MUC1 and intrahepatic cholangiocarcinoma: Abbreviations: chimeric antigen receptor 4th generation (CAR4 T), epidermal growth factor receptor (EGFR), interleukin (IL), intrahepatic cholangiocarcinoma (ICC), mucin 1 (MUC1), natural killer (NK), programmed cell death protein (PD-1), T cell immunoglobulin and ITIM domain (Tigit), T cell immunoglobulin and mucin domain-containing-3 (TIM-3), transforming growth factor-β (TGF-β).