Virus, gene mutation linked to prostate cancer

St.Petersburg Times

06-12-06

A virus, XMRV, that causes cancer in mice was recently identified in human prostate cancer tissues of men who were genetically susceptible for prostate cancer.

This raises the suspicion that chronic XMRV infection of the prostate may lead to cancer. It also lends credence to the hypothesis that chronic inflammation of the prostate may lead to cancer.

XMRV was most frequently identified in patients who had mutations of both the copies of a prostate cancer susceptibility gene, HPC1. Most men have two normal copies of this gene.

Those who have one mutant copy are somewhat susceptible but those who carry mutations in both the copies of HPC1 are highly vulnerable to prostate cancer ( a greater than twofold risk ).

This gene forms a vital cog in the body's defense system. It codes for an enzyme that helps kill invading viruses.

When both normal copies of this gene become defunct owing to mutation, the virus has easy access to the prostate, where it can cause chronic infection, inflammation and possibly cancer.

Dr. Eric Klein, head of Urologic Oncology at the Cleveland Clinic, extracted DNA from the prostate cancer tissue of several of his patients and submitted it to Joe DiRisi, a researcher at the University of California, San Francisco.

DiRisi developed a "viro chip" - based on the micro array technology - which contains 20,000 fragments of important genetic material from practically every known virus.

It is the same viro chip that DiRisi used to detect the SARS virus three years ago.

XMR virus was found in 45 percent of the prostate cancer samples with mutation in both the copies of the HPC1 gene in contrast to only 1.9 percent of the samples from patients with two normal HPC1 gene copies.

More than 1,000 viruses were screened for, and only the XMR virus was found in these samples. Whether this virus is actually causing the cancer or is simply co-existing with cancer in the HPC1 mutation-carrying patients will be the next big question for researchers to answer.

If the virus is found to be actually causing the cancer, then prostate cancer might be viewed as an infectious disease and treated as such.

Some cancers of the cervix and liver are already known to be caused by chronic viral infections.

Other cancers where viruses are incriminated are stomach and breast.

The possibility of a viral connection to prostate cancer makes one suspicious that there may be similar links to others cancers and creates further opportunities for research.

It is not clear how this virus got into humans, but it is suspected that it may have been passed on genetically over many generations.

Researchers are developing a test to detect this virus in the blood. They plan to test thousands of patients and nonpatients to study this issue further.

The presence of this virus, especially in men with two mutated copies of the HPC1 gene will be of great significance because of the high risk of prostate cancer that this combination of viral infection and gene mutation confers.

V. Upender Rao, MD, FACP, practices at the Cancer and Blood Disease Center in Lecanto.

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