Pathologic features of mucin-producing bile duct tumors: two histopathologic categories as counterparts of pancreatic intraductal papillary-mucinous neoplasms.

Tumors with clinically recognizable mucin production arising from bile duct, "mucin-producing bile duct tumors (MPBTs)," have not been studied yet for their pathologic features and classification in details. The clinical findings of MPBT have a lot of similarities to those of pancreatic intraductal papillary-mucinous neoplasm. In the present study, we examined 30 MPBTs and classified them into two distinct morphologic categories: 22 cases of "columnar type" composed of pseudostratified columnar cells with basophilic cytoplasm and columnar nuclei and 8 cases of "cuboidal type" composed of pancreaticobiliary and/or oncocytic pattern. Pancreaticobiliary pattern showed abundantly branched papillae lined by acidophilic cuboidal cells with round nuclei, whereas oncocytic pattern was characterized by intraepithelial lumina and cribriform pattern composed of abundant oxyphilic cells with round nuclei, and these patterns overlapped frequently. There were significant differences in the clinicopathologic findings including macroscopic findings, morphometric data, mucin expression profiles (MUC2 expression in columnar type and MUC6 expression in cuboidal type), and cell proliferative activities between columnar type and cuboidal type. Patients with columnar type showed significantly poorer survival than those with cuboidal type. We concluded that columnar type and cuboidal type of MBPTs belong to different lineage of neoplasm and that they are counterparts of "intestinal type" and "pancreaticobiliary type" of pancreatic intraductal papillary-mucinous neoplasm, respectively.