What are carcinoid tumours?

Men and women discussing carcinoid cancer

This page explains what carcinoid tumours are.

A quick guide to what's on this page
How and where carcinoid tumours develop
Carcinoid tumours and the neuroendocrine system
What carcinoid syndrome is

What are carcinoid tumours?

Carcinoids are rare, mostly slow growing, tumours that may not cause any symptoms for several years. Most of these tumours occur in people over the age of 60. Carcinoid tumours are also sometimes just called carcinoid. They are one type of tumour of the neuroendocrine system.

Most carcinoid tumours are found in the digestive system, but they can also develop in the lung, pancreas, kidney, ovaries or testicles. Some carcinoid tumours can spread to the liver.

Carcinoid tumours and the neuroendocrine system

The neuroendocrine system is made up of nerve and gland cells. It makes hormones and then releases them into the bloodstream. There are neuroendocrine cells in the gut, including the food pipe (also called the gullet or oesophagus), in the lungs and in the pancreas. Carcinoid tumours develop when these neuroendocrine cells become cancerous.

What is carcinoid syndrome?

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Carcinoids are rare, mostly slow growing, tumours that may not cause any symptoms for several years. Most of these tumours occur in people over the age of 60.

Carcinoid tumours are also sometimes just called carcinoid. They are one type of tumour of the neuroendocrine system. There is more about the neuroendocrine system further down this page and there is a separate question and answer about what neuroendocrine tumours are which includes information about the different types.

More than 8 out of 10 carcinoid tumours start in the digestive system - around 85%. Doctors call the digestive system the gastrointestinal (GI) tract. It includes the food pipe (oesophagus), stomach, small bowel, appendix, large bowel (colon), and rectum.

Around 1 in 10 carcinoid tumours develop in the lung (10%). Around 3 out of 100 carcinoids develop in the pancreas (3%). And about 2 out of 100 develop in the kidney, ovary or testicle (2%).

The diagram below shows the areas where carcinoid can develop.

Diagram showing the areas that might be affected by carcinoid

There are two types of lung carcinoid. Doctors can only tell the difference by looking at the cells under the microscope

Typical lung carcinoids grow slowly and rarely spread to other parts of the body
Atypical lung carcinoids are much rarer, tend to grow faster and are slightly more likely to spread to other parts of the body than typical lung carcinoids

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

There are neuroendocrine cells in

The gut, including the food pipe (also called the gullet or oesophagus)
The lungs
The pancreas

Neuroendocrine cells have different functions depending on where they are in the body. For example, the ones in the gut make hormones to control

The release of digestive juices into the gut
The muscles that move food through the bowel

And neuroendocrine cells in the lung release hormones that control the flow of air and blood in the lungs.

Carcinoid tumours develop when a change happens and these neuroendocrine cells become cancerous.

Some carcinoid tumours release hormones that cause particular symptoms. Doctors call this collection of symptoms carcinoid syndrome. About 1 in 10 people with a carcinoid tumour (10%) have carcinoid syndrome. But it is more likely to happen if the carcinoid tumour has spread from its original place to other parts of the body, especially the liver.

The symptoms of carcinoid syndrome include