Equity Incentive Plans (Tables)

3 Months Ended

Mar. 31, 2021

Summary of Estimated Fair Value of Employee Stock Options

We estimated the fair value of employee stock options using the Black-Scholes option-pricing model for the three months ended March 31, 2021 and 2020 using the following weighted-average assumptions:

	Three Months Ended March 31,
	2021	2020
Fair Value Assumptions
Expected volatility	81.0% - 82.5%	81.2% - 81.3%
Expected dividend yield	0%	0%
Expected term (in years)	5.5	6.0 - 6.1
Risk-free interest rate	0.5% - 1.0%	1.4%

2020 Plan and 2014 Plan

Summary of Activity Under Stock Option Plans

Activity under our 2020 Plan and 2014 Plan, which excludes options to purchase 66,982 shares granted outside of the 2020 Plan and 2014 Plan, was as follows:

				Options Outstanding
Stock Option Activity	Options Available for Grant			Number of Options			Weighted- Average Exercise Price Per Share		Weighted- Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value
Balances — December 31, 2020		4,651,149			5,121,549		$	4.99
Additional shares authorized		2,553,579			—
Options granted		(79,000	)		79,000		$	26.56
Options exercised		—			(267,208	)	$	1.82
Options forfeited		136,924			(136,924	)	$	21.73
Balances — March 31, 2021		7,262,652			4,796,417		$	5.05		7.95	$	73,165
Vested and expected to vest — March 31, 2021					4,796,417		$	5.05		7.95	$	73,165
Exercisable at March 31, 2021					2,141,639		$	2.37		6.97	$	37,225

2020 Employee Stock Purchase Plan

Summary of Estimated Fair Value of Shares Under Employee Stock Purchase Plan

We estimated the fair value of shares under the 2020 ESPP using the Black-Scholes option-pricing model for the three months ended March 31, 2021 and 2020 using the following weighted-average assumptions:

	Three Months Ended March 31,
	2021	2020
Fair Value Assumptions
Expected volatility	105.8% - 158.2%	N/A
Expected dividend yield	0%	N/A
Expected term (in years)	0.4 - 2.0	N/A
Risk-free interest rate	0.1% - 0.2%	N/A

2014 Plan, 2020 Plan and 2020 ESPP

Summary of Stock-based Compensation Expense

We recorded total stock-based compensation expense for the three months ended March 31, 2021 and 2020 related to the 2014 Plan, the 2020 Plan and the 2020 ESPP in the condensed statements of operations and allocated the amounts as follows:

	Three Months Ended March 31,
	2021		2020
	(In thousands)
Research and development	$	683	$	149
General and administrative		1,182		223
Total	$	1,865	$	372