Getting diagnosed

Large bowel and rectal neuroendocrine tumours (NETs) often don’t cause symptoms. Most people are diagnosed with a large bowel or rectal NET when they are having tests for something else. 

The tests you might have include blood tests and a test to look at the inside of your bowel (colonoscopy).

Large bowel and rectal NETs are rare cancers. So your doctor might ask you to have tests that check for other conditions first.

Seeing your GP

You usually start by seeing your GP. They will ask you about your general health, symptoms and may also examine you. 

Your GP might check your blood pressure, heart rate and temperature. They may arrange for you to have blood tests. Your doctor will then decide if you need to see a specialist.

Seeing a specialist

Your GP looks at your symptoms and decides which specialist to refer you to. For example, they might refer you to the gastrointestinal (GI) team if you have a change in your normal bowel habit.

If tests show that you have a large bowel or rectal NET, your specialist will refer you to a team of doctors and nurses who are experts in treating NETs.


You have tests to find out which type of NET you have, the size of the tumour and whether it has spread. This helps your team plan your treatment.

Tests you might have include:

Blood tests

Blood tests can check your general health. They can also check the levels of certain substances in the blood which are sometimes raised with NETs.


A colonoscopy looks at the whole of the inside of the large bowel. A doctor or nurse (colonoscopist) uses a flexible tube called a colonoscope. The tube has a small light and camera at one end. The colonoscopist puts the tube into your back passage and passes it along the bowel. They can see pictures of the inside of your bowel on a TV monitor.

They can take samples from your large bowel and rectum if they spot any abnormal areas. A specialist doctor looks at these samples under a microscope.

CT scan

This scan can show up a NET and see whether it has spread anywhere else in your body.

MRI scan

An MRI scan can show up a NET and see whether it has spread. 

Ultrasound scan of your tummy (abdomen) and back passage (rectum)

Ultrasound scans use high frequency sound waves to make a picture of organs inside your body.

To have an ultrasound of your tummy, your doctor or nurse moves a handheld probe over your skin. For an ultrasound scan of your back passage, your doctor gently pushes an ultrasound probe inside your back passage (rectum).

Radioactive scans

These are octreotide scans (or octreoscans) and MIBG scans. You have an injection of a low dose radioactive substance, which is taken up by some NET cells. The cells then show up on the scan.

PET scan

A PET scan can show the size of the tumour and whether it has spread. There are different types of PET scans that you can have. Gallium dotatate PET scan is a specific scan for neuroendocrine tumours. 

Chromogranin A (CgA) test

You usually have a blood test to measure the amount of a protein called chromogranin A. This is sometimes higher than normal when you have a NET. 

Chromogranin A is not always raised in bowel and rectal NETs. 

You may have other tests, depending on your symptoms. Your doctor can tell you which tests you need.
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  • Carcinoid and Neuroendocrine Tumors of the Colon and Rectum
    T Philip Chung and Steven R Hunt 
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    Suayib Yalcin and Kjell Oberg
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Last reviewed: 
16 Jun 2021
Next review due: 
16 Jun 2024

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