Bristol-Myers Squibb said its blockbuster immunotherapy, Opdivo, failed to improve survival in previously untreated patients with a form of lung cancer, without their disease progressing.
Bristol-Myers' shares were down 20 percent at $60 in premarket trading. Shares of Merck & Co, which makes rival drug Keytruda, were up 11 percent at $64.60.
The trial was testing Opdivo against chemotherapy in patients with advanced non-small cell lung cancer (NSCLC).
Opdivo, first approved in late 2014, is already approved for use in NSCLC patients who have failed prior therapy, as well as forms of melanoma, kidney cancer and blood cancer.
— CNBC contributed to this report.