Types of NETs

The three main areas where NETs originate from in the body are the gastrointestinal tract (digestive system), the pancreas and the lungs.

• Gastrointestinal NETs (GI-NETs)
  GI-NETs are the most common type of NETs and can be found anywhere in the gastrointestinal (GI) tract (digestive system). This includes in the small intestine, stomach, large intestine, rectum, duodenum and appendix.
• Pancreatic NETs (pNETs)
  Pancreatic NETs are formed from the islet cells of the pancreas and include several uncommon types of NETs.

• Gastroenteropancreatic NETs (GEP-NETs)
  When NETs are found in both the digestive system and the pancreas these are referred to as GEP-NETs.
• Lung NETs
  Lung NETs account for about one quarter of NETs.
• Other sites
  Other uncommon sites of NETs include the female reproductive system, other endocrine glands, and the ear, nose and throat.

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 cancer, after colon cancer.

Pancreatic NETs (pNETs) may be classified as functioning tumours or non-functioning tumours:

Functioning pancreatic NETs 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.

Non-functioning pancreatic NETs account for the majority of pancreatic NETs. 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.

Lung NETs

Lung NETs account for around one quarter of all NETs. Within this group there are two major types:

• Typical carcinoids
• Atypical carcinoids – these are faster progressing tumours

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:

• Coughing
• Chest pain
• Shortness of breath
• Coughing up blood
• Fever
• Wheezing

Other types of NETs

Other rare NETs include those that start in the:

• Thyroid gland – medullary thyroid tumours
• Skin – Merkel cell cancer
• Adrenal glands – (e.g. pheochromocytoma)
• Thymus
• Other organs like breast, prostate and kidney

In about 10% of cases it is impossible to determine where the NET has originally started; in this case it is called cancer of unknown primary origin.