Neuroendocrine tumour; neuroendocrine tumor; NET; neuroendocrine carcinoma; carcinoid tumor
Carcinoid tumours are part of a group of tumours called neuroendocrine tumours. These tumours are made from specialised cells that produce and release hormones. These hormones are released into the bloodstream and can have effects on other organs.
Neuroendocrine tumours can appear in a number of places, including all parts of the digestive system (oesophagus, stomach, small bowel, appendix, large bowel, rectum, pancreas and liver), the respiratory system (bronchi and lungs) and, less commonly, the reproductive system (ovaries and testes).
Carcinoid syndrome is the name given to the wide range of signs and symptoms seen in people with a particular type of neuroendocrine tumour. These include flushing of the skin, diarrhoea and wheezing.
Carcinoid tumours begin when a specialised neuroendocrine cell begins to divide and reproduce uncontrollably. This results in the growth of a mass of similar cells – the ‘carcinoid tumour’. The triggers that cause the start of this process are not known. Carcinoid tumours tend to grow and spread much more slowly than other cancers of the digestive system.
In some cases, a genetic link may be the cause. Multiple endocrine neoplasia type 1 is a genetic disorder that increases the risk of neuroendocrine tumours, including carcinoids, while digestive system conditions (such as pernicious anaemia and atrophic gastritis) can increase the risk of carcinoid tumours of the digestive tract.
Carcinoid tumours may be discovered by chance, for example, from a routine chest X-ray or during surgery being performed on the gut for another reason, and they can produce very few symptoms. However, they do sometimes cause signs and symptoms and these can be divided into several groups:
Carcinoid tumours are relatively rare. Each year a total of around 2,000 people in the UK are diagnosed with neuroendocrine tumours of which a proportion are carcinoid tumours. As survival rates with these tumours are generally good, the number of people living with these conditions is relatively higher. There are thought to be around 15,000 people in the UK living with neuroendocrine tumours of all types, including carcinoid.
It is believed that there is a genetic link for some forms of this type of cancer. However, usually there is not a clear pattern of inheritance within families.
The diagnosis of a carcinoid tumour depends on the way in which it is discovered. Most of these tumours are detected by chance on an abdominal scan or chest X-ray carried out for other reasons. On computerised tomography (CT) scans, the tumours often have a particular appearance and looking at a sample of tumour tissue under the microscope (histology) will usually provide a definitive diagnosis.
In a patient with symptoms such as diarrhoea and flushing suggestive of carcinoid syndrome, a 24 hour urine sample is collected to measure the levels of 5-hydroxyindolacetic acid, which is produced when a particular chemical (tryptophan) breaks down. This test can be performed as an outpatient although it is necessary to stick to a special diet during the collection period, avoiding foods such as bananas, chocolate, walnuts and avocado. This is because these foods can also cause higher levels of 5-hydroxyindolacetic acid in the urine.
Measuring chromogranin A levels in blood is a very useful marker to assess for presence of carcinoid tumour as well as providing vital information about disease load. Chromogranin A levels are measured after surgery to assess if there is any residual carcinoid tumour left and are also helpful for monitoring disease progression while the patient is on medication.
A CT scan may subsequently be arranged to demonstrate the disease extent and spread. In some cases an isotope bone scan may be used. Specialist nuclear medicine scans such as octreotide or MIBG scans may be used after the tumour is diagnosed. These are helpful to assess the tumour spread and extent along with planning future therapy. The doctor may also arrange some tests to evaluate if any damage has been caused to the heart valve by arranging an echocardiogram.
It is recommended that multidisciplinary teams at referral centres give guidance on the management of the patient. The main aim should be to keep the patient disease and symptom-free for as long as possible and to maintain a good quality of life.
The definitive treatment to cure a carcinoid tumour is by surgical removal of the tumour. However, as most of these tumours are detected incidentally or show features of spread to other organs, surgical cure of the tumour may not be possible in many patients.
Injections of octreotide (or of by-products that last longer), which is an equivalent of a naturally produced hormone called somatostatin, may help fight the symptoms of excess hormone production and even possibly slow down the growth and spread of the tumour.
In selected cases, chemotherapy or other radiotherapy treatments or blocking the main artery to the liver (embolisation) may be used to reduce the total number of tumour cells in the blood circulation. This then controls the excess hormone production and improves symptoms.
Surgery is associated with a risk of bleeding and infection. Medical treatment with octreotide is associated with symptoms of indigestion, worsening of blood sugar control in patients with diabetes and development of gallstones with long-term use. If the patient has any concerns following treatment, they should discuss these with their doctor.
As with all cancers, the main implication of carcinoid tumours is their continued growth and spread, together with the signs and symptoms of too much hormone production. Tumour growth usually occurs fairly slowly compared with other cancers. It is possible to live for a long time and with a good quality of life with a carcinoid tumour.
Carcinoid tumours may remain undiagnosed until they eventually spread to other organs, for example, from the small bowel to the liver.
Sometimes patients with carcinoid syndrome may have a particularly bad attack that can be triggered by drugs or when given some type of anaesthetic. This is called a carcinoid crisis and needs specialist management. Management of heart valve damage caused by the excess hormones may also need attention and treatment in selected centres.
Last reviewed: Mar 2019