Stockholders' Equity and Stock Options (Tables)

9 Months Ended

Sep. 30, 2021

Stockholders Equity Note [Abstract]

Assumptions used to Determine Fair Value of Stock Options Granted

The following table presents, on a weighted average basis, the assumptions used in the Black-Scholes option-pricing model to determine the grant-date fair value of stock options granted to employees:

	September 30,	December 31,
	2021	2020
Risk-free interest rate	0.88%	0.37%
Expected term (in years)	6.19	6.08
Expected volatility	91%	91%
Dividend yield	0.00%	0.00%

Summary of Stock Option Activity

The following table summarizes the Company’s stock option activity for the nine months ended September 30, 2021 (amounts in millions, except for share and per share data):

				Weighted		Weighted Average		Aggregate
				Average		Remaining		Intrinsic
	Number of			Exercise		Contractual		Value (a)
	Shares			Price		Term (in years)		(in millions)
Outstanding as of December 31, 2020		2,008,902		$	22.31		7.9
Granted		617,150			15.62
Forfeited/Expired		(80,090	)		62.42
Outstanding as of September 30, 2021		2,545,962		$	19.43		7.8	$	0.4
Exercisable as of September 30, 2021		944,249		$	29.29		5.8	$	—
Vested and expected to vest as of September 30, 2021		2,545,962		$	19.43		7.8	$	0.4

(a)The aggregate intrinsic value is calculated as the difference between the exercise price of the underlying options and the fair value of the common stock for the options that were in the money at September 30, 2021.

Summary of Stock-Based Compensation Expense

Stock-based compensation expense was classified in the condensed consolidated statements of operations as follows:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2021		2020		2021		2020
	(in thousands)
Research and development	$	567	$	231	$	1,520	$	442
General and administrative		896		139		2,473		709
	$	1,463	$	370	$	3,993	$	1,151