Sexual factors and the risk of prostate cancer.

A population-based case-control study of prostate cancer was performed in King County, Washington, in White men and Black men aged 40-64 years, between 1993 and 1996. Incident prostate cancer cases (n = 753) were identified from the Seattle-Puget Sound Surveillance, Epidemiology, and End Results (SEER) cancer registry. Controls (n = 703) were identified through random digit dialing and were frequency matched to cases on age. Sexual behavior, medical history, and other potential prostate cancer risk factors were ascertained through an in-person interview. There was no relation between sexual orientation and prostate cancer, although the number of men who had sex with men was small. Risk estimates increased directly with the lifetime number of female sexual partners (trend p < 0.001) but not with male partners (trend p = 0.62). Risk also increased with decreasing age at first intercourse, but this effect disappeared after adjusting for the number of female partners. Prior infection with gonorrhea was positively associated with risk (odds ratio = 1.50; 95% confidence interval: 1.0, 2.2), but no effect was seen among men with other sexually transmitted diseases. No relation between lifetime frequency of sexual intercourse and risk of prostate cancer was apparent. These findings are consistent with previous studies that support an infectious etiology for prostate cancer.