Background: Combining an immune checkpoint inhibitor with a targeted antiangiogenic agent may leverage complementary mechanisms of action for treatment of advanced/metastatic (a/m) hepatocellular carcinoma (HCC). Avelumab is a human anti–PD-L1 IgG1 antibody with clinical activity in various tumor types; axitinib is a tyrosine kinase inhibitor selective for VEGF receptors 1/2/3. VEGF Liver 100 (NCT03289533) is a phase 1b study evaluating safety and efficacy of avelumab + axitinib in treatment-naive patients (pts) with HCC; interim results are reported here. Methods: Eligible pts had confirmed a/m HCC, ≥1 measurable lesion, a fresh or archival tumor specimen, ECOG PS ≤1, and Child-Pugh class A. Pts received avelumab 10 mg/kg IV Q2W + axitinib 5 mg orally BID until progression, unacceptable toxicity, or withdrawal. Endpoints included safety and objective response (RECIST v1.1; modified [m] RECIST for HCC). Results: Interim assessment was performed after a minimum follow up of 6 months based on the released study data set (clinical cut-off date: Aug 1, 2018). As of the cut-off date, 22 pts (median age: 68.5 y) were treated with avelumab (median: 20.0 wk) and axitinib (median: 19.9 wk). The most common grade 3 treatment-related adverse events (TRAEs) (≥10% of patients) were hypertension (50.0%) and hand-foot syndrome (22.7%); no grade 4/5 TRAEs were reported. Immune-related AEs (irAEs) (≥10% of pts) were hypothyroidism (31.8%) and hyperthyroidism (13.6%). No grade ≥3 irAEs were reported; no pts discontinued treatment due to TRAEs or irAEs. Based on Waterfall plot calculations, tumor shrinkage was observed in 15 (68.2%) and 16 (72.7%) pts by RECIST and mRECIST, respectively. ORR was 13.6% (95% CI, 2.9%-34.9%) and 31.8% (95% CI, 13.9%-54.9%) by RECIST and mRECIST, respectively. OS data were immature at data cutoff. Conclusions: The preliminary safety of avelumab + axitinib in HCC is manageable and consistent with the known safety profiles of avelumab and axitinib when administered as monotherapies. This study demonstrates antitumor activity of the combination in HCC. Follow-up is ongoing. Clinical trial information: NCT03289533

*per investigator assessment.