Details of the new trial were made public at the annual meeting of the American Urological Association in Chicago.
Mitchell Gold, CEO of the Seattle-based biotech company Dendreon, which makes the vaccine, called the results from the company’s latest trial “unambiguous.”
“Today, Dendreon, our employees, and the scientific community have made a major step forward in demonstrating that the immune system can be harnessed in the fight against cancer,” he said in a presentation Tuesday afternoon. “We hope and sincerely believe that this is just the beginning of a new era in medicine.”
But American Cancer Society Chief Medical Officer Otis W. Brawley, MD, was more restrained in his enthusiasm.
While acknowledging that Provenge may prove to be an important new cancer treatment, Brawley tells WebMD that closer scrutiny of trial results is needed.
Men in the study who got the experimental immunotherapy lived, on average, four months longer than men in the placebo group of the study.
“At best, this is an effective treatment,” he says. “It is not a cure for metastatic prostate cancer.”
Provenge Patients Lived Longer
The study included 512 men with advanced prostate cancer who had stopped responding to hormone-blocking treatments and who had few other treatment options.
Active treatment consisted of three injections of Provenge given over the course of a month. Half the patients were treated with the immunotherapy and the other half got placebo treatments.
Side effects were mild; consisting mainly of flu-like symptoms that resolved within a few days, study co-author David Penson, MD, of the University of Southern California’s Keck School of Medicine, said in a Tuesday afternoon news conference.
Penson also revealed that:
- Provenge improved three-year survival by 38%, with about 31% of patients who got the immunotherapy surviving this long, compared to 23% of the placebo-treated patients.
- Average survival among patients who got the active vaccine was slightly less than 26 months, compared to 22 months among patients in the placebo arm.
- The survival advantage seen among the Provenge-treated patients was similar to that reported in two smaller, company-sponsored trials comparing the immunotherapy to placebo. Patients in the three trials lived, on average, between 3.3 and 4.5 months longer than the placebo-treated patients.
- There was no statistically significant difference in disease progression between the two treatment groups. The two previous trials also failed to show that Provenge slows the progression of disease.
Dendreon plans to seek approval of the immunotherapy drug later this year, Gold said.
FDA Move Prompted Protests
The FDA considered, and rejected, such a request two years ago in a move that angered prostate cancer patients and patient advocates.
Considering evidence from the first two trials, an FDA board concluded that Dendreon had failed to prove that Provenge was both safe and effective.
The decision reportedly led to protests outside FDA headquarters by patients and company investors, and to death threats directed at board members who voted against approval.
It also led to the newly published trial, which Brawley says addresses many of the concerns about Provenge, if, as he says, “the results hold up to scrutiny.”
“I do believe this is the trial that needed to be completed in order to approve this treatment,” he says. “If it had been approved after the last FDA hearing there would have been a lot of questions that never would have been answered. I have seen the harm done when a bad drug is approved without adequate evaluation.”
Biostatician Donald Berry, MD, of Houston’s University of Texas M.D. Anderson Cancer Center, tells WebMD that the three studies together suggest that patients do benefit from the novel treatment. But he characterized the benefits as “marginal.”
“This is not the magic bullet that we had hoped for to cure cancer,” he says. “It is not a panacea.”
Treatment Offers Hope
But prostate cancer patients who attended Tuesday's news conference said the new treatment offers hope to patients who currently have little.
Nine-year prostate cancer survivor Thomas Farrington said many advanced cancer patients with no other treatment options reject or stop chemotherapy because of the side effects.
Patient Jim Kiefert, of the prostate cancer education and support group Us Too, said most patients he knows would embrace a treatment with minimal side effects for the chance to gain even a few extra months of life.
“This is additional hope that men need when they are at that last stage of prostate cancer,” he says.