ORLANDO, Fla. -- There's word of medical success in the treatment of men with advanced prostate cancer.

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In a study of 127 men with prostate cancer, researchers at the University of California in San Francisco found that a new vaccine trains the immune system to fight tumors.

The vaccine, called Provenge, made by Dendreon Corp., improved the survival rate to 34 percent at the end of three years, compared to 11 percent who received placebo treatments. Men who received the vaccine treatment lived an average of 4½ months longer than those who received a placebo.

Dr. Eric Small will present the findings Saturday at the 2005 Multidisciplinary Prostate Cancer Symposium, which begins Thursday in Orlando.

"The survival benefit seen with Provenge is the largest ever reported in this patient population with any therapy," Small said in a Dendreon news release.

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.

Experts caution that additional research is needed.