Dendreon Corporation recently reported encouraging phase III study results for Provenge, a “vaccine” that uses a patient's own immune system to fight advanced prostate cancer. The results offer hope to men with advanced disease, though it may be some time before they see the vaccine, which has yet to be submitted to the FDA for approval.

Over 500 men with advanced prostate cancer that was no longer responding to hormone therapy were enrolled in the study. Two thirds of the men received 3 infusions of Provenge over the course of a month; the other third received a placebo.

The men who received Provenge infusions lived an average of 4 months longer than men who were getting the placebo. The 3-year survival rate for the men getting Provenge was 32%, compared to 23% for placebo.

"These results confirm the clinical value of Provenge to prolong survival in patients with advanced prostate cancer. Moreover, it validates the longstanding but elusive aspiration to harness a patient's own immune system to fight cancer," said one of the lead researchers, Philip Kantoff, MD, head of the prostate cancer program and chief of the division of solid tumor oncology at the Dana-Farber Cancer Institute and Harvard Medical School.

Patients receiving Provenge reported few side effects, and those they did report -- chills, fever, headache, fatigue, shortness of breath, vomiting, and tremor – usually went away within a few days.

These initial study results were presented at a scientific meeting, but the full results have not yet been published in a peer-reviewed medical journal. However, the findings echo those of a previous, smaller study.

"Provenge suggests that we may in fact be able to stimulate our body's own defense mechanisms to aid our fight against cancer. This in itself is a truly remarkable accomplishment,” said Len Lichtenfeld, MD, deputy chief medical officer of the American Cancer Society.

But, he says, there are some “potential pitfalls” of the study and says that a “more detailed analysis and publication of the results—not to mention review by the FDA—still must be done.”

For one, while Provenge improved survival, there was no evidence that the drug slows progression of the disease.

"Usually, the situation is the other way around: the new drug delays progression of the disease, but may not increase survival. The normal way we think suggests that delay of progression is necessary before you see a survival benefit. That did not happen with Provenge. So, did the men who receive the placebo have something happen to them that may have shortened their lives compared to those who received Provenge? It isn't likely, but it is possible," said Lichtenfeld.

Dendreon plans to submit the drug for FDA approval later this year.

This won't be the first time the drug has crossed the FDA's desk. In 2007, the FDA refused to grant the drug accelerated approval, requesting more information about whether the drug prolongs survival.

"The sooner we can see all of the data from the study, the sooner we can move forward with getting this drug to men who need it if it indeed meets the expectations that have been set with the release of today’s results. That would be true progress,” said Lichtenfeld.

Men with advanced prostate cancer often have few treatment options available to them. Drugs that affect the body’s hormone levels are often effective for a time, but eventually the cancer stops responding to them. Chemotherapy helps some men at this point, but can have its own serious side effects.

Provenge is just one of several prostate cancer "vaccines" in development. Another, known as PROSTVAC-VF, uses a virus that has been genetically modified to contain prostate-specific antigen (PSA). The patient's immune system should respond to the virus and begin to recognize and destroy cancer cells containing PSA. The drug is still in early-stage clinical trials.

For more information about prostate cancer vaccines and other treatments, see the American Cancer Society’s Detailed Guide: Prostate Cancer, especially the section "What's New in Prostate Cancer Treatment?"

Reviewed by: Members of the ACS Medical Content Staff