The Cancer of the Bladder Risk Assessment (COBRA) score for estimating cancer-specific survival after radical cystectomy: external validation in a large bi-institutional cohort.

We performed an external validation of the COBRA score in a large bi-institutional cohort. We observed that several risk groups had overlapping CSS, demonstrating suboptimal performance of the COBRA score. Therefore, we constructed a simplified model with three COBRA score risk categories. This model resulted in demarcated risk groups with non-overlapping CSS and good predictive accuracy. However, both COBRA score models were outperformed by the AJCC staging system. Therefore, we conclude that the AJCC staging system should remain the current standard for stratifying patients after RC for CSS.