External validation of European Association of Urology NMIBC risk scores to predict progression after transurethral resection of bladder tumor in Korean patients with non-muscle-invasive bladder cancer

PURPOSE: This study aimed to validate the newly proposed risk model in Korean patients diagnosed with non-muscle-invasive bladder cancer (NMIBC). MATERIALS AND METHODS: A retrospective review was performed with 1,238 patients who underwent transurethral resection of bladder tumor from 2009 to 2020. We included 973 patients and categorized them into four risk groups according to the European Association of Urology (EAU) NMIBC risk stratification standards, which incorporate the World Health Organization 2004/2016 grading classification. Kaplan–Meyer survival analysis and multivariable analysis of time to progression were performed to calculate the probability of progression for all risk groups. RESULTS: A total of 973 patients were followed for 54.85 months. Patients were classified according to the risk factors proposed by the new NMIBC risk table and stratified into low, intermediate, high, and very high-risk groups based on the table. Cancer progression into muscle-invasive bladder cancer (MIBC) in each risk group was observed in 7 (4.4%), 24 (15.2%), 76 (48.1%), and 51 (32.3%) individuals, respectively. The progression rate was distinguishable between risk groups in the Kaplan–Meier progression-free survival analysis, and higher risk was associated with a higher rate of progression. The new NMIBC risk variables were demonstrated to have prognostic value in the multivariate analysis. The very high-risk group was associated with progression to muscle-invasive disease. CONCLUSIONS: This study demonstrates that the new EAU NMIBC risk group categorization is feasible in predicting the progression of NMIBC into MIBC in the Korean population and thus should be applied to clinical practice in Korea.