The experimental prostate cancer treatment Provenge improved overall survival in men with advanced stages of the disease, bolstering the chances of it becoming the first approved therapeutic vaccine for cancer, the drug-maker Dendreon Corp said on Tuesday.

The late-stage clinical trial met the main study goal of improving survival, prompting the company to announce that it will seek U.S. regulatory approval of Provenge in the fourth quarter.

“The successful outcome from the phase III IMPACT study provides validation of the long-pursued goal of harnessing the human immune system against a patient’s own cancer,” Dendreon Chief Executive Mitchell Gold said in a statement.

Unlike traditional vaccines that prevent disease, Provenge treats it.

The study included 512 men with late-stage prostate cancer who did not benefit from drugs that lower testosterone - the male sex hormone that fuels progression of the cancer.

An outside advisory panel of doctors recommended in March 2007 that the U.S. Food and Drug Administration approve Provenge, based on favorable efficacy and safety results from an earlier phase III study.

But the FDA declined to approve the medicine - a therapeutic vaccine containing traces of a protein linked to prostate cancer - until data from the IMPACT study confirmed earlier trends.

It would be the first approved cancer immunotherapy - a drug that fights cancer by stimulating the immune system to attack cancer cells.

A number of rival biotechnology companies, including Genitope Corp and Cell Genesys, have failed in their own long quests to develop successful therapeutic cancer vaccines.

Dendreon has said it plans to market Provenge without a U.S. partner if the vaccine is approved to maximize profits, unless a potential partner provides an overwhelming incentive.

But the company has said it remains interested in a marketing partner overseas.

Prostate cancer is the most common non-skin cancer in the United States and the third most common cancer worldwide, Dendreon said.

The leading current treatment for advanced prostate cancer is Taxotere, a drug that can cause harsh side effects, including neuropathy, hair loss, nausea and vomiting.

By Ransdell Pierson
NEW YORK (Reuters)