[BRAF V600E-positive intrahepatic cholangiocarcinoma with suspected malignant transformation of the bile duct adenoma:a case report].

A 69-year-old woman was diagnosed with extrahepatic portal vein occlusion and liver cirrhosis. Computed tomography (CT) and magnetic resonance imaging (MRI) revealed a ring-enhanced liver tumor. A liver tumor biopsy detected small bile duct proliferation without atypia and a map-like pattern on immunostaining for glutamine synthetase, resulting in a focal nodular hyperplasia diagnosis. CT after 4 years revealed the increased liver tumor. The patient was suspected of intrahepatic cholangiocarcinoma based on MRI findings. A liver tumor biopsy was re-conducted, and the patient was diagnosed with intrahepatic cholangiocarcinoma (small duct type), which was positive for BRAF V600E on immunostaining. We re-investigated the initial liver tumor biopsy tissue and diagnosed the BRAF V600E-positive bile duct adenoma, indicating a malignant transformation of the bile duct adenoma to an intrahepatic cholangiocarcinoma.