Prostate Cancer Provenge Strong in Trial

April 29, 2009 - A novel, experimental treatment vaccine improved the survival of men with advanced prostate cancer in the largest trial yet of the therapy, researchers reported Tuesday.

The vaccine, known as Provenge, is poised to become the first treatment to employ the immune system in the fight against cancer, but the road to approval has been a rocky one.

Details of the new trial were made public at the annual meeting of the American Urological Association in Chicago.

Mitchell Gold, CEO of the Seattle-based biotech company Dendreon, which makes the vaccine, called the results from the company’s latest trial “unambiguous.”

“Today, Dendreon, our employees, and the scientific community have made a major step forward in demonstrating that the immune system can be harnessed in the fight against cancer,” he said in a presentation Tuesday afternoon. “We hope and sincerely believe that this is just the beginning of a new era in medicine.”

But American Cancer Society Chief Medical Officer Otis W. Brawley, MD, was more restrained in his enthusiasm.

While acknowledging that Provenge may prove to be an important new cancer treatment, Brawley tells WebMD that closer scrutiny of trial results is needed.

Men in the study who got the experimental immunotherapy lived, on average, four months longer than men in the placebo group of the study.

“At best, this is an effective treatment,” he says. “It is not a cure for metastatic prostate cancer.”

Provenge Patients Lived Longer

The study included 512 men with advanced prostate cancer who had stopped responding to hormone-blocking treatments and who had few other treatment options.

Only one approved treatment -- the chemotherapy drug Taxotere -- has been shown to improve survival in men with metastatic prostate cancer.

Active treatment consisted of three injections of Provenge given over the course of a month. Half the patients were treated with the immunotherapy and the other half got placebo treatments.

Side effects were mild; consisting mainly of flu-like symptoms that resolved within a few days, study co-author David Penson, MD, of the University of Southern California’s Keck School of Medicine, said in a Tuesday afternoon news conference.

Penson also revealed that:

• Provenge improved three-year survival by 38%, with about 31% of patients who got the immunotherapy surviving this long, compared to 23% of the placebo-treated patients.
• Average survival among patients who got the active vaccine was slightly less than 26 months, compared to 22 months among patients in the placebo arm.
• The survival advantage seen among the Provenge-treated patients was similar to that reported in two smaller, company-sponsored trials comparing the immunotherapy to placebo. Patients in the three trials lived, on average, between 3.3 and 4.5 months longer than the placebo-treated patients.
• There was no statistically significant difference in disease progression between the two treatment groups. The two previous trials also failed to show that Provenge slows the progression of disease.

Dendreon plans to seek approval of the immunotherapy drug later this year, Gold said.