Optimal timing for the first cystoscopic follow-up using time-to-treatment initiation analysis of oncologic outcomes in primary non-muscle invasive bladder cancer

Various guidelines recommend the first follow-up cystoscopy at 3 months; however, no data exist on the optimal timing for initial follow-up cystoscopy. We tried to provide evidence on the timing of the first cystoscopy after the initial transurethral resection of bladder tumor (TUR-BT) for patients with non-muscle invasive bladder cancer (NMIBC) using big data. This was a retrospective National Health Insurance Service database analysis. The following outcomes were considered: recurrence, progression, cancer-specific mortality, and all-cause mortality. Exposure was the time-to-treatment initiation (TTI), a continuous variable representing the time to the first cystoscopy from the first TUR-BT within 1 year. Additionally, we categorized TTI (TTIc) into five levels: