The impact of micropapillary histology and clinical staging on overall survival in bladder cancer: A retrospective analysis.

744 Background: Micropapillary variant bladder cancer (MPC) is a rare subtype of urothelial carcinoma, representing 0.01–2.2% of cases, with a higher stage at diagnosis and increased metastatic potential. The prognostic role of MPC remains uncertain, and previous studies have been limited by small cohort sizes, with only a few larges studies. This study analyzed the prognostic impact of MPC on clinical stage and survival outcomes in the largest single-institution cohort of patients with MPC who underwent radical cystectomy (RC). Methods: This retrospective study included 130 patients who underwent RC at Memorial Sloan Kettering Cancer Center for MPC between June 21, 1995, and April 14, 2023. Data included demographic, histologic, and clinical variables, as well as overall survival (OS) outcomes. Cystectomy specimens were reviewed by genitourinary pathologists to determine the proportion of the MPC component (MPC%) in each tumor. For OS comparison, a separate cohort of 430 patients with urothelial carcinoma not otherwise specified (UC NOS) who also underwent RC was used. Patients with MPC were further stratified by stage at diagnostic transurethral resection of bladder tumor (TURBT) as either non-muscle-invasive bladder cancer (NMIBC) or muscle-invasive bladder cancer (MIBC). Additional stratifications included MPC% ( < 50% vs. ≥50%, < 20% vs. > 80%) and receipt of neoadjuvant chemotherapy (NAC). Results: MPC was associated with a significantly shorter OS compared to UC NOS patients (p = 0.011). The MPC cohort had a mean OS of 83.8 months (95% CI: 62.2–105.4) and a median OS of 36.8 months (95% CI: 22.3–51.3), whereas the UC NOS cohort had a mean OS of 72.1 months (95% CI: 66.6–77.6) and a median OS of 84.4 months (95% CI: 64.5–104.2). Within the MPC cohort, patients with MIBC at initial TURBT had significantly worse OS compared to those with NMIBC (p = 0.0005). MPC% did not impact OS, with no differences between patients with < 50% versus ≥50% MPC (p = 0.59) or < 20% versus > 80% MPC (p = 0.57). Additionally, NAC did not affect OS within the MPC cohort (p = 0.055). N stage at cystectomy (N0 vs. N1+) was also not predictive of OS (p = 0.16). Conclusions: The presence of MPC, regardless of its proportion or the use of NAC, predicts poor outcomes. Clinical stage—particularly the presence of muscle invasion—remains the key predictor of survival. These findings emphasize the importance of clinical staging in guiding treatment decisions and prognostic assessments in the management of this disease.