included as a component of accumulated other comprehensive income (loss), which is a separate component of stockholders’ equity (deficit), until such gains and losses are realized. The fair value of these securities is based on quoted prices for identical or similar assets. If a decline in the fair value is considered other‑than‑temporary, based on available evidence, the unrealized loss is transferred from other comprehensive loss to the consolidated statements of operations and comprehensive loss. The Company reviews investments for other‑than‑temporary impairment whenever the fair value of an investment is less than the amortized cost and evidence indicates that an investment’s carrying amount is not recoverable within a reasonable period of time. To determine whether an impairment is other‑than‑temporary, the Company considers the intent to sell, or whether it is more likely than not that the Company will be required to sell, the investment before recovery of the investment’s amortized cost basis. Evidence considered in this assessment includes reasons for the impairment, compliance with the Company’s investment policy, the severity and the duration of the impairment and changes in value subsequent to year end. Realized gains and losses are determined using the specific identification method and are included in interest income in the consolidated statements of operations and comprehensive loss. There were no realized gains or losses on investments for the years ended December 31, 2017, 2016 or 2015. There were no investments that had been in an unrealized loss position for more than 12 months as of December 31, 2017 or December 31, 2016. There were 5 debt securities in an unrealized loss position for less than 12 months at December 31, 2017 and there were 14 debt securities that had been in an unrealized loss position for less than 12 months at December 31, 2016. The aggregate unrealized loss on these securities as of December 31, 2017 and December 31, 2016 was approximately $2,000 and $24,000, respectively, and the fair value was $9.9 million and $23.6 million, respectively. The Company considered the decline in the market value for these securities to be primarily attributable to current economic conditions. As it was not more likely than not that the Company would be required to sell these securities before the recovery of their amortized cost basis, which may be at maturity, the Company did not consider these investments to be other-than-temporarily impaired as of December 31, 2017. Cash, cash equivalents and investments consist of the following (in thousands): December 31, 2017 Gross Gross Amortized Unrealized Unrealized Fair Cost Gains Losses Value Cash and cash equivalents: Cash and money market accounts $ 76,760 $ — $ — $ 76,760 Corporate bonds and commercial paper $ 5,418 $ — $ (2) $ 5,416 Total cash and cash equivalents $ 82,178 $ — $ (2) $ 82,176 Investments: Corporate bonds and commercial paper (due within 1 year) $ 4,496 $ — $ — $ 4,496 Total investments $ 4,496 $ — $ — $ 4,496 Total cash, cash equivalents, and investments $ 86,674 $ — $ (2) $ 86,672 December 31, 2016 Gross Gross Amortized Unrealized Unrealized Fair Cost Gains Losses Value Cash and cash equivalents: Cash and money market accounts $ 22,349 $ — $ — $ 22,349 Overnight repurchase agreements 10,000 — — 10,000 Total cash and cash equivalents $ 32,349 $ — $ — $ 32,349 Investments: Corporate bonds and commercial paper (due within 1 year) $ 48,519 $ 53 $ (24) $ 48,548 Total investments $ 48,519 $ 53 $ (24) $ 48,548 Total cash, cash equivalents, and investments $ 80,868 $ 53 $ (24) $ 80,897
Concentrations of credit risk and off-balance sheet risk	Concentrations of credit risk and off‑balance sheet risk Cash and cash equivalents and investments are financial instruments that potentially subject the Company to concentrations of credit risk. The Company mitigates this risk by maintaining its cash and cash equivalents and investments with high quality, accredited financial institutions. The management of the Company’s investments is not discretionary on the part of these financial institutions. As of December 31, 2017, the Company’s cash, cash equivalents and investments were deposited at two financial institutions and it has no significant off‑balance sheet concentrations of credit risk, such as foreign currency exchange contracts, option contracts or other hedging arrangements.
Property and equipment	Property and equipment Property and equipment consists of laboratory equipment, office furniture, computer equipment and leasehold improvements. Expenditures for repairs and maintenance are recorded to expense as incurred, whereas major betterments are capitalized as additions to property and equipment. Depreciation and amortization is calculated using the straight‑line method over the following estimated useful lives of the assets: Laboratory equipment 5 years Furniture 5 years Computer equipment 3 years Leasehold improvements Lesser of useful life or life of lease 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 its long‑lived assets for impairment whenever events or changes in business circumstances indicate that the carrying value of assets may not be recoverable. Recoverability is measured by comparison of the asset’s 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 exceed their fair value, which is measured based on the projected discounted future net cash flows arising from the assets. No material impairment losses have been recorded through December 31, 2017.
Other assets	Other assets Other assets primarily consists of prepayments made to contract research organizations (CROs). As of December 31, 2017 and 2016, other assets was primarily comprised of approximately $755,000 of prepaid CRO expenses that the Company assumed and paid to Infinity Pharmaceuticals, Inc. (Infinity) pursuant to the license agreement between the Company and Infinity.
Research and development costs	Research and development costs The Company expenses research and development costs to operations as incurred. Research and development expenses consist of: · employee‑related expenses, including salaries, benefits, travel and stock‑based compensation expense; · external research and development expenses incurred under arrangements with third parties, such as CROs, clinical trial sites, manufacturing organizations and consultants, including the scientific advisory board; · license fees; and · facilities, depreciation and other expenses, which include direct and allocated expenses for rent and maintenance of facilities, depreciation of equipment, and laboratory supplies. The Company accounts for nonrefundable advance payments for goods and services that will be used in future research and development activities as expenses when the services have been performed or when the goods have been received rather than when the payment is made.
Stock-based compensation	Stock‑based compensation The Company expenses the fair value of employee stock-based awards on a straight-line basis over the requisite service period, which typically is the vesting period. Compensation expense is measured using the fair value of the award at the grant date, net of estimated forfeitures, and is adjusted to reflect actual forfeitures as they occur. Awards subject to performance based vesting requirements are expensed utilizing an accelerated attribution model if achievement of the performance criteria is determined to be probable. The grant date fair value of employee stock options is estimated using the Black‑Scholes option pricing model that takes into account the fair value of its common stock, the exercise price, the expected life of the option, the expected volatility of its common stock, expected dividends on its common stock, and the risk-free interest rate over the expected life of the option. The Company uses the simplified method described in the Securities and Exchange Commission Staff Accounting Bulletin Topic 14.D.2 to calculate the expected term as it does not have sufficient historical exercise data to provide a reasonable basis upon which to estimate the expected term for options granted to employees. The expected term is applied to the stock option grant group as a whole, as the Company does not expect substantially different exercise or post‑vesting termination behavior among its employee population. The computation of expected volatility is based on the historical volatility of five companies, including the Company and a representative group of four public biotechnology and life sciences companies with similar characteristics to the Company, including similar stage of product development and therapeutic focus. The risk‑free interest rate is based on a treasury instrument whose term is consistent with the expected term of the stock options. Historically, the Company has recognized stock-based compensation net of estimated forfeitures over the vesting period of the respective grant. Effective January 1, 2017, the Company adopted