Dendreon's Vaccine for Prostate Cancer Extends Life in Published Study

Dendreon Corp.’s prostate cancer vaccine, Provenge, extended lives by 4.1 months in a study published in the New England Journal of Medicine. The data, released previously, led to the drug’s U.S. approval in April.

Provenge is the first drug designed to train the body’s immune system to fight cancer and is the most effective treatment for certain patients with advanced prostate tumors, said Philip Kantoff, a professor of medicine at Harvard Medical School and the study’s lead author. Researchers still don’t know precisely how the vaccine works or who is most likely to benefit, he said.

As many as 100,000 prostate cancer patients are eligible to receive Provenge, though Dendreon has said it has capacity to accommodate just 2,000 patients in the first year. Dendreon shares have increased eightfold since today’s published results were first presented at a science meeting in April 2009. In the last three months the shares have tumbled about 40 percent amid supply shortages and concern over whether U.S. government’s Medicare program will pay for the $93,000 treatment.

“I think we need to better detect how it works and how it can be made better,” said Harvard’s Kantoff, who is also chief of solid tumor oncology at the Dana-Farber Cancer Institute in Boston, in a telephone interview. “This is really the first step in the field of immunotherapy,”

Provenge takes a new approach to treating cancer. Doctors draw blood from the patient’s body and produce a personalized dose of the vaccine. Results from the study, being published today, in 512 patients were consistent with two smaller studies that failed to convince U.S. regulators to approve the drug in 2007, researchers said.

Patients in the study had a median survival of 25.8 months with Provenge, compared with 21.7 months with a placebo. The men had advanced tumors that had overcome available treatments.

Mystery Mechanism

Patients who had a strong antibody response to Provenge were more likely to live longer, indicating a possible signal of how the drug works, according to the study. However, the drug didn’t shrink tumors or delay malignancy growth. The lack of a measurable effect on the cancer remains a mystery and could mean results were influenced by treatments or patient conditions that weren’t considered in the study, said Dan Longo, deputy editor of the journal, in an editorial that that accompanied the study.

“By the time the data was presented to the FDA, this was a pretty mature trial,” said Robert Dreicer, chair of solid tumor oncology at the Cleveland Clinic in Ohio and an author of the study, in a phone interview. “We still don’t know any more about the mechanism.

“These issues of cost and availability are going to affect how rapidly this is going to play into disease management,” Dreicer said.

Dendreon fell $1.47, or 4.2 percent, to $33.39 at 4 p.m. today in Nasdaq Stock Market composite trading.

To contact the reporter on this story: Tom Randall in New York at trandall6@bloomberg.net.

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