Receiver-operating characteristic as a tool for evaluating the diagnostic performance of prostate-specific antigen and its molecular forms - What hasto be considered?

BACKGROUND. Receiver-operating characteristic (ROC) analysis is often appli ed as evaluation tool to compare the diagnostic validity of laboratory test s. The aim of this study was to draw attention to preconditions which shoul d be taken into account when ROC analysis is used to assess the diagnostic performance of total prostate-specific antigen (tPSA) and its molecular for ms in differential diagnosis between prostate cancer and benign prostatic h yperplasia (BPH). METHODS. Using a standard software (GraphROC for Windows), ROC analyses wer e performed and the areas under the curves were calculated for four hypothe tical pairs of groups. Every group included 40 patients with prostate cance r and with BPH showing different tPSA concentrations (range of 2-10 mug/L), but similar free-to-total PSA ratios (fPSA%). RESULTS. The area under the fPSA% ROC curve showed the highest value, where as the areas under the tPSA ROC curves were dependent on the distributions of tPSA concentrations in the patients. The ability of fPSA% to improve the differential diagnosis between prostate cancer and BPH in comparison to tP SA was not furthermore evident, if the prostate cancer group included more patients with higher tPSA concentrations than the BPH group. CONCLUSIONS. When the diagnostic performance of tPSA and its derivatives Li ke molecular forms in patients with prostate cancer and BPH should be compa red by ROC analysis, a matching procedure is recommended prior to ROC analy sis to compensate the effect of possible unequal tPSA distributions in both groups. Each BPH (or PCa) patient should be matched with a PCa (or BPH) pa tient with nearest tPSA concentration so that an optimum of overlapping tPS A concentrations in both groups can be achieved. Prostate 46:307-310, 2001. (C) 2001 Wiley-Liss,Inc.