Nervous investors on Tuesday drove Genentech Inc.'s shares down 6% after the South San Francisco biotechnology company said six of 1,100 patients in an experimental cancer drug study had small tears in their bowels.
Genentech said it did not know whether the injuries were related to the cancer drug Avastin. None of the patients dropped out of the study, which should be completed by midyear, the company said.
Avastin is one of several potential biotechnology drugs being tested on humans that attack tumors by closing off the blood vessels that feed them. If the drug is successful, it could be an important product for Genentech, with annual sales in the hundreds of millions. It could also renew interest in development of similar drugs.
Consequently, investors are sensitive to any hint of bad news about Avastin. Last summer, investors pounded the stock after Genentech reported that Avastin in a test study did not prolong the lives of women with advanced breast cancer.
Genentech shares Tuesday fell $2.11 to $32.89 on the New York Stock Exchange.
The most recent drug trial is testing Avastin in patients with colon cancer that has spread to other organs. Patients are divided into two groups: One receives Avastin with chemotherapy and the other group receives chemotherapy alone. Genentech wants to see if patients on Avastin live longer.
It is not unusual for colon cancer patients to develop bowel perforations caused by their tumors, said Genentech spokeswoman Colleen Sweeney. The company did not know whether the six patients received Avastin, she said.
Analysts said patients probably would accept a small risk of bowel tears if Avastin works. "These are people with metastatic colon cancer who probably have only 8 to 12 months to live," said Eric Schmidt of SG Cowen.