To the Editor.
—In a recent issue of JAMA, Giovannucci et al1,2 report in two studies an association between vasectomy and prostate cancer, concluding in both that their work supports a causal relationship. However, a major study flaw invalidates any possible conclusion regarding causality. Namely, Giovannucci et al failed to obtain reliable information on the incidence of prostate cancer in their study population in a systematic manner and have therefore identified only a fraction of the clinically detectable cases of prostate cancers in their study population. Index cases were identified entirely on the basis of self-reports or spousal reports, a particularly insensitive assay for the presence of a disease such as prostate cancer, which may be asymptomatic even at advanced stages. As an illustration, Labrie and coworkers3 identified 57 cases of prostate cancer among 1002 men selected from electoral rolls, for a detection rate of 5.7%, whereas Giovannucci
Morgentaler A, DeWolf WC. Vasectomy and Increased Risk of Prostate Cancer. JAMA. 1993;270(6):705–706. doi:10.1001/jama.1993.03510060051019
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