A case of biliary adenosquamous carcinoma suggesting adeno-to-squamous transition by immunohistochemistry

Abstract

A 78-year-old woman presenting with elevated liver enzyme levels and a biliary tumor was referred to our hospital. Contrast-enhanced computed tomography revealed circumferential thickening of the lower bile duct with delayed enhancement and dilatation of the upstream bile duct. Endoscopic ultrasound fine needle biopsy provided a diagnosis of adenocarcinoma, and subtotal gastric-sparing pancreaticoduodenectomy was performed. The final pathological diagnosis was adenosquamous carcinoma, and the final staging was T2N1M0, Stage IIB. The patient was treated with S-1 as postoperative adjuvant chemotherapy for six months. No tumor recurrence was noted two years posttreatment. Immunostaining of the lesion with carcinoembryonic antigen for adenocarcinoma and cytokeratin 5/6 for squamous cell carcinoma revealed a gradual transition from adenocarcinoma to squamous cell carcinoma. Adenosquamous carcinoma is a relatively rare tumor, and immunostaining findings suggest a stepwise transition from adenocarcinoma to squamous cell carcinoma.