SMAD4 and cholangiocarcinoma: Based on the levels of AMDHD1 and SMAD4 expression, CCA patients were classified into three groups: Group A with high expression of both AMDHD1 and SMAD4 (n = 37), Group B with mixed expression profiles (high AMDHD1 and low SMAD4 expression or vice versa; n = 30), and Group C with low expression of both AMDHD1 and SMAD4 (n = 29).