Coexistence of Small Duct Type and Biliary Adenofibroma-Associated Large Duct Type Intrahepatic Cholangiocarcinoma within a Single Lesion: A Case Report.

INTRODUCTION: Biliary adenofibroma (BAF) is a rare biliary epithelial tumor with malignant potential, and it has been reported in association with intrahepatic cholangiocarcinoma (iCCA). Although the malignant transformation of BAF has been described in sporadic case reports, the coexistence of distinct histopathological subtypes of iCCA in association with a single BAF lesion is exceedingly rare. CASE PRESENTATION: An asymptomatic 75-year-old man was incidentally found to have a 35-mm hepatic mass in hepatic segment 7 during an evaluation for prostate cancer. Imaging studies suggested iCCA, and partial hepatectomy was performed. Histopathological examination revealed 2 distinct tumor components: a small duct type iCCA with cholangiolocellular subtype features and a large duct type iCCA arising from BAF. A distinct transition zone was identified between the BAF and large duct type iCCA components, whereas the small duct type iCCA component was present adjacent to the BAF-associated large duct type component. The postoperative course was uneventful, and the patient remained disease-free 10 months after surgery. CONCLUSIONS: We report a rare case of the coexistence of small duct type iCCA and BAF-associated large duct type iCCA within a single lesion. This case highlights the biological heterogeneity and malignant potential of BAF-associated biliary neoplasia and underscores the importance of complete resection and careful follow-up.