Stock-Based Compensation

6 Months Ended

Jun. 30, 2017

Stock-Based Compensation

Stock-Based Compensation

(8)  Stock-Based Compensation

A summary of stock option activity for the six months ended June 30, 2017 is as follows:

	Shares		Weighted Average Exercise Price Per Share		Weighted Average Remaining Contractual Term (In Years)
Options Outstanding at December 31, 2016	10,218,710		$	11.14	6.5
Granted	2,283,100		$	2.34
Exercised	—		$	—
Canceled	(413,100	)	$	10.66
Options Outstanding at June 30, 2017	12,088,710		$	9.49	6.5
Options Vested and Expected to Vest at June 30, 2017	11,931,869		$	9.54	6.5
Options Exercisable at June 30, 2017	7,085,429		$	10.93	4.7
Shares Available for Grant under the 2008 Plan	7,292,650

The weighted average grant-date fair value of stock options granted during the six month period ended June 30, 2017 was $1.57. Stock-based compensation expense for the three and six months ended June 30, 2017 and 2016 was recorded as follows:

	Three months ended June 30,				Six months ended June 30,
	2017		2016		2017		2016
	(In thousands)
Research and development	$	1,871	$	2,008	$	3,764	$	3,824
General and administrative	1,579		1,965		3,225		4,089
Total stock-based compensation expense	$	3,450	$	3,973	$	6,989	$	7,913

The fair value of employee and director stock options granted during the three and six month periods ended June 30, 2017 and 2016 were valued using the Black-Scholes option-pricing model with the following assumptions:

	Three months ended June 30,		Six months ended June 30,
	2017	2016	2017	2016
Expected stock price volatility	76%	77%	76 – 77%	70 – 77%
Expected option term	6.0 years	6.0 years	6.0 years	6.0 years
Risk-free interest rate	2.0 – 2.1%	1.5%	2.0 – 2.3%	1.5 – 1.6%
Expected dividend yield	None	None	None	None