Neuroendocrine tumours (NETs) are rare tumours that begin in specialised cells of the neuroendocrine system.
Based on studies in China, Taiwan and Singapore, NETs develop most commonly in the pancreas, rectum and stomach.
They may be cancerous or non-cancerous.
Types of neuroendocrine tumours
Some neuroendocrine tumours grow very slowly, while others are more aggressive and are able to spread to other parts of the body.
When neuroendocrine tumours produce excess hormones they are known as functional NETs. When they do not release hormones (or do not release enough to cause noticeable symptoms), they are known as non-functional NETs.
There are different types of NETs, depending on the site of origin or hormone produced. The most common ones are:
Gastrointestinal. These are the most common type of NETs and may develop in stomach, small intestine, large intestine or appendix.
Lung. Lung is the second most common site for the development of NETs. These are mostly non-functional and carcinoid.
Pancreatic. These are less common, mostly non-functional, and do not show symptoms.
In rare cases, neuroendocrine tumours may develop in other parts of the body. These types include:
Merkel cell carcinoma. It develops in the Merkel cells on the top layer of the skin, especially those parts that are exposed to sunlight.
Medullary thyroid cancer. It develops in the thyroid gland and is the rarest form of thyroid cancer.
Pheochromocytoma and paraganglioma. These develop in or on the adrenal glands.
Carcinoid syndrome is the collection of symptoms that some people with NETs may have. Symptoms include sweating, breathlessness, facial flushing and diarrhoea. It is more common when the tumour has spread to the liver and releases hormones such as serotonin into the bloodstream.
What are the symptoms of neuroendocrine tumours?
Symptoms may vary depending on the site of the tumour and the excess hormone produced. In the case of carcinoid tumours, symptoms may appear after years.
In general, symptoms of NETs include:
A growing lump in the body
Pain from a growing tumour
High blood pressure
Shortness of breath
Wheezing and coughing
Flushing of the skin
Unexplained weight loss
What causes neuroendocrine tumours?
There is no specific cause or risk factor associated with NETs. However, there are a number of inherited syndromes associated with NETs:
Multiple endocrine neoplasia type 1. This condition makes the adrenal, thyroid or parathyroid glands hyperactive.
Multiple endocrine neoplasia type 2. This condition makes the pituitary gland, pancreas, or parathyroid gland hyperactive.
Von Hippel-Lindau syndrome. It is a rare condition in which benign tumours develop in different parts of the body.
Neurofibromatosis type 1. It is a rare condition in which tumours grow on the nerves and skin.