Micropapillary Urothelial Carcinoma (mpuc): A Comparative Analysis of Oncologic Outcomes Compared to Conventional Urothelial Carcinoma (CUC)

459 Background: MpUC is a rare variant associated with adverse outcomes. We describe our institutional experience and compare clinicopathologic features and survival between patients with mpUC and CUC. Methods: Patients with mpUC or CUC at radical cystectomy (RC) or transurethral resection of bladder tumor were identified from a retrospective institutional RC database. Clinicopathologic/treatment data were extracted and compared using T-test and χ2 test. Recurrence free survival (RFS) and overall survival (OS) from RC to first recurrence or death were estimated using the KM method. Factors identified as significant in univariable (UVA) Cox regression analysis for OS were included in multivariable analysis (MVA). Results: 64 consecutive patients with mpUC and 457 with CUC were identified (2003 - 2018); 36 (56%) and 188 (41%) received neoadjuvant chemotherapy (NAC). MpUC had higher incidence of pT3/4 (41% vs. 28%) or pN+ disease (39% vs. 17%), carcinoma in-situ (52% vs. 24%) and lymphovascular invasion (LVI, 39% vs. 16%) at RC, compared to CUC (all p < 0.05). Rates of ypT0N0 after NAC were comparable between groups (25% vs. 35%, p = 0.26). Median follow-up was 62 months (95% CI 55.4 – 68.3). 5-year RFS was 24% (mpUC) vs. 58% (CUC), p = 0.001. 5-year OS was 40% (mpUC) vs. 69% (CUC), p = 0.001. MpUC histology was not independently associated with OS after adjusting for pT stage, node ratio (# nodes +/ # nodes removed) and ECOG status (Table). Conclusions: Patients with mpUC presented with advanced stage at RC, while they showed inferior RFS and OS, when compared to CUC. However, rates of pathologic response to NAC were comparable to CUC and mpUC was not associated with OS in MVA. Further studies are needed to define the optimal management of this variant. [Table: see text]