CLDN6 and hepatocellular carcinoma: The targeting of tumor lineage plasticity mechanism of HCC involving an interactive axis (CLDN6/TJP2/YAP1) has shown improved antitumor efficacy of a de novo anti-CLDN6 (claudin 6) monoclonal antibody conjugated to a cytotoxic agent, Mertansine DM1 (CLDN6-DM1) as a monotherapy or combined with Sorafenib (25).