What are neuroendocrine tumours (NETs)?

A neuroendocrine tumour (NET) is a tumour that develops from cells of the neuroendocrine system.

Neuroendocrine cells are similar to nerve cells, and they make chemical messengers called hormones. Hormones control how different organs in the body work.

Neuroendocrine cells are found all over the body, in organs such as the stomach, bowel, pancreas and lungs.

Tumours that develop from the neuroendocrine cells are known as neuroendocrine neoplasms (NENs). Most NENs are neuroendocrine tumours (NETs). A smaller number are described as neuroendocrine carcinomas (NECs).

Whether the tumour is described as a NET or NEC depends on the grade of the tumour. A doctor decides the grade of the cancer by looking at the cancer cells under the microscope. This gives an idea of how quickly the cancer might grow or spread.

NETs can be non-cancerous (benign) or cancerous (malignant). This information is about malignant NETs. It is mainly about NETs that affect the digestive system.

Types of NETs

Some NETs make extra hormones and cause symptoms. These are called functioning tumours.

Tumours that do not make extra hormones are called non-functioning tumours.

NETs are grouped according to where the cancer started (the primary tumour). For example:

  • small bowel NETs
  • large bowel NETs
  • rectal NETs
  • appendix NETs
  • pancreatic NETs
  • stomach (gastric) NETs
  • lung NETs.

Rarely, NETs occur in other areas, including the:

  • liver
  • gallbladder
  • bile ducts
  • kidneys
  • ovaries
  • testicles.

You may hear some NETs referred to as carcinoid tumours. These are usually found in the bowel or the lungs.

NETs often grow slowly. They can be difficult to diagnose, as they may not cause symptoms for several years. But some NETs grow faster and are more likely to spread to surrounding tissues and parts of the body.

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What are the symptoms of neuroendocrine tumours (NETs)?

Symptoms will depend on where in the body the NET is. For example, a NET in the digestive system can cause pain in the tummy, sickness or diarrhoea. A NET in the lung may cause chest infections and shortness of breath.

Some NETs don't cause symptoms and are found by chance.

NETs sometimes make too much of certain hormones. The type of hormone they make depends on the gland the tumour is affecting.

If you are worried about NETs, we have more information about the signs and symptoms.

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What are the causes of neuroendocrine tumours (NETs)?

It is not known what causes NETs. These tumours can affect people of any age, including children, but the average age to be diagnosed is around 50 or 60 years old.

Around 1 in 20 (5%) of NETs occur in people with a hereditary (genetic) condition. People with a rare genetic condition called multiple endocrine neoplasia 1 (MEN1) have a higher risk of developing NETs.

Other rare genetic conditions that can cause a higher risk of NETs are:

  • von Hippel-Lindau (VHL) disease
  • tubular sclerosis (TSC)
  • neurofibromatosis (NF).

NETs may occur at a younger age in people with hereditary conditions. If you are diagnosed with a NET at a younger age, you may be offered genetic testing. You may also be offered testing if you have a family history of NETs, or other symptoms that could be caused by one of these hereditary conditions.

Diagnosis of neuroendocrine tumours (NETs)

You usually start by seeing your GP. If they are unsure of the problem, they will refer you to a specialist at the hospital.

At the hospital, the doctor will ask about your general health and any previous medical problems. They will then examine you and talk about the tests you need to have.

Sometimes, NETs show up on a scan you may be having for another reason.

You may have some of the following tests.

  • Blood tests

    If you have a NET, the levels of some chemicals in the blood may rise. This is mainly serotonin, 5HIAA and a protein called chromogranin A (CgA). 

    Serotonin is a chemical the body makes that sends messages between different parts of the brain. It helps control lots of functions, such as how you sleep, your mood and your appetite

    You will need to give blood samples to check the levels of these chemicals. You may be asked to fast (not eat) before these tests.

    You may also have a blood test to look for hormones released by some NETs.

    You will also have general blood tests to count the number of healthy blood cells in your blood. This is called a full blood count or FBC. You may have other blood tests to check how well your kidneys and liver are working, hormone levels, and your level of vitamin B12.

  • Urine tests

    You may be asked to save all the urine you pass in a 24-hour period. Your doctor will then test it for 5HIAA.
    5HIAA is made from serotonin by the liver and then passes out the body in the urine. Certain food, drinks and medicines can raise your levels of 5HIAA. You may need to avoid these for a few days before and during the collection.

  • Ultrasound scan

    An ultrasound scan uses soundwaves to build up a picture of inside your body. Usually, you cannot eat or drink anything for at least 6 hours before the scan. You may also have an ultrasound of your heart, called an echocardiogram.

