ORLANDO—A new therapeutic vaccine called Prostvac-VF may prolong survival in men with metastatic hormone-refractory prostate cancer (HRPC), according to new data presented here at the 45th Annual Meeting of the American Society of Clinical Oncology.

In a phase 2 prospective, randomized, placebo-controlled study, men with HRPC who received the vaccine had a median overall survival that was 8.5 months longer than the placebo group, which translated into a significant 44% reduced risk of death. Prostvac was well-tolerated, according to investigators. About 60% of patients who received the drug had injection-site reactions, and 30% experienced fatigue, fever, and chills.

“There are few available treatments for advanced prostate cancer,” said principal study investigator Philip W. Kantoff, MD, Professor of Medicine at Harvard Medical School and Director of the Lank Center for Genitourinary Oncology at Dana-Farber Cancer Institute in Boston. “To see this extent of improvement in overall survival is very encouraging. These phase 2 data with Prostvac warrant confirmation with a phase 3 study.”

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The trial enrolled 125 patients (mean age 73 years) who were randomized 2-to-1 to receive the immunotherapy or placebo. Of the 125 patients, 120 were evaluable (80 patients in the Prostvac arm and 40 in the placebo arm). The primary end point was progression-free survival (PFS), with progression defined as appearance of two new lesions on bone scan or  nodal metastases changes defined by response evaluation criteria in solid tumors (RECIST). The secondary end point was overall survival. The researchers observed no difference in PFS.

Gerald L. Andriole, MD, Professor and Chief of Urologic Surgery at Washington University School of Medicine in Saint Louis, said the study findings are encouraging. “Castrate-resistant prostate cancer has been notoriously difficult to treat,” Dr. Andriole told Renal & Urology News.

“If these survival data are confirmed in a phase 3 trial, and the observed side effects of therapy remain low, it will be a pleasant problem to decide whether to use this agent or Provenge, if it is approved, as the initial therapy for men with castrate-resistant disease.”

At the recent annual meeting of the American Urological Association in Chicago, investigators reported promising findings regarding Provenge, the first immunotherapeutic vaccine for advanced prostate cancer. Results from the Immunotherapy for Prostate Adenocarcinoma Treatment study—a randomized, double-blind, placebo-controlled trial involving 512 men—showed that vaccine recipients survived a median of 4.1 months longer than placebo recipients (25.8 vs. 21.7 months).

The vaccine, which is administered as an IV infusion, improved three-year survival by 38% (31.7% vs. 23%) and reduced the risk of death by 22.5% compared with placebo. The vaccine did not significantly delay time to progression. Adverse events observed more commonly in vaccine-treated patients were chills, fever, and headache. These events were mainly low-grade and lasted one to two days following infusion.