Oct. 6 (Bloomberg) -- Dendreon Corp., the company developing a treatment for prostate cancer, rose the most in more than a year in Nasdaq trading after its experimental drug reduced the risk of death 20 percent in an ongoing study.

The Seattle drugmaker gained $1.73, or 33 percent, to $6.93 at 4 p.m. New York time in Nasdaq Stock Market composite trading. It was the biggest percentage jump since March 30, 2007. The treatment, Provenge, would be Dendreon's first product.

Dendreon expects the study in 512 men to meet its goal of improving survival 22 percent when it ends in mid-2009, Chief Executive Officer Mitchell Gold told investors today on a conference call. The U.S. Food and Drug Administration last year delayed Dendreon's application to sell the treatment and requested more evidence to support the survival claim.

``We maintain our view that any meaningful survival advantage of Provenge treatment would become apparent only upon final analysis,'' said Joel Sendek, an analyst at Lazard Capital Markets in New York, in a note to clients today. ``We assume a 50-50 likelihood that the trial may demonstrate a survival benefit upon final analysis.''

The company received the interim results from the study from an independent monitoring committee. Had the data showed the 22 percent survival benefit, Dendreon would have been able to submit the findings to the FDA, possibly expediting Provenge's approval. The study has shown no safety concerns, the company said.

`Success Probability'

``While we would like to receive a result that would have allowed us to amend'' our application, ``the final analysis by design has a higher probability for success,'' Gold said.

Provenge, if approved, would be the first drug to train the body's immune system to attack cancer cells. Prostate cancer kills 27,000 men a year in the U.S., and some analysts estimate that Provenge sales may reach up to $1 billion a year. Sendek predicts $105 million in global sales in 2011.

Dendreon asked for approval last year after a study of 127 men showed the drug prolonged lives with few side effects, while a second study didn't show a benefit. The FDA's decision not to approve Provenge in May 2007 sparked protests among advocates for prostate-cancer patients and almost led to a Congressional probe.

To contact the reporter on this story: Catherine Larkin in Washington at clarkin4@bloomberg.net.

Last Updated: October 6, 2008 16:23 EDT