Aberrant Expression of Pneumocytic Markers (TTF-1 and Napsin-A) in Biliary Duct and Gallbladder Adenocarcinomas; A Potential Diagnostic Pitfall

Cholangiocarcinomas and gallbladder carcinomas are epithelial tumours with biliary differentiation. On histology and immunohistochemistry, they resemble adenocarcinomas and possess overlapping immunohistochemical profiles. Diagnosing these tumours is best done using appropriate imaging and clinical features with compatible immunohistochemistry. Immuno-staining for thyroid transcription factor-1 (TTF-1) and novel aspartic proteinase of pepsin A (Napsin-A) is believed to be specific for primary pulmonary adenocarcinomas. We herein report uncommon instances of strong and diffuse expression of these markers in two examples of adenocarcinomas arising from the bile duct and gallbladder. A review of the literature and a summary of similar studies relating to aberrant TTF-1 and Napsin-A expression in biliary tract adenocarcinomas are presented.