Background: The randomized, open-label Phase III IMmotion151 study met its coprimary endpoint in PD-L1+ patients (pts) with improvement in investigator-assessed PFS for atezo + bev vs sun (HR 0.74; median 11.2 vs 7.7 mo, P = 0.02). Encouraging efficacy was also observed in the intent-to-treat (ITT) population (HR 0.83; 11.2 vs 8.4 mo) (Motzer, ASCO-GU 2018). PROs were evaluated as secondary and exploratory endpoints to document pt perspective on overall clinical benefit for each tx. Methods: Pts received atezo 1200 mg IV q3w + bev 15 mg/kg IV q3w (n = 454) or sun 50 mg PO QD 4 wk on/2 wk off (n = 461). Pts completed the MD Anderson Symptom Inventory (MDASI) and Functional Assessment of Cancer Therapy-Kidney Symptom Index 19 (FKSI-19) questionnaires on days 1 and 22 of each 6 wk cycle, at end of tx, and during survival follow-up. Prespecified concepts included symptom burden (MDASI symptom severity and symptom interference with daily living) and bother from tx side effects (FKSI-19 GP5 item). Health-related quality of life (HRQoL) was also assessed (FKSI-19 total). Descriptive analyses included summary statistics for scores (effect sizes [ES] ≥ 0.3 suggest clinically meaningful differences), score changes from baseline (BL), and time to deterioration (TTD; first ≥ 2-point score increase in MDASI interference). Results: BL completion in ITT pts was > 80% and ≥ 70% until wk 57. At post-BL visits, pts receiving atezo + bev had milder and more stable symptom severity, less interference (differences in mean score ES: mean 0.3; range 0.1 - 0.5), and better HRQoL (differences in mean score ES: mean 0.4; range 0.1 - 0.6) vs pts receiving sun, who more often reported worsened interference. TTD in interference was also delayed (HR 0.56; 95% CI 0.46, 0.68): median for atezo + bev was 11.3 mo vs 4.3 mo for sun. A greater proportion of atezo + bev-treated pts reported no or little bother from tx side effects vs sun-treated pts. Conclusions: PRO data suggest atezo + bev maintained day-to-day functioning with minimal symptom interference and delayed TTD vs sun, further supporting positive benefit-risk for the combination regimen in first-line mRCC. Clinical trial information: NCT02420821