Background: Angiogenesis and immunosuppression are hallmarks of tumor growth. This global phase 1 trial evaluates the combination of R (anti-VEGFR2) and D (anti-PD-L1) in pts with G/GEJ by simultaneously targeting these two processes. Methods: This ongoing, multi-cohort, phase 1a/b trial (NCT02572687) enrolled pts with confirmed G/GEJ adenocarcinoma with prior progression on 1 or 2 lines of systemic therapy, measurable disease, ECOG PS 0-1, and baseline tumor tissue. PD-L1 expression was assessed using the SP-263 IHC; MSI status was determined using PCR. Enrolled pts received R (8 mg/kg IV) and D (750 mg IV) every two weeks on a 28-day cycle. Primary objective was to assess safety and tolerability of R+D; preliminary efficacy was also examined. Results: As of 26-May-2017, 29 G/GEJ adenocarcinoma pts were treated. The median age was 55 y; 69% were male; 66% had ECOG PS of 1; 48% had PD-L1 ≥25% expression in tumor or immune cells, 3.5% were MSI-high; and 72% received study treatment as second line for advanced disease. Median duration of treatment was 2.5 mo for R and 3.0 mo for D. Treatment-emergent adverse events (TEAEs) occurred in 29 (100%) pts and 21 (72%) pts experienced grade 3/4 TEAEs, while treatment-related AEs (TRAE) occurred in 24 (83%) pts; none resulted in treatment discontinuation. Ten (35%) pts had grade 3 TRAEs, and no grade 4 or 5. All grade TRAEs occurring in ≥10% of pts were hypertension (34%), fatigue (31%), headache (24%), diarrhea (21%), pyrexia (10%) and decreased appetite (10%). Five pts (17%) reported a serious adverse event related to study treatment. Preliminary efficacy data (RECIST v1.1) showed 5 of 29 pts (17%) achieved a confirmed PR. Only 1 responding pt was MSI high. The overall response rate for pts with PD-L1 ≥25% was 36%. Median PFS was 2.6 mo (95% CI, 1.45 to 6.28). As of data cut-off, 6 pts (21%) remain on treatment. Conclusions: R+D generated no unexpected toxicity, and demonstrated antitumor activity in pts with previously treated advanced G/GEJ adenocarcinoma. Clinical trial information: NCT02572687