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Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2015	Mar. 04, 2016	Jun. 30, 2015
Document and Entity Information
Entity Registrant Name	COLLEGIUM PHARMACEUTICAL, INC
Entity Central Index Key	0001267565
Document Type	10-K
Document Period End Date	Dec. 31, 2015
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	Non-accelerated Filer
Entity Public Float			$ 189.0
Entity Common Stock, Shares Outstanding		23,507,347
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	FY

BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 95,697	$ 1,634
Refundable PDUFA fee		2,335
Prepaid expenses and other current assets	1,186	527
Total current assets	96,883	4,496
Property and equipment, net	738	514
Restricted cash	97	80
Total assets	97,718	5,090
Current liabilities:
Accounts payable	3,537	2,208
Accrued expenses	2,228	1,956
Current portion of deferred rent and lease note payable		59
Current portion of term loan payable	2,667	1,194
Convertible bridge notes with related parties		5,000
Total current liabilities	8,432	10,417
Lease incentive obligation	68	101
Term loan payable, long-term	4,146	6,813
Total liabilities	12,646	17,331
Commitments and contingencies (See Note 7)
Shareholders’ equity (deficit):
Common stock, $0.001 par value; authorized shares - 100,000,000 at December 31, 2015 and 72,000,000 at December 31, 2014; issued and outstanding shares - 20,739,351 at December 31, 2015 and 1,006,219 at December 31, 2014	21	1
Additional paid-in capital	214,062	12,407
Accumulated deficit	(129,008)	(101,753)
Treasury stock	(3)	(3)
Total shareholders' equity (deficit)	85,072	(89,348)
Total liabilities, convertible redeemable preferred stock and shareholders' equity (deficit)	$ 97,718	5,090
Series A convertible redeemable preferred stock
Convertible redeemable preferred stock
Convertible redeemable preferred stock		12,781
Series B convertible redeemable preferred stock
Convertible redeemable preferred stock
Convertible redeemable preferred stock		51,212
Series C convertible redeemable preferred stock
Convertible redeemable preferred stock
Convertible redeemable preferred stock		$ 13,114

BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Convertible redeemable preferred stock, authorized shares	5,000,000	54,481,000
Convertible redeemable preferred stock, issued shares	0
Convertible redeemable preferred stock, outstanding shares	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, authorized shares	100,000,000	72,000,000
Common stock, issued shares	20,739,351	1,006,219
Common stock, outstanding shares	20,739,351	1,006,219
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, authorized shares	5,000,000	0
Preferred stock, issued shares	0	0
Preferred stock, outstanding shares	0	0
Liquidation preference	$ 0	$ 0
Series A convertible redeemable preferred stock
Convertible redeemable preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Convertible redeemable preferred stock, authorized shares	0	18,498,419
Convertible redeemable preferred stock, issued shares	0	9,232,334
Convertible redeemable preferred stock, outstanding shares	0	9,232,334
Convertible redeemable preferred stock, liquidation preference	$ 0	$ 12,781
Series B convertible redeemable preferred stock
Convertible redeemable preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Convertible redeemable preferred stock, authorized shares	0	27,324,237
Convertible redeemable preferred stock, issued shares	0	27,324,237
Convertible redeemable preferred stock, outstanding shares	0	27,324,237
Convertible redeemable preferred stock, liquidation preference	$ 0	$ 51,212
Series C convertible redeemable preferred stock
Convertible redeemable preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Convertible redeemable preferred stock, authorized shares	0	8,658,344
Convertible redeemable preferred stock, issued shares	0	8,658,008
Convertible redeemable preferred stock, outstanding shares	0	8,658,008
Convertible redeemable preferred stock, liquidation preference	$ 0	$ 13,114

STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	12 Months Ended
STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating expenses:
Research and development	$ 7,975	$ 14,959	$ 14,157
General and administrative	18,932	2,706	1,885
Total operating expenses	26,907	17,665	16,042
Loss from operations	(26,907)	(17,665)	(16,042)
Other expense (income):
Interest expense, net	439	252	76
Gain (loss) on extinguishment of debt	(91)		79
Change in fair value of derivative liability			79
Total other expense, net	348	252	155
Net loss	$ (27,255)	$ (17,917)	$ (16,197)
Net loss per share - basic and diluted (in dollars per share)	$ (1.48)	$ (22.72)	$ (4.06)
Weighted-average number of common shares used in net loss per share-basic and diluted (in shares)	13,542,282	933,997	1,697,044

CONVERTIBLE REDEEMABLE PREFERRED STOCK - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Increase (decrease) in convertible redeemable preferred stock
Accruals of dividends and accretion to redemption value		$ 31,184
Conversion of preferred stock to common stock		$ 119,250
Balance at end of year (in shares)		0
Series A convertible redeemable preferred stock
Increase (decrease) in convertible redeemable preferred stock
Balance at beginning of year		$ 12,781	$ 12,277	$ 23,546
Balance at beginning of year (in shares)		9,232,334	9,232,334	18,464,674
Accruals of dividends and accretion to redemption value		$ 2,297	$ 504	$ 970
Conversion of preferred stock to common stock		$ (11,345)
Conversion of preferred stock to common stock (in shares)		(9,232,334)
Extinguishment of prior preferred stock dividends		$ (3,733)
Performance Adjustment	$ (12,239)			$ (12,239)
Performance Adjustment of (in shares)				(9,232,340)
Balance at end of year	$ 12,277		$ 12,781	$ 12,277
Balance at end of year (in shares)	9,232,334	0	9,232,334	9,232,334
Series B convertible redeemable preferred stock
Increase (decrease) in convertible redeemable preferred stock
Balance at beginning of year		$ 51,212	$ 49,376	$ 47,540
Balance at beginning of year (in shares)		27,324,237	27,324,237	27,324,237
Accruals of dividends and accretion to redemption value		$ 18,034	$ 1,836	$ 1,836
Conversion of preferred stock to common stock		$ (45,905)
Conversion of preferred stock to common stock (in shares)		(27,324,237)
Extinguishment of prior preferred stock dividends		$ (23,341)
Balance at end of year	$ 49,376		$ 51,212	$ 49,376
Balance at end of year (in shares)	27,324,237	0	27,324,237	27,324,237
Series C convertible redeemable preferred stock
Increase (decrease) in convertible redeemable preferred stock
Balance at beginning of year		$ 13,114
Balance at beginning of year (in shares)		8,658,008	8,658,008
Issuance of new convertible redeemable preferred stock, net of issuance costs				$ 12,034
Issuance of new redeemable preferred stock (in shares)				12,154,000
Accruals of dividends and accretion to redemption value		$ 2,996	$ 960	$ 120
Conversion of preferred stock to common stock		$ (12,000)
Conversion of preferred stock to common stock (in shares)		(8,658,008)
Extinguishment of prior preferred stock dividends		$ (4,110)
Balance at end of year			$ 13,114
Balance at end of year (in shares)	8,658,008	0	8,658,008	8,658,008
Series D convertible redeemable preferred stock
Increase (decrease) in convertible redeemable preferred stock
Issuance of new convertible redeemable preferred stock, net of issuance costs		$ 44,807
Issuance of new redeemable preferred stock (in shares)		37,500,000
Accruals of dividends and accretion to redemption value		$ 1,245
Conversion of notes to preferred stock		$ 5,000
Conversion of notes to preferred stock (in shares)		4,166,667
Conversion of preferred stock to common stock		$ (50,000)
Conversion of preferred stock to common stock (in shares)		(41,666,667)
Extinguishment of prior preferred stock dividends		$ (1,052)

CONVERTIBLE REDEEMABLE PREFERRED STOCK (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($)
Common stock \| Initial public offering
Sale of stock
Issuance costs	$ 2,408
Series D convertible redeemable preferred stock
Sale of stock
Issuance costs	$ 193

SHAREHOLDERS’ DEFICIT - USD ($) $ in Thousands	Series D convertible redeemable preferred stock	Initial public offering Common Stock	Initial public offering Additional Paid-In Capital	Initial public offering	Common Stock	Additional Paid-In Capital	Treasury Stock, at cost	Accumulated Deficit	Total
Balance at beginning of year at Dec. 31, 2012					$ 2	$ 11	$ (3)	$ (61,414)	$ (61,404)
Balance at beginning of year (in shares) at Dec. 31, 2012					1,924,845
Increase (decrease) in stockholders' equity (deficit)
Accruals of dividends and accretion to redemption value						(1)		(2,925)	(2,926)
Performance Adjustment of Series A					$ (1)	12,240			12,239
Performance Adjustment of Series A (in shares)					(962,962)
Stock-based compensation expense						62			62
Exercise of common stock options						1			1
Exercise of common stock options (in shares)					1,077
Net loss								(16,197)	(16,197)
Balance at end of year at Dec. 31, 2013					$ 1	12,313	(3)	(80,536)	(68,225)
Balance at end of year (in shares) at Dec. 31, 2013					962,960
Increase (decrease) in stockholders' equity (deficit)
Accruals of dividends and accretion to redemption value								(3,300)	(3,300)
Issuance of restricted stock awards to employees (in shares)					10,869
Stock-based compensation expense						22			22
Exercise of common stock options						72			72
Exercise of common stock options (in shares)					32,390
Net loss								(17,917)	(17,917)
Balance at end of year at Dec. 31, 2014					$ 1	12,407	(3)	(101,753)	(89,348)
Balance at end of year (in shares) at Dec. 31, 2014					1,006,219
Increase (decrease) in stockholders' equity (deficit)
Accruals of dividends and accretion to redemption value						(24,572)			(24,572)
Conversion of preferred stock to common stock	$ (50,000)				$ 13	119,237			119,250
Conversion of preferred stock to common stock (in shares)	(41,666,667)				12,591,463
Issuance of stock, net of issuance costs		$ 7	$ 72,022	$ 72,029		1,052			1,052
Issuance of stock (in shares)		6,670,000			87,662
Extinguishment of prior preferred stock dividends						31,184			31,184
Issuance of restricted stock awards to employees (in shares)					194,694
Stock-based compensation expense						2,209			2,209
Exercise of common stock options						517			517
Exercise of common stock options (in shares)					173,251
Exercise of warrants						6			6
Exercise of warrants (in shares)					16,062
Net loss								(27,255)	(27,255)
Balance at end of year at Dec. 31, 2015					$ 21	$ 214,062	$ (3)	$ (129,008)	$ 85,072
Balance at end of year (in shares) at Dec. 31, 2015					20,739,351

STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating activities
Net loss	$ (27,255)	$ (17,917)	$ (16,197)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	171	187	169
Lease incentive	(34)	(34)	(34)
Stock-based compensation expense	2,209	22	62
Non cash interest expense	6	7	12
Accrual of back end fees related to note payable		7	13
Change in fair value of derivative liability			79
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(659)	183	(11)
Refundable PDUFA fee	2,335	(2,335)
Accounts payable	1,298	990	(822)
Accrued expenses	362	943	199
Net cash used in operating activities	(21,567)	(17,947)	(16,530)
Investing activities
Purchases of property and equipment	(362)	(8)	(206)
Net cash used in investing activities	(362)	(8)	(206)
Financing activities
Proceeds from issuance of convertible bridge note		5,000
Proceeds from notes payable, net of original note payoff		7,056	500
Repayment of term note	(1,286)	(28)	(43)
Repayment of lease note payable	(59)	(62)	(62)
Restricted cash	(16)
Proceeds from the exercise of stock options	517	72	1
Net cash provided by financing activities	115,992	12,038	12,351
Net increase (decrease) in cash and cash equivalents	94,063	(5,917)	(4,385)
Cash and cash equivalents at beginning of period	1,634	7,551	11,936
Cash and cash equivalents at end of period	95,697	1,634	7,551
Supplemental disclosure of cash flow information
Cash paid for interest	353	181	73
Supplemental disclosure of noncash activities
Preferred stock conversion to common stock		944
Extinguishment of Preferred Stock	120,302
Accruals of dividends and accretion to redemption value	31,184
Conversion of bridge note to preferred stock	24,572	3,300	2,926
Repayment of term note with proceeds of notes payable	5,000
Performance Adjustment to Series A and common shares			12,239
Series C convertible redeemable preferred stock
Financing activities
Proceeds from issuance of stock, net of issuance costs			11,955
Supplemental disclosure of noncash activities
Accruals of dividends and accretion to redemption value	2,996	$ 960	$ 120
Series D convertible redeemable preferred stock
Financing activities
Proceeds from issuance of stock, net of issuance costs	44,807
Supplemental disclosure of noncash activities
Accruals of dividends and accretion to redemption value	1,245
Initial public offering \| Common stock
Financing activities
Proceeds from issuance of stock, net of issuance costs	$ 72,029

