CEACAM5 and cholangiocarcinoma: The most commonly used biomarkers are carbohydrate antigen 199 (CA199) and carcinoembryonic antigen (CEA) in the clinical diagnosis of CCA, whether used alone or in combination, but their value is limited due to the inconsistency in sensitivity (47.2%–98.2%) and specificity (89.7%–100%) (Tshering et al., 2018; Macias et al., 2019).