  • CT scan

    A CT scan uses x-rays to build a 3D picture of the inside of the body.

  • MRI scan

    An MRI scan uses magnetism to build up a detailed picture of areas of your body.

  • PET-CT scan
    A PET-CT scan is a combination of PET and a CT scan. CT scans take a series of x-rays to build up a 3D picture. A PET scan uses low dose radiation to measure the activity of cells in different parts of their body.
    PET-CT scans give more detailed information about the part of the body being scanned.

  • Nuclear medicine scans

    Nuclear medicine scans use a small amount of a radioactive substance called a tracer. The tracer shows up on scan pictures. The dose of radioactivity from these scans is low. It is about the same amount you get from an x-ray.

  • Biopsy

    During a biopsy, doctors take a small piece of tissue (or a sample of cells) from a tumour. They then look at it under a microscope. You have a local anaesthetic to numb the area before the sample is taken. Sometimes, you have a general anaesthetic for the biopsy. This depends on where the NET is in your body.

Waiting for test results can be a difficult time. We have more information that can help.

Further tests

Depending on the type of NET you have, your doctor may want to do other tests, including:

  • A bone scan finds any abnormal areas of bone. A mildly radioactive substance is injected into a vein. A scan of your bones is taken 2 or 3 hours later.
  • An endoscopy uses a thin, flexible tube with a camera at the end to look inside the gullet (oesophagus), stomach, small bowel or large bowel

Your doctor or nurse will explain the test to you and why you need it.

Staging and grading of neuroendocrine tumours (NETs)

The results of your tests help your doctors find out more about the size and position of the cancer and whether it has spread. This is called staging.

A doctor decides the grade of the cancer by how the cancer cells look under the microscope. This gives an idea of how quickly the cancer might grow or spread.

Knowing the stage and grade helps your doctors plan the best treatment for you.

Treatment for neuroendocrine tumours (NETs)

A team of specialists will meet to discuss the best possible treatment for you. This is called a multidisciplinary team (MDT).

They will discuss the results of your tests to plan your treatment. They will look at factors including:

  • where the NET started
  • the size of the tumour and whether it has spread (its stage)
  • whether you have symptoms of carcinoid syndrome or the over-production of other hormones
  • the appearance of the cells under a microscope (its grade).

Your doctor or cancer specialist or nurse will explain the different treatments and their side effects. They will also talk to you about things to think about when making treatment decisions.

The main treatment is surgery to remove the tumour. The aim of this is to cure the cancer. If surgery cannot completely remove the NET, treatment will aim to relieve symptoms and improve quality of life.

Surgery for NETs

Your team will plan your operation carefully. They will explain:

  • the surgery
  • the possible side effects
  • what to expect.

If you have a functioning NET, there is a risk that an operation can cause carcinoid crisis. Your doctors will try to prevent this and monitor you during treatment.

We have more information about preparing for surgery

  • Surgery to remove NETs

    Localised and low-grade NETs may be completely removed with surgery. The aim of the operation is to cure the cancer. Sometimes, this type of operation is also possible if there has been only limited spread. This is called regional spread. Depending on where the NET is, it may be possible to remove it during an endoscopy.
    An operation to remove all of the cancer may sometimes be possible for NETs that have spread to the liver. This will depend on where the tumours are in your liver. Your doctors will discuss this with you.

  • Surgery to improve NET symptoms

    If it is not possible to completely remove the tumour, doctors may try to remove as much as possible. This is called debulking. It can improve your symptoms by relieving pressure on other parts of the body. It can also help to reduce symptoms caused by the over-production of a hormone.
    Surgery can also help relieve symptoms of a NET that has spread to more distant sites in the body (metastatic). For example, if a tumour is blocking the small bowel, surgery can remove it or bypass the blockage. 

Other treatments for NETs

Other treatment options you may have include:

  • Watchful waiting

    Some NETs are slow-growing and may not change for months or years. If a NET spreads but is not causing symptoms, you may not need treatment straight away. Your doctor will monitor you with regular check-ups. If symptoms develop, you will have the option of treatment.

  • Somatostatin analogues

    Somatostatin analogues are drugs that treat the symptoms of carcinoid syndrome. They work by blocking the hormones the tumour makes. They may also control the growth of NETs. You may be given them along with other treatments.

  • Chemotherapy

    Chemotherapy uses anti-cancer (cytotoxic) drugs to destroy cancer cells. You may have chemotherapy to treat NETs that have spread. The type of chemotherapy you will have depends on where the NET started in the body. Chemotherapy treatments that can be used for NETs include: capecitabine and temozolomide (CAPTEM), FOLFOX, streptozocin and fluorouracil (5FU), etoposide and cisplatin (EP), carboplatin and etoposide.