STATEMENTS OF CASH FLOWS (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2013
Series C convertible redeemable preferred stock
Preferred stock
Stock issuance costs		$ 45
Series D convertible redeemable preferred stock
Preferred stock
Stock issuance costs	$ 193
Initial public offering \| Common stock
Preferred stock
Stock issuance costs	$ 2,408

NATURE OF BUSINESS	12 Months Ended
NATURE OF BUSINESS	Dec. 31, 2015
NATURE OF BUSINESS
NATURE OF BUSINESS	1. NATURE OF BUSINESS Organization Collegium Pharmaceutical, Inc. (the “Company”) was incorporated in Delaware in April 2002 and then reincorporated in Virginia in July 2014. The Company has its principal operations in Canton, Massachusetts. The Company is a specialty pharmaceutical company developing and planning to commercialize next‑generation abuse‑deterrent products that incorporate the Company’s patented DETERx® platform technology for the treatment of chronic pain and other diseases. The Company’s lead product candidate, Xtampza ER™, or Xtampza, is an abuse‑deterrent, extended‑release, oral formulation of oxycodone, a widely prescribed opioid medication. Xtampza has received Fast Track status from the U.S. Food and Drug Administration (“FDA”). The Company’s new drug application (“NDA”) filing for Xtampza was accepted by the FDA on February 10, 2015. On November 6, 2015, the FDA granted tentative approval to the Xtampza NDA for the management of pain severe enough to require daily around-the-clock, long-term opioid treatment and for which alternative treatment options are inadequate. With tentative approval, the FDA has determined that Xtampza meets the required quality, safety and efficacy standards for approval but that it was subject to an automatic stay of up to 30 months as a result of patent litigation filed by Purdue Pharma, L.P. (Purdue) in March 2015. In February 2016, the District Court of Massachusetts entered a judgment in the Company’s favor related to Purdue’s three Orange Book-listed patents that were the cause of the 30 month stay. The Company submitted its request for final approval of the Xtampza NDA to the FDA on February 26, 2016. The FDA has set a Prescription Drug User Fee Act, or PDUFA, goal date of April 26, 2016. The Company’s operations are subject to certain risks and uncertainties. The risks include negative outcome of clinical trials, inability or delay in completing clinical trials or obtaining regulatory approvals, the rate and degree of market acceptance of our product candidates, changing market conditions for products being developed by the Company, the need to retain key personnel and protect intellectual property, patent infringement litigation and the availability of additional capital financing on terms acceptable to the Company. Initial Public Offering In May 2015, the Company closed an initial public offering (“IPO”) of its common stock, which resulted in the sale of 6,670,000 shares of its common stock at a public offering price of $12.00 per share, including 870,000 shares of common stock upon the exercise by the underwriters of their option to purchase additional shares at the public offering price. The Company received proceeds from the IPO of approximately $72,029 after deducting underwriting discounts, commissions and expenses payable by the Company. In April 2015, in connection with preparing for the IPO, the Company’s board of directors and shareholders approved a one‑for‑6.9 reverse split of the Company’s common stock. All common stock share and per share amounts in the financial statements have been retroactively adjusted for all periods presented to give effect to the reverse split of our common stock, including reclassifying an amount equal to the reduction in par value to additional paid‑in capital In connection with the closing of the IPO, all of the Company’s outstanding convertible preferred stock and accrued dividends automatically converted to common stock in May 2015, resulting in an additional 12,591,463 shares of common stock of the Company becoming outstanding. The significant increase in common stock outstanding in May 2015 is expected to impact the year-over-year comparability of the Company’s net loss per share calculations in future periods. Basis of Accounting The consolidated financial statements include the accounts of Collegium Pharmaceutical, Inc. (a Virginia corporation) as well as the accounts of Collegium Securities Corp. (a Massachusetts corporation), incorporated in December 2015, a wholly-owned subsidiary requiring consolidation, and are prepared in conformity with accounting principles generally accepted in the United States of America. All significant intercompany balances and transactions have been eliminated in consolidation. Liquidity The Company has experienced net losses and negative cash flows from operating activities since its inception, and as of December 31, 2015 and December 31, 2014, had an accumulated deficit of $129,008 and $101,753, respectively. The Company expects to continue to incur net losses in the foreseeable future. A successful transition to attaining profitable operations is dependent upon achieving a level of revenues adequate to support the Company’s cost structure. The Company may never achieve profitability, and unless and until it does, the Company will continue to need to raise additional cash. Management intends to fund future operations through additional private or public debt or equity offerings, and may seek additional capital through arrangements with strategic partners or from other sources. The Company believes that its existing cash and cash equivalents, including the net proceeds from its January 2016 follow-on offering, will be sufficient to fund operations and future growth initiatives for at least the next twelve months; however, there can be no assurance that the Company will be successful in achieving its projections, reducing costs, or raising additional funds with terms acceptable to the Company. If the Company is unable to obtain financing or increase profitability, the related lack of liquidity will have a material adverse effect on the Company’s operations and future prospects.

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

12 Months Ended

Dec. 31, 2015

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

Use of Estimates

The preparation of the Company’s financial statements requires it to make estimates and assumptions that impact the reported amounts of assets, liabilities, revenues and expenses and the disclosure of contingent assets and liabilities in the Company’s financial statements and accompanying notes. The most significant estimates in the Company’s financial statements relate to the valuation of equity awards, fair value estimates of warrants, estimated useful lives of fixed assets and accruals related to clinical trials. The Company bases estimates and assumptions on historical experience when available and on various factors that it believes to be reasonable under the circumstances. The Company evaluates its estimates and assumptions on an ongoing basis. The Company’s actual results may differ from these estimates under different assumptions or conditions.

Fair Value Measurements

Disclosures of fair value information about financial instruments are required, whether or not recognized in the balance sheet, for financial instruments with respect to which it is practicable to estimate that value. The carrying amounts reported in the Company’s financial statements for cash and cash equivalents, accounts payable, loan payable and accrued liabilities approximate their respective fair values because of the short‑term nature of these accounts.

Fair value measurements and disclosures describes the fair value hierarchy based on three levels of inputs, of which the first two are considered observable and the last unobservable, that may be used to measure fair value, as follows:

Level 1 Unadjusted quoted prices in active markets that are accessible at the measurement date for identical, unrestricted assets or liabilities. The Company’s Level 1 assets and liabilities consist of money market investments.

Level 2 Quoted prices for similar assets, or inputs that are observable, either directly or indirectly, for substantially the full term through corroboration with observable market data. Level 2 includes investments valued at quoted prices adjusted for legal or contractual restrictions specific to the security. The Company does not have Level 2 assets or liabilities.

Level 3 Pricing inputs are unobservable for the assets or liabilities, that is, inputs that reflect the reporting entity’s own assumptions about the assumptions market participants would use in pricing the assets. Level 3 includes private investments that are supported by little or no market activity. The Company does not have Level 3 assets or liabilities.

Transfers are calculated on values as of the transfer date. There were no transfers between Levels 1, 2 and 3 during the years ended December 31, 2015 and 2014.

The following tables present the Company’s financial instruments carried at fair value using the lowest level input applicable to each financial instrument at December 31, 2015 and 2014.


					Significant
			Quoted Prices		other		Significant
			in active		observable		unobservable
			markets		inputs		inputs
Description	Total		(Level 1)		(Level 2)		(Level 3)
December 31, 2015
Money market funds, included in cash equivalents	$	94,912	$	94,912	$	—	$	—

December 31, 2014
Money market funds, included in cash equivalents	$	457	$	457	$	—	$	—

Concentration of Credit Risk

Financial instruments, which potentially subject the Company to significant concentration of credit risk, consist primarily of cash and cash equivalents. The Company maintains deposits in federally insured financial institutions in excess of federally insured limits. The Company has not experienced any losses in such accounts and management believes that the Company is not exposed to significant credit risk due to the financial position of the financial institutions in which those deposits are held. The Company has no financial instruments with off‑balance sheet risk of loss.

Cash and Cash Equivalents

Cash and cash equivalents include cash in readily available checking and savings accounts and money market funds. The Company considers all highly liquid investments with an original maturity of three months or less from the date of purchase to be cash equivalents.

The Company’s cash equivalents, which consist of money market funds, are measured at fair value on a recurring basis. As of December 31, 2015 and 2014, the carrying amount of cash and cash equivalents was $95,697 and $1,634, respectively, which approximates fair value and was determined based upon Level 1 inputs. Money market funds are valued using quoted market prices with no valuation adjustments applied. Accordingly, these securities are categorized as Level 1.

Property and Equipment

Property and equipment are recorded at historical cost. Maintenance and repair costs are expensed as incurred. Costs which materially improve or extend the lives of existing assets are capitalized. The Company provides for depreciation and amortization using the straight‑line method over the estimated useful lives of the assets, which are as follows:


Asset Category	Estimated Useful Life
Machinery and equipment		5	years
Computers and office equipment		5	years
Furniture and fixtures		7	years
Leasehold improvements		the shorter of the lease term or
		5	years

Upon retirement or sale, the cost of assets disposed and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is recorded in the statements of operations.

Impairment of Long‑Lived Assets

Long‑lived assets consist of property and equipment. When impairment indicators exist, the Company’s management evaluates long‑lived assets for potential impairment. An impairment loss is recorded if and when events and circumstances indicate that assets might be impaired and the undiscounted cash flows estimated to be generated by those assets are less than the carrying amount of those assets. While the Company’s current and historical operating losses and negative cash flows are indicators of impairment, management believes that future cash flows to be received support the carrying value of its long‑lived assets and, accordingly, has not recognized any impairment losses since inception.

Impairment losses, if any, are recognized in earnings. An impairment loss would be recognized in an amount equal to the excess of the carrying amount over the estimated fair value.

Deferred Financing Costs

The Company defers direct incremental costs attributable to public offerings of its common stock. These costs represent legal, accounting and other direct costs related to the Company’s efforts to raise capital through a public sale of its common stock. Costs will be deferred until the completion of the public offering, at which time they will be reclassified to additional paid‑in capital as a reduction of the public offering proceeds. If the Company terminates its plan for a public offering or delays such plan for more than 90 days, any costs deferred will be expensed immediately. Deferred financing costs were $353 and $233 at December 31, 2015 and 2014, respectively. Deferred financing costs are included in prepaid expenses and other assets in the balance sheet.

Restricted Cash

Restricted cash represents cash held in a depository account at a financial institution to collateralize a conditional stand‑by letter of credit related to the Company’s Canton, Massachusetts facility lease agreement. Restricted cash is reported as non‑current unless the restrictions are expected to be released in the next twelve months.

Deferred Rent

Deferred rent consists of the difference between cash payments and the recognition of rent expense on a straight‑line basis for the facilities the Company occupies. The Company’s lease for its facility provides for fixed increases in minimum annual rental payments and for additional rent in the form of maintenance and operating costs during the lease term. The total amount of rental payments due over the lease term is being charged to rent expense ratably over the life of the lease.

Research and Development Costs

Research and development costs are charged to expense as incurred and consist of costs incurred to further the Company’s research and development activities including salaries and employee related costs, costs associated with market research and design, costs associated with conducting preclinical, clinical and regulatory activities including fees paid to third‑party professional consultants and service providers, costs incurred under clinical trial agreements, costs for laboratory supplies and laboratory equipment, costs to acquire, develop and manufacture preclinical study and clinical trial materials, facilities, depreciation and other expenses including allocated expenses for rent and maintenance of facilities. Government grants are recognized as a reduction of the qualifying cost being reimbursed.

Patent Costs

Costs related to filing and pursuing patent applications are recorded as general and administrative expense as incurred since the recoverability of such expenditures is uncertain.

Stock‑Based Compensation

The Company accounts for grants of stock options and restricted stock to employees, including members of the board of directors, based on their grant date fair value and recognizes compensation expense over their vesting period. The Company estimates the fair value of stock options as of the date of grant using the Black‑Scholes option pricing model and restricted stock based on the fair value of the underlying common stock as determined by management or the value of the services provided, whichever is more readily determinable.

Stock‑based compensation expense represents the cost of the grant date fair value of employee stock option grants recognized over the requisite service period of the awards (usually the vesting period) on a straight‑line basis, net of estimated forfeitures. The expense is adjusted for actual forfeitures at year end. Stock‑based compensation expense recognized in the financial statements is based on awards that are ultimately expected to vest.

For stock option grants with performance‑based milestones, the expense is recorded over the remaining service period after the point when the achievement of the milestone is probable or the performance condition has been achieved. For stock option grants with both performance‑based milestones and market conditions, expense is recorded over the derived service period after the point when the achievement of the performance‑based milestone is probable or the performance condition has been achieved.

The Company accounts for stock options and restricted stock awards to non‑employees using the fair value approach. Stock options and restricted stock awards to non‑employees are subject to periodic revaluation over their vesting terms. There were no non‑employee grants in 2014. There was one non-employee grant in 2015.

