X0204 3 2012-01-31 0 0001274792 MERRIMACK PHARMACEUTICALS INC MACK 0001108494 PORTER MICHAEL E C/O MERRIMACK PHARMACEUTICALS, INC. ONE KENDALL SQUARE, SUITE B7201 CAMBRIDGE MA 02139 1 0 0 0 Common Stock 63000 D Series C Convertible Preferred Stock Common Stock 56509 D Series D Convertible Preferred Stock Common Stock 34286 D Series E Convertible Preferred Stock Common Stock 25000 D Series F Convertible Preferred Stock Common Stock 33000 D Series G Convertible Preferred Stock Common Stock 28570 D Stock Option (right to buy) 2.1900 2013-05-08 Common Stock 15000 D Stock Option (right to buy) 1.7100 2015-08-03 Common Stock 10000 D Stock Option (right to buy) 2.5900 2017-10-04 Common Stock 2500 D Stock Option (right to buy) 1.8100 2018-09-21 Common Stock 2500 D Stock Option (right to buy) 2.1200 2019-11-04 Common Stock 5000 D Stock Option (right to buy) 2.6900 2020-10-14 Common Stock 25000 D Stock Option (right to buy) 2.6900 2020-12-08 Common Stock 60000 D Stock Option (right to buy) 5.5400 2021-05-02 Common Stock 25000 D Each share of Series C Convertible Preferred Stock will automatically convert into one share of Common Stock upon the closing of the issuer's initial public offering. The shares have no expiration date. Each share of Series D Convertible Preferred Stock will automatically convert into one share of Common Stock upon the closing of the issuer's initial public offering. The shares have no expiration date. Each share of Series E Convertible Preferred Stock will automatically convert into one share of Common Stock upon the closing of the issuer's initial public offering. The shares have no expiration date. Each share of Series F Convertible Preferred Stock will automatically convert into one share of Common Stock upon the closing of the issuer's initial public offering. The shares have no expiration date. Each share of Series G Convertible Preferred Stock will automatically convert into one share of Common Stock upon the closing of the issuer's initial public offering. The shares have no expiration date. This option is fully vested. This option vested as to 1/12th of the shares on each of November 5, 2009 and February 1, 2010 and vests in equal quarterly installments thereafter until August 1, 2012. This option vested as to 1/12th of the shares on each of October 15, 2010 and January 1, 2011 and vests in equal quarterly installments thereafter until July 1, 2013. /s/ Jeffrey A. Munsie, attorney-in-fact 2012-02-01