A viral etiology for aggressive forms of prostate cancer?

There have been frequent suggestions over the years that specific viruses may be implicated in the development of certain types of cancer, and an article in this week’s Proceedings of the National Academy of Science discusses the possibility that this may be the case in aggressive forms of prostate cancer.

According to a media release from the University of Utah, discussed in commentary on Bloomberg.com, Singh and her colleagues have identified an “association” between the presence of a virus known as the XMRV virus (properly known as the xenotropic murine leukemia virus-related virus) and aggressive forms of prostate cancer. What Singh and her colleagues actually did seems to be the following:

  • They were able to develop tests that could indicate the presence of XMRV viruses inside cells.
  • They checked biopsy specimens from 233 men with prostate cancer and 101 with benign prostate hyperplasia (BPH).
  • They showed that the virus was present in biopsy tissue from 23 percent of the men with cancer and 4 percent of the men with BPH.
  • They showed that 44 percent of men with Gleason 9 tumors had evidence of XMRV.

The XMRV virus, a retrovirus first identified just 3 years ago, and previously associated with cancer in some animals, can be incorporated into the genome of the cells it infects. It has been suggested that  this virus may be able to trigger the development of cancer if it is located next to DNA that controls cell growth, and if it can disrupt genes responsible for cells replicatation. However, it would be a big mistake to leap to the conclusion that Singh and her colleagues have proved tnat the XMVR virus does, in fact, cause prostate cancer.

In the first place, is is possible that men with aggressive forms of prostate cancer are simply more susceptible to infection with the XMVR virus than other men. In other words, it may be that the infection is a consequence of the cancer as opposed to a cause. Singh and her colleagues suggest that this is not the case, but we will need further data toi clarify this point.

In the second place, we need a lot more information to be sure that what Singh and her colleagues are identifying really is the presence of the XMVR virus in prostate cancer tissue, and not some other genetic malformation.

And in the third place, if the XMVR virus really is a trigger for the onset of prostate cancer in some men with aggressive prostate cancer, is this sufficient on its own, or must other factors also be involved? This will be a particularly important question, since the presence of the virus only appears to have been an important factor in 44 percent of the patients with Gleason 9 disease.

In general, The “New” Prostate Cancer InfoLink advises readers to understand that an “association” between something that affects the genome of a patient with a specific type of cancer is usually not a singular “cause” of their cancer. This has been shown many, many times since the development of our ability to identify specific “snips” (properly SNPs) of genetic material. While the research by Singh and her colleagues is certainly very interesting, we need to interpret it with great caution until more data are available.

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