Fig. 2

Pathological findings of the initially resected specimen. a The tumor arose from the common bile duct and invaded the left hepatic bile duct. b Hematoxylin and eosin staining. The tumor nest consists of eosinophilic cells with round nuclei (left). A mitotic figure is indicated by the arrow (middle). Rosette formation is apparent (right). c Immunohistochemistry. The tumor cells are positive for all the neuroendocrine markers (CD56, chromogranin A, and synaptophysin). Ki-67 index is 7% (scale bars, 200 μm)