Accounting Standard Updated (ASU) 2016-09, Compensation – Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting , which simplified the accounting for share-based compensation arrangements, including the accounting for forfeitures. Upon adoption, the Company elected to begin accounting for forfeitures as they occur, rather than estimating a forfeiture rate, and recorded an immaterial cumulative-effect adjustment to opening accumulated deficit. Stock‑based awards issued to nonemployees, including directors for non‑board related services, are accounted for based on the fair value of such services received or of the equity instruments issued, whichever is more reliably measured. Stock option awards to non-employees are revalued at each reporting date and upon vesting using the Black‑Scholes option pricing model and are expensed on a straight‑line basis over the vesting period. Stock‑based compensation awards which allowed for greater than the minimum statutory tax withholdings were classified as liabilities. These awards were revalued at each reporting date and were expensed on a straight‑line basis over the vesting period. Upon settlement, the awards were revalued and the amounts were reclassified to additional paid‑in capital. Shares were withheld to cover the tax withholding and amounts paid to settle the tax liability were recorded as a reduction of additional paid‑in capital.
Income taxes	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. Tax benefits are recognized when it is more likely than not that a tax position will be sustained during an audit. Deferred tax assets are reduced by a valuation allowance if current evidence indicates that it is considered more likely than not that these benefits will not be realized.
Net loss per share	Net loss per share Basic and diluted net loss per common share is calculated by dividing net loss applicable to common stockholders by the weighted‑average number of common shares outstanding during the period, without consideration for common stock equivalents. The Company’s potentially dilutive shares, which include outstanding stock options, restricted stock units, unvested restricted stock and the warrant issued in 2014 are considered to be common stock equivalents and are only included in the calculation of diluted net loss per share when their effect is dilutive. All potentially dilutive securities were excluded from the calculation of diluted net loss per share as the securities were anti‑dilutive for all periods presented. The following potentially dilutive securities were excluded from the calculation of diluted net loss per share due to their anti‑dilutive effect: Year ended December 31, 2017 2016 2015 Outstanding stock options 8,719,978 5,848,470 5,390,130 Outstanding warrants — 142,857 142,857 Unvested restricted stock units — — 53,751 Total potentially dilutive securities 8,719,978 5,991,327 5,586,738
Recently Issued and/or Adopted Accounting Standards Updates	Recently Issued Accounting Standards Updates In May 2017, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2017-09, Compensation – Stock Compensation (Topic 718): Scope of Modification Accounting . ASU 2017-09 provides guidance about which changes to the terms or conditions of a share-based award require an entity to apply modification accounting under Topic 718. Specifically, an entity would not apply modification accounting if the fair value, vesting conditions and classification of the awards are the same immediately before and after a modification. ASU 2017-09 is effective for annual and interim periods beginning after December 15, 2017, with early adoption permitted. The Company has not elected to early adopt this standard and does not expect the adoption to have a material impact on its consolidated financial statements and related disclosures. In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash . ASU 2016-18 requires that a statement of cash flows explain the change during the period in the total of cash, cash equivalents and amounts generally described as restricted cash or restricted cash equivalents. Amounts generally described as restricted cash and restricted cash equivalents should 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. ASU 2016-18 is effective for annual and interim periods beginning after December 15, 2017, with early adoption permitted. The Company has not elected to early adopt this standard and does not expect the adoption to have a material impact on its consolidated financial statements and related disclosures. In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments. ASU 2016-15 adds or clarifies guidance on the classification of certain cash receipts and payments in the statement of cash flows. The standard is effective for annual and interim periods beginning after December 15, 2017, with early adoption permitted. The Company has not elected to early adopt this standard and does not expect the adoption to have a material impact on its consolidated financial statements and related disclosures. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842), which supersedes the guidance under FASB Accounting Standards Codification (ASC) Topic 840, Leases, resulting in the creation of FASB ASC Topic 842, Leases. ASU 2016-02 requires lessees to recognize in the statement of financial position a liability to make lease payments and a right-of-use asset representing its right to use the underlying asset for the lease term for both finance and operating leases. The guidance also eliminates the current real estate-specific provisions for all entities. ASU 2016-02 is effective for fiscal years, and interim periods within those years, beginning after December 15, 2018, with early adoption permitted. The Company has not elected to early adopt this standard and is currently evaluating the impact the adoption of the standard will have on its consolidated financial statements and related disclosures . Recently Adopted Accounting Standards Updates In January 2017, the FASB issued ASU 2017-03, Accounting Changes and Error Corrections (Topic 250) and Investments – Equity Method and Joint Ventures (Topic 323): Amendments to SEC Paragraphs Pursuant to Staff Announcements at the September 22, 2016 and November 17, 2016 EITF Meetings. ASU 2017-03 clarifies the SEC staff’s expectations about the extent of disclosures that a registrant is expected to provide regarding the impact that the adoption of ASUs 2014-09 (Revenue from Contracts with Customers), 2016-02 (Leases) and 2016-13 (Measurement of Credit Losses on Financial Instruments) will have on its financial statements. It also conforms SEC guidance on accounting for tax benefits resulting from investments in affordable housing projects to the guidance in ASU 2014-01, Investments -Equity Method and Joint Ventures (Topic 323) . The guidance under this ASU was effective upon issuance and did not have a material impact on the Company’s disclosures. In October 2016, the FASB issued ASU 2016-17, Consolidation (Topic 810): Interests Held through Related Parties That Are under Common Control . ASU 2016-17 updates ASU 2015-02. Under the amendments, a single decision maker is not required to consider indirect interests held through related parties that are under common control with the single decision maker to be the equivalent of direct interests in their entirety. Instead, a single decision maker is required to include those interests on a proportionate basis consistent with indirect interests held through other related parties. ASU 2016-17 is effective for annual and interim periods beginning after December 15, 2016. The Company adopted this standard effective January 1, 2017. The adoption of this ASU did not have an effect on the Company’s financial statements or disclosures. In March 2016, the FASB issued ASU 2016-09, Compensation – Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting . ASU 2016-09 simplifies the accounting for share-based compensation arrangements, including the accounting for forfeitures, income tax consequences, classification of awards as either equity or liabilities and classification on the statement of cash flows. The standard was effective for annual and interim periods beginning after December 15, 2016, with early adoption permitted. The Company adopted ASU 2016-09 effective January 1, 2017. Upon adoption, the Company elected to begin accounting for forfeitures as they occur, rather than estimating a forfeiture rate, and recorded an immaterial cumulative-effect adjustment to opening accumulated deficit. Also u pon adoption, the Company recognized all previously unrecognized tax benefits, which would have resulted in the recognition of an immaterial cumulative-effect adjustment to opening accumulated deficit; however, these unrecognized tax benefits were recorded as a deferred tax asset, which was fully offset by a valuation allowance. Therefore, the recognition of these benefits had no net cumulative-effect on opening accumulated deficit upon adoption.

