Combination of Two T1 Substaging Systems (T1a/b/c and T1m/e) Better Predicts Tumor Outcomes in Patients with T1 High Grade Bladder Cancer

BACKGROUND: T1 substaging is a predictive factor for non-muscle-invasive bladder cancer, and two types of T1 substaging systems (T1a/b/c and T1m/e) are currently in use. However, the predictive ability of both systems is poor, and there is debate over which system is better. OBJECTIVE: To confirm whether combination of two T1 substaging systems can improve the predictive ability of T1 substaging for tumor outcomes. METHODS: Patients with primary pT1 high-grade bladder cancer from three centers were included. All tumors were assessed with T1a/b/c and T1m/e substaging. A new variable named COMB was developed in which patients were stratified into T1a/bT1m, T1a/bT1e, T1cT1m or T1cT1e subgroups. A time-dependent receiver operating characteristic curve (ROC) analysis was used to test whether the accuracy of prediction could be improved with COMB. RESULTS: A total of 239 patients with primary pT1HG were analyzed. No tumor was T1cT1m, and therefore, only three types of combinations were evaluated: T1a/bT1m (62 patients), T1a/bT1e (124 patients) and T1cT1e (53 patients). Regardless of all patients or those treated with Re-TURBt and adequate BCG, patients with T1a/bT1m have the best prognosis, and those with T1cT1e have the poorest prognosis. The time-dependent ROC showed that, for both recurrence and progression, COMB had a higher AUC than T1a/b/c and T1m/e, regardless of population. CONCLUSIONS: Compared with either system alone, the combination of two T1 substaging systems improves the predictive ability of T1 substaging for tumor outcomes.