Vasectomy and the risk of prostate cancer in a cohort of multiphasic health-checkup examinees: second report.

The relationship of vasectomy to prostate cancer was studied in 5,119 men men with a self-reported history of vasectomy, identified at multiphasic health checkups undergone during 1977-82 while members of the Northern California Kaiser Permanente Medical Care Program. Three unvasectomized comparison subjects were identified for each vasectomized man, matched for age, race, marital status, and date and location of the examination. Follow-up for incident prostate cancer was conducted for a mean length of 6.8 years. The relative risk of prostate cancer associated with vasectomy was 1.0 (95% confidence interval = 0.7 - 1.6); the relative risk was approximately one, regardless of length of interval (less than 10 years, 10-20 years, more than 20 years) between vasectomy and multiphasic health checkup or the age at vasectomy (less than 40 years vs more than 40 years). These data support earlier findings reported in this study group of the lack of an association of vasectomy with subsequent risk of prostate cancer.