Poorly differentiated gastroenteropancreatic neuroendocrine carcinoma associated with X-linked hyperimmunoglobulin M syndrome.

Gastroenteropancreatic neuroendocrine tumors are uncommon tumors representing 2% of all gastrointestinal tumors. We report a case of a 21-year-old man with X-linked hyperimmunoglobulin M (hyper-IgM) syndrome who presented with diarrhea and jaundice. An ultrasound and magnetic resonance imaging showed multiple variable-sized lesions in the liver and peripancreatic lymphadenopathy. The morphologic and immunohistochemical features of the biopsies from the liver and lymph node were consistent with poorly differentiated neuroendocrine carcinoma. Hyper-IgM syndrome is a rare primary immunodeficiency disease characterized by low serum IgG, IgA, and IgE levels with normal or elevated IgM levels. These patients are at a higher risk for developing malignancies, particularly adenocarcinoma of the gastrointestinal tract and lymphoma. A review of the literature of gastroenteropancreatic neuroendocrine tumors is presented with the discussion of a possible relationship of these tumors with immunodeficiency.