A retrovirus known to cause cancer in animals may be linked to prostate cancer in humans, according to early research published online this week in Proceedings of the National Academy of Sciences USA.

 

The findings, if verified by further research, raise the possibility of developing a vaccine or using antiviral drugs to protect against the disease, say Robert Schlaberg, from Columbia University Medical Center in New York, and colleagues.

 

“This study is the first to find a virus, similar to that which can cause cancer in animals, in human prostate cancer cells,” says Chris Parker from the Institute of Cancer Research in Surrey, UK, a clinical oncologist not involved in the research. “It raises the possibility that the virus might contribute to the development of prostate cancer.”

 

Globally, 3% of men die from prostate cancer, with the figure set to rise as life expectancy in many countries increases. Studies have shown that inflammation of prostate tissue, a hallmark of infection, may have a part to play in the development of the disease. Previous research looking for what might cause this inflammation flagged up the Xenotropic murine leukemia virus-related virus (XMRV) as a possible candidate. Other retroviruses, such as HIV, have been implicated in the development of some human cancers. It is not yet known how people contract XMRV.

 

Schlaberg and colleagues collected samples of prostate tissue from 334 men undergoing medical procedures at the Columbia University Medical Center between August 2006 and April 2008. More than 230 of the samples were taken from prostate cancer patients, with the rest coming from patients undergoing treatment for benign enlargement of the prostate, which is common in old age. Using molecular tests the researchers analysed the tissues for the presence of XMRV DNA or proteins that could indicate infection with the virus.

 

These signs of infection were found in 27% of cancer patients and 6% of non-cancer patients. No measure of statistical significance was reported for the result. The fact that 6% of prostate samples from non-cancer cases had traces of XMRV could mean that the virus induces the disease some time after initiating infection, note Schlaberg and colleagues. “It is also possible that XMRV infection does not always lead to cancer.”

 

Nevertheless, “XMRV infection was associated with prostate cancer, especially higher-grade cancers,” the researchers write. ‘High-grade’ is a label given to cancer cells that grow quickly and spread to other parts of the body more rapidly than other types. Traces of XMRV infection were found primarily in cancerous epithelial cells, which the authors say suggests the infection itself may be directly linked to the formation of tumours.

 

Parker cautions that more research is needed to confirm whether the virus contributes to the development of prostate cancer. Other known risk factors include obesity, African American and African Caribbean ethnicity, and a family history of the disease. “But in the future, if it turns out to be true, then one could speculate about the possibility of vaccination to protect against prostate cancer, similar to the approach now used to prevent cervical cancer,” he says.

 

The research also raises the possibility that the infection could be treated with antiviral drugs to prevent prostate cancer from developing after someone becomes infected, say Schlaberg and colleagues. They also suggest it may be possible to improve cancer screening using a biomarker that identifies people with XMRV infection. “Large epidemiologic studies are needed to investigate correlation of XMRV with prostate cancer prognosis,” they add.

 

Previously, the researchers believed that only men with a certain genetic mutation were at risk of infection with XMRV. But the findings published this week suggest that all men may be vulnerable to the virus.