Vessels encapsulating tumor clusters predict better outcomes in advanced hepatocellular carcinoma treated with atezolizumab–bevacizumab

BACKGROUND & AIMS: Atezolizumab + bevacizumab and durvalumab + tremelimumab are the standard first-line therapies for advanced hepatocellular carcinoma (HCC). Histological variables routinely associated with outcomes remain poorly described. We aimed to assess the prognostic and predictive value of the vessels encapsulating tumor clusters (VETC) phenotype in this setting. METHODS: We retrospectively analyzed 208 patients in a discovery cohort with advanced HCC treated with atezolizumab + bevacizumab and available pre-treatment biopsies, and 163 patients in a validation cohort, including 99 treated with atezolizumab + bevacizumab and 64 with durvalumab + tremelimumab. In addition to baseline clinico-biological variables, we assessed histological features, including the VETC phenotype, defined as complete (≥55% of tumor area), or incomplete (1-54% of tumor area). Prognostic impacts were evaluated using multivariable Cox models. RESULTS: In the discovery cohort, the complete VETC phenotype (n = 32) displayed the highest objective response rate in the cohort (66% vs. 37% in non- or incomplete VETC-HCC, p = 0.002), according to the modified RECIST. The complete VETC phenotype was independently associated with better progression-free survival (PFS) (hazard ratio [HR] 0.42, 95% CI 0.26-0.69, p