Development and external validation of a nomogram for predicting cancer probability at initial prostate biopsy using the life expectancy- and prostate volume-adjusted biopsy scheme

BACKGROUND: We previously reported the diagnostic efficacy of the age-and prostate volume-adjusted prostate biopsy method (the adjusted biopsy method). Here, we developed a new nomogram for predicting cancer probability at initial biopsy using the adjusted method. METHODS: Between 2002 and 2010, 1059 Japanese men with PSA levels between 1.1 and 40 ng ml(-1) and biopsied for the first time using the adjusted method at Gunma University Hospital were enrolled. All subjects underwent digital rectal examination (DRE) and transrectal ultrasonography (TRUS). Data from the initial 849 subjects were used for development of the nomogram and those from the final 210 subjects were used for internal validation. External validation was conducted using data from two affiliated hospitals where the same adjusted biopsy method was used. The nomogram was developed through logistic regression analysis, and predictive accuracy and performance characteristics were assessed using the area under the curve (AUC) of the receiver operating characteristics and calibration plots. Furthermore, we compared the predictive accuracy of the newly developed nomogram with the 'Prostate Risk Indicator' using the development data set, as well as the two external data sets. RESULTS: The AUC of the logistic regression-based nomogram was significantly higher than those of any single clinical parameter. External validation showed significant correlations with the present model. The AUC-receiver operating characteristic of the 'Prostate Risk Indicator' was the second largest following the new nomogram using the development data set and one external data set and almost equal to the new nomogram using the other external data set. CONCLUSIONS: Nevertheless the present model does not include somewhat subjective findings on TRUS abnormality, which is necessary for the estimation by 'Prostate Risk Indicator', the predictive accuracy of the present simple nomogram could be excellent enough to contribute to accurate shared decision-making between doctors and men who are candidates for the adjusted biopsy scheme.