Data from an ongoing study designed to explore the biologic and clinical activity of cancer immunotherapy sipuleucel-T, or Provenge, in patients with early stage recurrent prostate cancer who have a rising serum prostate specific antigen (PSA) level, but who have not yet developed metastatic disease will be presented by Oregon Health & Science University Cancer Institute researchers.
The study showed that sipuleucel-T did not significantly delay the time it took for a patient's PSA to reach a value of 3 ng/ml, the primary endpoint of the study, but it did show a prolongation in prostate-specific antigen doubling time (PSADT). In addition, there was a trend observed in slowing the time to metastatic disease for patients who received sipuleucel-T compared with those who received placebo, but this early trend did not reach statistical significance. The findings were presented at the 43rd Annual Meeting of the American Society of Clinical Oncologists (ASCO) in Chicago.
"While there was no delay in the time to PSA recurrence, we did observe a slowing in the rate of rise of serum PSA in exploratory analyses. Additional follow-up is needed to determine if this effect on PSA will translate into patient benefits," said Tomasz Beer, M.D., lead investigator, director of the Prostate Cancer Research program at the OHSU Cancer Institute; and associate professor of medicine, (hematology/medical oncology) OHSU School of Medicine.
The ongoing trial, known as P-11, is a double-blind, multi-center, randomized, placebo-controlled study involving 176 men, all of whom had prostatectomies and then had recurrent cancer as detected by a rise in the serum tumor marker, PSA. After three months of hormone therapy, 117 men received sipuleucel-T and 59 received placebo.
Sipuleucel-T was found to have a favorable safety profile. The most common side effects seen more commonly in sipuleucel-T-treated patients were fatigue, chills and fever.
The effects of sipuleucel-T on prostate cancer progression were analyzed in several ways using measurements of serum PSA. The primary analysis focused on time until the PSA reaches 3.0 ng/ml. Although there was a trend, the immunotherapy did not significantly delay cancer progression by this measure. However, investigators found the rate at which PSA was rising was 30 percent to 48 percent slower in patients who received sipuleucel-T compared to those who received placebo.