Metastatic Urothelial Carcinoma of the Renal Pelvis and Ureter

Phase I of this research study will assess what doses of Sacituzumab Govitecan and Enfortumab Vedotin can be safely combined in the treatment of metastatic urothelial carcinoma (mUC). In Phase II of the study, patients in one of the two cohorts will receive Sacituzumab Govitecan, Enfortumab Vedotin, and Pembrolizumab to assess the efficacy of this drug combination. The names of the study drugs in these investigational combinations are: * Enfortumab Vedotin * Sacituzumab Govitecan * Pembrolizumab