Significant accounting polici23

Significant accounting policies (Tables)	12 Months Ended
	Dec. 31, 2017
Significant accounting policies
Schedule of financial instruments measured at fair value on a recurring basis	The following table presents information about the Company’s financial instruments that are measured at fair value on a recurring basis (in thousands): December 31, 2017 Description Total Level 1 Level 2 Level 3 Financial assets Cash equivalents $ 80,894 $ 75,478 $ 5,416 $ — Short-term investments 4,496 — 4,496 — Total financial assets $ 85,390 $ 75,478 $ 9,912 $ — December 31, 2016 Description Total Level 1 Level 2 Level 3 Financial assets Cash equivalents $ 30,540 $ 20,540 $ 10,000 $ — Short-term investments 48,548 — 48,548 — Total financial assets $ 79,088 $ 20,540 $ 58,548 $ —
Schedule of cash, cash equivalents and investments	Cash, cash equivalents and investments consist of the following (in thousands): December 31, 2017 Gross Gross Amortized Unrealized Unrealized Fair Cost Gains Losses Value Cash and cash equivalents: Cash and money market accounts $ 76,760 $ — $ — $ 76,760 Corporate bonds and commercial paper $ 5,418 $ — $ (2) $ 5,416 Total cash and cash equivalents $ 82,178 $ — $ (2) $ 82,176 Investments: Corporate bonds and commercial paper (due within 1 year) $ 4,496 $ — $ — $ 4,496 Total investments $ 4,496 $ — $ — $ 4,496 Total cash, cash equivalents, and investments $ 86,674 $ — $ (2) $ 86,672 December 31, 2016 Gross Gross Amortized Unrealized Unrealized Fair Cost Gains Losses Value Cash and cash equivalents: Cash and money market accounts $ 22,349 $ — $ — $ 22,349 Overnight repurchase agreements 10,000 — — 10,000 Total cash and cash equivalents $ 32,349 $ — $ — $ 32,349 Investments: Corporate bonds and commercial paper (due within 1 year) $ 48,519 $ 53 $ (24) $ 48,548 Total investments $ 48,519 $ 53 $ (24) $ 48,548 Total cash, cash equivalents, and investments $ 80,868 $ 53 $ (24) $ 80,897
Schedule of estimated useful lives of the assets	Laboratory equipment 5 years Furniture 5 years Computer equipment 3 years Leasehold improvements Lesser of useful life or life of lease
Schedule of potentially anti-dilutive securities excluded from calculation of diluted net loss per share	Year ended December 31, 2017 2016 2015 Outstanding stock options 8,719,978 5,848,470 5,390,130 Outstanding warrants — 142,857 142,857 Unvested restricted stock units — — 53,751 Total potentially dilutive securities 8,719,978 5,991,327 5,586,738

Property and equipment, net (Ta

Property and equipment, net (Tables)	12 Months Ended
	Dec. 31, 2017
Property and equipment, net
Schedule of property equipment and related accumulated depreciation	Property and equipment and related accumulated depreciation are as follows (in thousands): December 31, December 31, 2017 2016 Leasehold improvements $ 2,104 $ 2,104 Laboratory equipment 908 908 Furniture and fixtures 325 325 Computer equipment 279 279 3,616 3,616 Less: accumulated depreciation (2,755) (2,199) Total property, plant and equipment, net $ 861 $ 1,417

Accrued expenses (Tables)

Accrued expenses (Tables)	12 Months Ended
	Dec. 31, 2017
Accrued expenses
Schedule of accrued expenses	Accrued expenses consist of the following (in thousands): December 31, December 31, Contract research organization costs $ 3,774 $ 3,258 Compensation and related benefits 2,622 2,505 Professional fees 617 403 Consulting fees 579 527 Deferred rent 190 175 Other 160 28 Total accrued expenses $ 7,942 $ 6,896

