The researchers say the virus has never been seen in humans before and supports previous research which suggests that prostate cancer may be the result of a chronic inflammation, and is possibly the body's response to infection.

Eric Klein, M.D., Head of Urologic Oncology at the Glickman Urologic Institute of Cleveland Clinic, a co-author of the study found that in a group of 150 men the new virus, called XMRV, was 25 times more likely to be found in prostate cancer patients with a specific genetic mutation than men without the mutation.

Cleveland Clinic researcher, Robert H. Silverman, Ph.D., had previously discovered a gene called RNaseL that fights viral infections and found that men with mutations in this gene are at greater risk for prostate cancer.

In their study, Klein and Silverman examined tissue samples of 86 prostate cancer patients whose prostates had been surgically removed.

In these samples, the genetic variations found in RNaseL were sent to UCSF scientists Joe DeRisi, Ph.D., and Don Ganem, M.D.

By using a DNA-hunting "virus chip" (ViroChip) they discovered the new virus far more often in human prostate tumours shown to have the RNaseL mutation than not.

Dr. Silverman says the research was only possible because of the willingness of physicians and scientists in different areas of expertise to work closely together towards the common goal of identifying a new infectious agent in prostate cancer.

Dr.Klein says it will lead the way for future research to examine patients' sexual history, personal and family medical history and viral infections in relation to prostate cancer.

Dr. Klein presented the report to the American Society of Clinical Oncology (ASCO) prostate symposium in San Francisco last week.

The study is published in the journal PLoS Pathogens.