FDA Panel Backs Prostate Cancer Vaccine

Studies show it extends life of patients with metastatic disease by several months

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THURSDAY, March 29, 2007 (HealthDay News) -- A U.S. Food and Drug Administration advisory panel voted Thursday to support approval of Provenge, a vaccine aimed at extending survival for patients with deadly metastatic prostate cancer.

The FDA panel voted unanimously that the vaccine was "reasonably safe," noting that while it failed to meet some study endpoints, it did extend patient survival, according to published reports.

The panel then voted 13-to-4 to say there was substantial evidence to show the vaccine was effective for treating advanced prostate cancer that no longer responds to standard hormone treatment.

The FDA does not have to follow the advice of its advisory panels, but it typically does. The agency is expected to make its final decision by May 15.

Hopes have been high for the vaccine, which researchers said was the first ever shown to have an impact on cancer patients' survival. Those claims were based on a three-year study, released early in 2005, of 127 men with advanced, metastatic prostate cancer.

The trial found that patients infused with Provenge experienced an average 18 percent increase in survival, compared to those on a placebo. That worked out to 4.5 months of extra survival -- 25.9 months for those receiving Provenge vs. 22 months for those not taking the vaccine.

Provenge was developed by Seattle-based Dendreon.

"The concept behind the vaccine is to try to stimulate the patient's own immune system to recognize the prostate cancer cells and keeps them in check," said Dr. Simon Hall, a prostate cancer specialist at Mount Sinai Medical Center in New York City who worked on the trials for the vaccine.

In one phase III trial, men who had metastatic prostate cancer were three to four times more likely to be alive three years after vaccination, Hall said.

"However, the intent of that trial was not to show survival," Hall said. "The intent was to see if you could get patients to delay pain or new lesions in their bones. But they found it had no effect on that."

Before the panel met Thursday, FDA officials had expressed some reservations about the data submitted by Dendreon.

"The submitted data tend to support a finding of clinically meaningful increased survival, but doubts remain about the persuasiveness of the efficacy data," agency officials stated in documents released ahead of the meeting.

The advisory panel also noted that neither of the two studies submitted by Dendreon convincingly showed that Provenge met the primary goal of delaying progression of prostate cancer.

As reported by UPI, an increase in the frequency of "cerebrovascular accidents," such as stroke in men treated with Provenge, also "constitutes a potential safety concern," the FDA said. Stroke risk was 3.9 percent in treated patients compared to 2.6 percent in patients receiving a placebo.

Besides promising a potential benefit to men with prostate cancer, the therapy gives "proof of principle" to the idea that immune-based treatments can have a real impact on prostate cancer and other malignancies, experts said.

"There have been many failures with this kind of approach, and many have wondered if we shouldn't set the bar lower, somehow lower our expectations, and not hope for extended survival," Dr. Bruce Roth, a prostate cancer researcher at Vanderbilt University, told HealthDay when the 2005 study was released.

"But these findings are saying, 'No, looking for a survival advantage is a valid endpoint to look at for these agents,'" he said.

If caught early, prostate cancer remains very curable. However, despite advances in early detection, the disease remains the second leading cancer killer of U.S. men, according to the American Cancer Society. Even among men who develop the disease while it is still confined to the prostate, between 30 percent to 40 percent will experience a recurrence in years to come.

Because prostate cells depend heavily on testosterone to grow, therapies that reduce levels of circulating testosterone are often the first course of action in men who experience a recurrence. However, prostate cancer cells gradually grow resistant to hormonal therapy, and until very recently, doctors could only offer patients palliative therapies once that relapse occurred.

Hall said there was a new trial underway that was starting to confirm the survival results from the first study.

One advantage of the vaccine is that it has fewer side effects than chemotherapy, Hall added.

"The vaccine doesn't cure the disease, but it controls the disease for a period of time," he said. "And it is much less toxic than chemotherapy."

More information

For more on prostate cancer, head to the American Cancer Society.

SOURCES: Simon Hall, M.D., oncologist, Mount Sinai Medical Center, New York City; Bruce Roth, professor, medicine and urology, Vanderbilt University, Nashville, Tenn.; UPI

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