Share-Based Payments (Tables)

3 Months Ended

Mar. 31, 2014

Summary of Stock Option Activity and Related Information

A summary of the Company’s stock option activity and related information follows:

	Shares			Weighted-Average Exercise Price		Remaining Contractual Life (in years)
Outstanding at December 31, 2013		1,346,238		$	3.39		8.59
Granted		80,715			16.85
Exercised		(7,874	)		0.06
Cancelled or forfeited		(4,724	)		7.37
Outstanding at March 31, 2014		1,414,355		$	4.17		8.46
Exercisable at March 31, 2014		402,861		$	1.21		7.66
Vested and expected to vest at March 31, 2014(1)		1,060,715		$	4.60		8.62

(1) Represents the number of vested options, plus the number of unvested options expected to vest.

Summary of Status and Changes of Unvested Restricted Stock

A summary of the status of unvested restricted stock is presented below:

	Restricted Stock			Weighted-Average Grant Date Fair Value
Unvested at December 31, 2013		163,353		$	0.06
Granted		70,879			11.43
Vested		(30,479	)		0.06
Unvested at March 31, 2014		205,753		$	3.98

Summary of Stock-based Compensation Expense

During the three months ended March 31, 2014 and 2013, the Company recorded stock-based compensation expense for employee and non-employee stock options and restricted stock, which was allocated as follows in the statements of operations (in thousands):

	Three Months Ended March 31,
	2014		2013
Research and development expense	$	355	$	33
General and administrative expense		281		6
	$	636	$	39

Employees and Directors Stock Option [Member]

Estimation of Fair Value of Stock Option Granted using Black-Scholes Option-Pricing Model Assumptions

The fair value of each stock option granted to employees and directors was estimated on the date of grant using the Black-Scholes option-pricing model based on the assumptions noted in the following table:

	Three Months Ended March 31,
	2014	2013
Risk-free interest rate	1.80-2.02%	1.09-1.11%
Expected dividend yield	—	—
Expected term (in years)	5.75-6	6
Expected volatility	69.37-69.58%	77.66-77.80%

Non-employee Stock Options [Member]

Estimation of Fair Value of Stock Option Granted using Black-Scholes Option-Pricing Model Assumptions

The fair value of each non-employee stock option granted is estimated using the Black-Scholes option-pricing model based on assumptions noted in the following table:

	Three Months Ended March 31, 2013
Risk-free interest rate		1.91	%
Expected dividend yield		—
Expected option life (years)		10
Expected stock price volatility		79.15	%