Transmembrane carbonic anhydrase, MN/CA IX, is a potential biomarker for biliary tumours

Background/Aims: Carbonic anhydrase isoenzyme IX (MN/CA IX) is a transmembrane protein with a suggested function in maintaining the acid–base balance and intercellular communication. Previous studies have demonstrated that MN/CA IX is expressed in the basolateral plasma membrane of normal biliary epithelial cells, but not in hepatocytes. This study was designed to examine the expression of MN/CA IX in hepatobiliary neoplasms and to elucidate its value as a marker for biliary differentiation. Methods: Fifty-seven hepatobiliary lesions were immunostained for MN/CA IX using biotin–streptavidin complex method. Twenty samples containing normal biliary epithelium and five containing normal liver tissue were used as controls. Results: In the biliary epithelial tumours, immunostaining for MN/CA IX was mainly localized at the basolateral surface of the epithelial cells, like in normal mucosa. All non-invasive dysplastic lesions and 57% of invasive lesions of gall-bladder expressed MN/CA IX. In liver, 78% of cholangiocellular malignant lesions showed a positive reaction for MN/CA IX, whereas only 33% of hepatocellular carcinomas showed a weak immunoreaction. Conclusions: Our results suggest that abnormal expression of MN/CA IX may be linked to malignant transformation of hepatobiliary cells. In addition, it seems to be a promising marker for biliary differentiation in hepatobiliary neoplasms.