CEACAM5 and cholangiocarcinoma: Serum tumor markers such as carcinoembryonic antigen (CEA), carbohydrate antigen 19-9 (CA19-9), and liver function tests including serum bilirubin, alkaline phosphatase (ALP), and gamma-glutamyl transferase (GGT) are the most widely used markers for primary screening of CCA in routine clinical laboratory examinations (6, 7).