Background: Atezolizumab (atezo; anti–PD-L1) + bevacizumab (bev; anti-VEGF) showed first-line (1L) anti-tumor activity with a manageable safety profile in PD-L1+ mRCC pts in a Phase II study (McDermott ASCO-GU 2017). Here we describe the first randomized Phase III trial of a PD-L1/PD-1 pathway inhibitor combined with an anti-VEGF agent in 1L mRCC. Methods: IMmotion151 (NCT02420821) enrolled treatment-naïve pts regardless of prognostic risk group randomized 1:1 to receive atezo 1200 mg IV q3w + bev 15 mg/kg IV q3w or sunitinib (sun) 50 mg PO QD 4 wk on/2 wk off. Pts were stratified by PD-L1 status (< 1% vs ≥ 1% PD-L1 expression on tumor-infiltrating immune cells [IC]; SP142 IHC assay). Coprimary endpoints: progression-free survival (PFS; by investigator per RECIST v1.1) in PD-L1+ pts (≥ 1% IC) and overall survival (OS) in intent-to-treat (ITT) pts. Secondary endpoints included PFS in ITT pts, ORR and DOR. Results: Baseline characteristics were comparable between arms within PD-L1+ (40% of ITT) and ITT pts. Median survival follow-up was 15 mo. PFS HR for atezo + bev vs sun was 0.74 (95% CI 0.57, 0.96) in PD-L1+ pts and 0.83 (95% CI 0.70, 0.97) in ITT pts. OS was immature at first interim analysis. PFS benefit was consistent across analyzed subgroups, including MSKCC risk, liver metastases and sarcomatoid histology. In PD-L1+ pts, ORR was 43% and DOR was not reached for atezo + bev vs 35% and 12.9 mo for sun. 40% of atezo + bev–treated pts and 54% of sun-treated pts had treatment-related Gr 3-4 AEs; 12% and 8% of treatment-related all-Gr AEs led to discontinuation, respectively. Conclusions: The study showed longer PFS for atezo + bev vs sun in PD-L1+ pts. Improved PFS was also observed in ITT pts. Safety was consistent with that of the individual agents. These results support the use of atezo + bev as a 1L treatment option in mRCC. Clinical trial information: NCT02420821

NE, not estimable ^a Descriptive purposes only