Stock-Based Compensation Expense (Tables)

9 Months Ended

Sep. 30, 2019

Stock-Based Compensation Expense

Summary of Stock option activity under the 2015 and 2018 Plan

				Weighted-
		Weighted-		Average
		Average		Remaining	Aggregate
	Number of	Exercise		Contractual	Intrinsic
	Options	Price		Term (Years)	Value (in thousands)
Outstanding as of December 31, 2018	1,375,730	$	6.54	8.66	$	426
Granted	917,000		5.92
Exercised	(9,696)		4.08
Cancelled or forfeited	(98,530)		6.81
Outstanding as of September 30, 2019	2,184,504	$	6.28	8.54	$	1,831
Vested or expected to vest as of September 30, 2019	2,184,504	$	6.28	8.54	$	1,831
Exercisable as of September 30, 2019	728,538	$	5.42	7.49	$	1,036

Schedule of stock-based compensation expense

Stock‑based compensation expense was classified in the consolidated statement of operations as follows (in thousands):

	Three Months Ended September 30,				Nine Months Ended September 30,
	2019		2018		2019		2018
Research and development	$	212	$	128	$	635	$	307
General and administrative		359		205		1,113		499
Total stock-based compensation expense	$	571	$	333	$	1,748	$	806