Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2019

Share-based Payment Arrangement [Abstract]

The following table summarizes stock option activity for the 2002 Plan and 2018 Plan for the year ended December 31, 2019:



	Total Options		Weighted- Average Exercise Price Per Share		Weighted- Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value
Outstanding at Ended December 31, 2017	1,075,209		$	1.60	7.3	$	711,328
Granted	563,268		$	4.07
Exercised	(43,687	)	$	2.12
Cancelled or expired	(49,387	)	$	1.65
Outstanding at December 31, 2018	1,545,403		$	2.48	7.6	$	1,593,487
Granted	1,260,540		$	4.19
Exercised	(143,654	)	$	1.71
Cancelled or expired	(84,571	)	$	4.65
Outstanding at December 31, 2019	2,577,718		$	3.29	7.9	$	7,914,459
Vested and expected to vest at December 31, 2019	2,577,718		$	3.29	7.9	$	7,914,459
Vested and exercisable at December 31, 2019	1,157,120		$	2.25	6.7	$	4,469,348

Estimated Fair Value of Option on Grant Date using Weighted Average Assumptions

The fair value of each option was estimated on the date of grant using the weighted average assumptions in the table below:



	Year Ended December 31,
	2019			2018
Risk-free interest rate	2.36		%	2.88		%
Expected term (in years)	5.9			7.0
Expected volatility	69		%	69		%
Expected dividend yield	—			—
Fair value of common stock	$	4.19		$	4.07

Stock-based Compensation Expense

Stock-based compensation expense has been reported in the Company’s statements of operations for the years ended December 31, 2019 and 2018 as follows (in thousands):



	Year Ended December 31,
	2019		2018
General and administrative	$	1,135	$	208
Research and development	286		124
Total stock-based compensation	$	1,421	$	332