Genentech Halts Trial of Avastin

Genentech Inc. halted a clinical study Friday after ovarian cancer patients taking the drug Avastin suffered serious side effects.

After the announcement, Genentech’s shares fell. Avastin, already approved for the treatment of colon cancer, is considered Genentech’s most promising drug, so investors are sensitive to bad news.

Genentech said it stopped accepting participants in the ovarian cancer study after five of 44 patients suffered bowel tears. Although Avastin is known to cause such perforations, the percentage of patients suffering from them in the trial was higher than seen in other studies for reasons that were unclear.

The clinical trial was testing Avastin as a treatment for ovarian cancer in patients whose disease did not respond to chemotherapy drugs containing platinum.

South San Francisco-based Genentech said it hadn’t given up on ovarian cancer and that other studies were planned. Few bowel tears were seen in earlier ovarian cancer trials, the company said. Clinical tests of Avastin also are underway involving cancers of the lung, breast, prostate, kidney and pancreas.

Jim Reddich, an analyst with Friedman, Billings, Ramsey & Co., said in a note to clients that Avastin might not reach its peak sales potential of $7 billion if doctors became worried about safety. The drug is expected to have sales of $1 billion this year.

Shares of Genentech fell $2.17 to $85.83.