Long-term debt (Tables)

Long-term debt (Tables)	12 Months Ended
	Dec. 31, 2017
Long-term debt
Schedule of future principal payments under the Loan Agreement	The future principal payments under the Amended Loan Agreement are as follows as of December 31, 2017 (in thousands): 2018 $ — 2019 3,609 2020 11,391 Total principal payments $ 15,000

Common stock (Tables)

Common stock (Tables)	12 Months Ended
	Dec. 31, 2017
Common stock.
Schedule of shares of common stock reserved for the issuance of common stock for vested restricted stock units and the exercise of stock options	As of December 31, 2017 and 2016, the Company had reserved the following shares of common stock for the issuance of common stock for vested restricted stock units, the exercise of stock options, and an outstanding warrant (in thousands): December 31, December 31, 2017 2016 Shares reserved under equity compensation plans 8,264 7,189 Shares reserved for inducement grants 3,616 1,255 Shares reserved for outstanding warrants — 143 Total shares reserved 11,880 8,587

Stock-based compensation (Table

Stock-based compensation (Tables)	12 Months Ended
	Dec. 31, 2017
Stock-based compensation
Schedule of stock-based compensation expense as reflected in the Company's consolidated statements of operations and comprehensive loss	Stock‑based compensation expense as reflected in the Company’s consolidated statements of operations and comprehensive loss was as follows (in thousands): Year ended December 31, 2017 2016 2015 Research and development $ 1,381 $ 1,073 $ 2,411 General and administrative 3,652 5,145 7,273 Total stock-based compensation expense $ 5,033 $ 6,218 $ 9,684
Summary of stock option activity and related information	Weighted-average Weighted-average remaining Aggregate exercise price per contractual term intrinsic value Shares share (years) (in thousands) Outstanding at December 31, 2016 5,848,470 $ 6.35 8.0 $ 62 Granted 3,553,430 $ 2.60 Exercised (348,734) $ 1.27 Forfeited/cancelled (333,188) $ 2.04 Outstanding at December 31, 2017 8,719,978 $ 5.19 7.9 $ 6,150 Vested at December 31, 2017 4,795,186 $ 7.04 6.9 $ 2,562 Vested and expected to vest at December 31, 2017(1) 8,649,978 $ 5.20 7.9 $ 6,150 (1) This represents the number of vested options as of December 31, 2017, plus the number of unvested options expected to vest as of December 31, 2017.
Schedule of assumptions used to estimate fair value of each stock option on grant date	Year ended December 31, 2017 2016 2015 Risk-free interest rate 2.02 % 1.48 % 1.75 % Volatility 78 % 75 % 73 % Dividend yield — — — Expected term (years)

Income taxes (Tables)

Income taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income taxes
Schedule of reconciliation of income taxes computed using the U.S. federal statutory rate to that reflected in operations	December 31, 2017 2016 Income tax benefit using U.S. federal statutory rate 34.00 % 34.00 % State tax benefit, net of federal benefit 5.00 % 3.43 % Research and development tax credits 7.04 % 4.42 % Permanent items (1.24) % (3.88) % Effect of U.S. Tax Cuts and Jobs Act (45.19) % — % Change in the valuation allowance 0.19 % (36.71) % Other 0.20 % (1.26) % — % — %
Schedule of principal components of deferred tax assets	The principal components of the Company’s deferred tax assets are as follows (in thousands): December 31, 2017 2016 Deferred tax assets: Net operating loss carryforwards $ 64,677 $ 72,285 Capitalized research and development 2,780 1,836 Research and development credits 15,406 8,298 Stock-based compensation 2,560 3,083 Other 379 429 Gross deferred tax assets 85,802 85,931 Valuation allowance (85,802) (85,931) Net deferred tax asset $ — $ —

Commitments and contingencies (

Commitments and contingencies (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments and contingencies
Schedule of minimum aggregate future lease commitments	The minimum aggregate future lease commitments as of December 31, 2017 are as follows (in thousands): 2018 $ 2019 2020 — 2021 — 2022 — Thereafter — Total $

Quarterly financial informati31

Quarterly financial information (unaudited, in thousands, except per share data) (Tables)	12 Months Ended
	Dec. 31, 2017
Quarterly financial information (unaudited, in thousands, except per share data)
Schedule of Quarterly Financial Information	Quarterly financial information (unaudited, in thousands, except per share data) First Quarter Second Quarter Third Quarter Fourth Quarter Ended Ended Ended Ended March 31, June 30, September 30, December 31, 2017 2017 2017 2017 Operating expenses: Research and development $ $ $ $ General and administrative Total operating expenses Loss from operations Interest income Interest expense Net loss $ $ $ $ Net loss per share —basic and diluted $ $ $ $ Weighted-average number of common shares used in net loss per share —basic and diluted (a) (a)(b) First Quarter Second Quarter Third Quarter Fourth Quarter Ended Ended Ended Ended March 31, June 30, September 30, December 31, 2016 2016 2016 2016 Operating expenses: Research and development $ $ $ $ General and administrative Total operating expenses Loss from operations Interest income Net loss $ $ $ $ Net loss per share —basic and diluted $ $ $ $ Weighted-average number of common shares used in net loss per share —basic and diluted (a) In the third and fourth quarters of 2017, the Company sold 2,853,753 and 2,183,126 shares of its common stock under the Company’s at-the-market equity offering program, which resulted in net proceeds of $14.1 million and $9.0 million, respectively. (b) In December 2017, the Company closed an underwritten offering in which it sold 8,422,877 shares of its common stock at a price of $2.97 per share, for aggregate proceeds, net of underwriting discounts and offering costs of $24.7 million.

