Muscle-invasive bladder cancer (MIBC) is often accompanied by synchronous or metachronous upper tract urothelial carcinoma (UTUC), occurring in 2-5% of patients undergoing radical cystectomy (RCx) [1,2]. The optimal timing and oncological safety of concurrent nephroureterectomy (RNU) during RCx remain controversial. While one-stage concurrent surgery offers logistical advantages by avoiding risks of a second operation, concerns persist regarding potential adverse effects on perioperative morbidity and long-term survival outcomes [3,4].

Previous studies have yielded conflicting results regarding the oncological prognosis of concurrent RNU + RCx. Small sample sizes, lack of proper adjustment for baseline differences, and inherent selection bias have limited definitive conclusions [[5], [6], [7]]. Patients requiring concurrent RNU typically present with more advanced disease burden, higher stage tumors, and worse performance status, making direct comparisons problematic without statistical adjustment. Furthermore, most previous studies lacked rigorous multivariable analysis to determine whether concurrent RNU independently affects prognosis after adjusting for established prognostic factors, especially crucial in these studies as research is limited by small sample sizes and potential selection bias. Patients selected for concurrent RNU likely differ systematically from those undergoing RCx alone in terms of disease biology, tumor burden, comorbidities, and surgeon preference, in which propensity score matching (PSM) can be utilized to minimize selection bias in observational studies by creating balanced cohorts based on baseline covariates [8,9] with multivariable Cox proportional hazards regression to identify independent prognostic factors [10]. However, few studies have comprehensively evaluate the oncological safety of concurrent RNU during RCx to date.

This study aims to evaluate the oncological safety and prognostic implications of concurrent RNU performed during RCx using both propensity score matching and multivariable Cox regression, analyzing a large Korean multicenter database with extended follow-up and comprehensive outcome assessment.