Carcinoid tumours

Neuroendocrine tumours (NETs) are rare tumours that can occur in the cells of the neuroendocrine system.

The neuroendocrine system consists of nerve and gland cells. It produces hormones and releases them into the bloodstream.

NETs are tumours (abnormal growths) that develop in the cells of the neuroendocrine system.

NETs can be malignant (cancerous) or benign (non-cancerous) and often – but not always – grow slowly. There are a number of different types of NET, depending on the specific cells affected.

Types of neuroendocrine tumours

Gastroenteropancreatic neuroendocrine tumours (GEP NETs) are tumours that develop in the gut or pancreas.

Gastrointestinal neuroendocrine tumours (GI NETs) develop in the digestive system, which includes the bowel, stomach or oesophagus. Pancreatic neuroendocrine tumours (pNETs) develop in the pancreas.

Pulmonary neuroendocrine tumours develop in the lungs. Rarely, NETs can also develop in other parts of the body, including in the liver, gallbladder, bile ducts, kidneys, ovaries, or testicles.

Some NETs, known as functioning tumours, produce hormones that cause specific symptoms. Tumours that don't cause symptoms are known as non-functioning tumours.

Symptoms of neuroendocrine tumours

The symptoms of a neuroendocrine tumour can vary depending on where it is and what hormones it produces.

For example, a tumour in the digestive system may cause diarrhoea, constipation or tummy pains. A tumour in the lung may cause wheezing or a persistent cough.

Some tumours (functioning tumours) may cause abnormally large amounts of hormones to be released into the bloodstream.

This can cause symptoms such as diarrhoea, flushing, cramps, wheezing, low blood sugar (hypoglycaemia), changes in blood pressure and heart problems.

What causes neuroendocrine tumours?

What causes neuroendocrine tumours isn't fully understood. However, your chance of developing an NET is increased if you have one of the following rare conditions or syndromes:

• multiple endocrine neoplasia type 1 (MEN 1) – a rare inherited condition where tumours in the endocrine system develop, most commonly in the parathyroid glands, pituitary gland and the pancreas
• neurofibrmatosis type 1 – a group of genetic conditions that cause tumours to grow along your nerves
• Von Hippel-Lindau syndrome (VHL) – an inherited condition that causes blood vessels to grow abnormally

Research has also shown that your risk of developing an NET is slightly increased if one of your parents has had one in the past.

Diagnosing neuroendocrine tumours

There are many tests that can be used to diagnose NETs, including blood tests, urine tests, scans, and a biopsy (where a small tissue sample is taken for closer examination).

Different types of scans may also be used to identify or examine tumours. These include:

• ultrasound scans – including echocardiograms and endoscopic ultrasound scans
• computerised tomography (CT) scans
• magnetic resonance imaging (MRI) scans
• positron emission tomography (PET) scans
• octreotide scans – where mild radioactive liquid is injected into your veins and a special camera is used to highlight any cancerous cells

The Cancer Research UK website has more information about tests for rare cancers. 

Treating neuroendocrine tumours

How a neuroendocrine tumour is treated will depend on your individual circumstances. For example, your treatment will depend on:

• where the tumour is
• how advanced your condition is
• your overall health  

Unfortunately, many people are only diagnosed after other parts of their body are affected. However, it may still be possible to surgically remove the tumour, even if it has spread to other parts of your body.

If surgery can't be used to completely cure your condition, it may be used to help manage and reduce any symptoms that you have.

It may also be possible to shrink the tumour or stop further growth using treatments that block the blood supply to the tumour (embolisation), or chemotherapy, radiotherapy or radiofrequency ablation (where heat is used to destroy the cells).

The Cancer Research UK website has more information about neuroendocrine tumours (NETs).