Stock-Based Compensation

6 Months Ended

Jun. 30, 2018

(9) Stock-Based Compensation

A summary of stock option activity for the six months ended June 30, 2018 is as follows:


		Weighted		Weighted
		Average		Average
		Exercise		Remaining
		Price		Contractual
	Shares	Per Share		Term (In Years)
Options Outstanding at December 31, 2017	10,856,212	$	9.40	6.1
Granted	5,046,867		0.61
Exercised	(104,500)		2.80
Canceled	(1,832,387)		8.19
Options Outstanding at June 30, 2018	13,966,192		6.43	7.4
Options Vested and Expected to Vest at June 30, 2018	13,544,093		6.59	7.3
Options Exercisable at June 30, 2018	6,482,436		11.18	5.0
Shares Available for Grant Under the 2008 Plan	4,370,007

The weighted average grant-date fair value of stock options granted during the three and six month periods ended June 30, 2018 was $0.44. Stock-based compensation expense for the three and six month periods ended June 30, 2018 and 2017 was recorded as follows:


	Three months ended June 30,				Six months ended June 30,
	2018		2017		2018		2017
	(In thousands)				(In thousands)
Research and development	$	978	$	1,871	$	2,289	$	3,764
General and administrative		1,070		1,579		2,247		3,225
Total stock-based compensation expense	$	2,048	$	3,450	$	4,536	$	6,989

The fair values of employee and director stock options granted during the three and six month periods ended June 30, 2018 and 2017 were valued using the Black-Scholes option pricing model with the following assumptions:


	Three months ended June 30,		Six months ended June 30,
	2018	2017	2018	2017
Expected stock price volatility	85%	76%	73 - 85%	76 - 77%
Expected option term	6.0 Years	6.0 Years	6.0 Years	6.0 Years
Risk-free interest rate	2.9%	2.0 - 2.1%	2.8 - 3.0%	2.0 - 2.3%
Expected dividend yield	None	None	None	None