Well-differentiated adenocarcinoma, gastric foveolar type, of the extrahepatic bile ducts: A previously unrecognized and distinctive morphologic variant of bile duct carcinoma.

Abstract

Two examples of a rare but distinctive morphologic variant of extremely well-differentiated adenocarcinoma of the extrahepatic bile ducts are reported. One tumor arose in the common bile duct of a 51-year-old man; the other arose in the common hepatic duct of a 27-year-old man. Both tumors were composed predominantly (>95%) of gastric foveolar-type epithelium. Because of their bland nuclear features, low mitotic index, and focal polypoid and lobular architecture, they were initially confused with adenomas. Foci of less-differentiated adenocarcinoma and perineural invasion present in the deep portions of the tumors facilitated recognition. The neoplastic cells and extracellular mucin were periodic acid-Schiff- and alcian blue-positive. By immunohistochemistry, the tumor cells expressed cytokeratins 8 and 20 as well as cathepsin D, as reported in normal foveolar cells. Likewise, p53 overexpression was documented immunohistochemically in both adenocarcinomas, which also stained with the Ki-67 antibody. Despite the well-differentiated nature of the neoplasms and their deceptively benign microscopic appearance, one patient developed recurrence and liver metastasis 5 years after surgery. The other patient is disease-free 2 years following a segmental resection of the common hepatic duct, cystic duct, and gallbladder. The cell phenotype of these tumors can be explained by the ability of the bile duct epithelium to differentiate along gastric cell lines.