Decorative image

About neuroendocrine tumours (NETs)

Find out about the neuroendocrine system and what neuroendocrine tumours are.

The neuroendocrine system

The neuroendocrine system is made up of nerve and gland cells. It makes hormones and releases them into the bloodstream.

Neuro means nerve and endocrine means the cells of the endocrine system. The endocrine system is a network of glands and organs in the body that produce hormones. It's also called the hormone system.

Generally speaking, hormones control how our bodies work. This includes our growth and development, how we respond to changes such as stress, and many other things.

There are neuroendocrine cells in most organs of the body.

Diagram showing the parts of the body neuroendocrine tumours most commonly develop in

Neuroendocrine cells have different functions depending on where they are in the body.

 For example, neuroendocrine cells in the gut make hormones to control:

  • the release of digestive juices into the gut
  • the muscles that move food through the bowel

Neuroendocrine cells in the lung release hormones that control the flow of air and blood in the lungs.

What neuroendocrine tumours are

Neuroendocrine tumours (NETs) are rare tumours that develop in cells of the neuroendocrine system. There are a number of different types of neuroendocrine tumour. The type you have depends on the particular cells that are affected.

Most neuroendocrine tumours usually develop slowly over a number of years. Many people don’t have symptoms at first. It's not unusual for people to find that a neuroendocrine cancer has already spread to another part of the body when they are diagnosed.

Functioning and non functioning tumours

Some NETs produce extra hormones and cause symptoms. These are called functioning tumours. Those that don’t produce extra hormones are called non functioning tumours.

Cancerous and non cancerous tumours

There is some debate among doctors about how neuroendocrine tumours should be grouped and what they should be called. Although they develop from the same types of cell, they develop in different organs in the body. They also behave in different ways, for example some are slow growing while others are faster growing.

Neuroendocrine tumours can be non cancerous (benign) or cancerous (malignant). Generally speaking, benign neuroendocrine tumours tend to be slow growing and are low or intermediate grade. Neuroendocrine cancers tend to be faster growing and higher grade.

Other names

Other terms used for neuroendocrine tumours include:

  • gastroenteropancreatic neuroendocrine tumours (GEP NETs for short) – tumours in the gut or pancreas
  • pancreatic neuroendocrine tumours (pNETs) – tumours that develop in the pancreas
  • gastrointestinal neuroendocrine tumours (GI NETs) – tumours that develop in the bowel, stomach or food pipe (oesophagus)
  • functioning neuroendocrine tumours (F-NETs)
  • non functioning neuroendocrine tumours (NF-NETs)
  • carcinoid tumour
Last reviewed: 
20 Mar 2014
  • Guidelines for the management of gastroenteropancreatic neuroendocrine (including carcinoid) tumours
    JK. Ramage (and others)
    Gut. 2005 Jun;54 Suppl 4:iv1-16

  • An overview of the current diagnosis and recent developments in neuroendocrine tumours of the gastroenteropancreatic tract: the diagnostic approach
    P. Kuiper (and others)
    The Netherlands Journal of Medicine. 2011 Jan;69(1):14-20

  • Cancer Principles and practice of oncology (8th edition)
    VT. De Vita, TS. Lawrence, and SA. Rosenberg
    Lippincott, Williams and Wilkins, 2008

  • The pathologic classification of neuroendocrine tumors: a review of nomenclature, grading, and staging systems
    DS. Klimstra (and others)
    Pancreas. 2010 Aug;39(6):707-12

Information and help

Dangoor sponsorship

About Cancer generously supported by Dangoor Education since 2010.