Nature of business (Details)

Nature of business (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Nature of business
Cash, cash equivalents, and investments	$ 86,700
Deficit accumulated during the development stage	$ 303,142	$ 235,323

Significant accounting polici33

Significant accounting policies - Segment Information and Fair Value Financial Instruments (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)item	Dec. 31, 2016USD ($)
Segment and geographic information
Number of operating segments | item	1
Recurring basis
Financial assets
Cash equivalents	$ 80,894	$ 30,540
Short-term investments	4,496	48,548
Total financial assets	85,390	79,088
Recurring basis | Level 1
Financial assets
Cash equivalents	75,478	20,540
Total financial assets	75,478	20,540
Recurring basis | Level 2
Financial assets
Cash equivalents	5,416	10,000
Short-term investments	4,496	48,548
Total financial assets	$ 9,912	$ 58,548

Significant accounting polici34

Significant accounting policies - Investments (Details)	12 Months Ended
	Dec. 31, 2017USD ($)item	Dec. 31, 2016USD ($)item	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)
Investments
Realized gains or losses on investments	$ 0	$ 0	$ 0
Number of investments in unrealized loss position for more than 12 months | item	0	0
Number of investments in unrealized loss position for less than 12 months | item	5	14
Aggregate unrealized loss on these securities	$ 2,000	$ 24,000
Unrealized loss on fair value	9,900,000	23,600,000
Cash and cash equivalents	82,176,000	32,349,000	$ 24,870,000	$ 33,901,000
Gross unrealized gains		53,000
Gross unrealized losses	(2,000)	(24,000)
Total cash, cash equivalents, and investments, Fair Value	86,700,000
Amortized Cost
Investments
Cash and cash equivalents	82,178,000	32,349,000
Investments	4,496,000	48,519,000
Total cash, cash equivalents, and investments	86,674,000	80,868,000
Fair Value
Investments
Cash and cash equivalents, Fair value	82,176,000	32,349,000
Short-term investments	4,496,000	48,548,000
Total cash, cash equivalents, and investments, Fair Value	86,672,000	80,897,000
Cash and money market accounts | Amortized Cost
Investments
Cash and cash equivalents	76,760,000	22,349,000
Cash and money market accounts | Fair Value
Investments
Cash and cash equivalents, Fair value	76,760,000	22,349,000
Corporate bonds and commercial paper
Investments
Gross unrealized losses	(2,000)
Corporate bonds and commercial paper | Amortized Cost
Investments
Cash and cash equivalents	5,418,000
Corporate bonds and commercial paper | Fair Value
Investments
Cash and cash equivalents, Fair value	$ 5,416,000
Overnight repurchase agreements | Amortized Cost
Investments
Cash and cash equivalents		10,000,000
Overnight repurchase agreements | Fair Value
Investments
Cash and cash equivalents, Fair value		$ 10,000,000
Corporate bonds and commercial paper
Investments
Maturity period, investments	1 year	1 year
Gross unrealized gains		$ 53,000
Gross unrealized losses		(24,000)
Corporate bonds and commercial paper | Amortized Cost
Investments
Due within 1 year	$ 4,496,000	48,519,000
Corporate bonds and commercial paper | Fair Value
Investments
Due within 1 year	$ 4,496,000	$ 48,548,000

Significant accounting polici35

Significant accounting policies - Concentration of Credit Risk and Property and Equipment (Details)	12 Months Ended
	Dec. 31, 2017USD ($)item	Dec. 31, 2016USD ($)
Concentrations of credit risk and off-balance sheet risk
Number of financial institutions in which cash, cash equivalents and investments were deposited	2
Share-based compensation
Number of companies expected volatility is based	5
Number of companies with similar characteristics to the Company included in computation	4
Exclusive license agreement | Infinity
Other assets
Prepaid CRO Expenses | $	$ 755,000	$ 755,000
Laboratory equipment
Property and equipment, net
Estimated useful lives	5 years
Furniture and fixtures
Property and equipment, net
Estimated useful lives	5 years
Computer equipment
Property and equipment, net
Estimated useful lives	3 years

Significant accounting polici36

Significant accounting policies - Net Loss Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net loss per share
Potentially anti-dilutive securities excluded from calculation of diluted net loss per share (in shares)	8,719,978	5,991,327	5,586,738
Stock options
Net loss per share
Potentially anti-dilutive securities excluded from calculation of diluted net loss per share (in shares)	8,719,978	5,848,470	5,390,130
Outstanding warrants
Net loss per share
Potentially anti-dilutive securities excluded from calculation of diluted net loss per share (in shares)		142,857	142,857
Restricted Stock Units
Net loss per share
Potentially anti-dilutive securities excluded from calculation of diluted net loss per share (in shares)			53,751

Property and equipment, net (De

Property and equipment, net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property and equipment
Property and equipment, gross	$ 3,616	$ 3,616
Less: accumulated depreciation	(2,755)	(2,199)
Property and equipment, net	861	1,417
Depreciation expenses	556	670	$ 754
Leasehold improvements
Property and equipment
Property and equipment, gross	2,104	2,104
Laboratory equipment
Property and equipment
Property and equipment, gross	908	908
Furniture and fixtures
Property and equipment
Property and equipment, gross	325	325
Computer equipment
Property and equipment
Property and equipment, gross	$ 279	$ 279

Accrued expenses (Details)

Accrued expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accrued expenses
Contract research organization costs	$ 3,774	$ 3,258
Compensation and related benefits	2,622	2,505
Professional fees	617	403
Consulting fees	190	175
Deferred rent	579	527
Other	160	28
Total accrued expenses	$ 7,942	$ 6,896

Long-term debt (Details)

