Utah researchers have found a mouse cancer virus in many human patients with prostate cancer, suggesting that the virus may play a role in the onset of the disease and in the development of more aggressive forms. If their findings can be validated, it might provide a way to distinguish fast-growing tumors that require therapy from the slow-growing forms that can be safely ignored for many years.
Viruses are known to cause a variety of human cancers. Hepatitis viruses, for example, cause liver cancer, while human papilloma virus causes cervical cancer in women and anal and penile cancer in men. The mouse mammary tumor virus has been found in many human breast cancers, but researchers are not sure what role, if any, it plays in development of the disease.
Dr. Ila R. Singh of the University of Utah and her colleagues have been studying a mouse virus called xenotropic murine leukemia virus-related virus, or XMRV. They, as well as researchers from UC San Francisco, had previously reported finding the virus in some human prostate cancers, but had not looked for it in normal prostate tissues.
In the new study, they looked for the virus in 200 human prostate cancers and in 100 samples of healthy prostate tissue. They reported today in the Proceedings of the National Academy of Sciences that they found the virus in 27% of the cancerous tissues, but in only 6% of the healthy tissues. The virus was most likely to be present in tumors that are considered more aggressive on the Gleason scale of malignancy.
A sequence analysis of the virus showed that it is a gammaretrovirus, one of a family of viruses that are known to cause leukemias and other cancers in animals, but that have not yet been shown to do so in humans. The gammaretroviruses insert their genetic information into the DNA of cells they infect. When this insertion occurs in the wrong position, it can induce the host cell to begin replicating out of control, producing a tumor.
The researchers found that XMRV replicates easily in cultured human prostate tissue, but not in other types of human tissues. But they have not shown that the virus causes tumors to grow. There are also many other unanswered questions, such as whether the virus infects women, whether it is sexually transmitted, and how prevalent it is in the human population.
If the virus could be linked to prostate tumors, it might open the door to new treatments and to prevention. A vaccine against the virus might prevent many cases of prostate cancer, just as the human papilloma virus vaccines prevent cervical cancer. The need for new approaches to prostate cancer is clear: It is second only to skin cancer as the most common form of cancer in males, affecting more than 190,000 American men each year and killing 27,000. Any improvement would be gratefully accepted.
-- Thomas H. Maugh II