The Cancer of the Bladder Risk Assessment (COBRA) score for predicting cancer-specific survival after radical cystectomy for urothelial carcinoma of the bladder: External validation in a cohort of Korean patients

Abstract

ObjectivesTo validate the Cancer of the Bladder Risk Assessment (COBRA) score for predicting cancer-specific survival (CSS) in comparison with the American Joint Committee on Cancer (AJCC) staging system using an external cohort of urothelial carcinoma of the bladder (UCB) from South Korea. Materials and MethodsThe final validation cohort consisted of 855 patients who underwent radical cystectomy (RC) for UCB in a single institution. The impact of the COBRA score on CSS was estimated using Cox proportional hazard models. Discrimination accuracy was quantified with concordance index. Calibration plots were used to determine the relationship between model-predicted CSS and actual CSS at 2 years and 5 years after RC. Clinical usefulness of the COBRA score was assessed using decision curve analyses. ResultsOne-point increase in the COBRA score (range, 0–6) was closely related to a 1.50-fold increase (95% confidence interval [CI]: 1.39–1.62) in the risk of death from UCB. Discrimination accuracies of the COBRA score and AJCC staging system for CSS at 5 years were 70.6% (95% CI: 67.2–74.0) and 68.3% (95% CI: 65.0–71.6), respectively. Compared to the AJCC staging system, the COBRA score was generally well-calibrated for predicting CSS at 2 and 5 years after RC. On decision curve analyses, the use of the COBRA score showed more clinical net benefits across a wide range of threshold probabilities than the AJCC staging system. ConclusionsOur external validation results suggest that although the COBRA score is not perfectly accurate, it shows a reasonable level of discriminative ability, adequate calibration, and meaningful net benefit gain for predicting CSS after RC in a Korean UCB cohort.