Income Taxes

The Company accounts for income taxes under the liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements. Under this method, deferred tax assets and liabilities are determined on the basis of the differences between the financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the years in which the differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in income in the period that includes the enactment date.

The Company recognizes net deferred tax assets to the extent that the Company believes these assets are more likely than not to be realized. In making such a determination, management considers all available positive and negative evidence, including future reversals of existing taxable temporary differences, projected future taxable income, tax‑planning strategies and results of recent operations. If management determines that the Company would be able to realize its deferred tax assets in the future, in excess of its net recorded amount, management would make an adjustment to the deferred tax asset valuation allowance, which would reduce the provision for income taxes.

The Company records uncertain tax positions on the basis of a two‑step process whereby (i) management determines whether it is more likely than not that the tax positions will be sustained on the basis of the technical merits of the position and (ii) for those tax positions that meet the more likely than not recognition threshold, management recognizes the largest amount of tax benefit that is more than 50 percent likely to be realized upon ultimate settlement with the related tax authority. The Company will recognize interest and penalties related to uncertain tax positions within income tax expense. Any accrued interest and penalties will be included within the related tax liability. As of December 31, 2015 and 2014, the Company had no accrued interest or penalties related to uncertain tax positions and no amounts have been recognized in the Company’s statements of operations.

Net loss per Common Share

Basic net loss per common share is calculated by dividing the net loss attributable to common shareholders by the weighted‑average number of shares of common stock outstanding during the period, without consideration for potentially dilutive securities. Diluted net loss per share is computed by dividing the net loss attributable to common shareholders by the weighted‑average number of shares of common stock and potentially dilutive securities outstanding for the period. For purposes of the diluted net loss per share calculation, stock options, warrants, redeemable convertible preferred stock and unvested restricted stock are considered potentially dilutive securities. Because the Company has reported a net loss for the twelve months ended December 31, 2015, 2014 and 2013, diluted net loss per common share is the same as basic net loss per common share for those periods.

Diluted earnings per share is computed using the more dilutive of (i) the two‑class method, or (ii) the if‑converted method. The Company allocates earnings first to preferred shareholders based on dividend rights and then to common and preferred shareholders based on ownership interests. The weighted‑average number of common shares included in the computation of diluted earnings (loss) gives effect to all potentially dilutive common equivalent shares, including outstanding stock options, warrants, convertible redeemable preferred stock and the potential issuance of stock upon the conversion of the Company’s convertible notes. Common stock equivalent shares are excluded from the computation of diluted earnings (loss) per share if their effect is antidilutive.

Recently Issued Accounting Pronouncements

In February 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2016-02, Leases (Topic 842). The ASU requires lessees to put most leases on their balance sheets as a liability for the obligation to make lease payments and as a right-of-use asset, but recognize expenses on the income statements in a manner similar to today’s accounting. The guidance also eliminates the current real estate-specific provisions for all entities. For calendar-year public entities, the guidance becomes effective in 2019 and interim periods within that year. Early adoption is permitted for all entities. The Company has not chosen early adoption for this ASU and is currently evaluating its effect on the Company’s consolidated financial statements

In November 2015, the FASB issued ASU 2015-17, Income Taxes: Balance Sheet Classification of Deferred Taxes (Topic 740). ASU 2015-17 simplifies the presentation of deferred income taxes by eliminating the separate classification of deferred income tax assets and liabilities into current and noncurrent amounts in the consolidated balance sheet statement of financial position. The amendments in the update require that all deferred tax assets and liabilities be classified as noncurrent in the consolidated balance sheet. The amendments in this update are effective for annual periods beginning after December 15, 2017, and interim periods therein and may be applied either prospectively or retrospectively to all periods presented. Early adoption is permitted. The Company is currently evaluating its effect on the Company’s consolidated financial statements.

In May 2014, the FASB issued ASU No. 2014‑09, Revenue from Contracts with Customers. This ASU is a comprehensive new revenue recognition model that requires a company to recognize revenue to depict the transfer of goods or services to a customer at an amount that reflects the consideration it expects to receive in exchange for those goods or services. This ASU is effective for annual reporting periods beginning after December 15, 2016 and early adoption is not permitted. Accordingly, the Company will adopt this ASU on January 1, 2017. Management does not believe the adoption of this ASU will have a material impact on the Company’s financial condition, results of operations or cash flows.

In June 2014, the FASB issued ASU No. 2014‑12, Compensation — Stock Compensation (Topic 718): Accounting for Share‑Based Payments When the Terms of an Award Provide That a Performance Target Could Be Achieved after the Requisite Service Period. ASU 2014‑12 applies to all reporting entities that grant their employees share‑based payments in which the terms of the award provide that a performance target that affects vesting could be achieved after the requisite service period. That is the case when an employee is eligible to retire or otherwise terminate employment before the end of the period in which a performance target (for example, an initial public offering or a profitability target) could be achieved and still be eligible to vest in the award if and when the performance target is achieved. The standard is required to be adopted by public business entities in annual periods beginning on or after December 15, 2015 and interim periods within those annual periods. The Company plans to implement this standard in the first quarter of fiscal year 2016 and is currently evaluating the potential impact of this new guidance on its financial statements.

In August 2014, the FASB issued ASU No. 2014‑15, Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern. ASU 2014‑15 requires management to evaluate, at each annual or interim reporting period, whether there are conditions or events that exist that raise substantial doubt about an entity’s ability to continue as a going concern within one year after the date the financial statements are issued and provide related disclosures. ASU 2014‑15 is effective for annual periods ending after December 15, 2016 and earlier application is permitted. The adoption of ASU 2014‑15 is not expected to have a material effect on the Company’s financial statements or disclosures.

In November 2014, the FASB issued ASU No. 2014‑16, Derivatives and Hedging (Topic 815) — Determining Whether the Host Contract in a Hybrid Financial Instrument Issued in the Form of a Share is More Akin to Debt or to Equity. This ASU was issued to clarify how current U.S. generally accepted accounting principles should be interpreted in evaluating the economic characteristics and risk of a host contract in a hybrid financial instrument that is issued in the form of a share. In addition, this ASU was issued to clarify that in evaluating the nature of a host contract, an entity should assess the substance of the relevant terms and features (that is, the relative strength of the debt‑like or equity‑like terms and features given the facts and circumstances) when considering how to weight those terms and features. The effects of initially adopting this ASU should be applied on a modified retrospective basis to existing hybrid financial instruments issued in a form of a share as of the beginning of the fiscal year for which the amendments are effective. Retrospective application is permitted to all relevant prior periods. This ASU is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2015. Early adoption in an interim period is permitted. The Company is currently evaluating the impact of the adoption of this ASU on its financial statements.

NET LOSS PER COMMON SHARE

12 Months Ended

Dec. 31, 2015

NET LOSS PER COMMON SHARE

NET LOSS PER COMMON SHARE

3. NET LOSS PER COMMON SHARE

Basic net loss per share is computed by dividing net loss by the weighted‑average number of shares of common stock outstanding during the period. Diluted net loss per share is computed by dividing the net loss attributable to common shareholders by the weighted‑average number of shares of common stock and potentially dilutive securities outstanding for the period. Stock options, warrants, convertible preferred stock and unvested restricted stock are considered to be potentially dilutive securities and are only included in the calculation of diluted net loss per share when their effect is dilutive. For the twelve months ended December 31, 2015, 2014 and 2013, these securities were anti‑dilutive due to the net losses in those periods and, therefore, the number of shares used to compute basic and diluted earnings per share are the same for of those periods.

The following table presents the computations of basic and dilutive net loss per share:



	Years Ended December 31,
		2015		2014		2013

Net loss	$	(27,255)	$	(17,917)	$	(16,197)
Extinguishment of preferred stock - see note 10		31,806		—		—
Accretion and dividends of prior preferred stock - see note 10		(23,327)		(3,300)		(2,925)
Accretion and dividends of Series D preferred stock		(1,245)		—		—
Performance Adjustment of Series A		—		—		12,239
Loss attributable to common shareholders — basic and diluted	$	(20,021)	$	(21,217)	$	(6,883)
Weighted-average number of common shares used in net loss per share—basic and diluted		13,542,282		933,997		1,697,044
Net loss per share—basic and diluted	$	(1.48)	$	(22.72)	$	(4.06)

The following potentially dilutive securities outstanding have been excluded from the computations of diluted weighted‑average shares outstanding because such securities have an antidilutive impact due to losses reported (in common stock equivalent shares):



	Years Ended December 31,
	2015	2014	2013

Outstanding stock options	1,452,149	281,029	229,791
Warrants	2,445	18,809	4,170
Redeemable convertible preferred stock	—	6,552,820	6,552,820
Unvested restricted stock	75,718	15,387	55,298

PREPAID EXPENSES AND OTHER CURRENT ASSETS

12 Months Ended

Dec. 31, 2015

PREPAID EXPENSES AND OTHER CURRENT ASSETS.

PREPAID EXPENSES AND OTHER CURRENT ASSETS

4. PREPAID EXPENSES AND OTHER CURRENT ASSETS

Prepaid expenses and other current assets consisted of the following:


	As of December 31,
	2015		2014
Prepaid Insurance	$	420	$	—
Deferred financing costs		353		233
Other prepaid expenses		208		8
Other current assets		205		253
Employee advances		—		33
Prepaid expenses and other current assets	$	1,186	$	527

PROPERTY AND EQUIPMENT

12 Months Ended

Dec. 31, 2015

PROPERTY AND EQUIPMENT

PROPERTY AND EQUIPMENT

5. PROPERTY AND EQUIPMENT

Property and equipment consisted of the following:


	As of December 31,
	2015		2014
Machinery and equipment	$	755	$	741
Leasehold improvements		678		606
Computers and office equipment		262		26
Furniture and fixtures		117		44
Total property and equipment		1,812		1,417
Less: accumulated deprecation		(1,074)		(903)
Property and equipment, net	$	738	$	514

Depreciation expense related to property and equipment amounted to $171 and $187 for the years ended December 31, 2015 and 2014, respectively.

ACCRUED EXPENSES

12 Months Ended

Dec. 31, 2015

ACCRUED EXPENSES

ACCRUED EXPENSES

6. ACCRUED EXPENSES

Accrued expenses consisted of the following:


	As of December 31,
	2015		2014
Accrued compensation	$	1,567	$	635
Accrued audit and legal		209		249
Accrued other		186		31
Accrued marketing		157		—
Accrued development costs		80		970
Accrued interest		29		71
Total accrued expenses	$	2,228	$	1,956

COMMITMENTS AND CONTINGENCIES

12 Months Ended

Dec. 31, 2015

COMMITMENTS AND CONTINGENCIES.

COMMITMENTS AND CONTINGENCIES

7. COMMITMENTS AND CONTINGENCIES

Legal Proceedings

From time to time the Company may face legal claims or actions in the normal course of business. Except as disclosed below, the Company is not currently a party to any litigation and, accordingly, does not have any amounts recorded for any litigation related matters.

The Company’s NDA filing for Xtampza is a 505(b)(2) application, which allows the Company to reference data from an approved drug listed in the FDA’s Approved Drug Products with Therapeutic Equivalence Evaluations (commonly known as the “Orange Book”), in this case OxyContin OP. In connection with the 505(b)(2) process, the Company certified to the FDA and notified Purdue Pharma, L.P. (“Purdue”), as the holder of the NDA and any other Orange Book‑listed patent owners, that the Company does not infringe any of the patents listed for OxyContin OP in the Orange Book. Under the Hatch‑Waxman Act of 1984, Purdue had the option to sue the Company for infringement and receive a stay of up to 30 months before the FDA can issue a final regulatory approval for Xtampza, unless the stay is earlier terminated. Purdue exercised its option and elected to sue the Company for infringement in the District of Delaware in March 2015 asserting infringement of three of Purdue’s Orange Book‑listed patents and one non-Orange Book-listed patent. Purdue filed another case in Massachusetts asserting the same four patents as in the Delaware case. In October 2015, the Delaware case was transferred to Massachusetts. In November 2015, Purdue filed suit asserting infringement of another non-Orange Book-listed patent. On November 9, 2015, the Company filed a motion for partial judgment on the pleadings in relation to three Orange Book-listed patents asserted against the Company, which had been previously invalidated by the court in the Southern District of New York in Purdue’s suit against another company. On February 1, 2016, the Court of Appeals for the Federal Circuit affirmed the New York judgment of invalidity. On February 9, 2016, the District Court of Massachusetts ordered judgment in favor of the Company on the three Orange Book-listed patents that were the basis of the 30-month stay, Patent Nos. 7,674,799, 7,674,800, and 7,683,072 and dismissed the claims asserting infringement of those patents with prejudice. Purdue continues to assert infringement of two patents against the company, neither of which is associated with any stay of FDA approval. The Company has moved for judgment of invalidity of one of those patents based on collateral estoppel and that motion remains pending.

At this time the Company is unable to provide meaningful quantification of how this potential litigation may impact its future financial condition, results of operations, or cash flows.

