Development of a nomogram to predict probability of positive initial prostate biopsy among Japanese patients

Objectives. Several nomograms for prostate cancer detection have recently been developed. Because the incidence of prostate cancer is lower among Asian men, nomograms based on Western populations cannot be directly applied to Japanese men. We, therefore, developed a model for predicting the probability of a positive initial prostate biopsy using clinical and laboratory data from a Japanese male population. Methods. Data were collected from 834 Japanese male referrals who underwent initial prostate biopsies as individual screening. We analyzed age, total prostate-specific antigen (PSA) level, free/total PSA (f/t PSA) ratio, prostate volume, and digital rectal examination findings. Of these data, we randomly reserved 20% for study validation. Logistic regression analysis estimated relative risk, 95% confidence intervals, and P values. Results. Independent predictors of a positive biopsy result included elevated PSA levels, decreased f/T PSA ratio, advanced age, small prostate volume, and abnormal digital rectal examination findings. We developed a predictive nomogram for an initial positive biopsy using these variables. The area under the receiver operating characteristic curve for the model was 81.8%, which was significantly greater than that of the prediction based on PSA alone (area under the receiver operating characteristic curve 67.8%). If externally validated, applying this model could reduce unnecessary biopsy procedures by 32% and reduce the overall need for prostate biopsies by 26%. Conclusions. In this study of a Japanese population, incorporating clinical and laboratory data into a prebiopsy nomogram significantly improved the prediction of prostate cancer compared with predictions based solely on the individual factors.