Effect of Atezolizumab plus Bevacizumab in Patients with Hepatocellular Carcinoma Harboring CTNNB1 Mutation in Early Clinical Experience

Atezolizumab plus bevacizumab (ATZ/BV) treatment is a combined immunotherapy consisting of immune checkpoint inhibitor (ICI) and anti-vascular endothelial growth factor monoclonal antibody, which has brought a major paradigm shift in the treatment of unresectable hepatocellular carcinoma (HCC). Gain-of-function mutation of CTNNB1 contributes to resistance of ICI monotherapy through the framework of non-T-cell-inflamed tumor microenvironment. However, whether CTNNB1 mutation renders resistance to ATZ/BV similar to ICI monotherapy remains to be elucidated. In this study, a liquid biopsy sample in plasma of 33 patients with HCC treated with ATZ/BV was subjected to droplet digital PCR for detecting hotspot mutations at the exon 3 of CTNNB1 locus. A total of eight patients (24.2%) exhibited at least one CTNNB1 mutation. The objective response rate (ORR) in patients with wild-type (WT) and mutant (MT) CTNNB1 was 8.0% and 12.5%, respectively, and the disease control rate (DCR) was 68.0% and 87.5%, respectively. No significant difference in both ORR and DCR has been observed between the two groups. The median progression-free survival in patients with WT and MT CTNNB1 was 6.6 and 7.6 months, respectively (not statistically significant). Similarly, no significant difference in overall survival has been observed between patients with WT and MT CTNNB1 (13.6 vs. 12.3 months). In conclusion, the treatment effect of ATZ/BV in patients with HCC with MT CTNNB1 was comparable to those patients with WT CTNNB1. These results implicate that BV added to ATZ might improve immunosuppressive tumor microenvironment caused by CTNNB1 mutation.