Operating Leases

The Company leases its office and research facility under a non‑cancellable operating lease. Terms of the agreement provide for an initial two ‑month rent‑free period and future rent escalation, and provide that in addition to minimum lease rental payments, the Company is responsible for a pro‑rata share of operating expenses and taxes. In March 2015, the Company amended its lease to include an additional 9,660 square feet of space for a total of 19,335 square feet. In addition, the lease term was extended and now terminates on August 30, 2020. At the Company’s election, the lease term may be extended for an additional 5 -year term.

Aggregate minimum annual lease commitments of the Company under its non‑cancellable operating lease as of December 31, 2015 are as follows:



2016	$	216
2017		226
2018		234
2019		241
2020		164
Total minimum lease payments	$	1,081

Rent expense under the operating lease agreement amounted to approximately $112 and $69 for the years ended December 31, 2015 and 2014, respectively. In addition, the Company maintained a stand‑by letter of credit in connection with the Canton facility lease of $97 and $80 at December 31, 2015 and December 31, 2014, respectively. This amount is classified as restricted cash in the balance sheets.

As an inducement to enter into its Canton facility lease, the lessor agreed to provide the Company with an improvement allowance of up to $174 towards leasehold improvements. In addition the lessor provided the Company with a reimbursable allowance of $164 which is to be amortized and repaid by the Company at an 8% interest rate over the initial term of 36 months. Amounts provided by the lessor related to tenant improvements are considered inducements to enter into the lease. The Company has recorded these costs in the balance sheet as leasehold improvements, with the corresponding liabilities as deferred lease incentive and lease note payable. These liabilities are amortized on a straight‑line basis over the term of the lease.

DEBT

12 Months Ended

Dec. 31, 2015

DEBT

DEBT

8. DEBT

On August 28, 2012, the Company entered into a loan agreement (“Original Term Loan”) with Silicon Valley Bank (“SVB”) to borrow up to a maximum amount of $1,000. In August 2012, October 2012 and February 2013, the Company borrowed $250, $250 and $500, respectively. The Original Term Loan bore interest at a rate per annum of 2.25% above the prime rate fixed at the time of advance of the Original Term Loan (5.50%). The Original Term Loan provided for interest‑only payments for the first 12 months based on the date of each borrowing, and, thereafter, 36 monthly payments of principal and interest. In connection with the Original Term Loan, the Company granted SVB a warrant to purchase 23,810 shares of common stock at an exercise price of $0.07 per share (See Note 9).

In January 2014, the Original Term Loan was amended (“Amendment No. 1”) to provide for the following; borrowings of up to $6,000, repayment in full of the Original Term Loan balance outstanding, and an adjustment of the variable interest rate from 2.25% above the prime rate to 1.75% above the prime rate. In February 2014, the Company borrowed $2,000. The proceeds from the initial borrowing were used to pay down the Original Term Loan balance outstanding resulting in the Company receiving $1,056. Borrowings under Amendment No. 1 bore interest at a rate of 5.0%. Amendment No. 1 provided for interest‑only payments for the first 12 months based on the date of each borrowing, and thereafter, 36 monthly payments of principal and interest. In connection with Amendment No. 1, the Company granted to SVB a warrant to purchase 14,430 shares of common stock with an exercise price of $0.05 per share (See Note 9).

In August 2014 the Original Term Loan was further amended (“Amendment No. 2”) to provide for total borrowings of up to $8,000. In August 2014 and September 2014 the Company drew down $3,000 and $3,000, respectively. Pursuant to Amendment No. 2, interest‑only payments are to be made for the first 12 months based on the date of each borrowing; thereafter, 36 monthly payments of principal and interest are to be made. Borrowings under Amendment 2 bear interest at the rate of 5.0%. The warrant agreement contains a performance clause that the Company met, resulting in additional financing extended and issuance of a warrant to purchase 86,580 additional shares of common stock with an exercise price of $0.05 per share (See Note 9).

In September 2014, the Original Term Loan was further amended (“Amendment No. 3”) to extend the loan draw period.

In November and December of 2014 the Company entered into a Note Purchase Agreement (the “Bridge Notes”) allowing for the issuance of $5,000 of convertible promissory notes to a group of investors (the “Holders”) bearing interest at a rate per annum of 6.0%. The Holders are related parties of the Company. In March 2015, in connection with the Series D convertible preferred stock financing, the Bridge Notes converted into 4,166,667 shares of Series D convertible preferred stock. Upon the conversion, the Company recognized a gain on extinguishment of $91. The accrued interest on the Bridge Notes was waived.

As of December 31, 2015, future payments under the Company’s term loan are as follows:


2016	$	2,667
2017		2,667
2018		1,479
Balance	$	6,813

WARRANTS	12 Months Ended
WARRANTS	Dec. 31, 2015
WARRANTS.
WARRANTS	9. WARRANTS In November 2010, the Company issued a warrant to Comerica Bank. The warrant represents the right to purchase 2,445 shares of common stock with an exercise price of $12.27. The warrant expires in October 2017. In connection with the Term Loan Financings with Silicon Valley Bank, the Company issued warrants to purchase a total of 16,357 shares of common stock. In June 2015, SVB exercised all of its warrants.

EQUITY

12 Months Ended

Dec. 31, 2015

EQUITY

EQUITY

10. EQUITY

As of December 31, 2013 the authorized capital stock of the Company included 72,000,000 shares of common stock, par value $0.001 per share, 962,960 of which were issued and outstanding. As of December 31, 2013, 54,481,000 shares of preferred stock were authorized, designated as Series A, Series B and Series C preferred Stock of which 9,232,334, 27,324,237 and 8,658,008 were issued and outstanding, respectively.

As of December 31, 2014, the authorized capital stock of the Company included 72,000,000 shares of common stock, par value $0.001 per share, 1,006,219 of which were issued and outstanding. As of December 31, 2014, 54,481,000 shares of preferred stock were authorized, designated as Series A, Series B and Series C Preferred Stock of which 9,232,334, 27,324,237 and 8,658,008 were issued and outstanding, respectively.

In March 2015, the Company issued and sold an aggregate of 41,666,667 shares of Series D convertible preferred stock for aggregate consideration of $50,000, comprised of $45,000 in cash and conversion of $5,000 in Bridge Notes.

As of December 31, 2015, the authorized capital stock of the Company included 100,000,000 shares of common stock, par value $0.001 per share, 20,739,351 of which were issued and outstanding. As of December 31, 2015, 5,000,000 shares of preferred stock were authorized, and none were issued and outstanding.

Common Stock

In May 2015, the Company closed an initial public offering (“IPO) of its common stock, which resulted in the sale of 6,670,000 shares of its common stock at a public offering price of $12.00 per share, including 870,000 shares of common stock upon the exercise by the underwriters of their option to purchase additional shares at the public offering price. The Company received proceeds from the IPO of approximately $72,029 after deducting underwriting discounts, commissions and expenses payable by the Company.

In April 2015, in connection with preparing for the IPO, the Company’s board of directors and shareholders approved a one‑for‑6.9 reverse split of the Company’s common stock. All common stock share and per share amounts in the financial statements have been retroactively adjusted for all periods presented to give effect to the reverse split of our common stock, including reclassifying an amount equal to the reduction in par value to additional paid‑in capital

In connection with the closing of the IPO, all of the Company’s outstanding convertible preferred stock and accrued dividends automatically converted to common stock in May 2015, resulting in an additional 12,591,463 shares of common stock of the Company becoming outstanding. The significant increase in common stock outstanding in May 2015 is expected to impact the year-over-year comparability of the Company’s net loss per share calculations in future periods.

As of December 31, 2015 and 2014, the Company had reserved the following shares of common stock for the issuance of common stock for the exercise of stock options and warrants, the issuance of shares under the employee stock purchase plan and conversion of preferred stock (in thousands):


	As of December 31,
	2015	2014
Options to purchase common stock	2,642	3,413
Employee stock purchase plan	200	—
Warrants	2	19
Conversion of Series A Preferred	—	18,498
Conversion of Series B Preferred	—	27,324
Conversion of Series C Preferred	—	8,658
Total	2,844	21,930

Convertible Redeemable Preferred Stock

Series A, B and Series C Redeemable Convertible Preferred Stock

In February 2012, the Company exchanged all previously outstanding preferred stock into 18,464,674 shares of Series A Preferred Stock (“Series A”), par value $0.001. On the same date, the Company issued 27,324,237 shares of Series B Preferred Stock (“Series B”), par value $0.001 for $0.84 per share, which resulted in gross proceeds of $20,050. Closing costs associated with the issuance of the Series B amounted to $147. These costs were recorded as a reduction of the carrying amount of the Series B and were accreted to the carrying value of the applicable preferred stock. During 2013, the Company issued 8,658,008 shares of Series C Preferred Stock (“Series C”) in exchange for $12,000 in a series of tranches. Costs incurred in connection with the issuance of Series C amounted to $45 and have been recorded as a reduction to the carrying amount of Series C and were accreted to the carrying value of the applicable preferred stock. In accordance with the terms of the Series C Preferred Stock Purchase Agreement, the Company authorized the sale and issuance of up to 8,658,008 shares of Series C for total gross proceeds of $12,000. Closing costs associated with the issuance of Series C amounted to $45. The Series C financing was structured to close in two tranches. The Company determined the right of the investors to purchase shares of Series C in a future tranche met the definition of a freestanding financial instrument and was recognized as a liability at fair value. The Company adjusted the carrying value of the tranche obligations to its estimated fair value at each reporting date and upon closing of the second tranche in December 2013. Increases or decreases in the fair value of the tranche obligations were recorded as other expense, net, in the statements of operations.

The first tranche closed in August and September 2013 and resulted in the issuance of 2,886,004 shares of Series C for gross cash proceeds of $4,000. Upon the first tranche closing, the Company recognized a liability of $266 for the fair value of the future tranche obligations. The fair value of the freestanding instrument tranche obligations was determined using Black‑Scholes option‑pricing models on the date of the issuance using the following assumptions: fair value of Series C of $1.30, expected life of 0.35 to 0.43 years and expected volatility of 53% to 60%.

The liability related to the tranche obligations was remeasured at fair value up to the date of the closing of the second tranche in December 2013. Upon the closing of the second tranche, the Company derecognized the tranche obligation, which resulted in a net increase in the proceeds allocated to the Series C shares of $345. The fair value of the freestanding instrument tranche obligations was determined using Black‑Scholes option‑pricing models on the date of the issuance using the following assumptions: fair value of Series C of $1.27, expected life of 0.16 years and expected volatility of 52%.

The valuation of the tranche obligation liability was determined to be a Level 3 valuation based upon the use of unobservable inputs. A roll‑ forward of the recurring fair value measurements of the tranche liability categorized with Level 3 inputs are as follows:


Balance — December 31, 2013	$	—
Tranche liability upon issuance		266
Change in fair value		79
Tranche liability upon close of tranche		(345)
Balance — December 31, 2014	$	—

The closing of the second tranche of Series C in December 2013 triggered a performance adjustment of the outstanding shares of Series A and common stock to which the Series A and common stock were subject to modification in which every two shares of issued and outstanding Series A and common shares became one share of each class respectively. In connection with the performance adjustment, the Company adjusted the carrying value of the outstanding shares of Series A to its redemption amount by recording a decrease of $12,239.

In March 2015, the Company sold 41,666,667 shares of Series D convertible preferred stock for aggregate consideration of $50,000, comprised of $45,000 in cash and conversion of $5,000 in convertible notes with related parties. The convertible notes converted into 4,166,667 shares of Series D convertible preferred stock. The accrued interest on the convertible notes was waived. In this financing, the mandatory conversion for all series of preferred stock was modified so as to occur upon an initial public offering with gross proceeds in excess of $50,000.

STOCK BASED COMPENSATION

12 Months Ended

Dec. 31, 2015

STOCK BASED COMPENSATION

STOCK BASED COMPENSATION

11. STOCK‑BASED COMPENSATION

Restricted Stock Awards and Stock Options In May 2015, the Company adopted the Amended and Restated 2014 Stock Incentive Plan (the “Plan”), under which an aggregate of 2,700,000 shares of common stock are authorized for issuance to employees, officers, directors, consultants and advisors of the Company, plus an annual increase to be added on the first day of each fiscal year until the expiration of the Plan equal to 4% of the total number of outstanding shares of common stock on December 31st of the immediately preceding calendar year (or a lower amount as otherwise determined by the board of directors prior to January 1st). As of December 31, 2015, 1,452,149 of the shares of common stock authorized for issuance pursuant to the Plan were outstanding. In connection with the Company’s reincorporation into Virginia in July 2014, each outstanding option to purchase shares of common stock under the 2012 Stock Incentive Plan and 2002 Stock Plan, was automatically terminated and replaced with an option to purchase shares of common stock under the Plan having the same vesting terms and exercise price as the option that was replaced. The Plan provides for granting of both Internal Revenue Service qualified incentive stock options (“ISOs”) and non‑qualified options (“NQs”), restricted stock awards (“RSAs”) and restricted stock units (“RSUs”). Stock options generally vest over a four year period of service; however, certain options contain performance conditions. The options generally have a ten year contractual life and, upon termination, vested options are generally exercisable between one and three months following the termination date, while unvested options are forfeited immediately.

