IMmotion151: A randomized phase III study of atezolizumab plus bevacizumab vs sunitinib in untreated metastatic Renal Cell Carcinoma (mRCC)

578Background: 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-naive 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 (u003c 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 p...