Background: PD-(L)1-targeted immune checkpoint inhibitors (CPIs), such as pembrolizumab (P), are approved for patients (pts) with locally advanced or metastatic urothelial cancer (la/mUC) who progress after platinum, are ineligible for first-line (1L) cisplatin (PD-L1 positive), or are ineligible for 1L platinum. The ORR for CPI in all treated pts is ~25%, and a combination approach may provide additional benefit. Enfortumab vedotin (EV), an investigational antibody-drug conjugate, delivers the microtubule-disrupting agent monomethyl auristatin E to cells expressing Nectin-4, found in 97% of mUC pt samples (Petrylak ASCO 2017). In a phase 1 study (NCT02091999), EV (1.25 mg/kg) was generally well tolerated with a confirmed ORR of 43% in 112 mUC pts (Rosenberg ASCO-GU 2019). These encouraging results, with the potential for an enhanced immune response, suggest that EV+P may improve response rates and extend response durability. Methods: EV-103, a phase 1b trial for non–resectable la/mUC pts with no prior CPI, added an additional 4 cohorts (Parts 2 and 3) in an Oct 2018 amendment. It is now expected to enroll ~159 pts. Dose escalation pts (EV+P, 1L or 2L) must be ineligible for 1L cisplatin-based chemotherapy or have disease progression during/following treatment with ≥1 platinum-containing regimen. Dose expansion (Part 1) will evaluate EV+P in 1L (Cohort A) and 2L settings (Optional Cohort B). Part 2 will evaluate 1L EV+cisplatin (Cohort D), 1L EV+carboplatin (Cohort E), and 1L or 2L EV+gemcitabine (Optional Cohort F). Part 3 (Cohort G) will evaluate 1L EV+P+cisplatin or carboplatin, depending on pts cisplatin-eligibility. In all cohorts, pts receive EV on Days 1 and 8 of each 3-week cycle. In combination therapies, pts receive P, cisplatin, and carboplatin on Day 1 or gemcitabine on Days 1 and 8 of each cycle. The primary objective is to assess the safety/tolerability of EV+P and/or chemotherapy. Secondary objectives are establishing EV recommended dose for combination therapies, assessing ORR per RECIST for all cohorts and per iRECIST for therapies with pembrolizumab, as well as assessing disease control rate, duration of response, PFS, OS, PK, and biomarkers. The study opened Oct 2017. Clinical trial information: NCT03288545