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

Evaluation of the Cancer of Bladder Risk Assessment (COBRA) Score in the Cancer Genome Atlas (TCGA) Bladder Cancer Cohort

OBJECTIVE

To evaluate the Cancer of the Bladder Risk Assessment (COBRA) score in The Cancer Genome Atlas (TCGA) bladder cancer cohort. Second, to investigate the utility of the COBRA score within each bladder cancer molecular subtype following radical cystectomy (RC) and determine if it can help identify candidates for adjuvant therapies and clinical trials.

METHODS

Among the TCGA bladder cancer cohort (n = 412), RC pathology reports were reviewed to calculate COBRA scores. Kaplan-Meier survival curves along with univariable and multivariable Cox proportional hazard models were used to determine the clinical utility of the COBRA score to predict overall survival (OS) within the overall cohort and within each molecular subtype (if n>30 within subtype).

RESULTS

In the analytic cohort (n = 273) there was a median follow-up of 18 months. Higher COBRA score was associated with significant increased risk of death in both univariable (HR = 1.52 per point [PP] 95% CI [1.32, 1.75)] and multivariable models (HR = 1.54 PP 95% CI [1.32, 1.79]). This remained true in multivariable models stratified by molecular subtype for basal (HR = 1.37 PP 95% CI [1.07, 1.74]), luminal infiltrated (HR = 1.70 PP 95% CI [1.10, 2.64]), and luminal papillary (HR = 1.62 PP 95% CI [1.28, 2.06]) tumors.

CONCLUSION

Our findings validate the COBRA score in the TCGA bladder cancer cohort. This suggests the COBRA score can be used in conjunction with molecular subtyping information to help guide clinical decision-making following RC to improve risk stratification and allow for earlier identification of candidates for adjuvant therapies and clinical trials.

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

OBJECTIVE

To perform an external validation of the Cancer of the Bladder Risk Assessment (COBRA) score for estimating cancer-specific survival (CSS) after radical cystectomy (RC) in a large bi-institutional cohort of patients.

PATIENTS AND METHODS

Patients treated with RC and lymph node dissection (LND) between May 1996 and July 2017 were retrieved from the RC databases of Leuven and Turin. Collected variables were age at RC, tumour stage, lymph node (LN) density, neoadjuvant chemotherapy, the extent of LND, and nodal stage. The primary outcome was CSS visualised using Kaplan-Meier plots. Cox proportional hazard models were used to assess the impact of variables on CSS. We performed a pairwise comparison between the COBRA score levels using a log-rank test corrected by Bonferroni, and developed a simplified COBRA score with three risk categories. To compare models, we assessed concordance indices (C-indices), receiver operating characteristic curves with area under the curve (AUC), calibration plots, and decision curve analysis (DCA). Finally, we compared both COBRA and simplified COBRA models with the established American Joint Committee on Cancer (AJCC) model.

RESULTS

A total of 812 patients were included. All COBRA score variables had a significant impact on CSS in a Cox proportional hazard model. However, pairwise comparison of the COBRA subscores could not differentiate significantly between all COBRA score levels. Based on these findings, we developed a simplified COBRA score by introducing three categories within the following COBRA score ranges: low- (0-1) vs intermediate- (2-4) vs high-risk (5-7). A pairwise comparison could discriminate significantly between all COBRA risk categories. When finally comparing COBRA and simplified COBRA models with the AJCC model, AJCC performed better than both. C-indices, AUCs, calibration plots and DCA for AJCC were all better compared with the original and simplified COBRA models.

CONCLUSION

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.