Dendreon, a Seattle biotechnology company, said yesterday it will apply for U.S. Food and Drug Administration approval to market Provenge...

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Dendreon, a Seattle biotechnology company, said yesterday it will apply for U.S. Food and Drug Administration approval to market Provenge, its prostate cancer vaccine, based on the survival benefit the treatment has shown in two clinical trials.

The announcement pushed the company’s stock price up 12.7 percent, closing at $7.02 on the Nasdaq. After-hours trading lifted shares 23 cents more, or 3.3 percent.

Dendreon said it decided to seek approval for Provenge, which is designed to stimulate the body’s immune system to attack prostate cancer, after learning from FDA officials that the vaccine’s survival benefit and its relatively mild side effects were sufficient grounds on which to file a Biologics License Application.

A Phase 3 clinical study of 127 men with advanced prostate cancer found that those treated with Provenge lived an average 4.5 months longer than those given a placebo.

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A second Phase 3 trial, detailed results of which are expected later this year, showed a “substantially greater” percentage of treated patients were alive after three years than those who got a placebo.

Both studies failed to reach their main goals of demonstrating that Provenge slowed the rate at which the cancer progressed in patients. But Dendreon executives said the survival benefit is the most significant result.

“There is no more meaningful endpoint for patients than survival,” Dr. Mitchell Gold, president and chief executive, said during a conference call with analysts yesterday.

Application filing

The company expects to file its application next year, though it did not specify when. It could get an answer from the FDA six months to a year after it files.

Dendreon also needs to complete and gain approval for its Hanover, N.J., manufacturing facility, which analysts said could delay Provenge’s introduction to the market.

“Most people in Seattle remember the Immunex debacle and how important the manufacturing approval is,” said McAdams Wright Ragen analyst Paul Latta.

Immunex, later acquired by Amgen, initially wasn’t able to keep up with demand for Enbrel, its rheumatoid arthritis drug, because it lacked manufacturing capacity.

Number of U.S. cases

There are more than 220,000 new cases of prostate cancer in the U.S. each year. The disease kills 30,000 U.S. men annually. Sales of Provenge may reach $500 million by 2009, and may be higher if it’s approved for early-stage cancer, said Jenny Freeman, a Cheirologic Partners analyst in Weston, Mass.

In another clinical trial, Dendreon is expanding enrollment to 500 patients, including some who have only minimal symptoms of prostate cancer. Only safety results from that study will be part of the company’s FDA application.

Benjamin J. Romano: 206-464-2149 or bromano@seattletimes.com. Material from Bloomberg News is included in this report.