(Reuters) - Merrimack Pharmaceuticals Inc said its lead experimental cancer drug when used as a combination improved the overall survival rate in patients with metastatic pancreatic cancer, doubling its shares in premarket trading.
Merrimack said a combination of its drug, MM-398, and two others showed an overall survival of 6.1 months, compared with 4.2 months shown by the other two drugs alone.
The company said on Thursday it would apply for a U.S. marketing approval for the combination this year.
The late-stage study was testing the drug in patients who were earlier treated with chemotherapy drug gemcitabine.
The trial tested MM-398 in combination with another chemotherapy drug 5-fluorouracil (5-FU) and leucovorin, which helps enhance 5-FU's effectiveness.
Merrimack said its drug showed an overall survival of 4.9 months when used alone, which was not statistically significant.
The company said the most common serious adverse events in patients given the combination were an abnormally low count of a type of white blood cells, fatigue, diarrhea and vomiting.
Merrimack said patients taking only MM-398 experienced a higher level of adverse events than those who received the drug combination.
About 46,420 new cases of pancreatic cancer will occur in the United States in 2014, according to the American Cancer Society.
The company is also testing the drug as a treatment for colorectal cancer, a type of brain tumor and a rare form of bone cancer.
Merrimack's shares were trading at $8.10 before the bell after closing at $4.39 on the Nasdaq on Wednesday.
(Reporting by Vrinda Manocha in Bangalore; Editing by Sriraj Kalluvila)