STOCK-BASED COMPENSATION (Tables)

9 Months Ended

Sep. 30, 2018

STOCK-BASED COMPENSATION

Summary of option activity for employee and non employee awards

A summary of option activity for employee and non‑employee awards under the 2009 Plan, the 2017 Plan and inducement grants for the nine months ended September 30, 2018 is as follows (in thousands, except share and per share amounts):

				Weighted
		Weighted		Average
		Average		Remaining	Aggregate
	Number of	Exercise		Contractual	Intrinsic
	Shares	Price		Term	Value
				(Years)
Outstanding at January 1, 2018	3,738,928	$	6.93	8.4	$	44,578
Granted	1,449,690		13.74
Exercised	(107,233)		2.71
Forfeited	(144,152)		5.85
Outstanding at September 30, 2018	4,937,233	$	9.04	8.03	$	16,968
Vested or expected to vest at September 30, 2018	4,937,233	$	9.04	8.03	$	16,968
Options exercisable at September 30, 2018	2,414,308	$	5.29	7.14	$	13,198

Schedule of assumptions used in determining fair value of the stock options granted

	Nine Months Ended September 30,
	2018			2017
Expected volatility	80%	–	85%	103%	–	122%
Risk-free interest rate	2.63%	–	2.96%	1.81%	–	2.29%
Expected dividend yield		0%			0%
Expected term (in years)	5.27	–	6.13	5.04	–	9.82

Schedule of reserved common stock shares upon exercise of rights under equity compensation plans

Reserved Shares—As of September 30, 2018 and December 31, 2017, the Company had reserved the following shares of common stock issuable upon exercise of rights under equity compensation plans and inducement stock option awards:

	September 30,	December 31,
	2018	2017
ESPP	223,341	223,341
Shares reserved for outstanding inducement stock option award	219,500	—
2009 Plan	2,649,952	2,868,449
2017 Plan	3,118,430	2,025,633
Total	6,211,223	5,117,423

Schedule of stock based compensation expense

Stock-based Compensation Expenses—Stock‑based compensation expense was classified in the statements of operations as follows (in thousands):

	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2018		2017		2018		2017
Research and development	$	684	$	357	$	2,064	$	749
General and administrative		1,581		624		4,353		1,321
Total	$	2,265	$	981	$	6,417	$	2,070