Angiopoietin-2 and Biliary Diseases: Elevated Serum, but Not Bile Levels Are Associated with Cholangiocarcinoma

Background: The diagnosis of cholangiocarcinoma (CC) is challenging especially in patients with primary sclerosing cholangitis (PSC) and often delayed due to the lack of reliable markers. Angiopoietin-2 (Angpt-2) has been employed as a biomarker of angiogenesis and might be involved in tumor neoangiogenesis. Aim: To evaluate the diagnostic potential of Angpt-2 as a biomarker to detect patients with CC. Methods: Bile and serum Angpt-2 levels were measured in patients with CC (n = 45), PSC (n = 74), CC complicating PSC (CC/PSC) (n = 11) and patients with bile duct stones (n = 37) in a cross sectional study. Diagnostic accuracy of Angpt-2 was compared to carbohydrate antigen 19-9 (CA19-9). Fluorescent immunohistochemistry from human CC liver tissue samples was performed to localize the origin of Angpt-2. Results: Serum Angpt-2 concentration was significantly elevated in patients with CC compared to control patients (p<0.05). Diagnostic accuracy of Angpt-2 as determined by receiver operating characteristic (ROC) analysis resulted in a higher area under the curve (AUC) value compared to CA19-9 (AUC: 0.85 versus 0.77; 95% confidence interval (CI): 0.74-0.93 versus 0.65-0.87, respectively). Angpt-2 was also detectable in bile, but was not associated with the presence of CC. Immunohistochemistry revealed a strong induction of Angpt-2 expression in the tumor vasculature. Conclusions: Circulating Angpt-2 in serum might be a promising protein candidate locally derived from the tumor vasculature in patients with CC. Measurement of Angpt-2 in serum may be useful for diagnosis and further clinical management of patients with CC.