Prostate Cancer May be Caused by Virus

The researchers found virus causing the most aggressive form of prostate cancer, potentially leading the way to identifying men with the deadliest tumors and pinpointing their treatment. The discovery, reported today in the Proceedings of the National Academy of Sciences, involves the XMRV virus, discovered just three years ago, said Ila Singh, an associate professor of pathology at the University of Utah in Salt Lake City. Forty-four percent of men with tumors graded 9 out of 10 for severity on a standard scale had evidence of XMRV, Singh’s study found. More than 190,000 U.S. men will be diagnosed with prostate cancer this year and 27,000 will die, according to the National Cancer Institute. A more accurate way to identify the riskiest cases might improve therapy, since some tumors are slow growing and don’t require aggressive treatment with surgery, chemotherapy or radiation, all of which carry side effects. About 1 million men have been needlessly treated for prostate cancer over the past two decades, largely because of greater use of a blood test for the protein called prostate specific antigen, or PSA, at an estimated cost of $40 billion, according to a study reported Aug. 31 in the Journal of the National Cancer Institute. Singh and her colleagues developed tests that could spot signs of the XMRV virus inside cells, then checked tissue removed during biopsies from the prostates of 233 men with cancer and 101 with benign enlargement of the organ. The virus was present in 23 percent of men with cancer and 4 percent of non-cancerous prostates, the researchers found. The tumors that scored highest on the 10-point Gleason severity scale were more likely to contain the virus, the study found. XMVR is a retrovirus, a virus that gets incorporated into the genome of the cells it infects. It may trigger cancer by locating in the cell’s genome next to DNA that controls cell growth, and disrupting those genes in a way that allows cells to replicate uncontrollably, Singh said. It will take more work to prove that theory, show that the virus causes prostate cancers and demonstrate that the tests Singh and her colleagues devised can accurately detect its presence. She and other scientists will also look for evidence of XMRV in other types of cancer, Singh said. While research has shown that PSA levels are higher in men who have cancer cells in their prostate, the test by itself can’t detect cancer, said H. Gilbert Welch, the senior author of the Aug. 31 study on PSA testing and a researcher at the Dartmouth Institute for Health Policy and Clinical Practice, in Lebanon, New Hampshire, Bloomberg reports. Men who have elevated PSA tests are often urged to have a biopsy, a procedure that removes bits of tissue from the prostate to look for the presence of cancer cells. Biopsies are often inconclusive in showing that a patient has cancer cells that pose an actual threat, Welch said. Even so, patients who have positive biopsies are often urged to have surgery or other procedures, he said.