Clinical implications of unusual NeuroD and mASH1 expression in a patient with primary large-cell neuroendocrine carcinoma of the duodenum: report of a case.

A 69-year-old woman was referred to our hospital for investigation of tarry stools. Abdominal computed tomography (CT) showed a slightly enhanced heterogeneous mass in the first to second part of the duodenum, adjacent to the gallbladder and head of the pancreas. Endoscopy showed a huge protruding tumor with ulceration in the first part of the duodenum. The preoperative histopathological diagnosis was neuroendocrine carcinoma with expression of synaptophysin. Thus, we performed pancreaticoduodenectomy with gallbladder bed resection. Histopathologically, the tumor was a large-cell neuroendocrine carcinoma (LCNEC) of the duodenum. To our knowledge, this is the first report of duodenal LCNEC arising outside the ampulla of Vater. The patient has been disease-free for 24 months since her operation, without additional therapy. Immunohistochemically, the tumor cells revealed positive expression to NeuroD and faint expression to mASH1 (hASH1): both essential transcriptional factors for normal neural development. The expression patterns of NeuroD and mASH1 suggest a favorable prognosis.