The benefits of Genentech's cancer drug Avastin in breast cancer should be weighed against some toxic side effects, including the potential for death, U.S. regulatory staffers said in documents released Monday.
Genentech shares were down as much as 2.86 percent Monday on the New York Stock Exchange.
The U.S. Food and Drug Administration staff review comes ahead of a Wednesday advisory panel on a bid by Roche Holdings and U.S. partner Genentech to extend use of Avastin, already approved to treat lung and colon cancer, to patients with breast cancer.
The expert panel will give advice to the FDA on broadening use of the drug as a first-line treatment for patients with breast cancer whose disease has spread.
The drug already reaps blockbuster sales, $2.65 billion in the first nine months of this year.
In a key trial, the drug failed to extend overall survival, although it did meet its primary goal of extending "progression-free survival," the probability that a patient will remain alive, without the disease getting worse.
A 5-1/2-month improvement in progression-free survival "must be weighted against the increased toxicity, including deaths associated" with the drug, FDA staffers wrote in an executive summary, posted on FDA's Web site.
Patients in the study were given either a commonly-used treatment called paclitaxel, or paclitaxel combined with Avastin, known generically as bevacizumab.
Among 722 total patients, those in the Avastin group had a 20 percent increase in serious toxicity, including hypertension, blood clots, and heart attacks, among other side effects, the FDA staff said.
Death attributed to the drug by the FDA was about 1.7 percent of the Avastin group, versus zero in the control group.
The FDA staff disagreed with Genentech's causes of death in some instances.
"Most importantly," staffers wrote, in the Avastin arm "five out of twelve deaths were found to be possibly/definitely related to" treatment.
Roche participation certificates, its most widely traded form of equity, were 2.5 percent lower on Monday.