Infectious disease-causing viruses are already blamed for causing some liver cancers and cervical cancer. That has planted nagging suspicions in the minds of scientists that some diseases may play important roles alongside genetics, environment and chance in causing breast, stomach and several other forms of cancer.

The virus, closely related to one previously found 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.

Infectious Disease-Causing Viruses

"It is a very exciting discovery," said Dr. Eric Klein of the Cleveland Clinic, who will present the findings today at an American Society of Clinical Oncology prostate symposium in San Francisco. "There is now a suggestion that prostate cancer could be caused by an infectious disease."

Infectious disease-causing viruses are already blamed for causing some liver cancers and cervical cancer. That has planted nagging suspicions in the minds of scientists that some diseases may play important roles alongside genetics, environment and chance in causing breast, stomach and several other forms of cancer.

Researchers are not sure how the virus infected people, but suspect it has been passed on genetically for thousands of years.

"This is a class of virus no one would have looked for in prostate cancer," said UCSF researcher Joe DeRisi.