Long-term debt (Details) $ in Thousands	Jan. 04, 2018USD ($)	Jan. 03, 2018USD ($)	Dec. 20, 2017USD ($)	Oct. 12, 2017USD ($)	Mar. 21, 2017USD ($)item	Dec. 31, 2017USD ($)
Long-term debt
Amount drawn						$ 14,811
Future principal payments
2,019						3,609,000
2,020						11,391,000
Total						$ 15,000,000
Term loan
Long-term debt
Maximum borrowing capacity	$ 50,000				$ 25,000
Amount drawn		$ 15,000
Remaining borrowing capacity	35,000
Interest rate					10.50%
Minimum cash proceeds to extend interest only payment period					$ 20,000
Amortization payments, installments | item					20
Number of business days prior written notice for prepayment					7 days
Percentage of total principal amount, as final payment					4.50%
Threshold for final debt payment					$ 5,000
Additional interest rate in an event of default					5.00%
Term loan | Advance prepaid within 12 months following closing date
Long-term debt
Prepayment charge (as a percent)					3.00%
Term loan | Advance prepaid between 12 months and 24 months following closing date
Long-term debt
Prepayment charge (as a percent)					2.00%
Term loan | Advance prepaid after 24 months
Long-term debt
Prepayment charge (as a percent)					1.00%
Term loan | Prime rate
Long-term debt
Basis spread					(4.50%)
Term loan | Minimum
Long-term debt
Interest rate					10.50%
Term loan | Minimum | Plan
Long-term debt
Amount drawn	5,000
Term loan | Maximum
Long-term debt
Number of separate advances | item					4
Interest rate					12.75%
Term loan, first tranche
Long-term debt
Amount drawn					$ 2,500
Term loan, second tranche
Long-term debt
Amount drawn				$ 2,500
Term loan, third tranche
Long-term debt
Amount drawn				5,000
Term loan, fourth tranche
Long-term debt
Amount drawn			$ 5,000
Term loan, fourth tranche | On or prior to June 30, 2018
Long-term debt
Amount drawn					$ 15,000
Term E Loan | Maximum | Plan
Long-term debt
Amount drawn	10,000
Term F Loan | Maximum | Plan
Long-term debt
Amount drawn	$ 25,000
Infinity | Exclusive license agreement
Long-term debt
Milestone payment				$ 6,000

Common stock (Details)

Common stock (Details) $ / shares in Units, $ in Thousands	Mar. 13, 2018USD ($)shares	Dec. 14, 2017USD ($)$ / sharesshares	Aug. 28, 2017USD ($)	Mar. 30, 2017USD ($)	Dec. 31, 2017USD ($)$ / sharesshares	Dec. 31, 2013USD ($)	Dec. 31, 2017USD ($)$ / sharesshares	Sep. 30, 2017USD ($)shares	Dec. 31, 2017USD ($)$ / sharesshares	Dec. 31, 2017USD ($)Vote$ / sharesshares	Dec. 31, 2016USD ($)shares	Dec. 31, 2015USD ($)shares
Common stock
Shares reserved for issuance | shares					11,880,000		11,880,000		11,880,000	11,880,000	8,587,000
Number of votes entitled for each share of common stock | Vote										1
At-the-market equity offering program
Net proceeds from issuance of stock | $										$ 48,069		$ 63,989
Outstanding warrants
Common stock
Shares reserved for issuance | shares											143,000
At-the-market equity offering program | Common stock
At-the-market equity offering program
Number of shares of common stock issued | shares							2,183,126	2,853,753		5,036,879		1,189,479
Net proceeds from issuance of stock | $							$ 9,000	$ 14,100
Follow-on offerings | Common stock
At-the-market equity offering program
Number of shares of common stock issued | shares		8,422,877			8,422,877					8,422,877		8,337,500
Net proceeds from issuance of stock | $		$ 24,700			$ 24,700
Share price (in dollars per share) | $ / shares		$ 2.97			$ 2.97		$ 2.97		$ 2.97	$ 2.97
Inducement Award Program
Common stock
Shares reserved for issuance | shares					3,616,000		3,616,000		3,616,000	3,616,000	1,255,000
2013 ATM Program | At-the-market equity offering program | Common stock
At-the-market equity offering program
Maximum value of common stock allowed to be sold | $						$ 35,000
Number of shares of common stock issued | shares										0	0	1,189,479
Net proceeds from issuance of stock | $												$ 12,900
Proceeds from issuance of common stock | $										$ 0	$ 0
2017 ATM Program | At-the-market equity offering program | Common stock
At-the-market equity offering program
Maximum value of common stock allowed to be sold | $			$ 75,000	$ 35,000
Number of shares of common stock issued | shares	97,078								5,036,879
Net proceeds from issuance of stock | $	$ 342,000								$ 23,100
Equity compensation plans
Common stock
Shares reserved for issuance | shares					8,264,000		8,264,000		8,264,000	8,264,000	7,189,000

Stock-based compensation - Stoc

Stock-based compensation - Stock-Based Compensation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stock-based compensation
Total stock-based compensation expense	$ 5,033	$ 6,218	$ 9,684
Adjustments to additional paid-in capital	5,033	6,287	10,085
Increase (decrease) in stock-based compensation award liability		(69)	(400)
Research and development
Stock-based compensation
Total stock-based compensation expense	1,381	1,073	2,411
General and administrative
Stock-based compensation
Total stock-based compensation expense	$ 3,652	$ 5,145	$ 7,273

Stock-based compensation - Equi

Stock-based compensation - Equity Plans (Details)	12 Months Ended
	Dec. 31, 2017item
Stock-based compensation
Number of equity compensation plans	2
Stock options
Stock-based compensation
Expiration term	10 years
Stock options | One year from vesting
Stock-based compensation
Vesting percentage	25.00%
Vesting period	1 year
Stock options | Each successive three-month period, thereafter
Stock-based compensation
Vesting percentage	6.25%
Vesting period	3 months

