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Prostate cancer may be virally mediated in certain patients.

SAN FRANCISCO -- A newly identified virus may be involved in the development of prostate cancer in men with a specific genetic mutation, a study has shown.

The findings provide the first evidence that some types of prostate cancer could be virally mediated, Dr. Eric Klein reported at a symposium on prostate cancer sponsored by the American Society of Clinical Oncology.

Previous studies have linked prostate cancer with a mutation in the RNaseL gene. Because this gene, also called the HPC1 (human prostate cancer 1) gene, produces an antiviral protein activated by viral infection and interferon, it has been suggested that mutation-related functional impairment could be a factor in prostate cancer susceptibility.

To test that hypothesis, Dr. Klein, head of urologic oncology at the Glickman Urological Institute of the Cleveland Clinic, and his colleagues at the University of California, San Francisco, used DNA chip technology to screen prostate tumor samples from 86 men who had undergone radical prostatectomy.

"RNA from the tumor tissue was hybridized to the chip," which simultaneously screened for the genetic sequences of nearly 1,000 viruses, he said at the meeting, which was cosponsored by the Society of Urologic Oncology and the American Society for Therapeutic Radiology and Oncology.

The investigators sought to compare the incidence of viral infection in the 20 men in the study who had the HPC1 mutation with the incidence in the 66 men with one or no copies of the altered gene.

The screening tool identified a novel retrovirus sequence found in 9 of the 20 men with two mutated copies of the HPC1 gene, compared with only 1 of the 66 other men.

The virus, called xenotropic murine-like retrovirus (XMRV), "has never before been seen in humans, but it is closely related to one that is associated with leukemia in mice," Dr. Klein said. It is not yet clear whether the virus is unique to prostate tumors because it is the first tumor type to be studied with the virus chip technology, he noted.

"Interestingly, the virus was not present in the prostate tumors but [rather] in the stromal cells adjacent to the tumors. The hypothesis is that when the virus infects these cells, it expresses a protein that affects the surrounding tissue," Dr. Klein said.

The relationship between viral infection and cancer is not unique, he said. "Chronic infection with hepatitis C virus is a risk factor for the development of hepatic cancer, and the human papilloma virus is implicated in cervical cancer, so the possibility that a virus could cause prostate cancer is reasonable."

Because the new virus is seen in prostate tissue, it could be sexually transmitted. "We're planning an epidemiology study to determine how widespread the virus is and whether there's an association between sexual history, medical history, viral infection, and prostate cancer," he said.

"There's a lot of scientific work ahead to determine the possible therapeutic impact of this discovery," Dr. Klein said. The virus "could be a target for drug treatment or for the development of a vaccine."

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Publication:Family Practice News
Geographic Code:1USA
Date:Mar 15, 2006
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