0001274792 2020-11-05 2020-11-05 MERRIMACK PHARMACEUTICALS INC false 0001274792 8-K 2020-11-05 DE 001-35409 04-3210530 One Broadway 14th Floor Cambridge MA 02142 (617) 441-1000 Common stock, $0.01 par value per share MACK NASDAQ false false false false false