Experimental Vaccine Halts Prostate Canc...( Human trials may start in two years C...),Health

Human trials may start in two years, California researcher says

FRIDAY, Feb. 1 (HealthDay News) -- An experimental prostate cancer vaccine has stopped the progress of the disease in 90 percent of the mice who got it, California researchers report.

"The vaccine turned the cancer into a chronic, manageable disease," said W. Martin Kast, lead author of a report published in the Feb. 1 issue of Cancer Research.

Twenty mice, genetically bred to develop prostate cancer, were given the vaccine in a two-step process, said Kast, a professor of molecular microbiology and immunology at the University of Southern California, Los Angeles.

When the mice were 8 weeks old, they got one injection consisting of a fragment of DNA that coded for prostate stem cell antigen (PSCA), a protein that is overproduced as prostate cancers grow. That injection alerted the immune system, Kast said.

A second shot, given two weeks later, used a modified horse virus to deliver the gene for PSCA, throwing the immune system into full action against the tumor.

Only two of the 20 vaccinated mice developed full-blown prostate cancer at the end of one year. Twenty other similarly bred mice who did not get the vaccine died of their cancers.

A vaccine for prostate cancer already exists, but it is only designed to extend survival for men in advanced stages of the disease and it has not been approved for use in the United States.

The new vaccine is designed to be used much earlier, Kast said. "Our vaccine approach would be to give it before you actually develop the disease," he said. Candidates for vaccination would be men who have high levels of prostate-specific antigen (PSA), a protein associated with the cancer.

Physicians now perform biopsies in most such cases, looking for evidence of cancer, which is usually inconclusive. The vaccine could be given instead of the "watchful waiting" now common fo
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