Impact Of Pure Versus Mixed Metastatic Urothelial Carcinoma (Muc) Histology On Response With Immune Checkpoint Inhibitors (Icis).

479Background: PD1/PD-L1 inhibitors have been evaluated in trials enrolling patients (pts) with pure urothelial or mixed urothelial histology containing non-urothelial components. However, any differential impact of pure vs. mixed urothelial histology on ICI benefit is unclear. We conducted a retrospective study to evaluate the impact of pure vs. mixed urothelial carcinoma histology on outcomes with ICIs in pts with metastatic urothelial carcinoma (mUC). Methods: We obtained data from 120 pts with mUC from a single institution (DFCI) who received ICI therapy. Demographic, clinical variables and outcomes (overall response rate [ORR], overall survival [OS]) were collected. Histology was reviewed at DFCI for all pts and recorded as pure urothelial if only urothelial carcinoma was seen or mixed urothelial if components of any other histology were observed in addition to urothelial. A Cox regression analysis was done to study the association of prognostic variables and histology with objective response. Result...