Alternative prostate cancer vaccine shows promise

* Researcher says prostate cancer vaccines not rivals

* Vaccine helped advanced cancer patients live longer

WASHINGTON, Jan 25 (Reuters) - A prostate cancer vaccine that uses relatives of smallpox virus helped patients with advanced and otherwise untreatable cancer live longer, 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 BAVA.CO.

Tests on 125 men with advanced prostate cancer that was resistant to drugs showed they lived more than 8 months longer than men not treated with the vaccine, 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,” Kantoff said in a telephone interview. “At three years, 30 percent of the men who got the vaccine were still alive.”

He said a larger study with more men was being planned for later this year.

The study, reported in part at several cancer meetings over the past few months, is detailed in the Journal of Clinical Oncology.

Prostvac takes a different approach from and is earlier in development than Dendreon Corp's DNDN.O prostate cancer vaccine, called Provenge. Both are so-called therapeutic vaccines, which treat a disease as opposed to vaccines that prevent infection.

The Dendreon vaccine uses a patient’s own immune system cells, manipulating them to better fight the cancer and then re-infusing them.

“So it is a cell-based vaccine,” said Kanthoff, who worked on both studies. “(Prostvac) is a virus that has been engineered genetically.”

The viruses are the same cowpox virus that forms the basis of the smallpox vaccine and a bird virus called fowlpox. They are genetically engineered to carry prostate specific antigen or PSA, which is made only by prostate cells.

Prostate tumors make excess amounts of PSA and the vaccine is designed to focus the immune system on these out-of-control tumor cells.

Kanthoff said he 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.

Analysts have predicted a prostate cancer vaccine might become $1 billion drug if approved for use among men with early stage disease.

Editing by Cynthia Osterman