Bristol-Myers Squibb Co. said its blockbuster drug Opdivo was not better than chemotherapy in prolonging the lives of patients with small-cell lung cancer, a hard-to-treat, aggressive type of the disease.

The company was studying the medicine against chemotherapy in a late-stage clinical trial called CheckMate-331, which failed to meet its main goal of overall survival. Patients enrolled in the study had seen their disease return after platinum-based chemotherapy.

The drug's safety profile was consistent with the previous findings in trials involving small-cell lung cancer, or SCLC, patients.

Opdivo is only approved for SCLC patients in the U.S. whose disease has spread across the body and whose disease progressed after platinum-based chemotherapy and at least one other line of therapy.

SCLC accounts for about 10% to 15% of all lung cancers. About 27,000 cases of SCLC are expected to be diagnosed in the U.S. in 2018.

Opdivo, a so-called immune checkpoint inhibitor, is approved for multiple cancer types, including a type of melanoma. It uses the body's immune system to fight disease.