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Colorectal Cancer

What is colorectal cancer?

Colorectal cancer, also known as bowel cancer, can affect any part of the large bowel (colon) and rectum.

Most colorectal cancers develop on the inner wall of the colon and rectum and usually start with growths called polyps.

These polyps are benign growths and usually harmless, however they can become cancerous if left undetected.

Colorectal cancer may also be called colon cancer or rectal cancer, depending on where the cancer is located and the area it originates from.

Is colorectal cancer hereditary?

One third of colorectal cancer cases are caused by genetics and family history.1

The three common inherited disorders which have been linked to colorectal cancer are:

  • 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
  • MYH – Associated Polyposis (MAP) – caused by a genetic mutation in the gene MYH gene which results in numerous (10-100) polyps (abnormal tissue growth) which can become cancerous.1
  • Familial adenomatous polyposis (FAP) – causes significant numbers (100 – 1000) of adenomatous polyps (gland-like tissue growths) in the lining of the large intestine.1

Stages of colorectal cancer

The TNM system is used to stage colorectal cancer, which 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 colorectal 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, 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 colorectal cancer stages from II – IV, which are known as A, B and 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

Signs and symptoms of bowel cancer

Not everyone experiences symptoms of colorectal cancer, however some common signs include: 3

Sudden changes in bowel motions

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

Bright red or dark blood in your stool or on the toilet tissue

A lump or pain around the anus

Constant gas or bloating in the bowel or rectum

Unexplained weight-loss, or loss of appetite

Unexplained anaemia (low iron)

which can cause tiredness and breathlessness

Pain in your stomach, with or without swelling


Frequently asked questions

What causes colorectal cancer?

The cause of colorectal cancer is not fully known, however factors which contribute to the risk of bowel cancer developing include: 5

  • Being 50-years-old and over.
  • Certain life-style related factors such as:
    • Being overweight
    • Drinking alcohol
    • A diet high in processed and red meat
    • Smoking
  • Family history of colorectal cancer
  • Having a history of colorectal disease such as Crohn’s disease or ulcerative colitis significantly increases your risk.
  • Smoking
How common is colorectal cancer?

Colorectal cancer affects both men and women, young and old, with the disease being more common in people over 50 years.1

What can I do to decrease my risk of bowel cancer?

Things you can do to reduce your risk of getting bowel cancer include:6

  • Exercising regularly and maintaining a healthy weight
  • Limiting your alcohol intake
  • Eating a healthy and balanced diet, rich in wholegrains and fibre
  • Regular screening for colorectal cancer.
How do you know if it’s colorectal 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 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.

Since the symptoms of haemorrhoids and colorectal cancer can be similar, you should talk to your doctor if you are experiencing these symptoms. 3


For a full list of references, click here.
  1. Genetic Inheritance. (n.d). Bowel Cancer Australia. Retrieved on 13th February 2019 from
  2. (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 15th February 2019 from
  9. Finding bowel cancer early.(2018). Cancer Council SA. Retrieved on 15th February 2019 from
  10. Colorectal cancer. (2019). Health Hub. Retrieved on 30th May 2019 from
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