  • Targeted therapies

    Targeted therapies are anti-cancer medicines that interfere with how cancer cells grow and divide. The two main targeted therapy drugs used are sunitinib (Sutent®) and everolimus (Afinitor®). You take these drugs as capsules or tablets. Other targeted therapies may be available as part of a clinical trial.

  • Interferon alpha (IntronA®)

    Interferon is a drug that can treat the symptoms of NETs. It may also control how the tumour grows. Interferon is a protein that you naturally have small amounts of in your body. If you have it as a drug, it can stimulate the body’s immune system to destroy cancer cells. You will have it as an injection under the skin.

  • Radiotherapy

    Radiotherapy uses high-energy x-rays to destroy cancer cells, while doing as little harm as possible to normal cells. You may have radiotherapy if it is not possible to remove the tumour with surgery, or if it has already spread.

  • Targeted radionuclide therapy

    You may have radionuclide therapy to relieve symptoms of carcinoid syndrome and control the growth of NETs. This therapy uses a radioactive substance called a radionuclide. It is injected into the bloodstream.

Treatments for NETs in the liver

Treatments that directly target the liver can sometimes treat NETs in the liver:

  • Hepatic artery embolisation

    A hepatic artery embolisation can sometimes shrink NETs in the liver. It can also relieve the symptoms of carcinoid syndrome. Hepatic artery embolisation works by reducing blood flow to the tumours. Tumours need a blood supply to survive.

  • Radiofrequency ablation (RFA)

    Radiofrequency ablation (RFA) can treat NETs in the liver. It uses laser or radio waves to destroy the cancer cells by heating them to high temperatures. 

  • Selective internal radiation therapy (SIRT)

    Selective internal radiation therapy is a type of cancer treatment that uses tiny radioactive beads. It can treat NETs that are found in the liver.

Cancer research trials

Cancer doctors use cancer research trials to assess new treatments. Current studies are looking at new treatments for NETs.

Your doctor may ask you to take part in a cancer research trial. They will discuss the treatment with you, so you understand the trial and what it means to take part.

After neuroendocrine tumours (NETs) treatment

You have regular follow-up appointments after treatment. You may be monitored with blood tests and scans.

After treatment, some people may be cured of NETs. Others may continue to have treatment when they need it to help keep it under control.

If the cancer is advanced there are different things that can be done to control the symptoms. You can read more about this in our information on advanced cancer.

Well-being and recovery

Even if you already have a healthy lifestyle, you may choose to make some positive lifestyle changes during and after treatment. For example, if you smoke or drink alcohol, it is best to avoid smoking or reduce the amount of alcohol.

Eating well and keeping active can improve your health and well-being. It can also help your body recover. Your dietitian can help with any difficulties you might have with eating after treatment.

Your feelings after treatment

You may have many different emotions, including anxiety, anger and fear. These are all normal reactions. It may help to get support from family, friends or support organisations, like Neuroendocrine Cancer UK, who can give you information about counselling in your area.

Macmillan is also here to support you. If you would like to talk, you can:

Macmillan is also here to support you. If you would like to talk, you can:

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About our information

  • References

    Below is a sample of the sources used in our neuroendocrine tumours (NETs) information. If you would like more information about the sources we use, please contact us at cancerinformationteam@macmillan.org.uk

    Esmo clinical practice guidelines: endocrine and neuroendocrine cancers. Available from: www.esmo.org/guidelines/endocrine-and-neuroendocrine-cancers (accessed May 2021).

  • Reviewers
    This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert medical and health professionals and people living with cancer. It has been approved by Senior Medical Editor, Dr Paul Ross, Consultant Medical Oncologist.

    Our cancer information has been awarded the PIF TICK. Created by the Patient Information Forum, this quality mark shows we meet PIF’s 10 criteria for trustworthy health information

  • Reviewers

    This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert medical and health professionals and people living with cancer. It has been approved by Chief Medical Editor, Professor Tim Iveson, Consultant Medical Oncologist.

    Our cancer information has been awarded the PIF TICK. Created by the Patient Information Forum, this quality mark shows we meet PIF’s 10 criteria for trustworthy health information.

Date reviewed

Reviewed: 05 January 2022
Next review: 05 January 2025
Trusted Information Creator - Patient Information Forum
Trusted Information Creator - Patient Information Forum

Our cancer information meets the PIF TICK quality mark.

This means it is easy to use, up-to-date and based on the latest evidence. Learn more about how we produce our information.