The approach is called a cancer vaccine although unlike traditional vaccines, it treats disease rather than prevents it.
In a study of 127 men with advanced prostate cancer, those who got the vaccine lived an average of 4 1/2 months longer than those who were given fake treatments. After three years, survival was 34 percent in the vaccine group and only 11 percent in the other.
"That's a huge difference. These are people who have relatively few options, with limited survival," said Dr. Eric Small of the University of California in San Francisco, who led the study and will give results at a first-of-its-kind prostate cancer research meeting that opens Thursday in Orlando.
The meeting is intended to bring more muscle to fighting the disease, which is the most common non-skin cancer in American men. About 230,000 new cases and 30,000 deaths from it are expected this year.
The vaccine, called Provenge, doesn't work like chemotherapy, and its side effects typically are only a couple days of fevers and chills, like what people feel when they are fighting off a cold.
The vaccine combines a protein found in most prostate cancers with a substance that helps specialized immune system cells recognize cancer as a threat, just as they recognize and confront germs that enter the body.
The treatment is customized for each patient. Doctors collect immune system cells from a patient's blood, mix them with the vaccine, and then give the concoction back to the patient in three infusions over a month.
In the study, men treated with Provenge survived an average of 26 months compared with 21.4 months for those who received dummy vaccine. After three years, 28 of the 82 men who got the vaccine were alive but only five of the 45 in the placebo group were.
"This is provocative, it is promising. We now need to confirm this with an independent study," said Dr. Philip Kantoff, a Harvard Medical School professor who heads prostate cancer treatment at the Dana-Farber Cancer Institute in Boston. He was not involved in the study.
He and other specialists noted that the study didn't achieve its primary goal of delaying the time when men's disease worsened — something that could be expected if the vaccine were truly helping men live longer.
"Time to progression is interesting but it isn't the gold standard. The gold standard is survival. We've improved survival," Small countered.
Neither Small nor Kantoff has any financial ties to the vaccine or its maker, Seattle-based Dendreon Corp.
If a second study in about 100 men gives similar results later this year, Dendreon will seek Food and Drug Administration approval for Provenge, which already is being fast-tracked by the agency, said the company's president, Dr. Mitchell Gold.
Dendreon also is testing Provenge for less serious cases of prostate cancer. Partial results from one such study are to be presented at the meeting on Saturday.
"We see it moving into earlier and earlier stages of disease," Gold said of Provenge.
Another Dendreon vaccine, Neuvenge, is being tested for advanced breast cancer. A very large nationwide study also is testing a different type of cancer vaccine for the deadly skin cancer melanoma.
Dr. Durado Brooks, who heads prostate cancer research for the American Cancer Society, said Dendreon's vaccine is the farthest along for prostate cancer.
"Is it ready for market? I don't know," he said, but called the new results encouraging.