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NETs: key facts

Dr Geboes defines NETs


The neuroendocrine system, also known as the hormone system, is made up of nerve and gland cells called neuroendocrine cells. These cells release hormones into your body that generally regulate the function of different organs.

When neuroendocrine cells change and grow uncontrollably, NETs can develop. NETs may be non-cancerous (benign) or cancerous (malignant).

Benign NETs are those that tend to grow slowly and be confined to a limited area of the body and may generally be considered non-life threatening if they do not squeeze or replace other nearby areas of the body.

If feasible, benign NETs should be removed by surgery or otherwise treated in their early stages of development as they may spread to other sites of the body and develop into malignant tumours.

Malignant NETs are those that are often growing faster or more uncontrollably, perhaps affecting the surrounding tissues or have moved from one area of the body to another (metastasised).

If surgery is not possible there are still treatment options for people with metastatic NETs.

Functioning vs non-functioning tumours

You may hear NETs referred to as being functioning or non-functioning. Some NETs produce too many hormones that can cause various symptoms and complications, depending upon the tumour’s location and the hormones that it releases.

These NETs are called functioning tumours. NETs that don’t produce hormones are called non-functioning tumours, although they can still cause complications.


What are carcinoid tumours?

Many people still refer to NETs as carcinoid tumours. This is an older term that is sometimes still used as an alternative for either NETs in general, or NETs that do not originate in the pancreas.

In 1907, NETs were first named carcinoid tumours because scientists thought their slow growth meant they were ‘cancer-like’ (benign) tumours rather than truly cancerous (malignant).

But it is now clear that that NETs can be malignant and spread from one part of the body to another, like other forms of cancer.

What is carcinoid syndrome?

Dr Khan talks about carcinoid syndrome


Carcinoid syndrome is a distinct group of symptoms that some people with NETs may get when tumours in the gastrointestinal (digestive) system spread to other parts of the body – usually the liver. The main symptoms of this condition include diarrhoea, flushing of the skin (particularly the face), stomach cramping, heart problems such as palpitations, and wheezing.

The symptoms can vary from person to person, and can occur when GI NETs release an excessive amount of hormones such as serotonin, histamine and somatostatin among others, into the bloodstream.

Carcinoid syndrome affects approximately 10% of people with GI NETs, even if the cancer has spread. People with carcinoid syndrome may experience these symptoms unexpectedly over time since the hormones may be produced at any time. This can have a major impact on quality of life.

These symptoms are often misdiagnosed as signs of other illnesses, such as irritable bowel syndrome (IBS), Crohn’s disease, peptic ulcer disease, gastritis or the menopause.

Visit the practical tips and tools section for information on managing carcinoid syndrome symptoms.

Ronny, Patient – Living with NETs

“Facial flushing is where you start to get really hot in the face and it is like having pins and needles. It was something I had never experienced before.”

View Ronny’s story >

Symptoms of carcinoid syndrome

Primary tumour sites Examples of hormones involved Main symptoms
  • Stomach
  • Bowel
  • Small intestine
  • Serotonin
  • Histamine
  • Bradykinin
  • Diarrhoea (including night-time diarrhoea)
  • Flushing of the skin (particularly the face)
  • Stomach pain
  • Heart problems (palpitations)
  • Wheezing and breathlessness

Symptoms of carcinoid syndrome may be triggered by emotional stress and anxiety, drinking alcohol and caffeinated drinks, and by certain food types.

Carcinoid syndrome symptoms may be avoided or alleviated, however, by:

  • Avoiding stressful situations or practicing relaxation techniques
  • Reducing the consumption of alcoholic and caffeinated beverages
  • Avoiding eating foods that contain high levels of the amino acid tryptophan (e.g. chocolate, milk and cheese, red meat, fish and poultry) or serotonin (e.g. bananas)
  • Exercise

Untreated carcinoid syndrome can result in vitamin deficiencies and regular bouts of diarrhoea, which can cause dehydration. A more serious complication, however, is carcinoid crisis. Carcinoid crisis is the immediate onset of debilitating and potentially life-threatening manifestations of the same symptoms that are associated with carcinoid syndrome. Carcinoid crisis may be triggered by taking a biopsy or surgical intervention. Please make sure you let doctors know that you have NETs so that they can manage you accordingly.

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Find out more about NETs

Diagnosis & Testing

Diagnosing NETs

Find out how NETs are diagnosed and the tests that healthcare professionals may use to monitor NETs

Diagnosis & Testing
Treating NETs

Treating NETs

Read about treatment options for NETs, including surgery, radiotherapy and medications

Treatment Options
FAQs by experts


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This site is intended for a UK audience only. SOM-UK-003737 September 2018