Impact of Bladder Neck Involvement on Recurrence in Patients With Non–muscle-invasive Bladder Cancer: An Analysis Based on a Time-dependent Model

Background: Tumor location in bladder neck has reported to be a prognostic factor for non–muscle-invasive bladder cancer (NMIBC). We investigated the impact of bladder neck involvement (BNI) on recurrence in NMIBC using time-dependent covariate analysis. Patients and Methods: We enrolled 585 Japanese patients who underwent transurethral resection for bladder tumors at a single center from 2000 to 2016 and were pathologically diagnosed with Ta and T1 NMIBC. Each patient at each recurrence was assigned to a separate time-dependent stratum with its own baseline hazard function according to the Prentice-Williams-Peterson gap time model for analyzing recurrent events. Results: Over a median follow-up period of 41.3 months (interquartile range, 18.0-82.3 months), 253 (43.2%) patients experienced a total of 475 recurrences. Among the 1001 total transurethral resection procedures, BNI was observed in 122 (12.2%) cases. The 3-year cumulative recurrence rates of patients with and without BNI were 62.5% and 46.3%, respectively. Multivariable analysis revealed that number of tumors ≥ 4 (sub-hazard ratio [SHR], 1.48; P = .004), intravesical bacillus Calmette-Guérin therapy (SHR, 0.44; P < .001), and BNI (SHR, 1.59; P = .004) were all independent predictors of recurrence. Assigning 1 point for each of these 3 predictive factors, the resulting scores enabled us to classify patients into 3 prognostic groups that were clearly stratified according to recurrence. Conclusions: Our time-dependent covariate analysis shows that BNI is a significant risk factor for recurrence in NMIBC. Our prognostic model incorporating BNI is an easy means of estimating recurrence risk and determining optimal management for individual patients.