In a breakthrough for tens of thousands of men suffering from prostrate cancer, Dendreon Corpn.'s experimental cancer vaccine has been seen to improve three-year survival of patients with advanced prostate cancer by 38% compared with placebos.

The 512-patients, who participated in the tiny bio-tech company's study lived an average 4.1-months longer taking Dendreon's Provenge, than those taking placebos, with no major adverse side-effects in the late-stage clinical trial, according to researchers. Chills, fever and headache lasting one to two days following infusion are the only adverse events seen in patients taking Provenge, an enormous advantage over chemotherapy's typically debilitating side effects.

According to data from the closely watched study unveiled on Tuesday, patients lived 25.8-months after taking the vaccine as compared with 21.7-months for those taking placebos.

Dr. David Penson, associate professor of urology at the University of Southern California presenting the study's data at the American Urological Association meeting in Chicago believes if the drug becomes commercially available in the United States, it will replace chemotherapy.

The results further raise the likelihood that Provenge, known chemically as sipuleucel-T, will become the first approved therapeutic vaccine for any type of cancer, as Dendreon plans to seek U. S. approval in the fourth quarter of 2009.

A pretty significant breakthrough, the vaccine works on large tumours with minimal toxicity. Unlike traditional vaccines used to prevent disease, Provenge works by stimulating the body's own immune system to attack cancer cells. If approved, Provenge, administered in three doses at two-week intervals, will be the first cancer immunotherapy on the market.

Dendreon says it will not look for a U. S. marketing partner for Provenge, however, it will consider an overseas partnerships for the drug.