Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2020

Stock-Based Compensation

Summary of stock option activity

	Options Outstanding and Exercisable
				Weighted
		Weighted		Average	Aggregate
		Average		Remaining	Intrinsic
	Number of	Exercise		Contractual	Value(1)
	Shares	Price		Life (Years)	(in thousands)
Outstanding as of December 31, 2019	2,170,212	$	6.51	8.6	$	113,295
Granted	1,105,045	$	37.34	9.9		—
Exercised	(53,829)	$	2.05	7.8		—
Cancelled	(259)	$	7.63	8.7		—
Forfeited	(71,528)	$	23.35	9.3		—
Outstanding as of September 30, 2020	3,149,641	$	17.02	9.1	$	6,963
Vested and expected to vest as of September 30, 2020	3,149,641	$	17.02	—	$	6,963
Exercisable as of September 30, 2020	1,107,818	$	5.01	—	$	4,755

The aggregate intrinsic value is calculated as the difference between the exercise price of the underlying options and the estimated fair value of the common stock for the options that were in the money at September 30, 2020 and December 31, 2019.

Summary of stock based compensation expense recorded

	Three Months Ended				Nine Months Ended
	September 30,				September 30,
(in thousands)	2020		2019		2020		2019
Research and development	$	897	$	182	$	2,245	$	482
General and administrative		1,475		342		3,322		837
Total stock-based compensation expense	$	2,372	$	524	$	5,567	$	1,319

Summary of assumptions used in the Black Scholes option pricing model for stock options granted

	Nine Months Ended
	September 30,
	2020		2019
Expected term	5.4 - 6.08	years	6.08	years
Expected volatility	69.7 - 81.1	%	69.7	%
Risk free interest rate	0.3 - 1.0	%	1.96	%
Expected dividend yield	—	%	—	%