(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
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.