Neuroendocrine tumors

Neuroendocrine tumors (NETs) (historically called APUDomas) represent a wide spectrum of disease. They consist of a large heterogeneous group of malignancies that are derived from embryonic neural crest tissue found in various organ such as the hypothalamus, pituitary gland, thyroid gland, adrenal medulla, and gastrointestinal tract. 

The spectrum of neuroendocrine tumors range from:

• carcinoid tumor: arising from enterochromaffin cells and can occur at various sites such as thymus, lung, ovary 
• pheochromocytoma: typically occurs in the adrenals but can also occur in extra-adrenal sites
• location dependant entities
  • abdomen
    • gastrointestinal tract neuroendocrine tumors
    • pancreatic neuroendocrine tumors (pNET)
  • thorax/lung: pulmonary neuroendocrine tumors
  • endocrine glands 
    • thyroid: medullary thyroid tumors
• Merkel cell carcinoma

Pathology

They can also be divided by their biochemical behavior as functioning or non-functioning, by their aggressiveness as slow-growing and more aggressive lesions and so on.

Because of secretory products by amine precursor uptake and decarboxylation (APUD) they were historically known as APUDomas.

Genetics

Mostly occur sporadically, some are linked to multiple endocrine neoplasia syndromes.