Merck & Co said it paused enrolments in two late-stage studies testing its immunotherapy drug, Keytruda, for multiple myeloma, in combination with other therapies, as the U.S. drugmaker looks to better understand more reports of death in the Keytruda groups.
The company's shares were down 1.4 pct at $63.50 in after-market trading on Monday.
Merck said the action followed recommendation by an external data monitoring committee and that patients currently enrolled in the two studies would continue to receive the treatment.
The trials included combinations with Celgene Corp's Pomalyst and Revlimid.
Multiple myeloma is a type of aggressive and incurable blood cancer that develops in the bone marrow.
Keytruda belongs to a closely watched new class of drugs called PD-1 inhibitors that help the immune system fight cancer by blocking a mechanism tumors use to evade attack.
In May, Keytruda became the first cancer drug ever approved by the U.S. Food and Drug Administration based on a patients' specific genetic traits, regardless of where in the body the disease originated.
Keytruda is also approved to treat lung cancer, bladder cancer, advanced melanoma, as well as refractory classical Hodgkin lymphoma, a type of cancer that starts in white blood cells.
(Reporting by John Benny in Bengaluru; Editing by Sriraj Kalluvila)