Most NETs are classified as either a carcinoid tumor or islet cell tumor, however other rare types exist, too.
- Carcinoid tumors typically develop in the organs of the gastrointestinal tract, such as the stomach, small intestine, pancreas, appendix, colon or rectum. Carcinoid tumors may also develop in the lungs and less commonly in the liver, ovaries, testicles and other organs. Carcinoid tumors tend to grow slowly, but they can metastasize and cause life-threatening complications.
- Pancreatic neuroendocrine tumors (Islet cell tumors) develop in the hormone-secreting cells of the pancreas, known as Islets of Langerhans. Each year, about 1,000 people are diagnosed with islet cell tumors in the United States, which make up 3-5 % of all pancreatic cancers. Other subtypes of islet cell tumors are classified according to the type of hormone they produce:
- Gastrinoma produces excess levels of gastrin
- Insulinoma produces excess levels of insulin
- Glucagonoma produces excess level of glucagonoma
- VIPoma produces excess level of vasoactive intestinal peptide (VIP)
- Somatostatinoma produces excess level of somatostatin
- Pheochromocytoma is a neuroendocrine tumor that develops from the cells located in the adrenal glands that produce adrenaline and noradrenaline. Although pheochromocytoma is a benign tumor, it can lead to life-threatening circumstances as a result of a severe rise in blood pressure and heart rate caused by excess levels of these hormones.
- Merkel cell cancer is a rare and aggressive neuroendocrine cancer of the skin. The risk of this type of cancer increases with age.
- Neuroendocrine carcinoma refers to neuroendocrine tumors that do not fall into the other specific categories. They can develop in various organs of the body including the brain, GI tract and lungs.
Is the Tumor Functional or Nonfunctional?
Additionally, neuroendocrine tumors are classified as functional or nonfunctional.
- Functional tumors secrete hormones that can cause symptoms including flushing, asthma attacks and diarrhea. Fewer than 10% of patients have functional tumors.
- Nonfunctional tumors don’t secrete hormones. Because these don’t produce symptoms, they tend to be diagnosed at later stages.