[Neuroendocrine carcinoma of the ampullar region with oat-cell histological features and adenocarcinoma].

We report a case of primary duodenal carcinoma showing neuroendocrine and glandular differentiation, in a 65-years-old male. Both components were closely related and transition between them was observed. The neuroendocrine component was composed of an undifferentiated "oat-cell" type, with positive immunostaining for neuroendocrine and epithelial markers. Ultrastructural findings confirmed this double differentiation, with dense cytoplasmatic granules of neurosecretory type. The neuroendocrine component showed greater aggressiveness with lymph node metastasis.