Vasectomy not a risk factor for prostate cancer - Patient-Oriented Evidence that Matters - Brief Article

Journal of Family Practice, Sept, 2002 by Scott M. Strayer

Cox B, Sneyd MJ, Paul C, Delahunt B, Skegg DCG. Vasectomy and the risk of prostate cancer. JAMA 2002; 287:3110-5.

* BACKGROUND Several case-control and cohort studies since the early 1990s have shown conflicting results on a possible association between vasectomy and prostate cancer risk. A recent systematic review failed to show a causal association and suggested several possible mechanisms for inconclusive results. This study addressed some of these limitations.

* POPULATION STUDIED The study included 923 men in New Zealand between the ages of 40 and 74 years with newly diagnosed prostate cancer (cases). All men were on the general electoral roll and had a history of marriage. The control group was randomly selected from the general electoral roll (n = 1224), and frequency matching to cases was performed in 5-year age groups. The mean age for cases and controls was 66.3 and 65.1 years, respectively. All cases and controls had telephone numbers for data collection purposes. Because nearly all study subjects were of European descent (97%), the results may not apply to other ethnic groups.

* STUDY DESIGN AND VALIDITY This national, population-based, case-control study was performed on all newly diagnosed cases of prostate cancer during a specified time (April 1, 1996, to December 31, 1998). Controls were randomly selected from the general electoral roll in which about 95% of adults are listed. Of potential cases and controls, only 12% and 20%, respectively, could not be contacted due to death, doctor or subject refusal, severe illness, inability to trace, or language difficulties.

Data on cases and controls were collected using interviewers who were initially blind to whether they were contacting a case or a control subject. Information regarding previous illnesses, smoking and alcohol consumption, prostate-specific antigen testing, digital rectal examination, previous urological symptoms and operations, family history of cancer, sociodemographic characteristics, and vasectomy was collected. The study hypothesis was not revealed to the patients being interviewed.

Due to the high prevalence of vasectomies in New Zealand (reportedly the highest in the world) and the large number of cases and controls, the study had 99% statistical power to detect a relative risk of 1.5 or higher at a 5% significance level. Even after 25 years since vasectomy, the study had 80% statistical power to detect the same risk.

To assess the possibility of recall bias for a history of vasectomy (ie, men with prostate cancer would be more likely to remember that they had a vasectomy than men without cancer), the authors attempted to obtain the records of a random sample of 103 men. Only 49 records were obtained during the study time period, but all self-reports were confirmed. Although recall is a potential source for error, it would seem unlikely that many men would have doubts about having undergone a vasectomy. Other possible sources of bias including interviewer bias and detection bias (due to close surveillance by a urologist) were adequately addressed in the study.

* OUTCOMES MEASURED The primary outcome measured was the relative risk (RR) of prostate cancer for men who had vasectomies compared with that for men who had not undergone the procedure.

* RESULTS No association between prostate cancer and vasectomy was found (RR = 0.92; 95% confidence interval [CI], 0.75-1.14). Even after 25 years since vasectomy, no association was found (RR = 0.92; 95% CI, 0.68-1.23). Adjustments were made for social class, geographic region, religious affiliation, and family history of prostate cancer without any effect on the risk.

RECOMMENDATIONS FOR CLINICAL PRACTICE

This study found that having a vasectomy does not increase a man's risk of developing prostate cancer, even after 25 or more years of follow-up. Because a previous systematic review also showed no conclusive evidence for an increased risk of prostate cancer after vasectomy, practitioners can confidently advise patients requesting vasectomies of the safety advantages compared with other methods of sterilization.

Scott M. Strayer, MD, MPH
Department of Family Medicine
University of Virginia Health System
Charlottesville
E-mail: sstrayer@virginia.edu