The biotech is hoping to win recommendation from an FDA panel on Wednesday to peddle Avastin as a treatment for breast cancer. But data posted on the FDA web site today suggests this may be a hard sell. The med failed to help breast cancer patients live longer and had serious side effects, including deaths, according to the FDA. Wall Street reacted by beating up Genentech stock on very heavy volume.

The drug, which is currently approved as a part of a regimen for treating colon and non-small cell lung cancer, did slow the spread of metastatic breast cancer by an extra 5.5 months when used chemo, compared with patients who received only chemo. But Avastin patients had a 20 percent increase in serious side effects, and the med didn’t show a statistically significant ability to extend lives, according to the FDA. Patients receiving Avastin lived an average of 1.7 months longer than those given only chemo, but that wasn’t statistically significant. (This is the briefing document).

Of the 363 patients in the study, 1.7 percent who took Avastin died from side effects, compared with none of the 348 people on chemo, the FDA medical reviewers wrote. Those side effects included high blood pressure, blood clots and heart attack. A separate clinical trial of patients who took Avastin after relapsing on chemo found the med failed to slow cancer or extend lives, the FDA noted. UPDATE: An advocacy group, Breast Cancer Action, is urging the FDA to reject approval because the evidence makes “sick women guinea pigs.” (see below).

Genentech is seeking FDA approval of Avastin as a breast-cancer treatment in combination with Taxol in women with advanced breast cancer who previously haven’t received chemo. But any benefit in slowing cancer “must be weighed against the increased toxicity,” the FDA reviewers wrote.

“The market is expecting the FDA’s expert panel to vote negatively against Avastin in metastatic breast cancer, which could wipe $1 billion off estimates” for additional revenue, Martin Voegtli, an analyst at Sal Oppenheim in Zurich, tells Bloomberg News.

The FDA does not love progression-free survival as a primary endpoint… (and) there’s still the issue of whether tumor shrinkage equates with prolonged surivival,” write Jim Reddoch, an analyst with Friedman Billings Ramsey, in an investor note this afternoon. “Avastin in breast cancer is important, because it’s the next growth for the drug. Odds are the panel is fine, but there’s definitely more downside than upside.”

Meanwhile, Breast Cancer Action is urging the FDA to deny approval if no benefit in overall survival is shown. “To date, the data Genentech has made available indicate that Avastin delays time to progression of metastatic disease, but there is no indication that it improves patient survival. The use of surrogate end points like time to progression, which are used as an early indicator of a drug’s effectiveness, are meaningless unless that end point is shown to correlate with overall survival,” the group writes in an e-mail.

“BCA looks forward to the day when we can say with confidence that a drug is effective at increasing survival for women with metastatic breast cancer. However, approving Avastin based on the kind of evidence currently available makes very sick women guinea pigs for evaluating the long-term effects of the drug, as well as its dangers,” says BCA executive director Barbara Brenner.