X0306 4 2013-11-29 0 0001274792 MERRIMACK PHARMACEUTICALS INC MACK 0001368753 Sinskey Anthony J C/O MERRIMACK PHARMACEUTICALS, INC. ONE KENDALL SQUARE, SUITE B7201 CAMBRIDGE MA 02139 1 0 0 0 Common Stock 2013-11-29 4 P 0 3800 3.915 A 392543 D /s/ Jeffrey A. Munsie, attorney-in-fact 2013-12-03