NEW YORK (AP) — Shares of the Princeton, New Jersey, company Bristol-Myers Squib plunged 17 percent when trading opened Friday.
Shares of rival Merck & Co., which makes a rival cancer drug, spiked 8 percent to reach a one-year high.
Bristol's drug, Opdivo, and Merck's drug Keytruda are immunotherapies, which bolster the immune system so that patients can better fight cancer. Both drugs are already approved to treat melanoma and lung cancer, but only after chemotherapy.
In June, Merck reported positive results from a key study focusing on Keytruda as a lone treatment for lung cancer. The negative results from Bristol appear to put Merck in the lead for treating cancer patients without resorting to chemotherapy and its drastic side effects.
The latest late-stage study for Opdivo involved 541 patients who had received no prior treatment for lung cancer.
"We remain committed to improving patient outcomes through our comprehensive development program," said Bristol-Myers CEO Dr. Giovanni Caforio.
Shares of Bristol-Myers Squibb Co. slumped $12.82 to $62.50.