I think this is an underreported story, so I want to highlight it:
SAN FRANCISCO – In a surprising discovery, researchers said Friday they had found a virus in some prostate cancer patients, a finding that opens new research avenues in the most common major cancer among men in the United States.
The virus, closely related to one previously seen only in mice, was found in cancerous prostates removed from men with a certain genetic defect. The researchers, with the University of California, San Francisco and the Cleveland Clinic, warn that they have not discovered any links between the virus and prostate cancer, but they were nonetheless excited about prospects for future research.
"It is a very exciting discovery," said Dr. Eric Klein of the Cleveland Clinic, who presented the findings at an American Society of Clinical Oncology meeting. "There is now a suggestion that prostate cancer could be caused by an infectious disease."