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What are neuroendocrine tumours (NETs)?

Neuroendocrine tumours (NETs) start in cells of the neuroendocrine system. NETs can grow slowly (indolent) or grow quickly (aggressive). When NETs are aggressive, they can grow into and destroy nearby tissue. They can also spread (metastasize) to other parts of the body.

The neuroendocrine system is made up of neuroendocrine cells, which are spread throughout the body. They are found in most organs in the body, including the gastrointestinal (GI) tract, pancreas, thyroid and lungs.

Neuroendocrine cells are like nerve cells (neurons), but they also make hormones like cells of the endocrine system (endocrine cells). They receive messages (signals) from the nervous system and respond by making and releasing hormones. These hormones control many body functions such as digestion and breathing.

Neuroendocrine cells sometimes change and no longer grow or behave normally. These changes may lead to NETs. Some NETs are found early before they spread. But sometimes changes to neuroendocrine cells can cause cancer and spread to other parts of the body. This type of cancer is called neuroendocrine carcinoma.

NETs are named and grouped according to where the tumour started in the body. NETs can develop in organs of the GI tract, including the small intestine, rectum, stomach, colon, esophagus and appendix. These types of tumours are called GI NETs. NETs can also develop in the lungs (called lung NETs) or the islet cells of the pancreas (called pancreatic NETs or pNETs).

Other types of NETs can also develop. These include medullary thyroid cancer, pheochromocytoma and Merkel cell carcinoma.

gastrointestinal (GI)

Referring to or having to do with the digestive organs.

The gastrointestinal (GI) tract, or digestive tract, includes the mouth, pharynx (throat), esophagus, stomach, small intestine and large intestine.


A specialized cell that sends and receives messages (electrical or chemical signals) within the nervous system.

Also called nerve cell.

endocrine system

The group of glands and cells in the body that make and release hormones (which control many functions such as growth, reproduction, sleep, hunger and metabolism) into the blood.

The endocrine system is made up of the hypothalamus, pituitary gland, pineal gland, thyroid, parathyroid gland, adrenal gland, pancreatic islet cells (also known as islets of Langerhans) and the ovaries or testicles.

nervous system

The network of neurons (nerve cells) throughout the body that work together to control organ functions and body movements.

The nervous system is made up of the central nervous system (CNS) and peripheral nervous system (PNS).

islet cell

A specialized cell in the pancreas that produces insulin and other hormones that help control the level of sugar (glucose) in the blood.

Also called endocrine pancreas cell or islet of Langerhans cell.


A tumour that starts in an adrenal gland (the glands on top of each kidney that release hormones to help control heart rate and blood pressure).

Pheochromocytomas are usually non-cancerous (benign) and rarely become cancerous (malignant).

Merkel cell

A specialized cell below the epidermis (top layer of skin) that is involved in the sense of touch.