Possible Viral Link to Deadly Prostate Cancers May Improve Diagnosis and Treatment

Recent research has identified a possible link between a virus and particularly aggressive prostate cancer, a development that might eventually help doctors identify men with the deadliest tumors and tailor treatment accordingly.

Writing in the Proceedings of the National Academy of Sciences, researchers from Columbia University and University of Utah note that xenotropic murine leukemia virus-related virus (XMRV), part of a class of viruses known to cause cancer in animals, was recently discovered in human prostate cancers. It had not previously been found in humans, noted the team led by Ila R. Singh of University of Utah.

The researchers also established that XMRV is a retrovirus, which inserts its genetic map into the cells it infects. In doing so, the virus can kill a cell or turn it cancerous by altering its genes. Other retroviruses, including human immunodeficiency virus (HIV, the virus that causes AIDS), have been linked to cancers in humans.

More importantly, Singh's team found evidence of a link between XMRV and aggressive prostate cancer after analyzing 334 prostate cancer samples with both a DNA test to detect the virus itself and another test that detects proteins indicating the body's immune response to the virus. The team found XMRV DNA in 6% of the prostate cancers and XMRV protein expression in 23%. Furthermore, they noted that about 30% of the high-grade tumors, those associated with metastasis and a poorer prognosis, were positive for XMRV. The most aggressive cancers had the highest percentage of positive results (44%).

Could XMRV cause aggressive cancer?
Researchers believe that viral infection with XMRV may be directly linked to development of tumors. That's because they found XMRV proteins that came primarily from cancerous cells lining the prostate. The proteins were associated especially with more advanced and deadly cancers.

Other studies have revealed that other viruses cause cancers, including the human papillomavirus (HPV) that causes cervical cancer. Currently, a vaccine is available to prevent infection with the most common forms of HPV. Viruses have also been shown as the cause of some cases of penile, anal, and head and neck cancers.

Singh's team calls for more study of XMRV's link to aggressive prostate cancers in order to help develop better tests and therapies. "If established, a direct role for XMRV in prostate cancer tumorigenesis would open up opportunities to develop new diagnostic markers as well as new methods to prevent and treat this cancer with antiretroviral therapies or vaccines," the team writes.

Better prostate cancer diagnosis needed
Singh's research comes on the heels of a study that raises questions about the value of current prostate cancer screening. Writing in the Journal of the National Cancer Institute, scientists from Dartmouth Medical School and University of Connecticut estimate that 1 million U.S. men have been diagnosed and treated for tumors that would never have harmed them. "Many cases of prostate cancer are unlikely to manifest themselves during the patient's lifetime," these researchers write. Echoing the Singh team's call for better prostate cancer tests, they add, "There is a clear need for better markers to detect cancers that pose a significant health threat and to specifically target these for therapy."

Two other studies published earlier this year in the New England Journal of Medicine left doubts about the usefulness of screening for prostate cancer. To read more about these, see the article: Prostate Cancer Screening Studies Don't Settle Question of Clinical Utility.

Tests: PSA
Conditions: Prostate Cancer

Robert Schlaberga et al. XMRV is present in malignant prostatic epithelium and is associated with prostate cancer, especially high-grade tumors. Proc Natl Acad Sci 106(38): 16351–16356. Available online at http://www.pnas.org/content/early/2009/09/04/0906922106.full.pdf+html through http://www.pnas.org. Posted September 8, 2009. Accessed September 30, 2009.

News article. Virus might be one cause of prostate cancer-study. Reuters Health. Available online at http://www.reuters.com/article/healthNews/idUSTRE58646320090907 through http://www.reuters.com. Posted September 7, 2009. Accessed September 30, 2009.

Carmen Phillips. Study Questions Value of Prostate Cancer Screening. NCI Cancer Bulletin. Available online at http://www.cancer.gov/ncicancerbulletin/090809/page2 through http://www.cancer.gov. Posted September 8, 2009. Accessed September 30, 2009.