Intraductal oncocytic papillary neoplasm of the bile duct: clinicopathologic and immunohistochemical characteristics of 6 cases.

Intraductal oncocytic papillary neoplasm is known as a distinct subtype of intraductal papillary mucinous neoplasm of the pancreas. Similar neoplasms of the bile duct are rarely reported, and their disease characteristics are not well established. In this study, we examined 6 cases of biliary neoplasms consisting of oncocytic cells with almost exclusively intraductal growth. The patients were 5 women and 1 man of 51 to 68 years. Grossly, 4 appeared to be cystic neoplasms with papillary projections located in the liver and the other two were papillary neoplasms of the dilated hilar bile duct that ranged from 1.5 to 16 cm in size. The most prominent neoplastic cells were cuboidal epithelial cells that showed abundant eosinophilic granular cytoplasm with strongly positive staining for antimitochondrial antibody. Four neoplasms were mixed with minor components of nononcocytic cells. All neoplasms showed arborized papillary and/or cribriform formations except one, which showed a villous architecture. All neoplasms were adenocarcinomas accompanied by a microscopic minimally invasive carcinoma. The oncocytic neoplastic cells, as well as the nononcocytic cells, produced gastric-type mucin (MUC5AC and MUC6) and showed claudin18 and HepPar-1 positivity. Five patients lived disease-free for 10 to 112 months after resection, and 1 died of tumor recurrence at 26 months postoperatively. The present series of biliary tumors are intraductal papillary neoplasms with oncocytic features and can be clinicopathologically regarded as counterparts of pancreatic intraductal oncocytic papillary neoplasm. Our results also suggest that oncocytic changes occur in epithelial cells of biliary tracts that show a predominant gastric phenotype.