A Rare Case of Adenosquamous Carcinoma Arising from Intraductal Papillary Neoplasm of the Bile Duct.

INTRODUCTION: Intraductal papillary neoplasm of the bile duct (IPNB) is an uncommon biliary tumor that often exhibits invasive growth but generally shows a more favorable prognosis than conventional cholangiocarcinoma. In contrast, adenosquamous carcinoma (ASC) of the bile duct is rare and associated with markedly poor outcomes. We report an extremely rare case of ASC arising from IPNB in the intrapancreatic bile duct.

CASE PRESENTATION: A 78-year-old woman was referred to our hospital for evaluation of jaundice. Contrast-enhanced CT revealed a low-density mass in the pancreatic head, with upstream common bile duct dilatation. Endoscopic retrograde cholangiopancreatography and endoscopic US demonstrated distal bile duct stenosis and a 25-mm hypoechoic mass in the pancreatic head. Biopsy indicated adenocarcinoma, and the lesion was preoperatively diagnosed as pancreatic head cancer involving the distal bile duct. Owing to renal dysfunction, preoperative chemotherapy was not administered, and subtotal stomach-preserving pancreaticoduodenectomy was performed. Histopathological examination revealed high-grade IPNB with invasion into the pancreatic parenchyma. The invasive component demonstrated dual differentiation into adenocarcinoma and squamous cell carcinoma, establishing a final diagnosis of ASC arising from IPNB. Despite curative resection, local recurrence and liver metastases developed 7 months postoperatively, and the patient died 15 months after surgery.

CONCLUSIONS: This is an extremely rare case of ASC presumed to have arisen from IPNB in the intrapancreatic bile duct. Awareness of this pathological progression is essential for accurate diagnosis and prognostic assessment, underscoring the need for meticulous histopathological evaluation.