SEATTLE – An experimental treatment that takes an entirely new approach to fighting prostate cancer extended survival in a late-stage study, its maker announced Tuesday.
Seattle-based Dendreon Corp. said that its Provenge cancer vaccine improved overall survival when compared to a dummy treatment in a study of 512 men with advanced disease.
No survival details or information on side effects were given. Full results will be presented at an American Urological Association meeting later this month, and Dendreon said it would seek federal approval of the treatment later this year.
Provenge is not like traditional vaccines that prevent disease. It's a so-called therapeutic vaccine that treats cancer by training the immune system to fight tumors. If approved, Provenge would be the first such treatment on the market.
This is the second major study in which Provenge has shown a survival benefit, leading some scientists to hope not just for its approval but for a new approach to fighting cancer beyond the surgery, radiation, hormones and chemotherapy used now.
"This is an exciting result, demonstrating that harnessing a patient's own immune system can successfully attack prostate cancer," said Dr. Eric Small, cancer specialist at the University of California at San Francisco. "Now we have more confidence that the initial results we saw were real."
He enrolled some patients in the new study and led the earlier one, but has no financial ties to the company or the vaccine.
In the earlier study of 127 men, those treated with the vaccine lived an average of 4 1/2 months longer than those given dummy treatments. After three years, survival was 34 percent in the vaccine group and only 11 percent in the other.
Those results led advisers to the Food and Drug Administration to recommend Provenge's approval two years ago. But the FDA delayed action and asked for more data, because extending survival wasn't the main goal of that study — slowing progression of the cancer was, and the vaccine failed to do that.
The decision sparked protests from men's groups and cancer advocates because the vaccine did prolong survival, which they considered a more important result.
Provenge is a treatment that is customized for each patient. Doctors collect specialized cells from each patient's blood. Those cells help the immune system recognize cancer as a threat, much as it would germs that enter the body.
The cells are mixed with a protein found on most prostate cancer cells to help activate the immune system. The resulting "vaccine" is given back to the patient as three infusions two weeks apart.
So far, the vaccine has been tested on men with cancer that has spread beyond the prostate and is no longer responding to hormone treatments to curb its growth.
If Provenge proves safe and wins approval, "it would be an important breakthrough," said Dr. William Oh, a cancer specialist at Dana-Farber Cancer Center in Boston. Three years ago, he consulted for Dendreon on the vaccine but has had no financial ties to it since then.
"There are so few treatments available" for men whose prostate cancer has spread widely — a situation that affects 40,000 to 60,000 American men, he said.
Prostate cancer is the most common non-skin cancer in American men. An estimated 186,000 new cases and 28,660 deaths from it occurred last year.