Yesterday, the FDA posted its review of Genentech's (NYSE:DNA) marketing application to expand the Avastin label to front-line metastatic breast cancer patients. Anyone betting on Avastin's approval in this indication had better think twice.

On Wednesday, an FDA advisory committee is set to meet and discuss whether cancer therapy Avastin, which is already approved to treat colorectal and lung cancer, should be approved as a treatment for breast cancer.

Genentech filed a supplemental Biologics License Application to expand the Avastin label in May 2006. But the FDA rejected the application, because of what it described as an "incomplete" and "inadequate" set of data accompanying the application.

Now that Genentech's finally collected all the requested data, this advisory-panel hearing lets the agency gather recommendations ahead of its Feb. 23 review for Avastin's label expansion.

From the briefing document (PDF file) that the FDA submitted for the advisory panel hearing, the agency seems unconvinced that Avastin's benefits for late-stage breast cancer patients outweigh its risks.  

Avastin was tested in two phase 3 studies as a treatment for breast cancer. In both studies, the drug failed to show any statistically significant overall survival benefits, but in one, it did show a rather large progression-free survival (PFS) benefit.

The FDA primarily wants the advisory panel to decide "whether an estimated 5.5 month improvement in median PFS, with no statistically significant improvement in (overall) survival" is good enough for the agency to approve Avastin for breast cancer treatment.

The FDA telegraphed its own feelings on the matter in these three telling excerpts in the discussion section of its briefing document:

  • "It is important to stress that for FDA-approved therapeutic proteins and cytotoxic drugs for this (front line breast cancer) and other settings, previous studies have demonstrated prolongation of life ..."

  • "... the requirement for a favorable effect on survival is important for proof of drug efficacy as well as demonstration of safety (toxicity) ..."

  • "... it is not always possible to discern whether the cause of death (from any drug) is due to drug toxicity or tumor progression, or both. Survival is the net effect of deaths from both tumor and drug toxicity. Whether the lack of survival advantage observed in the (Avastin breast cancer) trials is due to the increased toxic effect of (Avastin) in breast cancer patients, is not known." (Emphasis mine)

Those three statements suggest that the agency won't be convinced by Genentech's arguments until the company can prove that Avastin also increases overall survival for breast cancer patients. The FDA rarely approves a compound without being certain that its benefits exceed its risks.

GPC Biotech (NASDAQ:GPCB) was set to receive a similar rebuff from the agency this year, after trying to get its chemotherapeutic approved based on PFS data (which I erroneously expected to produce positive overall survival data). Dendreon's (NASDAQ:DNDN) prostate-cancer treatment also received an approvable letter in May, after the FDA wasn't completely convinced on its overall survival evidence.

Unless tomorrow's advisory panel provides extremely strong reasoning for approving Avastin on the evidence of PFS benefits alone, Genentech and its investors should expect another approvable letter come January.

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Fool contributor Brian Lawler does not own shares of any company mentioned in this article. The Fool has an A-plus disclosure policy.