Stock-Based Compensation

6 Months Ended

Jun. 30, 2016

Stock-Based Compensation

Stock-Based Compensation

(11)  Stock-Based Compensation

A summary of stock option activity for the six months ended June 30, 2016 is as follows:

	Shares		Weighted Average Exercise Price Per Share		Weighted Average Remaining Contractual Term (In Years)
Options Outstanding at December 31, 2015	8,110,239		$	13.13	6.7
Granted	2,291,250		$	4.86
Exercised	(37,942	)	$	2.93
Canceled	(103,474	)	$	15.92
Options Outstanding at June 30, 2016	10,260,073		$	11.29	7.0
Options Vested and Expected to Vest at June 30, 2016	10,175,654		$	11.30	7.0
Options Exercisable at June 30, 2016	5,558,678		$	10.20	5.3
Shares Available for Grant under the 2008 Plan	3,542,107

The weighted average grant-date fair value of stock options granted during the six months ended June 30, 2016 was $3.23. Stock-based compensation expense for the three and six months ended June 30, 2016 and 2015 was recorded as follows:

	Three months ended June 30,				Six months ended June 30,
	2016		2015		2016		2015
	(In thousands)
Research and development	$	2,008	$	1,244	$	3,824	$	2,512
General and administrative	1,965		1,283		4,089		2,296
Total stock-based compensation expense	$	3,973	$	2,527	$	7,913	$	4,808

The fair values of employee and director stock options granted during the three and six months ended June 30, 2016 and 2015 were valued using the Black-Scholes option-pricing model with the following assumptions:

	Three months ended June 30,				Six months ended June 30,
	2016		2015		2016		2015
Expected stock price volatility	77	%	67	%	70 - 77	%	67 - 69	%
Expected option term	6.0 years		6.0 years		6.0 years		6.0 years
Risk-free interest rate	1.5	%	2.2	%	1.5 – 1.6	%	1.8 - 2.2	%
Expected dividend yield	None		None		None		None