About 42 to 60 million couples worldwide rely on vasectomy to prevent pregnancy. Over the years, some studies have reported an increased risk of prostate cancer in men who have had vasectomies (one study reported a relative risk [RR] of 6.7), while other studies discount such claims. Some urologists have even recommended prostate cancer screening for men who have had vasectomies and against performing vasectomies in men with a strong family history of prostate cancer. Cox and colleagues sought to determine whether there was, in fact, any change in prostate cancer risk in post-vasectomy patients, especially many years later.

New Zealand was selected as the site of the study because it has the highest prevalence of vasectomies and also has mandatory notification of cancer. The researchers enrolled men of European descent (to avoid issues related to ethnicity) who were 40 to 74 years of age and newly diagnosed with prostate cancer. Ultimately, 953 men with prostate cancer and 1,260 age-matched control patients participated in the study. Telephone interviews were conducted with each participant to collect details of previous illnesses, urologic symptoms and surgeries, prostate-specific antigen testing, and so forth. If available, information about the TNM stage of the cancer was recorded. Interviewers were unaware of whether each interviewee was a case patient or a control patient until about halfway through the interview process.

Men who had a father or brother with prostate cancer had an increased risk (RR, 2.63) of developing prostate cancer themselves. Prostate cancer risk was not related to religious affiliation, location of residence, socioeconomic status, history of smoking, alcohol intake, or number of children. The risk of prostate cancer was not increased in men who had undergone vasectomy (RR, 0.92), even in those who had had the procedure at least 25 years earlier (RR, 0.92; this latter group represented 38 percent of the group under consideration). An increased risk of prostate cancer that was not statistically significant was noted in men 40 to 49 years of age at diagnosis.

The authors conclude that this large population-based study provides evidence that there is no increased risk of prostate cancer in men who have had vasectomies. Previous studies may have suffered from selection and publication bias and, thus, overestimated prostate cancer risk.