CN2 - PREDICTING UTILITY SCORES IN LOCALIZED PROSTATE CANCER: MAPPING FROM EPIC TO PORPUS

Abstract

The Patient-Oriented Prostate Utility Scale (PORPUS-U) is the only econometric instrument specifically designed for prostate cancer patients. The Expanded Prostate cancer Index Composite (EPIC) and the SF-36 are the most used instruments in these patients. This study aims to estimate the PORPUS-U index by EPIC and SF-36 scores to allow cost-utility analysis. The Spanish Multicentric Localized Prostate Cancer Study in new therapeutic modalities included patients diagnosed between 2014 and 2017 (n=469). PORPUS-U, EPIC and SF-36 were administered by telephone. The predictive model was constructed with the evaluation 3 months after treatment, and validated with evaluations at 6, 12, 24 and 36 months. A linear regression model was constructed with the logarithmic transformation of the PORPUS-U index as the dependent variable, and EPIC scores and the SF-36 physical and mental summary components as explanatory variables. All possible first level interactions were tested. R2 and Root Mean Square Error (RMSE) of the model were considered. Agreement between the estimated index and the observed one was calculated with the Intraclass Correlation Coefficient (ICC). The model chosen included six EPIC scores (urinary incontinence and irritative-obstructive, sexual function and bother, bowel and hormonal) and the two summary components of the SF-36: R2=0.793, RMSE=0.036 and ICC=0.914. The validation models showed RMSE ranging 0.031-0.045 and ICC ranging 0.838-0.922. The means (SD) of the PORPUS-U index observed and predicted by the model were: 0.97 (0.04) vs. 0.96 (0.05) at 6 months, 0.97 (0.05) vs. 0.96 (0.06) at 12 months, 0.96 (0.05) vs. 0.96 (0.07) at 24 months and 0.97 (0.06) vs. 0.95 (0.06) at 36 months. The model constructed with EPIC scores and the two SF-36 summary components presented a good predictive capacity to estimate the PORPUS-U utility index, which could be useful to allow cost-utility analysis in studies without an econometric instrument.