Bowel Cancer

Bowel cancer, also known as colorectal cancer, can affect any part of the large bowel (colon) or rectum.

What is bowel cancer?

Bowel cancer, also known as colorectal cancer, can affect any part of the large bowel (colon) or rectum. Most bowel cancers develop from the inner lining of the bowel, and usually start with growths called polyps.

These polyps are benign growths and are usually harmless, however they can turn into a cancerous tumour if left undetected. Bowel cancer may also be called colon cancer or rectal cancer, depending on where the cancer is located and begins.

Is bowel cancer hereditary?

Approximately 30% of bowel cancer cases are due to genetics and family history.1

There are three common inherited disorders which have been linked to bowel cancer, these include;

MYH – Associated Polyposis (MAP)
caused by a genetic mutation in the gene MYH gene which results numerous (10-100) polyps (abnormal tissue growth) which can become cancerous.1

Hereditary Non-Polyposis Colorectal Cancer (HNPCC) (known as Lynch Syndrome)
results in mutations to the genes that protect cells from growing abnormally and turning into cancerous cells.1

Familial adenomatous polyposis (FAP)
is characterised by significant numbers (100 – 1000) of adenomatous polyps (gland-like tissue growths) in the lining of the large intestine.1

Signs and symptoms of bowel cancer

Not everyone experiences symptoms of bowel cancer, however below are some common symptoms of bowel cancer which include: 3

Sudden changes

in bowel motions, such as diarrhoea, constipation, having narrower stools, or stools that contain mucus

Unexplained weight-loss, or loss of appetite

Bright red or dark blood

in your stool or on the toilet tissue

Pain in your stomach

with or without swelling

A lump or pain around the anus

Constant gas or bloating

in the bowel or rectum

Unexplained anaemia (low iron)

which can cause tiredness and breathlessness

If you experience any of the above symptoms, it doesn’t necessarily mean it is bowel cancer, but it is important to see your GP or healthcare professional to discuss your symptoms.5

Stages of bowel cancer

The TNM system is used to stage bowel cancer, and it helps doctors understand what your cancer looks like. The TNM stands for:

  • Tumour – the degree to which the tumour has affected other tissue, for example has it grown outside the wall of the rectum or colon? 4
  • Node – is a measure of whether lymph nodes have been affected.
  • Metastasis – the degree to which the cancer has spread to other organs of the body.


There are five stages (0 – IV) of bowel cancer, which are explained below:

Stage 0
(also called carcinoma in Situ) – is where abnormal cells are found in the first layer (mucosa) of the wall of the bowel. These abnormal cells have the ability to become cancerous, grow and spread. 4

Stage I
Cancer cells have been found in the mucosa, and they have spread to the next layer in the wall of the bowel called the submucosa, and possibly even the muscle layer of the bowel wall. However no cancer cells have been found in the lymph nodes or other tissue.4

Stage II – IV
There are three sub-categories in each of the bowel cancer stages from II – IV; known as; A, B, C. The sub-categories and stages are dependent on the involvement of lymph nodes, associated tissue, organs and distal sites (sites further away in your body from the bowel).4

For more detailed information on bowel cancer staging, please visit Bowel Cancer New Zealand.


Frequently asked questions

What causes bowel cancer?

The cause of bowel cancer is not fully known, however there are some factors which contribute to the risk of bowel cancer developing, including: 5

  • Being older in age, the risk for bowel cancer increases for people over 50 years.
  • Certain life-style related factors such as;
    • Being overweight
    • Drinking alcohol
    • A diet high in processed and red meat
    • Smoking
  • Family history of bowel cancer
  • Having a history of bowel disease such as Crohn’s disease or ulcerative colitis significantly increases your risk.
  • Smoking
What can I do to decrease my risk of bowel cancer?

There a number of things you can do to help reduce your risk of getting bowel cancer, which include:6

  • Being physically active and maintaining a healthy weight
  • Limiting your alcohol intake
  • Eating a healthy and balanced diet, rich in wholegrains and fibre
  • Regular screening for bowel cancer

The Cancer Council Australia recommends regular (2 yearly) screening for over 50’s using a faecal occult blood test (FOBT), which tests for the presence blood in your bowel motion. This test can be done in the privacy of your own home.7

How do you know if it’s bowel cancer or haemorrhoids (piles)?

Haemorrhoids, or piles are soft lumps of enlarged blood vessels around and inside the anus. They usually result from a sudden increase in pressure – such as during pregnancy, constipation or heavy weight lifting.

Symptoms of haemorrhoids can include: 2

  • Painful bowel motions
  • Bright red blood on toilet tissue, or in the stool
  • Extreme itching around the anal area
  • A lump or swelling around the anus

Because the symptoms of haemorrhoids and bowel cancer can be similar, it is extremely important that you see your GP or healthcare professional if you are experiencing any symptoms of haemorrhoids or bowel cancer so that a diagnosis can be made.3


For a full list of references, click here.
  1. Genetic Inheritance. (n.d). Bowel Cancer Australia. Retrieved on 13th February 2019 from
  2. Haemorrhoids. (n.d). Healthline. Retrieved on 13th February 2019 from
  3. Bowel cancer symptoms (n.d). Bowel Cancer Australia. Retrieved 14th February 2019 from
  4. Bowel cancer staging. (n.d). Bowel Cancer Australia. Retrieved 14th February 2019 from
  5. Bowel Cancer. (n.d). Cancer Council. Retrieved on 14th February 2019 from
  6. Bowel Cancer prevention (2018). HealthDirect. Australian Government Department of Health. Retrieved on 14th February 2019 from
  7. Bowel cancer screening (2019). Cancer Council. Retrieved on 14th February 2019 from
  8. Treatment options for bowel cancer. (n.d). Bowel Cancer Australia. Retrieved on 15thFebruary 2019 from
  9. Finding bowel cancer early.(2018). Cancer Council SA. Retrieved on 15th February 2019 from

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