A 73-year-old man with a papillary adenoma located in the distal common bile duct is reported. He underwent pylorus-preserving pancreatoduodenectomy. The lesion in the common bile duct featured papillary proliferation of the epithelium and fibrous elements with diffuse infiltration by inflammatory cells. Positive staining for MIB-1 (Ki-67) and p53 was identified in the nuclei of the proliferative epithelium. These findings suggested the malignant potential of this lesion. Further progress in imaging diagnostic techniques should increase the frequency with which such lesions are discovered. Even now, if mural irregularities and defects are found in the extrahepatic biliary system, especially the distal common bile duct, the possibility of such borderline biliary adenoma should be taken into consideration when making a diagnosis.
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