4539 Background: In EV-301, a randomized, open-label phase 3 study (NCT03474107), enfortumab vedotin (EV), a Nectin-4–directed therapy, significantly prolonged median overall survival by ̃3.9 months and reduced the risk of death by 30% compared with standard chemotherapy (SC; docetaxel, paclitaxel, or vinflunine) in patients with previously treated locally advanced/metastatic urothelial carcinoma. Understanding patient perspectives and experiences is important to further contextualize the benefits/risks of EV. Here, we report key prespecified quality-of-life (QoL) endpoints, a secondary objective of EV-301. Methods: Patients completed the validated European Organization for Research and Treatment of Cancer Core Quality of Life Questionnaire Core 30 (QLQ-C30) at baseline, on Day 1 of each week for the first 12 weeks, and then every 12 weeks until discontinuation. The QLQ-C30 assessed functional domains, symptom scales/items, financial impact, and overall health/QoL. Descriptive statistics were used to summarize instrument compliance rates and scores; mixed model repeated measures were used to evaluate changes from baseline over time. Logistic regressions were conducted to assess confirmed improvement rates, defined as clinically meaningful improvement (predefined per domain) over two subsequent visits. Results: Of the 608 randomized patients (EV, n = 301; SC, n = 307), 77.3% were male, median age was 68 (range: 30-88), and 30.9% had liver metastasis. Questionnaire compliance rates at baseline were ̃90% in both groups; during the study, average rates were 70.2% (EV) and 66.9% (SC). Baseline QLQ-C30 scores were similar between groups. At Week 12, scores on the global health status (GHS) scale were similar between groups (EV: -2.8, SC: -5.0; P=.2429), but SC was associated with numerically greater deterioration and more variability in QoL over the first 12 weeks. Patients receiving EV had significant reduction in pain symptoms (EV: -5.62, SC: +0.11; adjusted difference: -5.73, P<.05), but significant worsening of appetite loss (EV: +8.55, SC: +1.26; adjusted difference: 7.29, P<.05) compared with SC. Other symptom scores were not significantly different between groups. Higher proportions of patients on EV vs SC had significant confirmed improvements across all functioning domains (role, physical, emotional, social, cognitive), GHS, and several symptom scales (pain, fatigue, dyspnea, constipation). The greatest difference in improvement was reported for pain (EV: 51.6%, SC: 28.8%; OR = 2.76[1.81, 4.22]). Conclusions: Compared with SC, patients receiving EV had numerically less deterioration and variability in QoL during the first 12 weeks of treatment. More patients in the EV group had improvements over SC in 10 of 15 QLQ-C30 domains; improvement in pain showed the largest benefit. Clinical trial information: NCT03474107.