Hepatocellular carcinoma (HCC) is the third leading cause of cancer death worldwide. Treatment options for advanced HCC remain very limited. Until recently, multikinase inhibitor were the gold standard for advanced hepatocellular carcinoma but associated with poor outcome and important side effects. Recently, the positive results of the Imbrave 150 study (a randomized study comparing Atezolizumab + Bevacizumab versus Sorafenib) prompted us to redefine our management strategy for advanced hepatocellular carcinoma by proposing the combination of Atezolizumab/Bevacizumab as treatment first-line in patients with advanced hepatocellular carcinoma. However, only 1/3 of the patients will respond to the combination of treatment and identifying predictive factors of response and new immune checkpoint inhibitors in order to target more tumors appear as a major issue. In this context, recent work has underlined the importance of the activating CD226/DNAM-1 receptor as an original immunotherapeutic target in various cancers (solid and hematopoietic tumors). CD226 is a transmembrane receptor that is part of the immunoglobulin superfamily. It is expressed by most T lymphocytes (CD8+, CD4+), by Natural Killer (NK) cells, by promoting their cytotoxicity. The investigators propose to prospectively analyze the frequency and phenotype (expression of CD226) of circulating immune cells before the initiation of treatment with Atezolizumab/Bevacizumab, 3 weeks after the first injection and its variation to determine whether this biomarker could predict the response to the treatment.