Stock option activity under the Plan is summarized as follows:



				Weighted-
		Weighted-		average
		average		remaining	Aggregate
		exercise price		contractual	Intrinsic
	Shares	per share		term (years)	Value
Outstanding at December 31, 2014	281,029	$	0.69	7.49	$	1,505
Granted	1,350,952		11.46
Exercised	(173,251)		2.99
Cancelled	(6,581)		14.54
Outstanding at December 31, 2015	1,452,149	$	10.37	10.36	$	24,887
Exercisable at December 31, 2015	205,891	$	3.75	7.9	$	4,890
Vested and expected to vest at December 31, 2015	1,436,582	$	10.46	9.1	$	26,061

As of December 31, 2015, the unrecognized compensation cost related to outstanding options was $9,212, and is expected to be recognized as expense over approximately 3.4 years.

As of December 31, 2015, the weighted average fair value of vested options was $2.96. The weighted-average grant date fair value of options granted during the year ended December 31, 2015 was $7.85. The fair value of options that vested during the year ended December 31, 2015 was $3.43.

Restricted stock awards under the Plan are summarized as follows:


		Weighted average
		purchase price
	Shares	per share
Unvested at December 31, 2014	15,387		0.69
Granted	194,694		5.73
Vested	(134,363)		5.15
Unvested at December 31, 2015	75,718	$	5.73

The total fair value of restricted stock vested during the years ended December 31, 2015, was $692. As of December 31, 2015, the unrecognized compensation cost related to restricted stock awards was $434, and is expected to be recognized as expense over approximately 2.3 years.

Stock‑Based Compensation Expense

The Company granted stock options to employees for the years ended December 31, 2015, 2014 and 2013. The Company estimates the fair value of stock options as of the date of grant using the Black‑Scholes option pricing model and restricted stock based on the fair value of the award. Stock options and restricted stock issued to non‑board member, non‑employees are accounted for using the fair value approach and are subject to periodic revaluation over their vesting terms.

Stock‑based compensation for all stock options and restricted stock awards are reported within:


	Years Ended December 31,
		2015		2014		2013
Research and development	$	223	$	12	$	24
General and administrative		1,986		10		38
Total stock-based compensation expense	$	2,209	$	22	$	62

The weighted‑average assumptions used in the Black‑Scholes option pricing model to determine the fair value of the employee stock option grants were as follows:


	Years Ended December 31,
	2015		2014		2013
Risk-free interest rate	1.70	%	1.8	%	1.09 - 1.22	%
Volatility	77.0	%	77.1	%	87.8	%
Expected term (years)	6.20		6.25		6.25
Expected dividend yield	—	%	—	%	—	%

Risk‑free Interest Rate. The risk‑free interest rate assumption is based on observed interest rates appropriate for the expected term of the stock option grants.

Expected Volatility. Due to the Company’s limited operating history and lack of company‑specific historical or implied volatility, the expected volatility assumption is based on historical volatilities of a peer group of similar companies whose share prices are publicly available. The peer group was developed based on companies in the biotechnology and pharmaceutical industries. In evaluating similarity, we consider factors such as industry, stage of life cycle and size.

Expected Term. The expected term represents the period of time that options are expected to be outstanding. Because the Company does not have historical exercise behavior, through December 31, 2015 it determined the expected life assumption using the simplified method, which is an average of the contractual term of the option and its vesting period.

Expected Dividend Yield. The expected dividend yield assumption is based on the fact that the Company has never paid cash dividends and has no present intention to pay cash dividends.

INCOME TAXES

12 Months Ended

Dec. 31, 2015

INCOME TAXES.

INCOME TAXES

12. INCOME TAXES

For the years ended December 31, 2015, 2014 and 2013, the Company did not record a current or deferred income tax expense or (benefit) due to current and historical losses incurred by the Company. The Company’s losses before income taxes consist solely of domestic losses.

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


	As of December 31,
	2015		2014		2013
Federal income tax (benefit) at statutory rate	34.00	%	34.00	%	34.00	%
(Increase) decrease income tax (benefit) resulting from:
State income tax, net of federal benefit	5.29		—		—
Expiration of state net operating losses	—		—		(12.11)
Permanent items	(1.70)		(0.17)		(0.01)
Research and development credits	0.89		3.74		4.19
Change in valuation allowance	(38.48)		(37.57)		(26.07)
Income tax expense (benefit)	0.00	%	0.00	%	0.00	%

Deferred taxes are recognized for temporary differences between the basis of assets and liabilities for financial statement and income tax purposes. The significant components of the Company’s deferred tax assets and liabilities are comprised of the following:


	As of December 31,
	2015		2014
Deferred tax assets:
Net operating loss carryforwards	$	38,405	$	28,419
Research and development credits		3,421		3,070
Accruals and other		144		—
Depreciation and amortization		94		36
Deferred tax assets before valuation allowance		42,064		31,525
Valuation allowance		(42,064)		(31,525)
Net deferred tax assets	$	—	$	—

The Company has evaluated the positive and negative evidence bearing upon the realizability of its deferred tax assets. As of December 31, 2015 and 2014, based on the Company’s history of operating losses, the Company has concluded that it is not more likely than not that the benefit of its deferred tax assets will be realized. Accordingly, the Company has provided a full valuation allowance for deferred tax assets as of December 31, 2015 and 2014. The valuation allowance increased $10,539 and $7,737 during the years ended December 31, 2015 and 2014 respectively, due primarily to net operating losses generated.

As of December 31, 2015, 2014 and 2013, the Company had U.S. federal net operating loss carryforwards of $104,888, $78,276 and $60,380, respectively, which may be available to offset future income tax liabilities and expire at various dates through 2035. As of December 31, 2015, 2014 and 2013, the Company also had U.S. state net operating loss carryforwards of $59,875, $34,184 and $16,354, respectively, which may be available to offset future income tax liabilities and expire at various dates through 2035. Included in the federal and state net operating loss carryforwards are approximately $1,064, $0, and $0 respectively, of deductions related to the exercise of stock options which represent an excess tax benefit which will be realized when it results in the reduction of cash income tax in accordance with ASC 718.

As of December 31, 2015, 2014 and 2013, the Company had federal research and development tax credit carryforwards of approximately $3,110, $2,868, and $2,311, respectively, available to reduce future tax liabilities which expire at various dates through 2035. As of December 31, 2015, 2014 and 2013, the Company had state research and development tax credit carryforwards of approximately $469, $226, and $121, respectively, available to reduce future tax liabilities which expire at various dates through 2030.

Under the provisions of the Internal Revenue Code, the net operating loss and tax credit carryforwards are subject to review and possible adjustment by the Internal Revenue Service and state tax authorities. Net operating loss and tax credit carryforwards may become subject to an annual limitation in the event of certain cumulative changes in the ownership interest of significant shareholders over a three-year period in excess of 50 percent, as defined under Sections 382 and 383 of the Internal Revenue Code, respectively, 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. The Company has completed several financings since its inception which may have resulted in a change in control as defined by Sections 382 and 383 of the Internal Revenue Code, or could result in a change in control in the future.

The Company will recognize interest and penalties related to uncertain tax positions in income tax expense. As of December 31, 2015 and 2014, the Company had no accrued interest or penalties related to uncertain tax positions and no amounts have been recognized in the Company’s statements of operations and comprehensive loss.

For all years through December 31, 2015, the Company generated research and development credits but has not conducted a study to document the qualified activities. This study may result in an adjustment to the Company’s research and development credit carryforwards; however, until a study is completed and any adjustment is known, no amounts are being presented as an uncertain tax position for these two years. A full valuation allowance has been provided against the Company’s research and development credits and, if an adjustment is required, this adjustment would be offset by an adjustment to the deferred tax asset established for the research and development credit carryforwards and the valuation allowance.

The Company files income tax returns in the United States and Massachusetts. The federal and Massachusetts income tax returns are generally subject to tax examinations for the tax years ended December 31, 2012 through December 31, 2015. To the extent the Company has tax attribute carryforwards, the tax years in which the attribute was generated may still be adjusted upon examination by the Internal Revenue Service and state tax authorities to the extent utilized in a future period.

EMPLOYEE BENEFITS	12 Months Ended
EMPLOYEE BENEFITS	Dec. 31, 2015
EMPLOYEE BENEFITS
EMPLOYEE BENEFITS	13. EMPLOYEE BENEFITS The Company has a retirement savings plan, which is qualified under section 401(k) of the Code, for its employees. The plan allows eligible employees to defer, at the employee’s discretion, pretax compensation up to the Internal Revenue Service annual limits. Employees become eligible to participate after completing 3 months of service. The Company is not required to contribute to this plan. Total expense for contributions made by the Company was $35 for the year ended December 31, 2014 and $44 for the year ended December 31, 2015.

UNAUDITED QUARTERLY OPERATING RESULTS

12 Months Ended

Dec. 31, 2015

UNAUDITED QUARTERLY OPERATING RESULTS

UNAUDITED QUARTERLY OPERATING RESULTS

14. UNAUDITED QUARTERLY OPERATING RESULTS

The following is a summary of unaudited quarterly results of operations for the years ended December 31, 2015 and 2014:


	First		Second		Third		Fourth
Year ended December 31, 2015	Quarter		Quarter		Quarter		Quarter
Operating expenses:
Research and development	$	1,445	$	1,641	$	3,358	$	1,531
General and administrative		2,186		2,934		5,907		7,905
Total operating expenses		3,631		4,575		9,265		9,436

Loss from operations		(3,631)	$	(4,575)	$	(9,265)	$	(9,436)
Other expense, net		(63)		(99)		(97)		(89)
Net Loss	$	(3,694)	$	(4,674)	$	(9,362)	$	(9,525)

Shares used in computing net loss per share-basic		1,001,704		11,791,546		20,531,406		20,558,205
Shares used in computing net loss per share-diluted		7,554,524		11,791,546		20,531,406		20,558,205
Net loss per share-basic	$	0.34	$	(0.45)	$	(0.46)	$	(0.46)
Net loss per share-diluted	$	(0.65)	$	(0.45)	$	(0.46)	$	(0.46)

	First		Second		Third		Fourth
Year ended December 31, 2014	Quarter		Quarter		Quarter		Quarter
Operating expenses:
Research and development	$	3,269	$	3,565	$	5,818	$	2,307
General and administrative		476		523		687		1,020
Total operating expenses		3,745		4,088		6,505		3,327

Loss from operations		(3,745)		(4,088)		(6,505)		(3,327)
Other expense, net		(30)		(29)		(51)		(142)
Net Loss	$	(3,775)	$	(4,117)	$	(6,556)	$	(3,469)
Shares used in computing net loss per share-basic and diluted		912,616		926,239		940,621		955,957
Net loss per share-basic and diluted	$	(5.03)	$	(5.33)	$	(7.85)	$	(4.50)

SUBSEQUENT EVENTS	12 Months Ended
SUBSEQUENT EVENTS	Dec. 31, 2015
SUBSEQUENT EVENTS.
SUBSEQUENT EVENTS	15. SUBSEQUENT EVENTS The Company has completed an evaluation of all subsequent events through March 18, 2016, the date these financial statements are available to be issued. The Company has concluded that only one subsequent event that has occurred requires disclosure. In January 2016, the Company issued and sold in a public offering an aggregate of 2,750,000 shares of its common stock at $20.00 per share. This public offering resulted in approximately $51,700 of net proceeds, after deduction underwriting discounts and commissions but before deducting other offering expenses payable by the Company. At December 31, 2015, the Company capitalized $353 of costs related to expenses incurred in this public offering. These costs were reclassified to additional paid-in capital when the offering closed in January, 2016.

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies).

12 Months Ended

Dec. 31, 2015

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

Use of Estimates

Fair Value Measurements

Transfers are calculated on values as of the transfer date. There were no transfers between Levels 1, 2 and 3 during the years ended December 31, 2015 and 2014.

The following tables present the Company’s financial instruments carried at fair value using the lowest level input applicable to each financial instrument at December 31, 2015 and 2014.


					Significant
			Quoted Prices		other		Significant
			in active		observable		unobservable
			markets		inputs		inputs
Description	Total		(Level 1)		(Level 2)		(Level 3)
December 31, 2015
Money market funds, included in cash equivalents	$	94,912	$	94,912	$	—	$	—

December 31, 2014
Money market funds, included in cash equivalents	$	457	$	457	$	—	$	—

Concentration of Credit Risk

Cash and Cash Equivalents

Property and Equipment


Asset Category	Estimated Useful Life
Machinery and equipment		5	years
Computers and office equipment		5	years
Furniture and fixtures		7	years
Leasehold improvements		the shorter of the lease term or
		5	years

Upon retirement or sale, the cost of assets disposed and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is recorded in the statements of operations.

