Atezolizumab Plus Chemotherapy With or Without Bevacizumab in Advanced Biliary Tract Cancer: Clinical and Biomarker Data From the Randomized Phase II IMbrave151 Trial

PURPOSE Biliary tract cancers (BTCs) harbor an immunosuppressed tumor microenvironment and respond poorly to PD-1/PD-L1 inhibitors. Bevacizumab (anti–vascular endothelial growth factor) plus chemotherapy can promote anticancer immunity, augmenting response to PD-L1 inhibition. PATIENTS AND METHODS This randomized, double-blind, proof-of-concept phase II study enrolled patients (n = 162) with previously untreated advanced BTC (IMbrave151; ClinicalTrials.gov identifier: NCT04677504 ). Patients were randomly assigned 1:1 to receive cycles of atezolizumab (1,200 mg) plus bevacizumab (15 mg/kg) or atezolizumab plus placebo once every 3 weeks until disease progression or unacceptable toxicity. All patients received cisplatin (25 mg/m 2 ) plus gemcitabine (1,000 mg/m 2 ; cisplatin plus gemcitabine [CisGem]) on days 1 and 8 once every 3 weeks for up to eight cycles. Stratification of patients was by disease status, geographic region, and primary tumor location. The primary end point was progression-free survival (PFS). No formal hypothesis testing was performed. Exploratory correlative biomarker analysis was undertaken using transcriptome analysis (n = 95) and mutation profiling (n = 102) on baseline tumor samples. RESULTS Between February and September 2021, 162 patients were enrolled. Median PFS was 8.3 months in the bevacizumab arm and 7.9 months in the placebo arm (stratified hazard ratio [HR], 0.67 [95% CI, 0.46 to 0.95]). Median overall survival (OS) was 14.9 and 14.6 months in the bevacizumab and placebo arms, respectively (stratified HR, 0.97 [95% CI, 0.64 to 1.47]). The incidence of grade 3 or 4 adverse events was 74% in both arms. High VEGFA gene expression was associated with improved PFS (HR, 0.44 [95% CI, 0.23 to 0.83]) in the bevacizumab arm versus placebo. CONCLUSION In unselected patients with advanced BTC, adding bevacizumab to atezolizumab plus CisGem modestly improves PFS but not OS. High VEGFA gene expression may represent a predictive biomarker of benefit from atezolizumab/bevacizumab, warranting further investigation.