Will Dendreon's Cancer Vaccine Win Final Approval?

In a surprise move, an FDA advisory committee Thursday recommended approval of the cancer immunotherapy Provenge from Dendreon (DNDN). The drug treats prostate cancer, but it missed its endpoint in a Phase III trial, which was to extend the time-to-progression in prostate cancer patients whose disease did not respond to hormone therapy.

A subsequent analysis showed that the drug extended median survival by 4.5 months, raising it to 25.9 months from 21.4 months. The result was statistically significant, though the trial, which enrolled just 127 patients, was small. In an even smaller trial, the median survival increased only 3 months, missing the level of statistical significance.

Currently, Dendreon has Provenge in a larger trial, involving 500 patients, which is due to finish in 2010.

The news of the FDA recommendation had a powerful effect on the shares of Dendreon. They opened with a clear triple at $18. The stock closed Wednesday at $5.22 (it did not trade on Thursday while the FDA was discussing the drug). After an hour of trading, Dendreon was still up 166% at $13.85, a gain of $8.63. The news also had a positive effect on Cell Genesys (CEGE), which is developing a competitor immunotherapy for prostate cancer with Medarex (MEDX). Cell Genesys was 21% higher, rising 74 cents to $4.24.

The panel voted 13-4 in favor of considering Provenge effective. The tally was 17-0 in favor of calling Provenge safe. There is some worry that the drug causes strokes, but that hasn’t been proven. The only current competitor to Provenge is the chemotherapy taxotere, which does cause side effects. The FDA is scheduled to release its final opinion on Provenge on May 15. Usually, the agency follows the advice of the Advisory committee.

The FDA could, conceivably, wait until 2010 to see more data before approving the drug.

In the Provenge treatment, a portion of the patient’s white blood cells are removed and sent to Dendreon. The cells are mixed with a genetically engineered protein that combines an immune system booster and a molecule found in prostate cancer cells but nowhere else. The idea is to make the patient’s own immune system fight the cancer, which is why the treatment is called a vaccine.

Immunotherapy treatments for cancer have been tried before. No one knows why the immune system does not recognize the cancer cells as foreign and fight to eradicate them from the body. But until now, the treatments have not been able to prove that they helped.

Disclosure: none.

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