Stock-based compensation - St43

Stock-based compensation - Stock Plans and Activity (Details) - shares	Jan. 01, 2018	Jan. 01, 2017	Jan. 01, 2016	Dec. 31, 2017	Dec. 31, 2016	Feb. 29, 2012	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Stock options
Stock-based compensation
Granted (in shares)							3,553,430
Exercised (in shares)							348,734
Restricted Stock Units
Stock-based compensation
Granted (in shares)							0	0	0
2012 Plan
Stock-based compensation
Number of shares reserved						3,428,571
Additional number of shares authorized for issuance	1,285,714	1,285,714	1,285,714			30,101
Annual increase in number of shares reserved							1,285,714
Percentage of outstanding shares of common stock used to compute annual increase in number of shares reserved							4.00%
2012 Plan | Stock options
Stock-based compensation
Granted (in shares)							10,684,203
Forfeited (in shares)							3,005,939
Exercised (in shares)							137,127
2012 Plan | Restricted Stock Units
Stock-based compensation
Granted (in shares)							909,918
Forfeited (in shares)							150,101
Inducement Award Program
Stock-based compensation
Number of shares reserved										750,000
Additional number of shares authorized for issuance				2,500,000	580,000
Granted (in shares)							1,324,000
Forfeited (in shares)							75,000
Exercised (in shares)							138,750
Shares available for future grants				2,506,000			2,506,000

Stock-based compensation - St44

Stock-based compensation - Stock Options (Details) - USD ($)	1 Months Ended			12 Months Ended
	Sep. 30, 2017	Oct. 31, 2016	Jun. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Additional disclosures
Stock-based compensation expense				$ 5,033,000	$ 6,218,000	$ 9,684,000
Stock options
Shares
Outstanding at the beginning of the period (in shares)				5,848,470
Granted (in shares)				3,553,430
Exercised (in shares)				(348,734)
Forfeited/cancelled (in shares)				(333,188)
Outstanding at the end of the period (in shares)				8,719,978	5,848,470
Vested at the end of the period (in shares)				4,795,186
Vested and expected to vest at end of period (in shares)				8,649,978
Weighted-average exercise price per share
Outstanding at the beginning of the period (in dollars per share)				$ 6.35
Granted (in dollars per share)				2.60
Exercised (in dollars per share)				1.27
Forfeited/cancelled (in dollars per share)				2.04
Outstanding at the end of the period (in dollars per share)				5.19	$ 6.35
Vested at the end of the period (in dollars per share)				7.04
Vested and expected to vest at end of the period (in dollars per share)				$ 5.20
Weighted-average remaining contractual term
Outstanding at the end of the period				7 years 10 months 24 days	8 years
Vested at the end of the period				6 years 10 months 24 days
Vested and expected to vest at the end of the period				7 years 10 months 24 days
Exercisable at the end of the period				6 years 10 months 24 days
Aggregate intrinsic value
Exercised (in dollars)				$ 1,100,000	$ 0
Outstanding at the beginning of the period (in dollars)				62,000
Outstanding at the end of the period (in dollars)				6,150,000	62,000
Vested at the end of the period (in dollars)				2,562,000
Vested and expected to vest at end of the period (in dollars)				6,150,000
Aggregate intrinsic value of options exercised (in dollars)				$ 1,100,000	$ 0
Assumptions used to estimate fair value of each stock-based award on the grant date
Risk-free interest rate (as a percent)				2.02%	1.48%	1.75%
Volatility (as a percent)				78.00%	75.00%	73.00%
Dividend yield (as a percent)				0.00%	0.00%	0.00%
Expected term				5 years 9 months 18 days	5 years 10 months 24 days	6 years
Additional disclosures
Stock-based compensation expense				$ 4,500,000	$ 6,100,000	$ 7,900,000
Weighted-average grant date fair value (in dollars per share)				$ 1.83	$ 0.99	$ 3.80
Fair value of vested stock options				$ 4,800,000	$ 6,900,000	$ 9,500,000
Total unrecognized stock-based compensation expense (in dollars)				$ 6,800,000
Weighted-average recognition period				2 years 10 months 24 days
Performance shares
Shares
Granted (in shares)			500,000
Vested at the end of the period (in shares)	250,000	250,000
Additional disclosures
Stock-based compensation expense				$ 379,000	$ 222,000
Percentage of performance conditions achieved					50.00%

Stock-based compensation - Rest

Stock-based compensation - Restricted Stock (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Mar. 31, 2013
Additional disclosures
Cash used to settle tax on restricted stock liability awards		$ 5,000	$ 417,000
Restricted Stock Units
Additional disclosures
Granted (in shares)	0	0	0
Fair value of shares vested	$ 0	$ 65,000	$ 1,600,000
Unvested RSUs with amended terms				697,060
Cash used to settle tax on restricted stock liability awards	0	5,000	$ 417,000
Remaining tax liability relating to awards	$ 0	$ 0

Income taxes - Operating Loss C

Income taxes - Operating Loss Carryforwards (Details) $ in Millions	Dec. 31, 2017USD ($)
Federal
Operating loss carryforwards
Net operating loss carryforwards	$ 237
State
Operating loss carryforwards
Net operating loss carryforwards	$ 235.9

Income taxes - Tax Credits (Det

Income taxes - Tax Credits (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)
Tax credit carryforwards
Testing period for changes in ownership interest of significant shareholders	3 years
Federal
Tax credit carryforwards
Tax credits	$ 14.1
State
Tax credit carryforwards
Tax credits	$ 1.7

Income taxes - Reconciliation o

Income taxes - Reconciliation of Income Taxes and Deferred Tax Assets (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of income taxes computed using the U.S. federal statutory rate
Income tax benefit using U.S. federal statutory rate (as a percent)	34.00%	34.00%
State tax benefit, net of federal benefit (as a percent)	5.00%	3.43%
Research and development tax credits (as a percent)	7.04%	4.42%
Permanent items (as a percent)	(1.24%)	(3.88%)
Effect of U.S. Tax Cuts and Jobs Act (as a percent)	(45.19%)
Change in the valuation allowance (as a percent)	0.19%	(36.71%)
Other (as a percent)	0.20%	(1.26%)
Deferred tax assets:
Net operating loss carryforwards	$ 64,677,000	$ 72,285,000
Capitalized research and development	2,780,000	1,836,000
Research and development credits	15,406,000	8,298,000
Stock-based compensation	2,560,000	3,083,000
Other	379,000	429,000
Gross deferred tax assets	85,802,000	85,931,000
Valuation allowance	(85,802,000)	(85,931,000)
Additional disclosures
Increase (decrease) in valuation allowance	(129,000)
Unrecognized tax benefits	0
Interest and penalties accrued related to unrecognized tax benefits	0
Liability for uncertain tax positions	$ 0	$ 0	$ 0

