Abstract Background: The addition of bevacizumab (bev) to atezolizumab (atezo) has demonstrated enhanced anti-tumor immune responses in pts with solid tumors (Wallin 2016). In IMmotion150 (NCT01984242), a phase II trial that compared atezo+/-bev vs sunitinib (sun) in untreated mRCC, encouraging antitumor activity of atezo+bev vs sun was observed in PD-L1 expressing tumors. We performed integrated tumor genomic analyses to correlate molecular signatures with clinical outcomes. Methods: PD-L1 status on tumor infiltrating immune cells (IC) was assessed with the SP142 IHC assay (IC0, IC1, IC2/3) (n=297). Exploratory analyses included mutation evaluation by WES (n=170) and gene expression analysis by RNA-Seq (n=263). Established gene signatures at < median (low) or > median (high) expression levels representing T effector and IFNγ response (Teff) and angiogenesis (Ang) were evaluated in relation to PFS (RECIST v1.1 by independent review). Results: PFS was longer in PD-L1 IC2/3 and in PD-L1 IC1/2/3 in atezo+bev pts vs sun pts and in PD-L1 IC2/3 in atezo pts vs sun pts. High Teff signature expression was associated with PD-L1 IHC and longer PFS in atezo+bev pts vs sun pts. High Ang expression was associated with improved clinical activity in the sun arm; but not the atezo+bev arm. Atezo+bev had improved PFS vs sun in the Ang low subset. Additional data exploring association of high prevalence mutations with clinical outcome will be presented. Conclusions: These data indicate that the addition of bev to atezo may improve clinical benefit in patients with pre-existing anti-tumor immunity (as determined by high Teff score or PD-L1 IHC) compared to sun. Molecular profiles identified in these analyses suggest that prediction of differential outcomes to VEGF TKI and immunotherapy may be possible in front line mRCC. These results will be further explored in the ongoing phase III study IMmotion151 (NCT02420821). Atezo + Bev vs SunAtezo vs SunPFS HR (95% CI)PD-L1 IHC IC1/2/30.66 (0.41-1.07)0.97 (0.61-1.55)PD-L1 IHC IC2/30.36 (0.14-0.88)0.54 (0.23-1.28)Teff high0.55 (0.32-0.95)0.85 (0.50-1.43)Teff low1.41 (0.84-2.03)1.33 (0.76-2.33)Ang high1.36 (0.78-2.36)1.46 (0.81-2.60)Ang low0.58 (0.35-0.98)0.75 (0.45-1.25)PD-L1 IHC: IC1/2/3, ≥ 1% of TILs are PD-L1+; IC2/3, ≥ 5% of TILs are PD-L1+.Teff signature: CD8A, IFNG, PRF1, EOMES, PD-L1.Ang signature: VEGFA, KDR, ESM1, PECAM1, ANGPTL4, CD34. Citation Format: David McDermott, Mahrukh Huseni, Brian Rini, Robert Motzer, Michael Atkins, Berard Escudier, Dorothee Nickles, Zach Boyd, Shruthi Sampath, Jennifer Doss, Ning Leng, Christina Schiff, Daniel S. Chen, Gregg Fine, Thomas Powles, Priti S. Hegde. Molecular correlates of differential response to Atezolizumab +/- Bevacizumab vs Sunitnib in a Phase II study in untreated metastatic renal cell carcinoma (RCC) patients abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr CT081. doi:10.1158/1538-7445.AM2017-CT081