3,208 men were part of the Prostate Cancer & Environment Study (PROtEuS) in Montreal, Canada. Of these, 1,590 were diagnosed with prostate cancer between 2005 and 2009, while the remaining 1,618 men were free of the disease.
As part of this study, all men were required to complete a questionnaire that asked about their sexual activity, as well as sociodemographic, environmental and lifestyle factors.
Men were twice as likely to develop all types of prostate cancer, compared with men who had never had a sexual partner. Furthermore, men who had slept with more than 20 male partners had a 500% increased risk of developing a less aggressive prostate cancer, compared with those who had only slept with one man.
The researchers are unable to accurately identify the reasons behind these findings.