A panel of government advisers said that Genentech drug Avastin should not be approved for expanded use in breast-cancer patients.
Shares of Genentech's European Avastin partner Roche Holdings sank 4% in Swiss trading Thursday.
After weighing evidence on whether the drug meaningfully improves life for patients with advanced breast cancer, Food and Drug Administration advisers voted 5 to 4 against recommending approval. FDA is not required to follow the recommendations of its panel, though it usually does.
Shares of Genentech fell 6.58, or 9 percent, to $66.20 before trading in the stock was halted.
South San Francisco, Calif.-based Genentech asked the FDA to approve the drug for use alongside chemotherapy for breast cancer patients.
Prior to the meeting, FDA scientists said that while Avastin slowed the progression of cancer, it did not improve patients' lifespan overall. Scientists questioned whether the drug should be approved for the new use, considering side effects, which include heart attack, hypertension and blood clots.
Avastin is currently approved for patients with certain types of colon and lung cancer. It was the company's second best-selling product last year with revenue of $1.7 billion.
The negative panel vote Wednesday is the second FDA-related setback for Avastin as a breast cancer therapy. Last September the FDA asked the company to resubmit medical scans showing cancer progression in patients. The agency is scheduled to make its final decision on Avastin in February.