Validation of the risk stratification newly defined in the Japanese Urological Association guidelines 2019 for non‐muscle invasive bladder cancer: A multi‐institutional collaborative study

Objectives To validate the risk stratification newly defined in the Japanese Urological Association guidelines 2019 for non‐muscle invasive bladder cancer and provide a more accurate stratification model for a heterogeneous intermediate‐risk group. Methods A total of 1610 patients, who underwent transurethral resection, diagnosed with non‐muscle invasive bladder cancer in nine collaborating hospitals were retrospectively reviewed. They were classified into low‐risk, intermediate‐risk, high‐risk, and highest‐risk groups, and recurrence‐free survival, progression‐free survival, cancer‐specific survival, and overall survival were compared among the groups. The intermediate‐risk group was subdivided into two groups based on the multivariable Cox regression model of recurrence and progression risk factors, and a revised risk model was created. Results The progression‐free survival, cancer‐specific survival, and overall survival were well stratified, while the recurrence‐free survival of the intermediate‐risk group was the shortest among the four groups (p