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Symptoms and diagnosis - Bowel cancer

Bowel cancer is a general term for cancer that begins in the large bowel. Depending on where the cancer starts, bowel cancer is sometimes called colon or rectal cancer.

Bowel cancer is one of the most common types of cancer diagnosed in Ireland. Most people diagnosed with it are over the age of 60.


The symptoms of bowel cancer can be subtle and don't necessarily make you feel ill. But it's worth trying simple treatments for a short time to see if they get better.

More than 90% of people with bowel cancer have one of the following combinations of symptoms:

  • a persistent change in bowel habit. Going more often, with looser stools and sometimes stomach (abdominal) pain
  • blood in your poo especially if mixed through the stool. This makes it unlikely the cause is haemorrhoids (piles)
  • stomach pain, discomfort or bloating always brought on by eating. This can sometimes result in a reduction in the amount of food eaten and weight loss

Bowel cancer symptoms are also very common, and most people with them don't have cancer. For example:

  • a change in bowel habit or abdominal pain is usually the result of something you've eaten
  • a change in bowel habit to going less often, with harder poo, is not usually caused by any serious condition. It may be worth trying laxatives before seeing your GP
  • constipation, where you pass harder stools less often
  • fresh blood often separate from your poo or coating the stool. This, when associated with pain or soreness is more often caused by piles or a simple tear (fissure)

These symptoms should be taken more seriously as you get older and when they persist despite simple treatments.

When to seek medical advice

Although bowel cancer symptoms are very common, you should talk to your GP if they persist for more than 4 weeks. Most people with these symptoms don't have bowel cancer.

Talk to your GP if your symptoms persist or keep coming back after stopping treatment. Do this regardless of their severity or your age.

Bowel obstruction

In some cases, bowel cancer can stop digestive waste passing through the bowel. This is known as a bowel obstruction.

Symptoms of a bowel obstruction can include:

  • intermittent, and occasionally severe, abdominal pain – this is always provoked by eating
  • unintentional weight loss – with persistent abdominal pain
  • constant swelling of the tummy – with abdominal pain
  • vomiting – with constant abdominal swelling

A bowel obstruction is a medical emergency. If you suspect you have a bowel is obstruction, you should talk to your GP quickly. If this isn't possible, go to the emergency department (ED) of your nearest hospital.


When you first see your GP, they'll ask about your symptoms and if you have a family history of bowel cancer.

They'll usually carry out a simple examination of your bottom. This is known as a digital rectal examination (DRE). Your GP will also examine your tummy (abdomen).

This is a useful way of checking whether there are any lumps in your tummy or back passage.

The tests can be uncomfortable. Most people find an examination of the back passage a little embarrassing. But they take less than a minute.

Your GP will also check your blood to see if you have iron deficiency anaemia.

Most people with bowel cancer don't have symptoms of anaemia. But they may have a lack of iron as a result of bleeding from the cancer.

In most people with bowel cancer, iron deficiency anaemia is found incidentally.

Hospital tests

If your symptoms suggest you may have bowel cancer or the diagnosis is uncertain, you'll be referred to your local hospital for a simple examination. This is called a flexible sigmoidoscopy.

A small number of cancers can only be diagnosed by a more extensive examination of the colon. The two tests used for this are colonoscopy or computerised tomography (CT) colonography.

Emergency referrals, such as for people with bowel obstruction, will be diagnosed by a CT scan. Those with severe iron deficiency anaemia and few or no bowel symptoms are usually diagnosed by a colonoscopy.

Flexible sigmoidoscopy

A flexible sigmoidoscopy is an examination of your back passage (rectum) and some of your large bowel.

A sigmoidoscope is used to carry out the examination. This is a long, thin, flexible tube attached to a very small camera and light. It's inserted into your rectum and up into your bowel. The camera relays images to a monitor.

A biopsy, (small tissue sample) can be removed for further analysis.

It's better for your lower bowel to be as empty as possible when sigmoidoscopy is performed. You may be asked to carry out an enema – a simple procedure to flush your bowels – at home beforehand.

This should be done at least 2 hours before you leave home for your hospital appointment.

A sigmoidoscopy can feel uncomfortable. It only takes a few minutes and most people go home straight after the examination.


A colonoscopy is an examination of your entire large bowel using a device called a colonoscope. This is like a sigmoidoscope but a bit longer.

Your bowel needs to be empty when a colonoscopy is performed. The hospital will get you to eat a special diet for a few days beforehand. You'll take a medication (laxative) to help empty your bowel on the morning of the examination.

You'll be given a sedative to help you relax during the test. The doctor will then insert the colonoscope into your rectum and move it along the length of your large bowel. This isn't usually painful, but can feel uncomfortable.

The camera relays images to a monitor. This allows the doctor to check for any abnormal areas within the rectum or bowel that could be the result of cancer. As with a sigmoidoscopy, a biopsy may also be performed during the test.

A colonoscopy usually takes about 20 to 40 minutes to complete. Most people can go home once they've recovered from the effects of the sedative.

You will probably feel drowsy for a while after the procedure. You'll need to arrange for someone to go home with.

You'll be advised not to drive for 24 hours.

It's best for elderly people to have someone with them for 24 hours after the test.

In a small number of people, it may not be possible to pass the colonoscope completely around the bowel. It is then necessary to have a CT colonography.

CT colonography

CT colonography is also known as a "virtual colonoscopy". It involves using a computerised tomography (CT) scanner to produce 3D images of the large bowel and rectum.

During the procedure, gas is used to inflate the bowel using a thin, flexible tube placed in your rectum. CT scans are then taken from a number of different angles.

You may need to have a special diet for a few days and take a laxative before the test. This is to make sure your bowels are empty when it's carried out. You may also have to take a liquid called Gastrografin before the test.

This test can help identify cancerous areas in people who are not suitable for a colonoscopy because of other medical reasons.

A CT colonography is a less invasive test than a colonoscopy. You may still need to have colonoscopy or flexible sigmoidoscopy at a later stage. This is so any abnormal areas can be removed or biopsied.

Further tests

If a diagnosis of bowel cancer is confirmed, further testing is usually carried out. This is to check if the cancer has spread from the bowel to other parts of the body. These tests also help your doctors decide on the most effective treatment for you.

These tests can include:

  • a CT scan of your abdomen and chest. This is to check if the rest of your bowel is healthy and whether the cancer has spread to the liver or lungs
  • a magnetic resonance imaging (MRI) scan. This can provide a detailed image of the surrounding organs in people with cancer in the rectum

Stages of bowel cancer

After all tests have been completed, it's usually possible to determine the stage of your cancer.

There are two ways that bowel cancer can be staged. The first is known as the TNM staging system:

  • T – indicates the size of the tumour
  • N – indicates whether the cancer has spread to nearby lymph nodes
  • M – indicates whether the cancer has spread to other parts of the body (metastasis)

Bowel cancer is also staged numerically. The 4 main stages are:

  • stage 1 – the cancer is still contained within the lining of the bowel or rectum
  • stage 2 – the cancer has spread beyond the layer of muscle surrounding the bowel. It may have penetrated the surface covering the bowel or nearby organs
  • stage 3 – the cancer has spread into nearby lymph nodes
  • stage 4 – the cancer has spread beyond the bowel into another part of the body, such as the liver

Content supplied by the NHS and adapted for Ireland by the HSE

Page last reviewed: 30 May 2019
Next review due: 30 May 2022

This project has received funding from the Government of Ireland’s Sláintecare Integration Fund 2019 under Grant Agreement Number 123.