After spending 10 years and $400 million to develop and test its prostate cancer drug, Seattle-based Dendreon today faces the next-to-last hurdle.

An advisory panel for the U.S. Food and Drug Administration will decide whether to recommend approval of the drug, Provenge, evaluating whether the drug is both safe and effective.

Provenge presents a complex picture: Two clinical trials didn't achieve their stated goal of delaying the disease's progress, but a long-term statistical analysis suggests that patients receiving the treatment lived longer than others.

Dendreon is the only Seattle biotech company with a potential blockbuster drug, meaning that analysts project annual sales could reach $1 billion.

"This is huge for Dendreon," said David Miller, president of Seattle-based Biotech Stock Research.

The committee of 19 outside experts, meeting in Gaithersburg, Md., will influence the ultimate decision by the FDA. That final hurdle will come by May 15.

Shares of Dendreon climbed about 13 percent to $5.22 in trading Wednesday, with a trading volume of about 33 million. After-hours trading saw shares drop 3.8 percent. The stock rose about 40 percent in the past five trading sessions.

The drug stimulates the body's immune system — using white blood cells drawn from the patient and mixed with a genetically-engineered protein — to fight prostate cancer.

Provenge has several factors in its favor:

• It's the first treatment of its kind against cancer and one of the only drugs targeting late-stage prostate cancer patients. Prostate cancer kills about 27,000 men a year in the U.S., according to the American Cancer Society. It's the No. 2 cancer killer among men, after lung cancer. Only one other drug for late-stage prostate cancer, Docetaxel, has been shown to delay the progression of the disease.

• Provenge's side effects, including fever and chills, are generally fewer than chemotherapy drugs. However, according to FDA staff briefings filed before the panel meeting, 5.4 percent of Provenge patients had strokes compared with none on the placebo, a potential risk factor that will be a topic of discussion at the committee meeting today.

Factors working against the drug:

• There is conflicting data from Dendreon's clinical trials. One study of 127 patients with advanced, metastatic prostate cancer did not meet its goal, which was to delay the time toward progression of the disease. A companion study was terminated early and also failed to show the slowing of disease progression.

But a further three-year analysis of the same 127 men showed the median survival time for patients treated with Provenge was 4.5 months longer than patients taking the placebo. After three years, 34 percent of the men taking Provenge were still alive, versus only 11 percent receiving the placebo.

• The company is enrolling patients for a final study that won't produce results until 2010. The FDA might request to see that data before approving the drug.

Paul Latta, an analyst with McAdams Wright Ragen in Seattle, expects the advisory panel to give Provenge a favorable mark in the safety category, but he's unsure whether Dendreon will be able to convince committee members of its efficacy.

"The fact is, the survival benefit did show an improvement versus the placebo, but it wasn't a clean, convincing number," said Latta, who owns no Dendreon shares.

Miller, who does own Dendreon stock, gives the company a better than 50 percent chance of winning the panel's recommendation.

The company could run into some trouble because of the panel's makeup. It's largely a group of immunologists, which means the discussion could revolve around how the drug works, rather than whether it helps patients — a conversation that would likely be long and complex. Dendreon isn't required to prove to the FDA how the drug works.

"It's a situation that really is up in the air," Miller said.

Whether Provenge will ultimately receive FDA approval is much more of a gray area.

One skeptic is Jonathan Aschoff, senior biotechnology analyst with Brean Murray Carret & Co. in New York, who thinks that, at best, the drug will be given an "approvable" status. That would likely mean Dendreon will have to wait for three years until its current study wraps up before it can win approval. Aschoff, who does not own any shares of Dendreon, has had a "sell" rating on Dendreon's stock since 2004.

Kirsten Orsini-Meinhard: 206-464-2391 or kmeinhard@seattletimes.com