X0204 3 2012-01-31 0 0001274792 MERRIMACK PHARMACEUTICALS INC MACK 0001531962 Nielsen Ulrik B. C/O MERRIMACK PHARMACEUTICALS, INC. ONE KENDALL SQUARE, SUITE B7201 CAMBRIDGE MA 02139 0 1 0 0 SVP and CSO Common Stock 247443 D Stock Option (right to buy) 2.1900 2012-08-02 Common Stock 4368 D Stock Option (right to buy) 2.1900 2013-05-08 Common Stock 10483 D Stock Option (right to buy) 1.2500 2014-08-30 Common Stock 150000 D Stock Option (right to buy) 1.7100 2015-08-03 Common Stock 82977 D Stock Option (right to buy) 1.7100 2015-08-03 Common Stock 17023 D Stock Option (right to buy) 2.4700 2016-10-03 Common Stock 48175 D Stock Option (right to buy) 2.4700 2016-10-03 Common Stock 26825 D Stock Option (right to buy) 2.5900 2017-10-04 Common Stock 53378 D Stock Option (right to buy) 2.5900 2017-10-04 Common Stock 146622 D Stock Option (right to buy) 1.8100 2018-09-21 Common Stock 250000 D Stock Option (right to buy) 2.1200 2019-11-04 Common Stock 180000 D Stock Option (right to buy) 2.1200 2020-01-31 Common Stock 100000 D Stock Option (right to buy) 2.6900 2020-10-14 Common Stock 60000 D Stock Option (right to buy) 2.6900 2020-12-21 Common Stock 50000 D Stock Option (right to buy) 5.5400 2021-05-02 Common Stock 100000 D 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 April 1, 2010 and vests in equal quarterly installments thereafter until January 1, 2013. 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. This option vested as to 1/6th of the shares on January 1, 2011 and vests in equal quarterly installments thereafter until July 1, 2013. This option vested as to 1/12th of the shares on August 1, 2011 and vests in equal quarterly installments thereafter until May 1, 2014. /s/ Jeffrey A. Munsie, attorney-in-fact 2012-02-01