Find out what carcinoid tumours are, where they start and how common they are.
What they are
Carcinoids are a type of tumour of the neuroendocrine system. They are now classified as neuroendocrine tumours (NETs). But your doctor might still use the term carcinoid.
Carcinoid tumours tend to grow slowly. They might not cause any symptoms for several years.
The neuroendocrine system
The neuroendocrine system is made up of nerve cells and gland cells. It makes hormones and releases them into the bloodstream.
There are neuroendocrine cells in the:
- gut, including the food pipe (oesophagus)
Neuroendocrine cells have different functions, depending on where they are in the body. For example, neuroendocrine cells in the lung release hormones that control the flow of air and blood in the lungs. Neuroendocrine cells in the gut make hormones to control the:
- release of digestive juices into the gut
- muscles that move food through the bowel
Carcinoid tumours develop when changes happen in the neuroendocrine cells and they start to grow out of control.
Where they start
Around 70 out of 100 carcinoid tumours (70%) start in the digestive system. This is also called the gastrointestinal (GI) tract. It includes the food pipe (oesophagus), stomach, small bowel, appendix, large bowel (colon) and rectum. They are most often diagnosed in the small bowel.
Around 25 in 100 carcinoid tumours (25%) develop in the lung. There are 2 types of lung carcinoid:
- typical lung carcinoids, which grow slowly and rarely spread to other parts of the body
- atypical lung carcinoids, which tend to grow faster and are slightly more likely to spread to other parts of the body than typical lung carcinoids
Atypical lung carcinoids are much rarer than typical lung carcinoids.
Carcinoid tumours can also develop in the pancreas, kidney, ovary or testicle. In some cases doctors do not know where the original tumour developed.
Some carcinoid tumours can spread. The most common site of spread is to the liver, but they might also spread to the lymph nodes or bones. The lymph nodes are part of the lymphatic system that runs throughout the body.
The diagram below shows some of the areas where carcinoid tumours can develop.
What carcinoid syndrome is
Some carcinoid tumours release hormones that cause symptoms. Doctors call this collection of symptoms carcinoid syndrome. It is more likely to happen if the carcinoid tumour has spread to other parts of the body, especially the liver.
The symptoms of carcinoid syndrome include:
- flushing of the skin
- a fast heart beat
- dizziness due to sudden low blood pressure
Drinking alcohol can bring on the symptoms in some people with carcinoid.
How common carcinoid tumours are
Carcinoid tumours are rare. Around 2,900 people are diagnosed with them each year in the UK.
They are getting more common across the world. This might be partly because there are better tests to diagnose them.
Who gets them
Carcinoid tumours can develop at any age, but the average age of diagnosis is around 60.
Little is known about what causes carcinoid. Most cases happen by chance.
People with rare family syndromes such as multiple endocrine neoplasia type 1 (MEN 1) have an increased risk of developing carcinoid. People with a family history of carcinoid or other types of cancer might also have an increased risk of carcinoid.