A new immune system treatment for advanced prostate cancer is safe and effective enough to begin U.S. sales, a panel of FDA advisors concluded Thursday.

Many experts said they were uneasy about backing the vaccine-like treatment, known as Provenge, because it showed only slight evidence that it prolongs the lives of men with the disease. But most agreed to recommend approval anyway, citing the scant options available to patients, many of whom are facing a terminal illness.

"I wish we all could have voted ‘maybe’ on this, but I don’t think we can," said Farshid Guilak, PhD, a professor of surgery at Duke University who was a member of the panel.

New Treatment Class

Dendreon Corp., the biotech firm that makes Provenge, touted the treatment as the first cellular therapy against cancer. To undergo treatment, patients have immune cells removed and treated with immune agents.

The cells are then reintroduced into the body with chemical programming that, in theory, allows them to mount an immune response against cancer cells.

Men with advanced prostate cancer often undergo hormone treatment used to block the action of testosterone and related hormones. The treatment can cause disturbing side effects, including breast enlargement and sexual dysfunction.

Prostate Cancer: Combo Treatment Works

Limited Evidence

A pair of studies suggested Provenge may slow by one to two weeks the progression of prostate cancer in men who have cancer that does not respond to hormone treatment.

Men who used the treatment also showed some evidence of living longer than those who took a placebo. In one trial, men who got active treatment lived an average of 3.3 months longer. In another, they lived four and a half months longer.

Experts criticized the studies for enrolling only roughly 100 to 130 patients, a relatively small number that can limit scientists' ability to interpret results.

But most said they support Provenge anyway, given the limited choices for men with advanced disease.

"If we can buy them a couple of minutes or a couple of months or a couple of years, then it's our obligation to do that," said Robert J. Samuels, a member of the panel who said he was diagnosed with prostate cancer 13 years ago. "We understand it’s a risk. But it’s a risk most of us are willing to take."

Dendreon argued their studies showed the product has benefit. "Even though small, you can take the results with a great deal of confidence," said Mark Froelich, the company’s vice president for clinical affairs.

The company is conducting a third study to test whether it improves survival in more than 400 patients. Experts said the results of that trial should have a heavy bearing on whether the FDA decides to approve Provenge.

Federal regulations compel the FDA to make a decision on the treatment by May 15. The agency isn’t forced to follow advisory panels’ recommendations, but it usually does.

Approximately 27,000 American men will die of prostate cancer in 2007, according to estimates from the American Cancer Society. Dendreon estimates 27,000 patients per year could be candidates for Provenge.

Several experts said the company had not established that Provenge works, but then voted to back it once FDA officials told them to base their votes only on the question of whether the evidence was "substantial."

Panelist Richard Alexander, MD, chief of urology at the VA Maryland Health Care System, in Baltimore, voted against approving the drug. "But very close," he said.

Several patients testified before the committee about the need for more therapies, even ones of questionable benefit.

Patients "are pleading for something other than the one drug that’s been approved in the last 30 years," said Jim Kiefert, chairman of Us Too, a nonprofit group for prostate cancer patients.

Statins vs. Advanced Prostate Cancer

By Todd Zwillich, Reviewed by Louise Chang, MD