5.  STOCK-BASED COMPENSATION

Accounting for Stock-Based Compensation

The Company uses the Black-Scholes option-pricing model to calculate the grant-date fair value of stock option awards. The resulting compensation expense, net of expected forfeitures, for non-performance based awards is recognized on a straight-line basis over the service period of the award, which is generally three years for stock options. For stock options with performance-based vesting provisions, recognition of compensation expense, net of expected forfeitures, commences if and when the achievement of the performance criteria is deemed probable. The compensation expense, net of expected forfeitures, for performance-based stock options is recognized over the relevant performance period. Evaluation of the probability of meeting performance targets is evaluated at the end of each reporting period. Non-employee stock-based compensation is accounted for in accordance with the guidance of FASB ASC Topic 505, Equity.  As such, the Company recognizes expense based on the estimated fair value of options granted to non-employees over their vesting period, which is generally the period during which services are rendered and deemed completed by such non-employees.

The following table summarizes amounts charged to expense for stock-based compensation related to employee and director stock option grants and stock-based compensation recorded in connection with stock options granted to non-employee consultants:

During 2011, the Company granted options to purchase 670,200 shares of common stock that vest based upon the achievement of performance-based milestones. As of March 31, 2012, 335,100 of these performance-based awards remain outstanding. No compensation expense has been recognized related to the performance-based awards as the Company does not believe that it is probable that the performance targets will be met. 

 Stock Option Activity

A summary of stock option activity under stock option plans is as follows:

No stock option awards were granted in the three months ended March 31, 2012 or 2011.

The aggregate intrinsic value of options outstanding is calculated based on the positive difference between the estimated per-share fair value of common stock at the end of the respective period and the exercise price of the underlying options.  There have been no option exercises to date. Shares of common stock issued upon the exercise of options are from authorized but unissued shares.

As of March 31, 2012, there was $1,935,626 of total unrecognized compensation cost related to unvested stock-based compensation arrangements.  Of this total amount, the Company expects to recognize $748,791, $728,122, $352,444 and $106,269 during 2012, 2013, 2014 and 2015, respectively.  The Company expects 3,396,500 in unvested options, excluding performance-based awards, to vest in the future.  The weighted-average grant-date fair value of vested and unvested options outstanding at March 31, 2012 was $1.15 and $0.89, respectively. There were no Cellectar options outstanding as of March 31, 2011.