External Validation of the Cancer of the Prostate Risk Assessment Score to Predict Biochemical Relapse after Radical Prostatectomy for Prostate Cancer in Japanese Patients

Abstract

Objectives: The aim of the present study was external validation to determine whether the Cancer of the Prostate Risk Assessment (CAPRA) score predicts biochemical relapse (BCR) after radical prostatectomy (RP) in Japanese patients. Methods: From 1995 to 2008, 503 Japanese patients undergoing RP for clinically localized prostate cancer were included in the validation cohort. The BCR-free rate was estimated using the Kaplan-Meier method. Performance of the CAPRA score was assessed using Cox proportional hazards regression models, concordance index (c-index) and calibration plots. Results: Unlike the results in the Cancer of the Prostate Strategic Urologic Research Endeavor (CaPSURE) cohort, the BCR-free rate and the hazard ratio for CAPRA score 4 were inversely better than those for CAPRA scores 2 and 3 in Japanese patients. The c-index of the CAPRA score was 0.673. The calibration plot demonstrated that the CAPRA score was generally well calibrated. Conclusions: In Japanese patients, the CAPRA score can predict BCR after RP only to some degree. Although our c-index is comparable with the c-index of 0.66 in the original CaPSURE cohort, it is lower than the c-indices reported in other validation cohorts, which range from 0.68 to 0.81. The CAPRA score may not predict BCR after RP in Japanese patients as accurately as it did in Western patients.