Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2019

Schedule of Company's Stock Option Activity

The following table summarizes the Company’s stock option activity:

						Weighted-
				Weighted-		average		Aggregate
	Stock			average		Remaining		Intrinsic
	Options			Exercise		Contractual		Value
	Outstanding			Price		Life (Years)		(In thousands) (1)
Balance at December 31, 2018		357,089		$	8.73		8.8	$	4,302
Granted		67,500		$	23.87
Exercised		(14,653	)	$	2.75
Cancelled or forfeited		(9,000	)	$	18.71
Balance at March 31, 2019		400,936		$	11.28		8.8	$	8,670
Exercisable at March 31, 2019		93,468		$	5.82		8.2	$	2,531
Vested at March 31, 2019		112,364		$	5.30		8.2	$	3,102

(1) Aggregate intrinsic value represents the difference between the closing stock price of our common stock on March 31, 2019 and the exercise price of outstanding in-the-money options.

Summary of Stock Based Compensation Expense Related to Issuance of Stock Option Awards

The Company has recorded aggregate stock-based compensation expense related to the issuance of stock option awards to employees and non-employees in the condensed consolidated statements of operations for the three months ended March 31, 2019 and 2018 as follows (in thousands):

	Three Months Ended March 31,
	2019		2018
Research and development	$	117	$	46
General and administrative		87		19
Total stock-based compensation	$	204	$	65

Employee Stock Option [Member]

Fair Value of Stock Options, Valuation Assumptions

The fair value of options granted to employees was estimated at the date of grant using the Black-Scholes valuation model with the following weighted-average assumptions for the three months ended March 31, 2019 and 2018:

	Three Months Ended March 31,
	2019			2018
Expected stock price volatility		71	%		80	%
Expected term of the award (years)		6.25			6.25
Risk-free interest rate		2.46	%		2.71	%
Forfeiture Rate		10.00	%		0.00	%
Expected dividend yield		0	%		0	%