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What are neuroendocrine tumours (NETs)?

Neuroendocrine tumours (NETs) are rare tumours that start in neuroendocrine cells. There are a number of different types of NETs. The type you have depends on the type of cell that the cancer started in. 

Most NETs develop slowly over some years. They may not cause symptoms in the early stages. It’s not unusual for people to find that a NET has already spread to another part of the body when they are diagnosed. 

The neuroendocrine system

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

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

There are neuroendocrine cells in most organs of the body, including the:

  • food pipe (oesophagus)
  • stomach
  • lungs
  • small and large bowel
  • pancreas
  • liver
Diagram showing the parts of the body neuroendocrine tumours most commonly develop in

What neuroendocrine cells do

Neuroendocrine cells have different functions depending on where they are in the body. They control how our bodies work. This includes our growth and development, how we respond to changes such as stress, and many other things. 

For example, neuroendocrine cells of the lung make hormones that control the flow of air and blood in the lungs. And neuroendocrine cells of the gut (digestive system) make hormones to control:

  • the production of digestive juices
  • the muscles that move food through the bowel
Neuroendocrine tumours develop when changes happen in the neuroendocrine cells and they start to grow out of control.

Where NETs start

NETs can start in different parts of the body. Like all cancers, NETs are named after the place they start growing. For example, a NET that starts in the lung is called a lung NET. This is the primary cancer. If the cancer spreads to another part of the body, it’s called secondary cancer. 

Around 5 out of every 10 NETs (50%) start in the digestive system. This is also called the gastrointestinal (GI) system. It includes the:

  • stomach
  • small and large bowel
  • pancreas
  • back passage (rectum)

Around 2 out of every 10 NETs (20%) start in the lung. NETs can also start in other places such as the:

  • food pipe (oesophagus)
  • appendix
  • skin
  • prostate
  • womb
  • adrenal, parathyroid and pituitary glands

In some cases, doctors do not know where the original NET started. This is called cancer of unknown primary (CUP).

Cancerous or non cancerous

There is some debate among doctors about how NETs should be grouped and what they should be called. NETs develop in different parts of the body and behave in different ways. For example, some NETs grow slowly while others are faster growing. 

Some NETs grow so slowly that they are not classified as cancer. They are called benign neuroendocrine neoplasms.

How common NETs are

NETs are rare. Over 4,000 people are diagnosed with a NET each year in the UK. They are getting more common across the world. This might be because there are better tests to diagnose them. 

NETs can develop at any age, including in children. But the average age of diagnosis is around 50 to 60 years old. 

Last reviewed: 
14 May 2019
  • Incidence and survival in neuroendocrine tumours and neuroendocrine carcinomas (NETs/NECs) in England, 2013-2014
    Public Health England, 2016

  • Cancer Statistics for the UK
    Cancer Research UK, Last accessed October 2018

  • Cancer principles and practice of oncology (10th edition)
    DeVita and others
    Wolters Kluwer, 2015

  • Cancer and its Management (7th edition)
    J Tobias and D Hochhauser
    Wiley-Blackwell, 2015

  • Suspected cancer: recognition and referral
    The National Institute for Health and Care Excellence (NICE), June 2015

  • Trends in the Incidence, Prevalence, and Survival Outcomes in Patients with Neuroendocrine Tumors in the United States
    A Dasari and others
    JAMA Oncology, 2017. Vol 3, issue 10, pages 1335-1342

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