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What are neuroendocrine tumours (NETs)?

The neuroendocrine system is a network of glands and nerve cells that make hormones and release them into the bloodstream. These hormones help control normal body functions, for example digesting food.

Neuroendocrine cells are found throughout the body, but mainly in the gastro-intestinal tract (including large bowel and small bowel), pancreas and lungs. NETs are an uncommon type of tumour that forms in these cells. The type is generally defined by where the abnormal cells come from and can range from low grade (slow growing) to high grade (fast growing). NETs that produce extra amounts of hormones can cause certain symptoms and are referred to as functional tumours. However, not all NETs produce extra hormones (non-functional).

Malignant (cancerous) tumours have the potential to spread to other parts of the body through the blood stream or lymph vessels and form another tumour at a new site. This new tumour is known as secondary cancer or metastasis.

Types of NETs


These start in the large bowel and small bowel. Types of gastro-intestinal NETs include:

  • gastric NETs, in the stomach
  • duodenal NETs, in the duodenum (the first section of the small bowel)
  • small bowel NETs, including the jejunum and ileum
  • large bowel NETs, in the colon
  • appendiceal NETs, in the appendix
  • rectal NETs, near the anus.

If functional, these NETs may release high levels of hormones such as serotonin, which can be associated with symptoms of diarrhoea, flushing and tiredness.


Pancreatic NETs begin in the endocrine cells of the pancreas and make up approximately 7% of the more common pancreatic (adenocarcinoma) cancer  diagnoses. About 90% of pancreatic NETs do not produce extra hormones.

Functional pancreatic NETs are very rare and most are named after the hormone they overproduce:

  • insulinomas, produce too much insulin (causing low blood sugar levels)
  • glucagonomas, produce too much glucagon (causing high blood sugar levels)
  • gastrinomas, produce too much gastrin (causing stomach ulcers)
  • somatostatinomas, produce too much somatostatin (causing abdominal discomfort and weight loss)
  • VIPomas, produce too much vasoactive intestinal peptide (causing severe watery diarrhoea).


The four types of NETs that develop in the lung include:

  • typical carcinoid
  • atypical carcinoid
  • large cell neuroendocrine carcinoma
  • small cell lung neuroendocrine cancer.

Merkel cell carcinoma

Also known as neuroendocrine carcinoma of the skin, this is a rare cancer involving the Merkel cells in the top layer of the skin. Merkel cell carcinoma grows quickly and often returns and spreads. More information is available from the Australasian Merkel Cell Carcinoma Interest Group (AMIGOs) and the Australian Cancer Research Foundation.


This tumour typically starts in the adrenal glands (above the kidneys), but can also be found near the spinal cord. It affects immature or developing nerve cells in children. More information is available from Neuroblastoma Australia.

Other NETs

More information on all the different types of NETs (including others such as thymic, testicular, prostate, ovarian and endometrial, multiple endocrine neoplasia, pheochromocytoma, paraganglioma and medullary thyroid carcinoma) is available from NeuroEndocrine Cancer Australia.

Click on image to enlarge

How common are NETs?

NETs are not common but the number of people being diagnosed is slowly increasing. There is an almost equal risk for males and females.

  • Around 3700 Australians are diagnosed with a NET each year; with most new cases being diagnosed in people aged 40 years or over.
  • Australia has the highest number of Merkel cell carcinoma cases in the world, with older men most at risk.
  • Neuroblastoma is more likely in children under the age of 5 years.

Featured resources

Understanding Neuroendocrine Tumours

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Understanding Rare and Less Common Cancers

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This information is reviewed by

This information was last reviewed February 2021 by the following expert content reviewers: Dr David Chan, Medical Oncologist, Royal North Shore Hospital, NSW; Leslye Dunn, Consumer; Prof Gerald Fogarty, Radiation Oncologist, St Vincent’s Hospital, NSW; Katie Golden, Consumer; Dr Grace Kong, Nuclear Medicine Physician, Peter MacCallum Cancer Centre, VIC; Caitriona Nienaber, 13 11 20 Consultant, Cancer Council WA; Elizabeth Paton, Melanoma and Skin Cancer Trials Group, NSW.