Dendreon stock triples on cancer vaccine

It would be the first approved cancer immunotherapy, meaning a drug to fight cancer by stimulating the immune system to attack cancer cells.

To make the product, a fragment of the patient's tumor is sent to a laboratory, which isolates specific proteins linked to the cancer and incorporates them into the vaccine. Once injected, the body's immune system seeks out and destroys cells containing the target proteins.

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 until data from the IMPACT study confirmed earlier trends.

"If (the study) indeed is unambiguous, the FDA might have a little egg on their face for not approving it earlier," Latta said. "I imagine there's going to be a ton of pressure on the FDA to get the drug through as soon as possible."

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

$50,000 PRICE TAG?

Dendreon confirmed prior statements that it plans to market Provenge on its own in the United States, but it said it remains interested in a marketing partner overseas.

OrbiMed's Borho predicted Provenge, which is administered only once, would cost more than $50,000.

The leading current treatment for advanced prostate cancer is Taxotere, a Sanofi-Aventis (SASY.PA) chemotherapy that can cause harsh side effects, including neuropathy, hair loss, nausea and vomiting.

Gold in February told Reuters he was supremely confident the IMPACT study would succeed, saying, "We're on the 10-yard line and close to putting it into the end zone."

Still, Wall Street was skeptical. Dendreon shares touched a 52-week low of $2.55 in March, and no analysts polled by Reuters Estimates had a "buy" rating on the stock.

"Nobody wanted to stick their head out because over the last 15 years no cancer immunotherapies worked in clinical trials," said Borho.

Over 61 million shares in Dendreon had traded hands by 3:25 p.m. EDT.

(Reporting by Ransdell Pierson and Lewis Krauskopf; Editing by Lisa Von Ahn, Dave Zimmerman)