Vaccine approach extends life of metastatic prostate cancer patients

In a newly published clinical trial, patients with metastatic prostate cancer who received a vaccine of harmless poxviruses engineered to spur an immune system attack on prostate tumor cells lived substantially longer than patients who received a placebo vaccine, report researchers at Dana-Farber Cancer Institute and affiliated organizations.

The findings will be published by the Journal of Clinical Oncology on its web site and later in a print edition.

The randomized phase II study involved the PROSTVAC-VF vaccine, a combination of two weakened poxviruses that have been genetically programmed to produce slightly irregular versions of prostate specific antigen (PSA) — a protein on the surface of prostate cells that is abnormal in many prostate cancers — and three costimulatory molecules that spur the immune system to a more vigorous attack on tumor cells.

The double-blinded trial included 125 patients with metastatic prostate cancer who did not respond to standard, hormone-lowering therapy. Eighty-two of the participants received the vaccine, produced by BN ImmunoTherapeutics, Inc., of Mountain View, Cal., and 40 received a placebo.

At the three-year point after the study, 30 percent of the PROSTVAC-VF patients were alive, versus 17 percent of the control group. The median survival of the vaccine group was 24.5 months, compared to 16 months for the control group, an 8.5-month increase.

Patients tolerated the vaccine well; only a small number experienced side effects such as fatigue, fevers, and nausea.

"Although this study is relatively small, it offers encouraging evidence of a clinically meaningful benefit from this vaccine approach," says principal investigator and lead author Philip Kantoff, MD, of Dana-Farber, who helped design the trial. Investigators are planning a phase III trial that will enroll about 600 patients to further evaluate the vaccine's effectiveness.

The senior author of the study is Wayne Godfrey, MD, medical director of BN ImmunoTherapeutics. Co-authors include Brent Blumenstein, PhD, of Trial Architecture Consulting, of Washington, D.C.; Thomas Schuetz, MD, PhD, of Therion Biologics, of Cambridge, Mass.; Michael Glode, MD, of the University of Colorado; David Bilhartz, MD, of Urology Associates, of Nashville, Tenn.; Dennis Panicali, PhD, of Therion Biologics and BN ImmunoTherapeutics; Reiner Laus, MD, of BN ImmunoTherapeutics; and Jeffrey Schlom, PhD, William Dahut, MD, Philip Arlen, MD, and James Gulley, MD, PhD, of the National Cancer Institute.

The study was supported by funding from the National Cancer Institute.