The purpose of this study was to clarify the appropriate cystoscopic interval after nephroureterectomy (NU) for upper tract urothelial carcinoma (UTUC) using a hypothetical model.

A total of 155 patients who underwent NU in 15 years were retrospectively evaluated. Three hypothetical models for surveillance intervals were created: 3 (model 1), 6 (model 2) and 12 months (model 3). We superimposed these models on the actual surveillance of each patient and analyzed the observed timing of recurrence. The time from recurrence to scheduled cystoscopy (timeRCS) was defined as the time from recurrence to estimated cystoscopy. The gap risk ratio was calculated based on the average of timeRCS for model 1 at 0–1 year after surgery.

The median follow-up was 20.5 months. Intravesical recurrence was observed in 63 patients (40.6%). The 3-year intravesical recurrence-free survival rate in patients without a history of bladder cancer before NU was significantly higher than in those with a history of bladder cancer (61% vs. 42%, P = 0.034). The medians of timeRCS for models 1, 2, and 3 were 1.9, 2.9, and 8.4 months, respectively. The gap risk ratios for model 1 at 1–3 years, model 2 at 2–3 years for patients with a history of bladder cancer, and model 2 at 1–3 years for patients without a history of bladder cancer were less than 1.0.

Model analysis shows that the cystoscopic follow-up interval can be extended depending on the presence or absence of a history of bladder cancer and the time after NU.