Impairment of Long Lived Assets

Impairment of Long‑Lived Assets

Impairment losses, if any, are recognized in earnings. An impairment loss would be recognized in an amount equal to the excess of the carrying amount over the estimated fair value.

Deferred Financing Costs

Restricted Cash

Deferred Rent

Research and Development Costs

Patent Costs

Costs related to filing and pursuing patent applications are recorded as general and administrative expense as incurred since the recoverability of such expenditures is uncertain.

Stock-Based Compensation

Stock‑Based Compensation

Income Taxes

Net loss per Common Share

Recently Issued Accounting Pronouncements

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)

12 Months Ended

Dec. 31, 2015

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

Schedule of financial instruments measured at fair value by level within fair value hierarchy


					Significant
			Quoted Prices		other		Significant
			in active		observable		unobservable
			markets		inputs		inputs
Description	Total		(Level 1)		(Level 2)		(Level 3)
December 31, 2015
Money market funds, included in cash equivalents	$	94,912	$	94,912	$	—	$	—

December 31, 2014
Money market funds, included in cash equivalents	$	457	$	457	$	—	$	—

Schedule of estimated useful lives of property and equipment


Asset Category	Estimated Useful Life
Machinery and equipment		5	years
Computers and office equipment		5	years
Furniture and fixtures		7	years
Leasehold improvements		the shorter of the lease term or
		5	years

NET LOSS PER COMMON SHARE (Tables)

12 Months Ended

Dec. 31, 2015

NET LOSS PER COMMON SHARE

Schedule of computations of basic and diluted net loss per share



	Years Ended December 31,
		2015		2014		2013

Net loss	$	(27,255)	$	(17,917)	$	(16,197)
Extinguishment of preferred stock - see note 10		31,806		—		—
Accretion and dividends of prior preferred stock - see note 10		(23,327)		(3,300)		(2,925)
Accretion and dividends of Series D preferred stock		(1,245)		—		—
Performance Adjustment of Series A		—		—		12,239
Loss attributable to common shareholders — basic and diluted	$	(20,021)	$	(21,217)	$	(6,883)
Weighted-average number of common shares used in net loss per share—basic and diluted		13,542,282		933,997		1,697,044
Net loss per share—basic and diluted	$	(1.48)	$	(22.72)	$	(4.06)

Schedule of potentially dilutive securities excluded from computations of diluted weighted-average shares outstanding



	Years Ended December 31,
	2015	2014	2013

Outstanding stock options	1,452,149	281,029	229,791
Warrants	2,445	18,809	4,170
Redeemable convertible preferred stock	—	6,552,820	6,552,820
Unvested restricted stock	75,718	15,387	55,298

PREPAID EXPENSES AND OTHER CURRENT ASSETS (Tables)

12 Months Ended

Dec. 31, 2015

PREPAID EXPENSES AND OTHER CURRENT ASSETS.

Schedule of components of prepaid expenses and other current assets


	As of December 31,
	2015		2014
Prepaid Insurance	$	420	$	—
Deferred financing costs		353		233
Other prepaid expenses		208		8
Other current assets		205		253
Employee advances		—		33
Prepaid expenses and other current assets	$	1,186	$	527

PROPERTY AND EQUIPMENT (Tables)

12 Months Ended

Dec. 31, 2015

PROPERTY AND EQUIPMENT

Schedule of components of property and equipment


	As of December 31,
	2015		2014
Machinery and equipment	$	755	$	741
Leasehold improvements		678		606
Computers and office equipment		262		26
Furniture and fixtures		117		44
Total property and equipment		1,812		1,417
Less: accumulated deprecation		(1,074)		(903)
Property and equipment, net	$	738	$	514

ACCRUED EXPENSES (Tables)

12 Months Ended

Dec. 31, 2015

ACCRUED EXPENSES

Schedule of components of accrued expenses


	As of December 31,
	2015		2014
Accrued compensation	$	1,567	$	635
Accrued audit and legal		209		249
Accrued other		186		31
Accrued marketing		157		—
Accrued development costs		80		970
Accrued interest		29		71
Total accrued expenses	$	2,228	$	1,956

COMMITMENTS AND CONTINGENCIES (Tables)

12 Months Ended

Dec. 31, 2015

COMMITMENTS AND CONTINGENCIES.

Schedule of aggregate minimum annual lease commitments under non-cancellable operating lease



2016	$	216
2017		226
2018		234
2019		241
2020		164
Total minimum lease payments	$	1,081

DEBT (Tables)

12 Months Ended

Dec. 31, 2015

DEBT

Schedule of future payments under debt agreements


2016	$	2,667
2017		2,667
2018		1,479
Balance	$	6,813

EQUITY (Tables)

12 Months Ended

Dec. 31, 2015

EQUITY

Schedule of shares of common stock reserved for future issuance


	As of December 31,
	2015	2014
Options to purchase common stock	2,642	3,413
Employee stock purchase plan	200	—
Warrants	2	19
Conversion of Series A Preferred	—	18,498
Conversion of Series B Preferred	—	27,324
Conversion of Series C Preferred	—	8,658
Total	2,844	21,930

Schedule of roll-forward of recurring fair value measurements of tranche liability categorized with Level 3 inputs


Balance — December 31, 2013	$	—
Tranche liability upon issuance		266
Change in fair value		79
Tranche liability upon close of tranche		(345)
Balance — December 31, 2014	$	—

STOCK-BASED COMPENSATION (Tables)

12 Months Ended

Dec. 31, 2015

STOCK BASED COMPENSATION

Summary of stock option activity



				Weighted-
		Weighted-		average
		average		remaining	Aggregate
		exercise price		contractual	Intrinsic
	Shares	per share		term (years)	Value
Outstanding at December 31, 2014	281,029	$	0.69	7.49	$	1,505
Granted	1,350,952		11.46
Exercised	(173,251)		2.99
Cancelled	(6,581)		14.54
Outstanding at December 31, 2015	1,452,149	$	10.37	10.36	$	24,887
Exercisable at December 31, 2015	205,891	$	3.75	7.9	$	4,890
Vested and expected to vest at December 31, 2015	1,436,582	$	10.46	9.1	$	26,061

Summary of restricted stock awards


		Weighted average
		purchase price
	Shares	per share
Unvested at December 31, 2014	15,387		0.69
Granted	194,694		5.73
Vested	(134,363)		5.15
Unvested at December 31, 2015	75,718	$	5.73

Schedule of stock-based compensation for all stock options and restricted stock awards


	Years Ended December 31,
		2015		2014		2013
Research and development	$	223	$	12	$	24
General and administrative		1,986		10		38
Total stock-based compensation expense	$	2,209	$	22	$	62

Schedule of weighted-average assumptions used in Black-Scholes option-pricing model


	Years Ended December 31,
	2015		2014		2013
Risk-free interest rate	1.70	%	1.8	%	1.09 - 1.22	%
Volatility	77.0	%	77.1	%	87.8	%
Expected term (years)	6.20		6.25		6.25
Expected dividend yield	—	%	—	%	—	%

INCOME TAXES (Tables)

12 Months Ended

Dec. 31, 2015

INCOME TAXES.

Schedule of reconciliation of income tax expense (benefit) at statutory federal income tax rate to income taxes


	As of December 31,
	2015		2014		2013
Federal income tax (benefit) at statutory rate	34.00	%	34.00	%	34.00	%
(Increase) decrease income tax (benefit) resulting from:
State income tax, net of federal benefit	5.29		—		—
Expiration of state net operating losses	—		—		(12.11)
Permanent items	(1.70)		(0.17)		(0.01)
Research and development credits	0.89		3.74		4.19
Change in valuation allowance	(38.48)		(37.57)		(26.07)
Income tax expense (benefit)	0.00	%	0.00	%	0.00	%

Schedule of significant components of deferred tax assets and liabilities


	As of December 31,
	2015		2014
Deferred tax assets:
Net operating loss carryforwards	$	38,405	$	28,419
Research and development credits		3,421		3,070
Accruals and other		144		—
Depreciation and amortization		94		36
Deferred tax assets before valuation allowance		42,064		31,525
Valuation allowance		(42,064)		(31,525)
Net deferred tax assets	$	—	$	—

UNAUDITED QUARTERLY OPERATING RESULTS (Tables)

12 Months Ended

Dec. 31, 2015

UNAUDITED QUARTERLY OPERATING RESULTS

Summary of unaudited quarterly results of operations


	First		Second		Third		Fourth
Year ended December 31, 2015	Quarter		Quarter		Quarter		Quarter
Operating expenses:
Research and development	$	1,445	$	1,641	$	3,358	$	1,531
General and administrative		2,186		2,934		5,907		7,905
Total operating expenses		3,631		4,575		9,265		9,436

Loss from operations		(3,631)	$	(4,575)	$	(9,265)	$	(9,436)
Other expense, net		(63)		(99)		(97)		(89)
Net Loss	$	(3,694)	$	(4,674)	$	(9,362)	$	(9,525)

Shares used in computing net loss per share-basic		1,001,704		11,791,546		20,531,406		20,558,205
Shares used in computing net loss per share-diluted		7,554,524		11,791,546		20,531,406		20,558,205
Net loss per share-basic	$	0.34	$	(0.45)	$	(0.46)	$	(0.46)
Net loss per share-diluted	$	(0.65)	$	(0.45)	$	(0.46)	$	(0.46)

	First		Second		Third		Fourth
Year ended December 31, 2014	Quarter		Quarter		Quarter		Quarter
Operating expenses:
Research and development	$	3,269	$	3,565	$	5,818	$	2,307
General and administrative		476		523		687		1,020
Total operating expenses		3,745		4,088		6,505		3,327

Loss from operations		(3,745)		(4,088)		(6,505)		(3,327)
Other expense, net		(30)		(29)		(51)		(142)
Net Loss	$	(3,775)	$	(4,117)	$	(6,556)	$	(3,469)
Shares used in computing net loss per share-basic and diluted		912,616		926,239		940,621		955,957
Net loss per share-basic and diluted	$	(5.03)	$	(5.33)	$	(7.85)	$	(4.50)

NATURE OF BUSINESS (Details) $ / shares in Units, $ in Thousands	1 Months Ended		12 Months Ended
	May 31, 2015 USD ($) $ / shares shares	Apr. 30, 2015 shares	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Maximum period automatic stay in effect			30 months
Common stock split ratio		0.1449
Accumulated deficit
Accumulated deficit \| $			$ 129,008	$ 101,753
Initial public offering
Issuance of stock (in shares)	6,670,000
Offering price (in dollars per share) \| $ / shares	$ 12.00
Net proceeds from IPO \| $	$ 72,029
Common stock split ratio		0.1449
Conversion into common stock	12,591,463	12,591,463
Underwriters over-allotment option
Issuance of stock (in shares)	870,000

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	May 31, 2015	Dec. 31, 2015	Dec. 31, 2014
Fair value measurements
Asset transfers out of Level 1 into Level 2		$ 0	$ 0
Asset transfers out of Level 2 into Level 1		0	0
Asset transfers into (out of) Level 3		0	$ 0
Financial instruments with off balance sheet risk of loss, assets		0
Financial instruments with off balance sheet risk of loss, liabilities		$ 0
Initial public offering
Common stock sold (in shares)	6,670,000
Offering price (in dollars per share)	$ 12.00
Underwriters over-allotment option
Common stock sold (in shares)	870,000

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Carrying amount
Cash and Cash Equivalents
Cash and cash equivalents	$ 95,697	$ 1,634
Money market funds \| Estimate of fair value
Cash and Cash Equivalents
Cash and cash equivalents	94,912	457
Money market funds \| Estimate of fair value \| Quoted Prices in active markets (Level 1)
Cash and Cash Equivalents
Cash and cash equivalents	$ 94,912	$ 457

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Property, Plant and Equipment (Details)	12 Months Ended
	Dec. 31, 2015
Machinery and equipment
Property and Equipment
Estimate Useful Life	5 years
Computers and office equipment
Property and Equipment
Estimate Useful Life	5 years
Furniture and fixtures
Property and Equipment
Estimate Useful Life	7 years
Leasehold improvements
Property and Equipment
Estimate Useful Life	5 years

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Deferred IPO Costs (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Prepaid expenses and other current assets
Sale of stock
Deferred IPO costs	$ 353	$ 233

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Stock-Based Compensation (Details) - shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Non-employee stock options
Stock-based compensation
Options granted (in shares)	0	0
Restricted stock
Stock-based compensation
Restricted stock granted (in shares)	194,694
Restricted stock \| Non-employee
Stock-based compensation
Restricted stock granted (in shares)	0	0

