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.