Merck & Co Inc said on Wednesday it was discontinuing a late-stage trial of its blockbuster immunotherapy Keytruda in some prostate cancer patients after interim data showed it was unlikely to meet the study's main goals.

The interim analysis showed the therapy did not extend survival or help extend the time a patient lives without the disease worsening, the U.S. drugmaker said.

The drug was being tested in combination with androgen deprivation therapy and Xtandi, made by Pfizer Inc and Astellas Pharma Inc, in patients with hormone-sensitive prostate cancer that has spread to other parts of the body.

Separately, Merck said Keytruda in combination with a chemotherapy showed significant improvement in overall survival in patients with an advanced type of bile duct cancer.

The drugmaker's shares fell marginally to $107.86 in premarket trading.