A controversial prostate cancer vaccine produced by Dendreon Corp. of Seattle "significantly" improves survival of patients, the company said Tuesday morning without releasing further details of the trial. The trial was designed to detect a minimum 22% increase in survival and experts speculate that it did at least that well. Further results of the trial will be released April 28 at a meeting of the American Urological Assn. If those findings are upheld, the vaccine, called Provenge, could be the first cancer vaccine approved by the Food and Drug Administration.
Provenge is a so-called therapeutic vaccine designed to treat the disease rather than prevent it from occurring. Physicians collect specialized immune cells called dendritic cells from the patient's blood, mix them with proteins collected from the surface of tumor cells and inject them back into the patient in three doses at two-week intervals.
In an earlier study of the vaccine, the company found that it increased survival of patients with advanced prostate cancer that had spread beyond the prostate by 18 weeks compared to patients given a placebo. After three years, 34% of those in the vaccine group survived, compared to 11% of those in the placebo group. An FDA advisory committee recommended that the agency approve the vaccine for marketing, but the FDA disagreed, arguing that the study did not provide evidence that the vaccine slowed progression of tumors.
That decision provoked outrage among prostate cancer victims and advocates, who argued that the 18-week increase in survival was nearly double the 10-week increase seen with Taxotere, which had been approved. Three congressmen called for a probe of the agency, charging conflicts of interest among some members of the advisory committee.
The new trial in 512 patients was designed to overcome objections to the earlier study. Although few details are available yet, Dr. Eric Small of UC San Francisco told the Associated Press that "this is an exciting result, demonstrating that harnessing a patient's own immune system can successfully attack prostate cancer. Now we have more confidence that the initial results we saw were real."
Prostate cancer is the most common cancer in American men, with an estimated 186,000 new cases diagnosed each year and 28,660 deaths. There are currently no good treatments for disease that has spread beyond the prostate.
-- Thomas H. Maugh II