Alternative prostate cancer vaccine shows promise

WASHINGTON (Reuters) - A prostate cancer vaccine has helped patients with advanced refractory disease live longer in a phase II study, U.S. researchers reported on Monday.

The vaccine, called Prostvac-VF, is being developed by BN ImmunoTherapeutics, a division of Danish biotech firm Bavarian Nordic.

The study was conducted in men with minimally symptomatic castration-resistant metastatic prostate cancer. Those randomized to the vaccine group lived more than 8 months longer than men in the control group, said Dr. Philip Kantoff of the Dana-Farber Cancer Institute and Harvard Medical School in Boston, who helped lead the study.

"The average survival for these men is two years," Dr. Kantoff said in a telephone interview. "At three years, 30% of the men who got the vaccine were still alive."

He said a larger study is being planned for later this year.

The study, reported in part at several cancer meetings over the past few months, was reported online January 25 in the Journal of Clinical Oncology.

According to Dr. Kantoff and his coauthors, Prostvac contains two recombinant viral vectors, each encoding transgenes for PSA, and three immune costimulatory molecules (B7.1, ICAM-1, and LFA-3). Patients were randomized in a 2:1 ratio to Prostvac plus granulocyte-macrophage colony-stimulating factor or to sham vaccination.

The primary end point - progression-free survival -- was similar in the two groups. Three years after vaccination, however, the Prostvac patients had better overall survival, with 25 (30%) of 82 alive versus 7 (17%) of 40 controls. In addition, median survival was 8.5 months longer in the vaccinated group (25.1 v 16.6 months for controls), with an estimated hazard ratio of 0.56 (stratified log-rank P = .0061).

Prostvac takes a different approach from and is earlier in development than Dendreon Corp's prostate cancer vaccine, called Provenge. The Dendreon vaccine reinfuses autologous immune cells.

The Prostvac viral vectors are the same cowpox virus that forms the basis of the smallpox vaccine and a bird virus called fowlpox.

Dr. Kantoff is not sure which vaccine works better. "It's just exciting to think that you can alter the immune system," he said. "To me it is not one versus the other. Both companies are rejoicing in the fact this might work, and the whole field is rejoicing."

Prostate cancer is the second-leading cancer killer of U.S. men, after lung cancer, with more than 192,000 cases diagnosed in 2009 and 27,000 deaths, according to the American Cancer Society.

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