NEW YORK (Reuters Health) - The therapeutic prostate cancer vaccine sipuleucel-T (APC8015, Provenge, Dendreon Corp., Seattle, Washington) improved survival by three years and disease-free survival was more than four months longer than in a control group. Sipuleucel-T is an investigational vaccine designed to stimulate T cell immunity against prostatic acid phosphatase. It is manufactured from frozen leukapheresis cells.
In this phase III multicenter trial, Dr. Eric J. Small of the University of California, San Francisco, and colleagues randomized men with asymptomatic metastatic hormone-refractory prostate cancer in a two-to-one ratio, with roughly twice as many patients receiving the vaccine. If disease progression occurred, patients in the control arm could receive sipuleucel-T. The therapeutic vaccine was delivered intravenously every two weeks.
After the 36-week study period, 115 of the 127 patients had disease progression. Median time to disease progression in the vaccine group was 11.7 weeks compared with 10.0 weeks for placebo patients, for a hazard ratio of 1.45.
Median survival was 25.9 months in the sipuleucel-Y patients and 21.4 months for placebo patients, for a hazard ratio of 1.70.
Results of the trial are published in the July 1st issue of the Journal of Oncology.
"While we did not evaluate the durability of T cell responses in this trial, in our earlier phase 1 and 2 trials with the same agent, T cell responses appeared to be durable for up to a year. We didn't test beyond that in those trials," Dr. Small told Reuters Health."Down the line, treatment success may be improved by combining this therapy with other therapies, including other immune manipulations," Dr. Small continued. "Evaluation in other groups of patients, perhaps with less extensive disease, is also warranted."
The trial demonstrated a new facet of treatment of prostate cancer. "Overall, the excitement about this approach is a demonstration that the immune system can be harnessed to attack cancer, and in particular prostate cancer, thereby giving patients an additional treatment option. I don't view this as replacing chemotherapy, but as adding another weapon in our arsenal in our fight against prostate cancer," Dr. Small said.