May 1 (Reuters) - Merrimack Pharmaceuticals Inc said its experimental cancer drug, when used in combination with two other drugs, improved the overall survival rate in patients with metastatic pancreatic cancer in a late-stage study.

The company said the combination showed an overall survival of 6.1 months, compared with 4.2 months shown by the other two drugs in patients who were earlier treated with chemotherapy drug gemcitabine.

(Reporting by Vrinda Manocha in Bangalore; Editing by Sriraj Kalluvila)