In a newly published clinical trial, patients with metastatic prostate cancer who received a vaccine of harmless poxviruses engineered to trigger an immune system attack on prostate tumor cells lived considerably longer than patients who received a placebo vaccine.

The study's findings were published by the Journal of Clinical Oncology on its website in January 2010, and scheduled for later print publication. The randomized phase II study was performed by researchers from the Dana-Farber Cancer Institute (Boston, MA, USA) and affiliated organizations. The 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. (Mountain View, CA, USA), and 40 received a placebo.

At the three-year point after the study, 30% of the PROSTVAC-VF patients were alive, versus 17% 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,” said lead investigator and lead author Philip Kantoff, M.D., of Dana-Farber, who helped design the trial.

Investigators are now planning a phase III trial that will enroll about 600 patients to evaluate further the vaccine's effectiveness.

Related Links:
Dana-Farber Cancer Institute
BN ImmunoTherapeutics