Stock-Based Compensation

6 Months Ended

Jun. 30, 2013

Stock-Based Compensation

Stock-Based Compensation

(11)  Stock-Based Compensation

A summary of stock option activity for the six months ended June 30, 2013 is as follows:

	Shares		Weighted Average Exercise Price Per Share		Weighted Average Remaining Contractual Term (In Years)
Options Outstanding at December 31, 2012	5,349,810		$	5.98	7.0
Granted	38,750		$	13.01
Exercised	(370,627	)	$	6.17
Canceled	(12,330	)	$	6.64
Options Outstanding at June 30, 2013	5,005,603		$	6.02	6.5
Options Vested and Expected to Vest at June 30, 2013	4,967,369		$	6.02	6.5
Options Exercisable at June 30, 2013	3,176,119		$	6.58	5.3
Shares Available for Grant under the 2008 Plan	3,313,661

The weighted average grant-date fair value of stock options granted during the six months ended June 30, 2013 was $8.31. Stock-based compensation expense for the three and six months ended June 30, 2013 and 2012 was recorded as follows:

	Three months ended June 30,				Six months ended June 30,
	2013		2012		2013		2012
	(In thousands)
Research and development	$	422	$	284	$	863	$	679
General and administrative	254		164		521		409
Total stock-based compensation expense	$	676	$	448	$	1,384	$	1,088

The fair values of employee and director stock options granted during the three and six months ended June 30, 2013 and 2012 were valued using the Black-Scholes option-pricing model with the following assumptions:

	Three months ended June 30,				Six months ended June 30,
	2013		2012		2013		2012
Expected stock price volatility	72	%	71	%	72	%	70 - 71	%
Expected option term	6.0 years		6.0 years		6.0 years		6.0 years
Risk-free interest rate	1.2 — 1.8	%	0.9 — 1.3	%	1.2 — 1.8	%	0.9 — 1.4	%
Expected dividend yield	None		None		None		None