Cystic and micropapillary epithelial changes of peribiliary glands might represent a precursor lesion of biliary epithelial neoplasms.

A tumorigenic role of peribiliary glands (PBGs) has been suggested recently. This study was performed to clarify the histological characteristics of PBGs showing cystic and micropapillary epithelial changes. From histological sections of a total of 938 autopsy livers, cases with cystic and micropapillary changes of the epithelial cells of intrahepatic PBGs were collected. PBGs with cystic change that lacked micropapillary epithelial changes were referred to as cystic lesion. Mucin staining and immunohistochemical analysis were performed, and the results were compared between cystic and micropapillary (C-P) lesions and cystic lesions. C-P and cystic lesions were observed in 9 (1 %) and 40 (4 %) , respectively. The atypia of micropapillary epithelium was usually mild, but in a single case, invasive adenocarcinoma accompanied a C-P lesion. Abundant mucin expression was observed in all cases of C-P lesion, which was similar to mucinous acini of normal PBGs rather than serous acini. Immunohistochemical analysis showed that MUC5AC was more frequently expressed in C-P lesions than in cystic lesions. Immunohistochemical expression of cyclin D1 and S100P was characteristically found in C-P lesions. Mean Ki-67 labeling index of C-P lesions was significantly higher than that of cystic lesions. The immunoprofile of C-P lesions was similar to that of the branch-type intraductal papillary mucinous neoplasm of the pancreas. These results suggest that C-P lesions may have neoplastic features and might represent a precursor of biliary epithelial neoplasms, including branch-type intraductal papillary neoplasm of the bile duct as well as mucin-producing cholangiocarcinoma, a concept that we have recently proposed.