Neuroendocrine Tumors (NET)

Gastro-entero-pancreatic neuroendocrine (GEP NE) tumors are located in the digestive tract, primarily in the gut (stomach or intestine) or the pancreas. GEP NE tumors produce and secrete excessive amounts of hormones and other substances that are normally regulated in the body in smaller amounts; the specific hormones produced contribute to a person's symptoms.

The most common type of GEP NE tumor is a carcinoid tumor. Carcinoid and pancreatic islet cell tumors produce a variety of peptide hormones and biogenic amines, which vary by location and how they affect the body.

The types of GEP NE tumors include (listed in order of prevalence):

• Carcinoid tumors (55%), which arise from neuroendocrine cells in the appendix (38%), ileum (23%), rectum (13%), and bronchus (11.5%)
• Insulinomas (hypoglycaemic syndrome) (17%), an islet cell tumor that secretes excess insulin, and may occasionally secrete other hormones, including gastrin, ACTH and glucagons.
• Tumors of unknown type (15%)
• Gastrinomas (9%), a gastrin-releasing islet cell tumor of the pancreas (50% to 60%) or duodenum (40% to 50%) that is associated with Zollinger-Ellison syndrome
• Vasoactive intestinal peptide (VIP) tumors (VIPomas; Verner-Morrison syndrome) (2%), an islet cell tumor of the pancreas, lung, or ganglioneuromas that secretes an excess of VIP, a 28-amino acid peptide. VIP plays a role in water transport in the gastrointestinal tract, affects vascular tone, and acts as a local neurotransmitter and modulating ion. More than 80% of VIPomas are malignant
• Glucagonomas, an islet cell tumor of the pancreas that secretes an excess of glucagon, a 29-amino acid peptide

Neuroendocrine cell system of the gut and pancreas

 

Gut

• ECL-cells (histamine, chromogranin A, and possibly gastrocalcin)
• G-cells (gastrin)
• S-cells (somatostatin)
• P-cells (unknown secretory product)
• EC-cells (serotonin, tachykinins, and chromogranin A)
• Peptidergic neurons and other neuroendrocrine cells

 

Pancreas

• ß-cell (insulin)
• α-cell (glucagon)
• D-cell (somatostatin)
• Common stem cells in the pancreatic ducts
• PP-cell (pancreatic polypeptide)
• D1 (unknown secretory product)

GEP NE tumors as a whole are rare, affecting only 1 to 2 people in 100,000. Carcinoid syndrome caused by carcinoid tumors occurs in less than 10% of people with carcinoid tumors, and affects 3 to 5 people out of a million.

 

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