What are small bowel neuroendocrine tumours?

Small bowel neuroendocrine tumours (NETs) are rare bowel tumours. They start in the neuroendocrine cells of the small bowel. They often develop slowly and don’t always have specific symptoms.

What are neuroendocrine cells?

Neuroendocrine cells are part of our neuroendocrine system. Neuroendocrine cells don’t form an actual organ. Instead, they are scattered throughout other organs like the oesophagus, stomach, pancreas, intestines, and lungs. They make hormones which control how our bodies work.

The digestive system is large and has more neuroendocrine cells than any other part of the body.

The small bowel

The small bowel makes up most of the digestive tract. It is about 6 metres long, but it is folded up so that it fits inside the abdomen.

It has 3 sections:

  • duodenum (dew-oh-dean-um) – the top part of the small bowel, which connects to the stomach
  • jejunum (jej-you-num) – the middle part
  • ileum (ill-ee-um) – the lower part, which connects to the large bowel (colon)

Right at the end of the ileum, just before it joins to the colon, is a small pouch called the appendix.

Diagram showing the position of the small bowel in the digestive system
Diagram showing the parts of the small bowel

Small bowel NETs include any that develop in the ileum and the jejunum. Doctors group some NETs that develop in the duodenum with NETs that start in the pancreas.

How common are small bowel NETs?

Small bowel NETs are rare cancers. Around 4 out of 10 small bowel tumours (around 40%) are neuroendocrine tumours. Most NETs start somewhere in the digestive system (gut). And around 40 out of every 100 of these digestive system neuroendocrine tumours (around 40%) start in the small bowel. 

The average age of people diagnosed with a NET of the jejunum or ileum is 66. Small bowel NETs are more common in men than women.

Risks and causes

A risk factor is anything that increases your risk of getting a disease. Different diseases have different risk factors. Small bowel neuroendocrine tumours are rare. At the moment, no clear risk factors have been found that increase your chance of developing a small bowel NET.

Having a family history of cancer is a risk factor for all types of NET including small bowel NETs.

What next?

You might be interested to read about the possible symptoms of small bowel NETs.

Last reviewed: 
10 Jun 2021
Next review due: 
09 Jun 2024
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    Aaron T. Scott and James R. Howe
    American Society of Clinical Oncology, 2018. Volume 14, Issue 8

  • Gastroenteropancreatic neuroendocrine neoplasms: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up
    M. Pavel and others
    Annals of Oncology 2020, Vol 31, Issue 5 

  • Guidelines for the management of gasterenteropancreatic neuroendocrine (including carcinoid) tumours (NETs) 
    JK Ramage and others
    Gut, 2012 
    Volume 61

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    The Annals of Surgery, 2009
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    Best Practice & Research Clinical Gastroenterology, 2012
    Volume 26

  • Neuroendocrine tumor epidemiology: contrasting Norway and North America
    O Hauso, Bl Gustafsson and M Kidd and others
    Cancer, 2008
    Volume 113

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