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Prostate cancer virus link

Many newspapers today reported on research that has found a link between a virus known to cause leukaemia in animals and human prostate cancer. This viral link has led many newspapers, including The Times to suggest that the finding, “may lead to more effective screening and vaccination to prevent men from developing the disease”.

This research looked at prostate cancer cells and normal cells and found that a virus, the xenotropic murine leukaemia virus-related virus (XMRV), was more common in the cancer cells. This finding suggests that similar to some other cancers such as cervical cancer, prostate cancer may be related to a virus. This research is at an early stage and much more is needed. As the lead author of the study Ila R Singh says, “We still don't know that this virus causes cancer in people, but that is an important question we're going to investigate.”

 

Where did the story come from?

The research was carried out by Dr Ila R Singh and colleagues from the University of Utah and Columbia University medical schools. The study is due to be published in the peer-reviewed scientific journal, Proceedings of the National Academy of Sciences of the USA. This appraisal is based on a press release from the University of Utah. The funding sources for the study were not reported in the press release.

 

What kind of scientific study was this?

Very limited information about the methods of the study was available from the press release.

The researchers tested more than 200 human prostate cancers and more than 100 samples of non-cancerous prostate tissue for the XMRV virus. They confirmed that XMRV is a type of virus called a gammaretrovirus. Retroviruses copy their own genetic material and insert it into their host’s DNA. This can disrupt the function of nearby genes and can, in some cases, cause the uncontrolled cell division that leads to cancer, although this has not yet been shown to be the case for XMRV. The press release reports that gammaretroviruses “are known to cause cancer in animals, but have not been shown to do so in humans”.

The researchers also looked at which cells the virus’ proteins were found in.

Additionally, they appear to have looked at the characteristics of the XMRV virus and at whether a particular genetic mutation affected a person’s susceptibility to XMRV infection.

 

What were the results of the study?

The researchers found that the XMRV virus was present in 27% of prostate cancers tested and only 6% of the non-cancerous prostate tissue. The viral proteins were reported to be present “almost exclusively” in malignant prostate cells. The virus was also said to be associated with more aggressive tumours.

The researchers found that a particular genetic mutation did    not affect susceptibility to XMRV infection, as had been previously suggested.

 

What interpretations did the researchers draw from these results?

The researchers say, “we still don't know that [XMRV] causes cancer in people, but that is an important question we're going   to investigate."

 

What does the NHS Knowledge Service make of this study?

This research is at a very early stage and it is not possible to say at present whether this virus causes prostate cancer. Limited details of the study’s methods and results were available from the press release. However, one factor that would influence the reliability of the results would be the similarity of the men who provided the prostate cancer samples to those who provided the normal prostate tissue.

This finding does support further investigation but it is not known whether this virus actually causes prostate cancer. Therefore, the possibility of a vaccine to prevent prostate cancer remains a long way off.

Additionally, the decision to carry out screening for any condition is never made lightly. The risks and implications of false positive (indicating you have cancer when you don’t) and false negative results (indicating you don’t have cancer when you actually do) have to be considered.

The causes of prostate cancer are at present uncertain. The most established factors are increasing age, family history and ethnicity (African Americans and African Caribbeans being considered to have the highest risk). The role of dietary factors, infections or environmental factors are not clearly established.

 

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