Background: Patients (pts) with unresectable locally advanced or metastatic urothelial cancer (mUC) who progress after platinum-based chemotherapy and checkpoint inhibitor (CPI) therapy and pts ineligible for platinum-based chemotherapy who progress after CPI have limited treatment options and poor outcomes. Trop-2 is an epithelial cell surface antigen that is overexpressed in UC. Sacituzumab govitecan (SG) is a novel antibody-drug conjugate that targets Trop-2 and delivers the active metabolite (SN38) of the topoisomerase I inhibitor irinotecan to tumor cells. In a phase 1/2 single-arm trial, pts with advanced cancers received SG 10 mg/kg intravenously on days 1 and 8 of a 21-day cycle; preliminary results in the cohort of 41 evaluable pts with mUC and a median of 3 (range 1–6) prior therapies showed an objective response rate (ORR) of 34%. Adverse events (AE) were mostly low grade, including diarrhea (63%), nausea (56%), and fatigue (49%). Neutropenia (all grades) occurred in 49% of pts (≥ grade 3/4, 39%; treatment-related serious AE of febrile neutropenia, 5%). Median overall survival was 16.1 months, and median progression-free survival was 7.1 months. These results warrant further investigation in a dedicated phase 2 trial. Methods: TROPHY-U-01 is a single-arm, open-label, global phase 2 trial evaluating the antitumor activity and safety of SG in 140 pts with advanced UC. The primary cohort (progression after platinum chemotherapy and CPI) will enroll 100 pts in a Simon 2-stage design with > 90% power accounting for dropouts to exclude the null hypothesis or ORR < 12%, while a second cohort (40 pts) will comprise cisplatin-ineligible pts who received prior CPI. The primary objective is ORR per RECIST 1.1, assessed by central review. Secondary objectives include response duration, PFS, OS, and safety/tolerability. Enrollment began in August 2018. Clinical trial information: NCT03547973