Does vasectomy cause prostate cancer?

Vasectomy is the process in which a man's vas deferens are severed, with the cut ends folded back and tied off to prevent the release of sperm from his testicles to the urethra and out of the penis. The procedure may be conducted in a doctor's office under local anesthesia, is almost 100% effective in preventing pregnancy, and leaves sexual function fully intact. Since sperm comprise less than 5% of semen, even the amount of ejaculated fluid does not change noticeably. 20% of American men over age 35 years have had a vasectomy. Despite vasectomy's simplicity and effectiveness, debate exists over whether vasectomy may increase the risk of prostate cancer, the most common malignancy in men. Two large, well-designed Harvard studies were published in 1993 in the Journal of the American Medical Association which suggest that such a relationship may exist. The two studies compared the number of prostate-cancer diagnoses in almost 25,000 men who had undergone vasectomy with nearly 50,000 men who had not. Men who had undergone vasectomy more than 20 years earlier were almost twice as likely as their unsterilized counterparts to have been diagnosed with prostate cancer. Overall, the rate of such diagnoses was about 60% higher among the men who had been sterilized. These widely-reported studies rekindled earlier fears of a possible prostate-cancer risk and no doubt convinced some men to avoid the operation or to have it reversed if they had already gone through with it. Four earlier studies also suggested a link between prostate cancer and vasectomy. Seven other reports, however, have found no connection. Several studies even indicate that men who undergo vasectomy live longer than other men. Many researchers believe that the Harvard studies' findings are simply the result of earlier and better diagnosis of prostate cancer among sterilized men rather than due to an actual increased risk of the cancer.