The three main areas where NETs are found in the body are the gastrointestinal tract (digestive system), the pancreas and the lungs.
*When NETs are found in both the gastrointestinal system and the pancreas these are called gastroenteropancreatic NETs (GEP-NETs)
Diagram showing where neuroendocrine tumours (NETs, which you may also hear referred to as carcinoid tumours, GI-NETs, GEP-NETS, pancreatic NETs and lung NETs) may develop in the body.
Gastrointestinal NETs (GI-NETs) are the most common type of NETs (previously called carcinoid tumours). They are found in the gastrointestinal (GI) tract, including tumours that develop in the small intestine, the appendix, the stomach, the oesophagus, the colon and the rectum.
NETs that occur in the GI tract or pancreas are sometimes grouped together and called gastroenteropancreatic neuroendocrine tumours or GEP NETs for short. The combined number of GEP-NETs cases is now ranked as the second most prevalent gastrointestinal problem, after colon cancer.
Pancreatic NETs (pNETs) may be classified as functioning or non-functioning:
Functioning pancreatic tumours make extra amounts of hormones, such as gastrin, insulin and glucagon, or other substances known as peptides, such as vasoactive intestinal peptide (VIP), that cause an associated syndrome – or collection of identifiable symptoms in the body. Most functioning tumours are initially benign.
Non-functioning pancreatic tumours account for around 30-40% of pancreatic tumours. Most non-functioning pancreatic tumours are malignant at diagnosis. They may release certain hormones but these do not cause an associated syndrome. Later on, these tumours may cause abdominal symptoms such as pain due to tumour growth.
There are several subtypes of pancreatic NETs. Each is named according to the type of hormone or substance they produce, as shown in the table below.
|Pancreatic NET types||Main hormone or substance involved||Associated syndrome||Major symptoms|
|Gastrinomas||Gastrin||Zollinger-Ellison syndrome (ZES)||Ulcers|
|Insulinomas||Insulin||Hypoglycaemia syndrome||Very low blood sugar|
|VIPomas||Vasoactive intestinal peptide (VIP)||Verner-Morrison syndrome||Watery diarrhoea (pancreatic cholera), which can cause potassium deficiency in the blood or reduced acid secretion in the stomach|
|Glucose intolerance (diabetes)|
|Somatostatinoma||Somatostatin||n/a||High blood sugar (glucose)|
|Diarrhoea (bulky, greasy)|
|Reduced acid secretion in the stomach|
Lung NETs account for around one quarter of all NETs. Within this group there are two major types:
The most frequent symptoms of lung NETs are very common in other conditions, which can make lung NETs very difficult to diagnose.
These symptoms include:
Other rare NETs include those that start in the:
In about 10% of cases it is impossible to determine where the NET has originally started; in this case it is called carcinoma of unknown primary origin (CUP).
Find out how NETs are diagnosed and the tests that healthcare professionals may use to monitor NETsDiagnosis & Testing
Read about treatment options for NETs, including surgery, radiotherapy and medicationsTreatment Options
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