(10) Stock-Based Compensation

A summary of stock option activity for the six months ended June 30, 2019 is as follows:


		Weighted		Weighted
		Average		Average
		Exercise		Remaining
		Price		Contractual
	Shares	Per Share		Term (In Years)
Options Outstanding at December 31, 2018	866,132	$	93.70	7.1
Granted	863,290		2.78
Exercised	—		—
Canceled	(39,348)		131.86
Options Outstanding at June 30, 2019	1,690,074		46.37	8.4
Options Vested and Expected to Vest at June 30, 2019	1,538,046		50.45	8.3
Options Exercisable at June 30, 2019	529,136		132.85	5.7
Shares Available for Grant Under the 2008 Plan	433,391

The weighted average grant-date fair value of stock options granted during the three and six month periods ended June 30, 2019 was $2.09. Stock-based compensation expense for the three and six month periods ended June 30, 2019 and 2018 was recorded as follows:


	Three months ended June 30,				Six months ended June 30,
	2019		2018		2019		2018
	(In thousands)				(In thousands)
Research and development	$	654	$	978	$	1,410	$	2,289
General and administrative		810		1,070		1,747		2,247
Total stock-based compensation expense	$	1,464	$	2,048	$	3,157	$	4,536

The fair values of employee and director stock options granted during the three and six month periods ended June 30, 2019 and 2018 were valued using the Black-Scholes option pricing model with the following assumptions:


	Three months ended June 30,		Six months ended June 30,
	2019	2018	2019	2018
Expected stock price volatility	91%	85%	91%	73 - 85%
Expected option term	6.0 Years	6.0 Years	6.0 Years	6.0 Years
Risk-free interest rate	1.9 – 2.4%	2.9%	1.9 – 2.5%	2.8 – 3.0%
Expected dividend yield	None	None	None	None