To the Editor.
—Giovannucci et al1,2 reported associations between prostate cancer and vasectomy from two cohort studies in The Journal.3 The publication of two positive articles from Harvard University left many physicians resigned to a vasectomy risk for prostatic carcinoma. Young families now need to be informed when making permanent contraceptive choices; however, a recent National Institutes of Health panel4 stated that there is insufficient basis for changing current practices and that screening for prostate cancer need not be different for sterilized men.This position may not change very soon. Given past contraceptive safety study history, weak associations between contraception and cancer may require 50 or more observational studies before a causal link, if any, can be established. This is supported by contradictory negative findings in other existing investigations and, among weakly positive studies such as those from Harvard, inconsistent findings among subgroups.4 Among the recent weakly
Perlman JA, Brawley OW, Ford LG, Kramer BS. Vasectomy and Increased Risk of Prostate Cancer. JAMA. 1993;270(6):706-707. doi:10.1001/jama.1993.03510060051021