NOTCH1 and cholangiocarcinoma: In line with the microscopic tumor morphology, immunohistochemical analyses revealed nuclear expression of HNF4α, a representative hepatocytic marker, in tumors induced by TAZS89A plus BRAFV600E while TAZS89A plus PI3KE545K tumors exhibited high expression of Notch1 and Notch2, critical players in development of CC (Fig. 6 and Supplementary Fig. 3).