CD8A and cholangiocarcinoma: Emerging multi-omics analyses of the bile duct microenvironment in CCA reveal that alterations in BA pool composition (e.g., increased lithocholic acid, taurolithocholic acid) correlate with reduced CD8+ T-cell infiltration and higher checkpoint ligand (PD-L1) expression, suggesting that the BA–immune axis contributes to immune exclusion and therapy resistance.