Link Found Between Virus and Prostate Cancer
By Thomas H. Maugh II, Times Staff Writer
2:16 PM PST,February 24 2006

Researchers have found a previously unknown virus in some men with prostate cancer, a discovery that could open doorways to understanding and treatment of the disease, the most common type of cancer among men.

The discoverers do not know exactly why the virus is present in the men, but "there is now a suggestion that prostate cancer could be caused by an infectious disease," said Dr. Eric Klein of the Cleveland Clinic, who reported the discovery today at a prostate cancer symposium in San Francisco.

The virus is 96% identical to a virus that is normally found in the genome of mice. The researchers do not believe that it is routinely transmitted from mice to humans, but rather that it jumped species in the past and is now transmitted from human to human through an unknown mechanism.

The virus was discovered using Virochip technology developed by Dr. Don Ganem and geneticist Joe DeRisi of UC San Francisco.

The Virochip is a glass slide, about 3 inches long and 1 inch wide, coated with DNA and RNA fragments from every known animal and plant virus, about 1,000 in all. When unknown samples containing potential viruses are applied to the plate, any virus present in the sample selectively binds to its counterpart on the slide, emitting a fluorescent glow.

The technology was previously used by Ganem and DeRisi to identify the SARS virus.

The San Francisco team screened prostate samples from 86 men, supplied by Klein. They found the virus in eight of 20 samples from men who have a specific genetic defect that is known to confer susceptibility to prostate cancer, but in only one of 66 men who did not have the defect. No other virus was found, and they did not screen healthy men.

The genetic defect is known to interfere with the ability of prostate tissues to fight off a viral infection. Some researchers have speculated that inflammation from a persistent infection is a trigger for prostate cancer.

The structure of the newly discovered virus is very similar to that of the murine leukemia virus, which causes cancer in mice, Klein said. And studies showed that the virus was active in the prostate tissues rather than simply laying there dormant.

"The discovery is very exciting and intriguing," he added, "but there is a tremendous amount of scientific work to be done" before researchers know exactly what the virus is doing.