Tumor base diameter and recurrence in non–muscle-invasive bladder cancer: an ambispective observational study

Current risk stratification systems for non–muscle-invasive bladder cancer (NMIBC) rely primarily on established clinicopathological variables and do not consider the extent of tumor attachment to the bladder wall. This study evaluated whether tumor base diameter is associated with recurrence in patients with primary NMIBC. This ambispective observational study included 130 patients who underwent transurethral resection for primary NMIBC between March 2021 and September 2023. Tumor base diameter was measured intraoperatively using the 5-mm resection loop as a standardized reference. Recurrence-free survival was assessed using Kaplan–Meier analysis and compared with the log-rank test. Factors associated with recurrence were evaluated using Cox proportional hazards regression models. During a median follow-up of 24.3 months, recurrence occurred in 36 patients. In the primary multivariable Cox model, tumor base diameter was independently associated with recurrence (HR: 1.028 per mm increase, 95% CI: 1.010–1.046, p = 0.002). This association remained significant in a secondary model incorporating tumor size and in the subgroup analysis restricted to patients with T1 disease (HR: 1.035, 95% CI: 1.016–1.055, p < 0.001). Tumor size itself was not independently associated with recurrence. Tumor base diameter was associated with recurrence in patients with NMIBC and may provide additional morphological information beyond conventional tumor measurements. Given its association with adverse pathological features, it is more likely to reflect underlying tumor aggressiveness than to function as a completely independent prognostic factor. Further prospective multicenter studies are required to validate these findings. NCT06632340.