Types of NETs

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.

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 – 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 carcinoma of unknown primary origin (CUP).