Dendreon Shares Plummet After FDA Asks for More Data on Cancer Drug

Shares of Biotech drug maker Dendreon sank as much as 64% after the Food and Drug Administration requested more clinical data on the effectiveness of its prostate cancer treatment, Provenge, delaying the drug's approval.

The company received an "approvable" letter on Tuesday from the agency that also sought more information on the chemistry, manufacturing and controls of its application. Dendreon said it is seeking clarification on what kind of efficacy data the FDA needs, but believes it can supply the chemistry and manufacturing data promptly.

In late March, an FDA advisory committee reviewed Dendreon's application and agreed 17 to 0 that the submitted data showed Provenge was reasonably safe and 13 to 4 that the drug was shown to be effective.

"Given our strong belief in the survival benefit and safety profile of Provenge, coupled with the positive outcome of the advisory committee meeting, we are disappointed that this decision will cause a delay in the availability of Provenge for patients who suffer from advanced prostate cancer," said Mitchell H. Gold, president and chief executive of Dendreon.

Prostate cancer is the most common non-skin cancer in the U.S. and the third most common cancer worldwide. More than 1 million men in the U.S. have prostate cancer, with an estimated 218,890 new cases expected to be diagnosed in 2007.

Dendreon has said about 95% of prostate cancer cells contain an antigen called prostatic acid phosphatase, or PAP. Provenge is a new kind of cancer treatment designed to help a man's immune cells recognize those cells that carry PAP as foreign and attack them.

Provenge has been studied in a double-blind, placebo-controlled Phase 3 study that showed that a group of men with asymptomatic, metastatic prostate cancer who received Provenge lived an average of 4.5 months longer than those taking placebo. For the men taking Provenge, the study showed a 41% overall reduction in the risk of death, and 34% of patients were alive 36 months after treatment, compared with just 11% of patients receiving placebo.