[Spindle and giant cell type undifferentiated carcinoma of the distal bile duct: a case report].

Undifferentiated carcinoma of the biliary tract is rare and more frequently occurs in the gall bladder than in the extrahepatic bile ducts. We report on an extremely rare case of a spindle and giant cell type undifferentiated carcinoma of the distal bile duct. In the presented tumor, atypical glands and single-cell clusters arising from the bile duct epithelium gradually transitioned into a predominantly sarcomatoid architecture, which constituted more than 98 % of the whole tumor volume. Focally, osteoclast-like giant cells were intermixed with the spindle cells. The tumor showed a high proliferation activity (Ki-67) and was demonstrated to harbor mutations in the genes for cyclin D3 (CCND3), fibroblast growth factor receptor 4 (FGFR4), neurofibromin 1 (NF1) and NOTCH3, as assessed by next-generation sequencing analysis. The presented case underscores the relevance of this tumor entity beyond the pancreas and gall bladder and emphasizes the indispensable combination of morphology and immunohistochemistry regarding the diagnostic process.