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Validation of the Prostate Cancer Risk Index (PRIX): a simple scoring system to predict risk of biochemical relapse after radical prostatectomy for prostate cancer.

OBJECTIVE
The Prostate Cancer Risk Index (PRIX) is a simple scoring system for risk stratification of clinically localized prostate cancer that relies on three variables: prostate-specific antigen level at diagnosis, Gleason score at biopsy and clinical T stage. The aim of this study was validation of the ability of the PRIX score to predict biochemical relapse after radical prostatectomy in a series of patients from a single Japanese center.


METHODS
From 1995 to 2008, 519 patients who underwent radical prostatectomy for clinically localized prostate cancer with no adjuvant therapies were included in the validation cohort. The biochemical relapse-free rate was estimated using the Kaplan-Meier method. The performance of the PRIX score was assessed with Cox proportional hazards regression model, concordance index and a calibration plot. For comparison, the performance of the D'Amico classification was also assessed.


RESULTS
Biochemical relapse-free rate continuously decreased as the PRIX score increased. Each 1-point increment in the PRIX score led to an increase in hazard ratio for biochemical relapse. The concordance index of the PRIX score and the D'Amico classification to predict biochemical relapse was 0.719 and 0.730, respectively. The Kaplan-Meier plots and the calibration plots demonstrated the possibility that the PRIX score could present more detailed stratification than the D'Amico classification.


CONCLUSIONS
The results of our investigation showed that in Japanese patients treated at a single center, the PRIX score can accurately predict biochemical relapse after radical prostatectomy and demonstrates reasonable calibration. The PRIX score may be one option as a prediction model for biochemical relapse after radical prostatectomy.