NET LOSS PER COMMON SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net loss per common share
Net loss	$ (9,525)	$ (9,362)	$ (4,674)	$ (3,694)	$ (3,469)	$ (6,556)	$ (4,117)	$ (3,775)	$ (27,255)	$ (17,917)	$ (16,197)
Extinguishment of preferred stock									31,806
Accretion and dividends of prior preferred stock									(23,327)	(3,300)	(2,925)
Loss attributable to common stockholders - basic and diluted									$ (20,021)	$ (21,217)	$ (6,883)
Weighted-average number of common shares used in net loss per share-basic and diluted (in shares)					955,957	940,621	926,239	912,616	13,542,282	933,997	1,697,044
Net loss per share - basic and diluted (in dollars per share)					$ (4.50)	$ (7.85)	$ (5.33)	$ (5.03)	$ (1.48)	$ (22.72)	$ (4.06)
Earnings per share - basic	$ (0.46)	$ (0.46)	$ (0.45)	$ 0.34
Earnings per share - diluted	$ (0.46)	$ (0.46)	$ (0.45)	$ (0.65)
Shares used in computing net loss per share-basic (in shares)	20,558,205	20,531,406	11,791,546	1,001,704
Weighted-average number of common shares used in earnings per share - Diluted	20,558,205	20,531,406	11,791,546	7,554,524
Series D convertible redeemable preferred stock
Net loss per common share
Accretion and dividends of prior preferred stock									$ (1,245)
Series A convertible redeemable preferred stock
Net loss per common share
Performance Adjustment											$ 12,239

NET LOSS PER COMMON SHARE - Antidilutive (Details) - shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Stock options
Anti-dilutive securities
Potentially dilutive securities outstanding excluded from the computations of diluted weighted-average shares outstanding (in shares)	1,452,149	281,029	229,791
Warrants
Anti-dilutive securities
Potentially dilutive securities outstanding excluded from the computations of diluted weighted-average shares outstanding (in shares)	2,445	18,809	4,170
All series of convertible redeemable preferred stock
Anti-dilutive securities
Potentially dilutive securities outstanding excluded from the computations of diluted weighted-average shares outstanding (in shares)		6,552,820	6,552,820
Restricted stock
Anti-dilutive securities
Potentially dilutive securities outstanding excluded from the computations of diluted weighted-average shares outstanding (in shares)	75,718	15,387	55,298

PREPAID EXPENSES AND OTHER CURRENT ASSETS (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
PREPAID EXPENSES AND OTHER CURRENT ASSETS.
Prepaid Insurance	$ 420
Deferred financing costs	353	$ 233
Other prepaid expenses	208	8
Other current assets	205	253
Employee advances		33
Total prepaid expenses and other current assets	$ 1,186	$ 527

PROPERTY AND EQUIPMENT (Details) - USD ($) $ in Thousands	12 Months Ended
PROPERTY AND EQUIPMENT (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Property and Equipment
Total property and equipment	$ 1,812	$ 1,417
Less: accumulated deprecation	(1,074)	(903)
Property and equipment, net	738	514
Depreciation and amortization	171	187	$ 169
Machinery and equipment
Property and Equipment
Total property and equipment	755	741
Leasehold improvements
Property and Equipment
Total property and equipment	678	606
Computers and office equipment
Property and Equipment
Total property and equipment	262	26
Furniture and fixtures
Property and Equipment
Total property and equipment	$ 117	$ 44

ACCRUED EXPENSES (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
ACCRUED EXPENSES
Accrued compensation	$ 1,567	$ 635
Accrued audit and legal	209	249
Accrued other	186	31
Accrued marketing	157
Accrued development costs	80	970
Accrued interest	29	71
Total accrued expenses	$ 2,228	$ 1,956

COMMITMENTS AND CONTINGENCIES (Details) - patent			1 Months Ended		12 Months Ended
COMMITMENTS AND CONTINGENCIES (Details) - patent	Feb. 09, 2016	Nov. 09, 2015	Nov. 30, 2015	Mar. 31, 2015	Dec. 31, 2015
Purdue Pharma, L. P. patent infringement suits
Contingencies
Total number of no stay patents asserted to have been infringed					2
Total number of no stay patents asserted to have been infringed moved for judgment based on collateral estoppel					1
Total number of Orange Book patents asserted to have been infringed previously invalidated in a suit against another company		3
Total number of non-Orange Book patents asserted to have been infringed			1
Purdue Pharma, L. P. patent infringement suit, District of Delaware
Contingencies
Total number of Orange Book patents asserted to have been infringed				3
Total number of non-Orange Book patents asserted to have been infringed				1
Purdue Pharma, L. P., patent infringement suit, District of Massachusetts
Contingencies
Total number of patents asserted to have been infringed				4
Total number of Orange Book patents asserted to have been infringed dismissed by judgment	3
Hatch-Waxman Act of 1984 election to sue for patent infringement \| Purdue Pharma, L. P. patent infringement suits \| Maximum
Contingencies
Stay period before FDA can issue a final approval unless it is terminated					30 months

COMMITMENTS AND CONTINGENCIES - Minimum Annual Lease Commitments (Details) $ in Thousands	1 Months Ended	12 Months Ended
	Mar. 31, 2015 ft²	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Lease
Rent-free term		2 months
Aggregate minimum annual lease commitments under non cancellable operating lease
2016		$ 216
2017		226
2018		234
2019		241
2020		164
Total minimum lease payments		1,081
Rent expense under operating lease agreement
Rent expense		112	$ 69
Guarantees
Restricted cash		97	80
Maximum
Lease inducements
Leasehold improvement allowance		174
Amendment to office and research facility operating lease
Lease
Square of feet of space \| ft²	9,660
Office and research facility operating lease
Lease
Square of feet of space \| ft²	19,335
Term of lease extension option	5 years
Canton facility lease reimbursable allowance
Lease inducements
Reimbursable improvement allowance		$ 164
Interest rate (as a percent)		8.00%
Term		36 months
Stand-by letter of credit
Guarantees
Restricted cash		$ 97	$ 80

DEBT (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended							12 Months Ended
	Aug. 28, 2012	Sep. 30, 2014	Aug. 31, 2014	Feb. 28, 2014	Jan. 31, 2014	Feb. 28, 2013	Oct. 31, 2012	Aug. 31, 2012	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2015
Loan and Security Agreements
Maximum borrowing capacity	$ 1,000
Proceeds from notes payable, net of original note payoff									$ 7,056	$ 500
Exercise price of warrant (in dollars per share)											$ 12.27
Common stock warrant, Silicon Valley Bank, Original Term Loan
Loan and Security Agreements
Common stock that may be purchased upon exercise of warrant (in shares)	23,810
Exercise price of warrant (in dollars per share)	$ 0.07
Common stock warrant, Silicon Valley Bank, Term Loan, Amendment No. 1
Loan and Security Agreements
Common stock that may be purchased upon exercise of warrant (in shares)				14,430
Exercise price of warrant (in dollars per share)				$ 0.05
Common stock warrant, Silicon Valley Bank, Term Loan, Amendment No. 2
Loan and Security Agreements
Common stock that may be purchased upon exercise of warrant (in shares)			86,580
Exercise price of warrant (in dollars per share)			$ 0.05
Term loan \| Silicon Valley Bank loan agreement
Loan and Security Agreements
Maximum borrowing capacity	$ 1,000
Amount borrowed						$ 500	$ 250	$ 250
Initial period of interest only payments	12 months
Subsequent period of principal and interest payments	36 months
Term loan \| Silicon Valley Bank loan agreement \| Prime
Loan and Security Agreements
Variable interest rate margin (as a percent)									2.25%	2.25%
Interest rate (as a percent)	5.50%
Term loan \| Silicon Valley Bank loan agreement, Amendment No. 1
Loan and Security Agreements
Maximum borrowing capacity					$ 6,000
Amount borrowed				$ 2,000
Proceeds from notes payable, net of original note payoff				$ 1,056
Initial period of interest only payments				12 months
Subsequent period of principal and interest payments				36 months
Term loan \| Silicon Valley Bank loan agreement, Amendment No. 1 \| Prime
Loan and Security Agreements
Variable rate basis					1.75%
Interest rate (as a percent)				5.00%
Term loan \| Silicon Valley Bank loan agreement Amendment No. 2
Loan and Security Agreements
Maximum borrowing capacity			$ 8,000
Amount borrowed		$ 3,000	$ 3,000
Initial period of interest only payments			12 months
Subsequent period of principal and interest payments			36 months
Term loan \| Silicon Valley Bank loan agreement Amendment No. 2 \| Prime
Loan and Security Agreements
Interest rate (as a percent)			5.00%

DEBT - Related Party (Details) - USD ($) $ in Thousands	1 Months Ended	2 Months Ended	12 Months Ended
DEBT - Related Party (Details) - USD ($) $ in Thousands	Mar. 31, 2015	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2013
Related party transactions
Gain on extinguishment			$ 91	$ (79)
6.0% Convertible promissory notes
Related party transactions
Gain on extinguishment	$ 91
Series D convertible redeemable preferred stock
Related party transactions
Issuance of stock (in shares)	4,166,667
Bridge Notes Purchase Agreement \| Investors \| 6.0% Convertible promissory notes
Related party transactions
Amount issued		$ 5,000
Stated interest rate		6.00%

DEBT - Future Payments (Details) $ in Thousands	Dec. 31, 2015 USD ($)
Future payments under term loan
2016	$ 2,667
2017	2,667
2018	1,479
Total	$ 6,813

WARRANTS (Details) - $ / shares	Dec. 31, 2015	Aug. 28, 2012
Class of Warrant or Right, Number of Securities Called by Warrants or Rights	2,445
Exercise price of warrant (in dollars per share)	$ 12.27
Common stock warrant, Silicon Valley Bank, Original Term Loan
Class of Warrant or Right, Number of Securities Called by Warrants or Rights	16,357
Exercise price of warrant (in dollars per share)		$ 0.07

EQUITY (Details) $ / shares in Units, $ in Thousands	1 Months Ended				12 Months Ended
EQUITY (Details) $ / shares in Units, $ in Thousands	May 31, 2015 USD ($) $ / shares shares	Apr. 30, 2015 shares	Mar. 31, 2015 USD ($) shares	Dec. 31, 2013 $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2013 USD ($) $ / shares shares	Dec. 31, 2014 $ / shares shares	Dec. 31, 2012 shares
Equity
Authorized common stock (in shares)				72,000,000	100,000,000	72,000,000	72,000,000
Par value of common stock (in dollars per share) \| $ / shares				$ 0.001	$ 0.001	$ 0.001	$ 0.001
Common stock issued (in shares)				962,960	20,739,351	962,960	1,006,219
Common stock outstanding (in shares)				962,960	20,739,351	962,960	1,006,219
Authorized preferred stock (in shares)				54,481,000	5,000,000	54,481,000	54,481,000
Preferred stock issued (in shares)					0
Preferred stock outstanding (in shares)					0
Common stock split ratio		0.1449
Common stock reserved for future issuance (in shares)					2,844		21,930
Employee stock purchase plan
Equity
Common stock reserved for future issuance (in shares)					200
Initial public offering
Equity
Issuance of stock (in shares)	6,670,000
Issue price (in dollars per share) \| $ / shares	$ 12.00
Net proceeds from IPO \| $	$ 72,029
Common stock split ratio		0.1449
Conversion into common stock	12,591,463	12,591,463
Underwriters over-allotment option
Equity
Issuance of stock (in shares)	870,000
Employee stock options
Equity
Common stock reserved for future issuance (in shares)					2,642		3,413
Warrants
Equity
Common stock reserved for future issuance (in shares)					2		19
Series A convertible redeemable preferred stock
Equity
Authorized preferred stock (in shares)					0		18,498,419
Preferred stock issued (in shares)				9,232,334	0	9,232,334	9,232,334	18,464,674
Preferred stock outstanding (in shares)				9,232,334	0	9,232,334	9,232,334
Common stock split ratio				0.5
Common stock reserved for future issuance (in shares)							18,498
Series B convertible redeemable preferred stock
Equity
Authorized preferred stock (in shares)					0		27,324,237
Preferred stock issued (in shares)				27,324,237	0	27,324,237	27,324,237	27,324,237
Preferred stock outstanding (in shares)				27,324,237	0	27,324,237	27,324,237
Common stock reserved for future issuance (in shares)							27,324
Series C convertible redeemable preferred stock
Equity
Authorized preferred stock (in shares)					0		8,658,344
Preferred stock issued (in shares)				8,658,008	0	8,658,008	8,658,008
Preferred stock outstanding (in shares)				8,658,008	0	8,658,008	8,658,008
Aggregate consideration \| $						$ 12,034
Common stock reserved for future issuance (in shares)							8,658
Series D convertible redeemable preferred stock
Equity
Aggregate consideration \| $			$ 50,000		$ 44,807
Proceeds from Issuance of Convertible Preferred Stock \| $			$ 45,000
Conversion into bridge notes			5,000,000
Issuance of stock (in shares)			4,166,667

