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September 6, 1985

Problematic Prostatic Prediction

Author Affiliations

USNR Naval Hospital Charleston, SC

JAMA. 1985;254(9):1171-1172. doi:10.1001/jama.1985.03360090061009

To the Editor.—  Drs Chodak and Schoenberg1 provide encouraging data that the digital rectal examination can detect early prostate cancer in asymptomatic men. However, we should not overinterpret their results.The authors confuse specificity with predictive value. Eleven cancers were detected in 38 prostate biopsy specimens. Eleven (29% ) of 38 is not specificity, but the predictive value of a positive test result. As biopsy remains the gold standard for detection of prostate cancer, specificity cannot be determined because biopsies are not performed on men with normal prostate examinations. In this study, prostate biopsy yielded a diagnosis of cancer in 29% of cases. This actually is a reasonable predictive value for a screening program. But we have no data on sensitivity or specificity, and thus cannot calculate how many cancers are being missed by rectal examination.I raise several other minor points. First, the examinations were performed by urologic specialists, yet