Types of Neuroendocrine tumours (NETs)

  • Gastrointestinal - Gastric, duodenal, pancreatic, small intestine, appendiceal, colon, rectum, ovary, unknown primary.
  • Thorax – lung
  • Neck/Thorax - Thyroid, parathyroid, thymus
  • Pancreas – Non-functioning. Functioning (gastrinoma, Vasoactive Intestinal Peptide [VIP]-oma, insulinoma, somatostatinoma glucagonoma).
  • Multiple endocrine neoplasia (MEN) -
  • MEN1 - Parathyroid, anterior pituitary, enteropancreatic endocrine cells.
  • MEN2A - Medullary thyroid, phaeochromocytoma, primary parathyroid hyperplasia.
  • MEN2B - Medullary thyroid, phaeochromocytoma, mucosal neuromas, intestinal ganglioneuromas and marfanoid habitus and other skeletal abnormalities.
  • Adrenal - Phaeochromocytoma.
  • Extra-adrenal - Paraganglioma.
  • Goblet cell – Appendix
  • Other - Merkel cell skin cancer, pituitary neuroendocrine tumours.

Neuroendocrine tumours arising within the digestive system are classified as well-differentiated [slower growing] (traditionally referred to as carcinoid tumours when they arose in the tubular gastrointestinal tract and pancreatic neuroendocrine [islet cell] tumours when they arose in the pancreas or, in the case of gastrinomas, in the proximal portion of the duodenum), or poorly differentiated neuroendocrine carcinomas [fast growing] which are generally high grade and can resemble small cell or large cell neuroendocrine carcinoma of the lung.

Table 4: Nomenclature and classification for digestive system neuroendocrine tumours

Pulmonary carcinoids as a whole are well differentiated as opposed to small cell lung carcinoma and large cell neuroendocrine carcinoma, with typical carcinoids sharing some similarities to Grade 1 NETs and atypical carcinoids showing some similarities to Grade 2 NETs of the gastroenteropancreatic tract.

Typical carcinoid has fewer than 2 mitoses/2mm2 and absence of necrosis, and atypical carcinoid has 2-10 mitoses/2mm2 and/or foci of punctate necrosis.  Small cell lung carcinoma and large cell neuroendocrine carcinoma have more than 10 mitoses/2 mm2 and extensive necrosis.