Prognostic Interest in Discriminating Muscularis Mucosa Invasion (T1a vs T1b) in Nonmuscle Invasive Bladder Carcinoma: French National Multicenter Study with Central Pathology Review

PurposePredictive factors of T1 nonmuscle invasive bladder cancer evolution that could guide treatment decision making are lacking. We assessed the prognostic value of muscularis mucosa invasion in nonmuscle invasive bladder cancer.Materials and MethodsIn a national multicenter study patients with primary T1 nonmuscle invasive bladder cancer were recruited from 6 French hospitals. All patients had undergone transurethral resection of bladder tumor. All T1 tumors were substaged according to muscularis mucosa invasion as T1a—no invasion beyond the muscularis mucosa or T1b—invasion beyond the muscularis mucosa with muscle preservation. Subsequent central pathology review was then done by a single referent uropathologist. Muscularis mucosa invasion was tested as a prognostic factor for survival on univariate and multivariate analysis.ResultsA total of 587 patients were enrolled in the study, including 388 (66%) with T1a and 199 (34%) with T1b tumors. Median followup after transurethral resection of bladder tumor was 35 months (IQR 14-54). There was no significant difference between groups T1a and T1b except high tumor grade in T1b cases (p <0.0001). After central review, initial pathological substaging was confirmed in 84% of cases. On multivariate analysis muscularis mucosa invasion (T1b substage) was significantly associated with recurrence-free (p = 0.03), progression-free (p = 0.0002) and cancer specific (p = 0.02) survival. The main study limitation was absent systematic subsequent transurethral resection of bladder tumor.ConclusionsMuscularis mucosa invasion appears to be highly predictive of T1 nonmuscle invasive bladder cancer behavior. Consequently, systematic T1a vs T1b discrimination should be highly advocated by urologists and pathologists. We believe that it could aid in crucial decision making when choosing between conservative management and radical cystectomy remains a moot point.