A case of unclassified multicystic biliary tumor with biliary adenofibroma features.

A 40-year-old Japanese man was admitted to our hospital for evaluation of upper abdominal pain. Abdominal computed tomography (CT) revealed a well-circumscribed multicystic mass measuring approximately 7 × 6 cm. The mass contained a solid lesion measuring 3 × 2 cm. Biopsy of a swollen cervical lymph node led to a diagnosis of diffuse large B-cell lymphoma. After initial chemotherapy for lymphoma, the multicystic mass was surgically resected. The tumor was composed of a multicystic lesion and a solid lesion. Histopathologic examination of the multicystic lesion revealed that the locules were lined by biliary epithelium, demonstrating various degrees of cytological atypia. The stroma was fibrous, and the tumor showed marked apocrine snouts. Part of the tumor showed papillary growth with strong cytological atypia. The solid lesion showed tubulocystic proliferation of tumor cells, with prominent apocrine snouts, embedded in dense and partially hyalinized fibrous stroma. The morphology of the solid part was quite similar to that of reported biliary adenofibroma. Despite lengthy discussion, an appropriate pathological diagnosis could not be found among the current classifications of biliary tumor. The tumor was finally diagnosed as unclassified multicystic biliary tumor with adenofibroma features.