Summary: Sexual Partners, Sexually Transmitted Infections, and Prostate Cancer Risk
Andrea Spence, Ph.D.; Marie-Claude Rousseau, PhD; Marie-Elise Parent, PhD
The causes of prostate cancer are still not fully understood. Factors associated with a more active sex life, though, have been linked with prostate cancer risk. Drs. Andrea Spence, Marie-Claude Rousseau and Marie-Elise Parent have further explored the role of sexual activity in light of existing controversial evidence, with special attention to sexually transmitted infections (STIs) and the gender and number of sexual partners. To their knowledge, the researchers were the first to have discovered that subjects who had more than 20 sexual partners in their lifetime experienced a protective effect against prostate, likewise specifically for having had more than 20 female sexual partners. On the contrary, the same data indicated that having had several male sexual partners increased the risk of prostate cancer. There was also elevated risk for men who never had sexual intercourse. Subjects who considered themselves to be homosexual or bisexual appeared to have a slightly greater prostate cancer risk, compared to subjects who self-identified as heterosexual. This was similar by cancer aggressiveness. Lastly, they concluded that no associations were found for age at first intercourse or for having a history of STIs, but there were not many participants who reported STIs altogether.
It is possible that having numerous sexual partners implies a higher ejaculation frequency, which has been observed as being protective in both cohort and case-control study designs. This is because more frequent ejaculations may reduce the concentration of carcinogenic substances within prostatic fluid or reduce production of intraluminal prostatic crystalloids, both of which are highly associated with prostate cancer. The protective effect of many female sexual partners also argues against the infectious disease hypothesis, since a more active sex life would be expected to provide a higher chance of contracting STIs. While the researchers did observe an increase in STIs parallel to a higher number of lifetime sexual partners, this did not translate as providing an increased risk of prostate cancer.
These findings are promising as they encourage possible next steps in prostate cancer research. Previous studies only rarely separated prostate cancer risk associated with female versus male sexual partners. Similarly, there has been little focus on a potential link between sexual orientation and the disease. Future investigations can have the opportunity to further explore these results based on gender and number of sexual partner by collecting data on the frequency of sexual intercourse, the type of intercourse, ejaculation frequency, condom use, and masturbation practices.
The data in this study was based on information collected during in-person interviews which specifically addressed sexual activity and STI history, among other socio-demographic, lifestyle, and environmental factors. The interviews were conducted with 1590 individuals with recently confirmed cases of prostate cancers, and 1619 age-matched individuals without the disease, in the predominantly French-speaking population of Montréal.