Most people with large bowel or rectal neuroendocrine tumours (NETs) don’t have symptoms. Doctors often diagnose them when doing tests for something else.

When you do have symptoms, they are usually caused by the growth of the cancer. Or by the NET spreading to other parts of the body. You can also have symptoms caused by the hormones made by the tumour but this is rare. 

Most large bowel or rectal NETs do not make hormones. Or make hormones that do not cause specific symptoms (a syndrome). These tumours are called non functioning tumours.

The symptoms below could be due to a large bowel or rectal NET but can also be caused by other more common medical conditions. It’s important to get them checked by your doctor.


Symptoms usually develop slowly over some years. Symptoms might include:

A change in your normal bowel habit

You might have a change in your bowel habit that is not caused by changes to your diet or lifestyle.

Bowel problems are very common and they are usually not related to cancer. But it’s important to tell your doctor if you have a lasting change in your normal bowel habits.


Diarrhoea means having more than 3 watery poos (stools) in a 24 hour period. You might also have diarrhoea at night and problems controlling your bowels (incontinence).

Pain in the tummy and back passage

You might have pain that comes and goes. Some people have pain for several years before a diagnosis of a neuroendocrine tumour.


You might have bleeding from your bowel or rectum (back passage). You may not be able to see any blood if it is a small amount. Or you may see some blood in your poo. Over time, bleeding reduces the number of red blood cells in your body (anaemia).

Most often, blood in the stool is from piles (haemorrhoids), especially if it is bright red, fresh blood.

Weight loss

You might lose weight even if you haven't changed your diet.

Blockage in the bowel

Sometimes the cancer can block the bowel (bowel obstruction). Symptoms of bowel obstruction include:

  • griping pain in the tummy
  • feeling bloated
  • constipation and being unable to pass wind
  • feeling sick
A bowel obstruction is an emergency. You should see your doctor quickly or go to A&E if you think you have a bowel obstruction.

Symptoms caused by hormones

It’s rare for large bowel and rectal NETs to make hormones that go into the bloodstream. Doctors call these functioning tumours. These hormones can cause symptoms that don’t seem related to the cancer. This is called carcinoid syndrome.

Symptoms of carcinoid syndrome include:

  • flushing of the skin
  • diarrhoea
  • wheezing
  • fast heartbeat

When to see your doctor

You should see your doctor if you have:

  • symptoms that are unusual for you
  • symptoms that don't go away

Your symptoms are unlikely to be cancer but it is important to get them checked by your GP. Depending on your symptoms, you may need to see a specialist doctor.

What happens next?

We have information on seeing your GP and the tests you might have.

  • 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 

  • Gastrointestinal neuroendocrine tumors in 2020
    Monjur Ahmed
    World Journal of Gastrointestinal Oncology, 2020, Aug 15; 12(8): 791–807

  • ENETS consensus guidelines for the management of patients with digestive neuroendocrine neoplasms: colorectal neuroendocrine neoplasms
    M Caplin and others
    Neuroendocrinology, 2012. Vol 95, Pages 88-97

  • Carcinoid and neuroendocrine tumors of the colon and rectum
    T Chung and S Hunt 
    Clinics in colon and rectal surgery, 2006. Vol 19, number 2, pages 45-48

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

Related links