To the Editor.
—In their studies of the relationship of vasectomy to prostate cancer, Giovannucci et al1,2 relied on self-report by cohort members or their wives to identify incident prostate cancers and confirmed as many of these cases as possible by request for and review of medical records. Self-report of prostate cancer may potentially result in significant underascertainment of cases. The Kaiser Permanente Study3 of vasectomy and prostate cancer afforded an opportunity to assess the potential for underascertainment. In the Kaiser Permanente Study, incident prostate cases were identified in a cohort of multiphasic health checkup (MHC) examinees by linking the medical record number of the MHC examinee to computerized tumor registry and hospitalization records, a method that does not rely on self-report. Of the 38 MHC cohort members who had a second MHC after an incident prostate cancer, 17 (45%) did not report a history of any cancer
Sidney S, Quesenberry CP, Sadler MC, Cattolica EV. Vasectomy and Increased Risk of Prostate Cancer. JAMA. 1993;270(6):705. doi:10.1001/jama.1993.03510060051018
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