EQUITY - Redeemeble Preferred (Details) $ / shares in Units, $ in Thousands	1 Months Ended				2 Months Ended	12 Months Ended
	Apr. 30, 2015	Mar. 31, 2015 shares	Dec. 31, 2013 USD ($) $ / shares	Feb. 29, 2012 USD ($) $ / shares shares	Sep. 30, 2013 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014 USD ($) $ / shares	Dec. 31, 2013 USD ($) tranche $ / shares shares
Performance Adjustment
Performance adjustment ratio	0.1449
Common Stock
Performance Adjustment
Performance adjustment ratio			0.5
Series A convertible redeemable preferred stock
Preferred stock
Convertible redeemable preferred stock, par value (in dollars per share) \| $ / shares				$ 0.001		$ 0.001	$ 0.001
Performance Adjustment
Performance adjustment ratio			0.5
Performance Adjustment			$ 12,239					$ 12,239
Series B convertible redeemable preferred stock
Preferred stock
Convertible redeemable preferred stock, par value (in dollars per share) \| $ / shares				$ 0.001		0.001	0.001
Series C convertible redeemable preferred stock
Preferred stock
Issuance of stock (in shares) \| shares								12,154,000
Convertible redeemable preferred stock, par value (in dollars per share) \| $ / shares						$ 0.001	$ 0.001
Closing costs								$ 45
Series D convertible redeemable preferred stock
Preferred stock
Issuance of stock (in shares) \| shares		41,666,667				37,500,000
Closing costs						$ 193
Series B Preferred Stock financing February 2012 \| Series B convertible redeemable preferred stock
Preferred stock
Issuance of stock (in shares) \| shares				27,324,237
Issue price (in dollars per share) \| $ / shares				$ 0.84
Gross proceeds				$ 20,050
Closing costs				$ 147
Series C Preferred Stock financing 2013 \| Series C convertible redeemable preferred stock
Preferred stock
Issuance of stock (in shares) \| shares								8,658,008
Gross proceeds								$ 12,000
Closing costs								$ 45
Number of tranches into which financing was structured \| tranche								2
Series C Preferred Stock financing 2013 \| Series C convertible redeemable preferred stock \| Maximum
Preferred stock
Shares authorized for sale and issuance (in shares) \| shares								8,658,008
Amount authorized for sale and issuance								$ 12,000
Series C Preferred Stock financing 2013 \| Series C convertible redeemable preferred stock \| Stock purchase right
Preferred stock
Stock purchase right liability					$ 266
Series C Preferred Stock financing 2013, first tranche \| Series C convertible redeemable preferred stock
Preferred stock
Issuance of stock (in shares) \| shares					2,886,004
Gross proceeds					$ 4,000
Series C Preferred Stock financing 2013, second tranche \| Series C convertible redeemable preferred stock \| Stock purchase right
Fair value assumptions
Fair value of stock (in dollars per share) \| $ / shares			$ 1.27		$ 1.30			$ 1.27
Expected life			1 month 28 days
Volatility (as a percent)			52.00%
Roll forward of the recurring fair value measurements of the tranche liability categorized with Level 3 inputs
Tranche liability upon issuance							$ 266
Change in fair value							79
Tranche liability upon close of tranche							$ (345)
Series C Preferred Stock financing 2013, second tranche \| Series C convertible redeemable preferred stock \| Stock purchase right \| Minimum
Fair value assumptions
Expected life					4 months 6 days
Volatility (as a percent)					53.00%
Series C Preferred Stock financing 2013, second tranche \| Series C convertible redeemable preferred stock \| Stock purchase right \| Maximum
Fair value assumptions
Expected life					5 months 5 days
Volatility (as a percent)					60.00%
Conversion of preferred stock into Series A Preferred Stock \| Series A convertible redeemable preferred stock
Preferred stock
Number of shares issued in exchange for previously outstanding stock (in shares) \| shares				18,464,674

STOCK-BASED COMPENSATION - Restricted Stock Awards and Options (Details)	1 Months Ended		12 Months Ended
	May 31, 2015 shares	Apr. 30, 2015	Dec. 31, 2015 shares	Dec. 31, 2014 shares
Stock-based compensation
Performance adjustment ratio		0.1449
Stock options
Stock-based compensation
Shares of common stock authorized for issuance outstanding (in shares)			1,452,149	281,029
Vesting period			4 years
Contractual life			10 years
Stock options \| Minimum
Stock-based compensation
Period following termination date vested options are exercisable			1 month
Stock options \| Maximum
Stock-based compensation
Period following termination date vested options are exercisable			3 months
2014 Stock Incentive Plan
Stock-based compensation
Shares of common stock authorized for issuance (in shares)	2,700,000
Increase in number of authorized shares on the first day of each fiscal year, as a percentage of outstanding common stock (as a percent)	4.00%

STOCK-BASED COMPENSATION - Stock Option Activity (Details) - Stock options - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Stock option activity
Outstanding at beginning of year (in shares)	281,029
Granted (in shares)	1,350,952
Exercised (in shares)	(173,251)
Cancelled (in shares)	(6,581)
Outstanding at end of period (in shares)	1,452,149	281,029
Exercisable at end of period (in shares)	205,891
Vested and expected to vest at end of period (in shares)	1,436,582
Weighted average exercise price per share
Outstanding at beginning of year (in dollars per share)	$ 0.69
Granted (in dollars per share)	11.46
Exercised (in dollars per share)	2.99
Cancelled (in dollars per share)	14.54
Outstanding at end of period (in dollars per share)	10.37	$ 0.69
Exercisable at end of period (in dollars per share)	3.75
Vested and expected to vest at end of period (in dollars per share)	$ 10.46
Stock option activity, additional information
Outstanding at end of period, Weighted-average remaining contractual term	10 years 4 months 10 days	7 years 5 months 27 days
Exercisable at end of period, Weighted-average remaining contractual term	7 years 10 months 24 days
Vested and expected to vest at end of period, weighted-average remaining contractual term	9 years 1 month 6 days
Outstanding at beginning of period, Aggregate Intrinsic Value	$ 1,505
Outstanding at end of period, Aggregate Intrinsic Value	24,887	$ 1,505
Exercisable at end of period, Aggregate Intrinsic Value	4,890
Vested and expected to vest at end of period, Aggregate Intrinsic Value	26,061
Unrecognized compensation cost related to outstanding options	$ 9,212
Period over which unrecognized compensation cost is expected to be recognized as expense	3 years 4 months 24 days
Weighted average fair value of vested options (in dollars per share)	$ 2.96

STOCK-BASED COMPENSATION - Restricted Award Vesting (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based compensation.
Total stock-based compensation expense	$ 2,209	$ 22	$ 62
Restricted stock
Restricted stock awards
Unvested at beginning of year (in shares)	15,387
Granted (in shares)	194,694
Vested (in shares)	(134,363)
Unvested at end of year (in shares)	75,718	15,387
Weighted-average purchase price per share
Unvested at beginning of year (in dollars per share)	$ 0.69
Granted (in dollars per share)	5.73
Vested (in dollars per share)	5.15
Unvested at end of year (in dollars per share)	$ 5.73	$ 0.69
Unrecognized compensation cost
Total fair value of restricted stock units vested	$ 692
Unrecognized stock-based compensation expense	$ 434
Period over which unrecognized compensation cost is expected to be recognized as expense	2 years 3 months 18 days
Research and development
Share-based compensation.
Total stock-based compensation expense	$ 223	$ 12	24
General and administrative
Share-based compensation.
Total stock-based compensation expense	$ 1,986	$ 10	$ 38

STOCK-BASED COMPENSATION - Valuation Assumptions (Details)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Weighted-average assumptions used in the Black-Scholes option pricing model to determine the fair value of the employee stock option grants
Risk-free interest rate	1.70%	1.80%
Volatility	77.00%	77.10%	87.80%
Expected term (in years)	6 years 2 months 12 days	6 years 3 months	6 years 3 months
Minimum
Weighted-average assumptions used in the Black-Scholes option pricing model to determine the fair value of the employee stock option grants
Risk-free interest rate			1.09%
Maximum
Weighted-average assumptions used in the Black-Scholes option pricing model to determine the fair value of the employee stock option grants
Risk-free interest rate			1.22%

INCOME TAXES (Details)	12 Months Ended
INCOME TAXES (Details)	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Reconciliation of income tax expense (benefit) computed at the statutory federal income tax rate to income taxes as reflected in the financial statements
Federal income tax (benefit) at statutory rate (as a percent)	34.00%	34.00%	34.00%
State income tax, net of federal benefit	5.29%
Expiration of state net operating losses (as a percent)			(12.11%)
Permanent items (as a percent)	(1.70%)	(0.17%)	(0.01%)
Research and development credits	0.89%	3.74%	4.19%
Change in valuation allowance (as a percent)	(38.48%)	(37.57%)	(26.07%)
Income tax expense (benefit) (as a percent)	0.00%	0.00%	0.00%

INCOME TAXES - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Deferred tax assets:
Net operating loss carryforwards	$ 38,405	$ 28,419
Research and development credits	3,421	3,070
Accruals and other	144
Depreciation and amortization	94	36
Deferred tax assets before valuation allowance	42,064	31,525
Valuation allowance	(42,064)	(31,525)
Valuation allowance
Deferred tax asset valuation allowance increase	10,539	7,737
Net operating loss carryforwards
Operating Loss Carryforwards	1,064,000	0	$ 0
Interest and Penalties relating to uncertain tax positions	0	0
Amount recognized in statement of operations	0	0
U.S. federal
Deferred tax assets:
Research and development credits	3,110,000	2,868,000	2,311,000
Net operating loss carryforwards
Available net operating loss carryforwards as of the end of the year	104,888	78,276	60,380
State
Deferred tax assets:
Research and development credits	469	226	121
Net operating loss carryforwards
Available net operating loss carryforwards as of the end of the year	$ 59,875	$ 34,184	$ 16,354

EMPLOYEE BENEFITS (Details) - USD ($) $ in Thousands	12 Months Ended
EMPLOYEE BENEFITS (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
EMPLOYEE BENEFITS
Requisite service period of employees to be eligible to participate in the 401(k) plan	3 months
Total expense for contributions made to 401(k) plan	$ 44	$ 35

UNAUDITED QUARTERLY OPERATING RESULTS (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
UNAUDITED QUARTERLY OPERATING RESULTS
Research and development	$ 1,531	$ 3,358	$ 1,641	$ 1,445	$ 2,307	$ 5,818	$ 3,565	$ 3,269	$ 7,975	$ 14,959	$ 14,157
General and administrative	7,905	5,907	2,934	2,186	1,020	687	523	476	18,932	2,706	1,885
Total operating expenses	9,436	9,265	4,575	3,631	3,327	6,505	4,088	3,745	26,907	17,665	16,042
Loss from operations	(9,436)	(9,265)	(4,575)	(3,631)	(3,327)	(6,505)	(4,088)	(3,745)	(26,907)	(17,665)	(16,042)
Other expense, net	(89)	(97)	(99)	(63)	(142)	(51)	(29)	(30)	(348)	(252)	(155)
Net loss	$ (9,525)	$ (9,362)	$ (4,674)	$ (3,694)	$ (3,469)	$ (6,556)	$ (4,117)	$ (3,775)	$ (27,255)	$ (17,917)	$ (16,197)
Shares used in computing net loss per share-basic (in shares)	20,558,205	20,531,406	11,791,546	1,001,704
Shares used in computing net loss per share-diluted (in shares)	20,558,205	20,531,406	11,791,546	7,554,524
Net loss per share-basic (in dollars per share)	$ (0.46)	$ (0.46)	$ (0.45)	$ 0.34
Net loss per share-diluted (in dollars per share)	$ (0.46)	$ (0.46)	$ (0.45)	$ (0.65)
Shares used in computing net loss per share-basic and diluted (in shares)					955,957	940,621	926,239	912,616	13,542,282	933,997	1,697,044
Net loss per share - basic and diluted (in dollars per share)					$ (4.50)	$ (7.85)	$ (5.33)	$ (5.03)	$ (1.48)	$ (22.72)	$ (4.06)

SUBSEQUENT EVENTS (Details) - Subsequent events $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended
	Jan. 31, 2016 USD ($) $ / shares shares	Mar. 18, 2016 item
SUBSEQUENT EVENTS
Subsequent events number \| item		1
Issuance of stock (in shares) \| shares	2,750,000
Issue price (in dollars per share) \| $ / shares	$ 20.00
Net proceeds after deducting underwriting discounts and commissions but before deducting other offering expenses payable	$ 51,700
Deferred IPO costs	$ 353