Prostate cancer vaccine increased overall survival.
The study was the first trial of a cancer vaccine to report a significant increase in overall survival in patients with any kind of solid tumor, Eric J. Small, M.D., said at a press briefing at a symposium on prostate cancer sponsored by the American Society of Clinical Oncology.
The trial could be a landmark study, but it is not definitive without further studies, said Philip Kantoff, M.D., a medical oncologist at the Dana Farber Cancer Institute, Boston, who was not an investigator for the study.
In the phase III trial, 28 (34%) of 82 patients who received the vaccine APC8015 (Provenge) were alive after 36 months of follow-up, compared with 5 (11%) of 45 patients who received placebo, said Dr. Small, the lead investigator of the study. This difference in overall survival was statistically significant.
But overall survival was only a secondary end point in the trial. Median time to progression of cancer, which served as the trial's primary end point, was similar between the vaccine and placebo groups. Rapid tumor progression before the onset of the vaccine's immune effect may explain the discordance between the non-significant difference in the time to progression and the significant difference on overall survival, suggested Dr. Small, professor of medicine and urology at the University of California, San Francisco.
The results of the small study will have to be confirmed in a larger trial, Dr. Kantoff commented. Two other trials testing the vaccine are already underway, noted Dr. Small, who said he has no financial relationship with Dendreon Corp., the manufacturer of Provenge. Dendreon funded the trial.
The vaccine is an autologous cellular product composed of antigen-presenting cells enriched from peripheral blood mononuclear cells obtained via leukapheresis. The final product is a mix of dendritic, antigen-presenting cells and a fusion protein composed of prostatic acid phosphatase--present in about 95% of all prostate cancers--and granulocyte-macrophage colony-stimulating factor.
Provenge patients had a significantly longer median survival, compared with placebo patients (25.9 months vs. 21.4 months). The 4.5-month median increase in survival for vaccine patients is larger than the 2- to 2.5-month median increase reported for patients with metastatic prostate cancer treated with docetaxel (Taxotere) in two recently published studies of 1,006 men (N. Engl. J. Med. 2004;351:1502-12) and 770 men (N. Engl. J. Med. 2004;351:1513-20), Dr. Kantoff said.
All of the patients in those two trials had cancer that was refractory to androgen-deprivation therapy, and 36%-46% of the patients had significant bone pain, Dr. Small noted. Each patient in the vaccine study had asymptomatic metastatic prostate cancer (no bone pain) that was refractory to androgen-deprivation therapy.
Provenge could turn out to be an additional option for treatment besides chemotherapy, not a replacement for chemotherapy, Dr. Small said.
In a subset of patients, the median ratio of the number of T cells stimulated specifically against prostatic acid phosphatase at 4 weeks after the end of treatment to the number of nonstimulated T cells before treatment was significantly higher in 29 vaccine patients than in 16 placebo patients (ratios of 17 and 2, respectively).
The vaccine had a favorable toxicity profile. Flulike symptoms that resolved within 24 hours with acetaminophen constituted the most common side effects of the vaccine, Dr. Small said at the symposium, which was cosponsored by the Society of Urologic Oncology and the American Society for Therapeutic Radiology and Oncology.
BY JEFF EVANS
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|Title Annotation:||Across Specialties|
|Publication:||Clinical Psychiatry News|
|Date:||Jul 1, 2005|
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