What are large bowel and rectal NETs?

Large bowel and rectal NETs are rare cancers. They start in the neuroendocrine cells of the large bowel (colon) or back passage (rectum). They usually develop slowly over some years and don’t always have specific symptoms.

What are neuroendocrine cells?
Neuroendocrine cells are part of the neuroendocrine system. There are neuroendocrine cells in most organs of your body. They make hormones which control how our bodies work.

The large bowel and rectum are part of our digestive system. The digestive system is large and has more neuroendocrine cells than any other part of the body. So, most NETs start in the digestive system.

The large bowel (colon)

The colon is about 5 feet long and has 4 sections. NETs can start in any of these sections. The parts of the colon are:

  • ascending colon – runs up the right side of the tummy (abdomen) and is connected to the small bowel by the caecum
  • transverse colon – runs across the body, under the stomach
  • descending colon – runs down the left side of the abdomen
  • sigmoid colon – an ‘S’ shaped bend that joins the descending colon to the rectum
Diagram showing the parts of the large bowel

Between 30 and 40 out of every 100 large bowel NETs (between 30 and 40%) spread to other parts of the body. The most common places where they can spread to is the liver, lymph nodes and the sheet of tissue that lines the wall of the tummy (the peritoneum).

The rectum

The rectum (back passage) starts in the last part of the large bowel. This part of the bowel stores poo (stool) until it is ready to be passed out of the body.

Only about 2 out of every 100 rectal NETs (2%) spread to other parts of the body. Rectal NETs most commonly spread to the liver, lymph nodes and bones.

How common are bowel NETs?

NETs are rare cancers. Just over 4,000 people are diagnosed with a NET in England every year.

About 20 out of every 100 NETs (20%) diagnosed every year start in the large bowel or rectum.

Risks and causes

A risk factor is anything that increases your risk of getting a disease. Different diseases have different risk factors.

Some factors increase your risk of developing a large bowel or rectal NET. But having any of these risk factors doesn’t mean that you will definitely develop cancer.

Large bowel and rectal NETs are more common in older and middle age people. The average age of diagnosis is:

  • between 55 and 65 years old for large bowel NETs
  • around 56 years old for rectal NETs

Large bowel and rectal NETs are more common in black and Asian people than in those from other ethnic groups.

Researchers have found that your risk of developing a large bowel or rectal NET might be higher if you have a close relative (such as a parent, or brother or sister) who has had a neuroendocrine tumour. 

What next?

Most people read our information about symptoms of large bowel and rectal NETs.

Last reviewed: 
15 Jun 2021
Next review due: 
15 Jun 2024
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