Neuroendocrine tumors of the pancreas and gastrointestinal tract and carcinoid disease

The neuroendocrine, or islet cell, and carcinoid tumors of the pancreas and gastrointestinal tract are a group of similar neoplasms that, despite several differences in clinical and biochemical behavior, share many common features. Although originally thought to be of neural crest origin, these cells are now considered to originate from embryonic endoderm.1 They are capable of taking up and decarboxylating aromatic amines or their precursors, giving rise to the term APUD (amine precursor uptake and decarboxylation) cells or apudomas. This term has been replaced by their designation as neuroendocrine neoplasms of the gastrointestinal tract.2 Although largely concentrated in the stomach, midgut, and pancreas, neuroendocrine cells share a number of histochemical and ultrastructural characteristics with other endocrine cell types such as chromaffin cells of the adrenal medulla, melanotrophs and corticotrophs of the pituitary, parafollicular (C) cells of the thyroid, and neuroendocrine cells of the sympathetic ganglia and carotid body. They also share a similarity with carcinoid tumors.3,4 Histologically, these tumors are composed of monotonous sheets of small round cells with a uniform nucleus and cytoplasm and a general lack of mitotic figures.5,6 In general, they are well vascularized and tend to have a similar pattern of metastatic spread, involving primarily the regional lymph nodes and liver, although widespread metastases to lung, bone, and brain can also occur.7