Background: EV is an ADC that selectively targets and kills cells expressing Nectin-4 by delivering a potent microtubule-disrupting agent, monomethyl auristatin E. As mUC tumors express Nectin-4 in almost all pts, the EV clinical profile was assessed in an ongoing Phase 1 study (NCT02091999) at the recommended phase 2 dose (RP2D; 1.25 mg/kg) in mUC pts with CPI failure, a population with a high unmet medical need. Methods: Pts with mUC, treated with ≥1 prior chemotherapy or who were ineligible for platinum chemotherapy, and who had disease progression after CPI therapy received an IV infusion of EV at RP2D on Days 1, 8, and 15 of each 28-day cycle. Primary endpoint was tolerability; a secondary endpoint was investigator-assessed antitumor activity per RECIST v1.1. Results: As of 2 Oct 2017, 62 pts with mUC and prior CPI failure received EV at RP2D (48 M/14 F; median age, 68 yr [range: 41–83]; ECOG 0/1 29%/71%). Primary tumor site was bladder in 73% pts; 63% pts had visceral and 27% had liver metastasis (LM). Most pts (71%) had ≥2 prior therapies in the metastatic setting, including platinum (87%) or taxanes (26%). CPI was the most recent therapy in 76% pts; time from last CPI to first EV dose was < 12 wk for 58% pts. Median treatment duration was 14.8 wk (range: 1.6–40.4); 39 pts continue treatment. Treatment-related AEs occurring in ≥30% pts were fatigue, rash, nausea, alopecia, decreased appetite and diarrhea; most grade ≤2. Grade ≥3 AE reported in ≥5% pts, regardless of attribution, was hyponatremia (6.5%). One fatal AE (respiratory failure) was possibly treatment related. Response evaluable pts (n = 54) had ≥1 post baseline scan or discontinued prior to scan. ORR (confirmed + unconfirmed) was 54% (95% CI: 39.6–67.4); 15 pts had a confirmed PR, 5 had unconfirmed PR, and 9 are pending subsequent assessment. This ORR is similar to CPI-naïve pts (59%; 95% CI: 36.4–79.3). ORR from 17 evaluable pts with LM was 41% (95% CI: 18.4–67.1). Conclusions: EV is tolerable and exhibits antitumor activity in a cohort of pts with mUC and disease progression after CPI. A phase 2 study assessing EV in this population with high unmet need has been initiated (NCT03219333; EV-201 study). Clinical trial information: NCT02091999