University of Illinois's (US) Professor Karin Rosenblatt found a significant link between the number of partners with which a man had had unprotected sex during his life and his risk of developing prostate cancer. Those who had had 30+ partners had double the risk. Karin suggested that a sexually-transmitted virus might be involved in the disease.

Professor of Oncology Jonathan Waxman at Hammersmith Hospital agreed but could not explain the mechanism. He also pointed out that regular sex appeared to protect against the cancer because it cleansed the prostate gland.