[Synchronous double primary cancers of a mixed adenoneuroendocrine carcinoma of the distal bile duct and a carcinoma in situ in the perihilar bile duct].

We report the rare case of a 69-year-old man who underwent resection of a mixed adenoneuroendocrine carcinoma (MANEC) of the distal bile duct and a carcinoma in situ in the perihilar bile duct. The patient was admitted to our hospital for obstructive jaundice. Imaging studies revealed a mass in the distal bile duct, and an abnormal epithelium was detected in the perihilar bile duct using peroral cholangioscopy. Bile cytology and transpapillary biopsy of the tumor revealed adenocarcinoma. We diagnosed this patient with distal cholangiocarcinoma with extensive intraepithelial progression toward the perihilar bile duct and performed a subtotal stomach-preserving pancreaticoduodenectomy and left hepatectomy. According to the histological examination of the resected specimens, we found a MANEC in the distal bile duct and a carcinoma in situ in the perihilar bile duct. Together, they were diagnosed as synchronous double primary cancers due to the lack of pathological transition between them.