Income taxes - Tax Cuts And Job

Income taxes - Tax Cuts And Jobs Acts (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income tax benefit using U.S. federal statutory rate (as a percent)		34.00%	34.00%
Threshold compensation for deductibility	$ 1
Provision for deferred tax asset		$ 30.6
Scenario, Forecast
Income tax benefit using U.S. federal statutory rate (as a percent)	21.00%
Maximum
Income tax benefit using U.S. federal statutory rate (as a percent)		35.00%

Commitments and contingencies50

Commitments and contingencies (Details) - Office and Laboratory Space in Needham, Massachusetts	Apr. 15, 2014USD ($)ft²	Apr. 15, 2016USD ($)
Operating Leased Assets
Area of space | ft²	15,197
Initial annual base rent	$ 493,000
Period after which base rent increases	P12M
Base rent for last twelve-month period	$ 554,000
Tenant improvement allowance received	684,000
Letter of credit
Operating Leased Assets
Security deposit	$ 203,000	$ 162,000

Commitments and contingencies -

Commitments and contingencies - Future Lease Commitments (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Minimum aggregate future lease commitments
2,018	$ 542,000
2,019	415,000
Total	957,000
Rent expense	$ 352,000	$ 352,000	$ 352,000

License agreements (Details)

License agreements (Details) - Exclusive license agreement $ in Millions	Jul. 11, 2012USD ($)itemshares	Nov. 30, 2016USD ($)
Infinity
License agreements
Maximum exposure by licensor		$ 4.5
Payments upon study meeting certain pre-specified criteria		6
Payments on approval of new drug application		$ 22
Multiplier for issuance of common stock		1.025%
Period for computing average closing price		20 days
Royalty obligations term		10 years
Percentage of reduction in royalty on net sales		50.00%
Deduction in royalty payments as percentage of amount paid to third party		50.00%
Percentage royalty reductions capped		50.00%
Percentage of additional royalty on worldwide net sales		4.00%
Percentage of net sales for royalty obligations in the United States		1.00%
Percentage of reduction of royalty rate on basis of non-patent regulatory exclusivity		50.00%
PFIZER
License agreements
Royalty obligations term	10 years
Number of products required from licensor for an agreed upon price | item	1
One-time cash payment	$ 1.5
Number of shares of common stock issued | shares	192,012
PFIZER | Maximum
License agreements
Eligible amount payable on developmental milestones to Pfizer	$ 2
Additional payable on successful attainment of regulatory and commercial sales milestones	$ 125

Employee benefit plan (Details)

Employee benefit plan (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employee benefit plan
Contributions made under 401(k) plan	$ 273,000	$ 162,000	$ 295,000

Reduction in force (Details)

Reduction in force (Details) - Employee Severance	1 Months Ended	12 Months Ended		24 Months Ended
	Oct. 31, 2015item	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2016USD ($)
Restructuring Costs
Reduction of workforce (as a percent)	50.00%
Number of full time employees | item	20
Severance and related costs paid | $		$ 713,000	$ 349,000	$ 1,100,000

Quarterly financial informati55

Quarterly financial information (unaudited, in thousands, except per share data) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating expenses:
Research and development	$ 11,253	$ 17,743	$ 9,042	$ 8,385	$ 6,892	$ 4,216	$ 4,492	$ 4,179	$ 46,423	$ 19,779	$ 40,565
General and administrative	6,799	5,394	4,425	4,763	4,908	3,843	4,217	4,255	21,381	17,223	17,634
Total operating expenses	18,052	23,137	13,467	13,148	11,800	8,059	8,709	8,434	67,804	37,002	58,199
Loss from operations	(18,052)	(23,137)	(13,467)	(13,148)	(11,800)	(8,059)	(8,709)	(8,434)	(67,804)	(37,002)	(58,199)
Interest income	145	121	140	155	145	137	140	140	561	562	334
Interest expense	(328)	(110)	(109)	(12)					(559)
Net loss	$ (18,235)	$ (23,126)	$ (13,436)	$ (13,005)	$ (11,655)	$ (7,922)	$ (8,569)	$ (8,294)	$ (67,802)	$ (36,440)	$ (57,865)
Net loss per share - basic and diluted	$ (0.43)	$ (0.61)	$ (0.36)	$ (0.35)	$ (0.32)	$ (0.21)	$ (0.23)	$ (0.22)	$ (1.76)	$ (0.99)	$ (1.61)
Weighted-average number of common shares used in net loss per share—basic and diluted	42,027	37,630	36,992	36,992	36,992	36,992	36,992	36,975	38,422	36,988	35,932

Quarterly financial informati56

Quarterly financial information (unaudited, in thousands, except per share data) (Details) - USD ($) $ / shares in Units, $ in Thousands	Dec. 14, 2017	Dec. 31, 2017	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2015
Net proceeds from issuance of stock					$ 48,069	$ 63,989
At-the-market equity offering program | Common stock
Number of shares of common stock issued			2,183,126	2,853,753	5,036,879	1,189,479
Net proceeds from issuance of stock			$ 9,000	$ 14,100
Follow-on offerings | Common stock
Number of shares of common stock issued	8,422,877	8,422,877			8,422,877	8,337,500
Net proceeds from issuance of stock	$ 24,700	$ 24,700
Share price (in dollars per share)	$ 2.97	$ 2.97	$ 2.97		$ 2.97