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What is the bowel?

Diagram of the bowelPart of the digestive system, the bowel connects the stomach to the anus, allowing waste materials to be passed from the body. The bowel helps to complete the body’s digestive process, by absorbing nutrients and water. The bowel comprises three parts:
  • small bowel: predominantly responsible for absorbing food nutrients
  • colon: predominantly responsible for absorbing water
  • rectum: where waste material is stored until it is eliminated from the body via the anus.
The ‘large bowel’ is the collective name for the colon and rectum together, and this is the region affected by bowel (or ‘colorectal’) cancer.

What is bowel cancer?
Bowel cancer is cancer in any part of the colon or rectum. It is an abnormal growth of body cells lining the bowel, forming a lump called a malignant tumour. The cancer cells may spread outside the bowel from the primary cancer to lymph glands or other organs and these clusters of cells are called metastases or secondary cancer.

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How it starts
Most bowel cancers start as warty-like growths, known as polyps, on the wall of the bowel. The word polyp refers to any visible structure which projects from the lining of the bowel wall. Polyps are very common as we get older – one in 10 people over 50 have them – but most polyps do not turn to cancer. If potentially cancerous polyps can be found at an early stage, they can be removed painlessly without the need for an operation. When polyps are discovered, they are best removed and carefully examined by a pathologist. It may take up to 10 years for a benign polyp (adenoma) to become an invasive cancer.

There are different types of polyps, but those that are associated with bowel cancer are termed adenomatous polyps or simply adenomas. This variety of polyp is important because there is strong evidence that some adenomas may undergo malignant change to produce cancer. Patients who are found to have adenomas are considered at risk of developing bowel cancer. This risk is difficult to quantify. It varies from patient to patient, and usually requires periodic surveillance by telescopic examination of all of the large bowel (colonoscopy).

Adenomas, when pre-cancerous are composed of abnormal, rapidly dividing cells whose suspicious appearance and behaviour can only be accurately recognised by the pathologist when examined under the microscope.

Therefore, when polyps are discovered they are best removed (polypectomy) so that they can be carefully examined and classified by a pathologist. Large adenomas (greater than two centimetres in diameter) are always suspected of having developed a small focus of cancer until proven otherwise by a pathologist.

Although polyps are very common, they usually don’t produce symptoms and are usually discovered by chance at the time of a colonoscopy, or uncovered due to the presence of blood in the faeces (detected by a FOB Test).

A colonoscopy enables doctors to get a clear view of the whole length of the lining of the bowel, to search for and remove any polyps found, and have them examined. Up to 90% of polyps can be safely and completely removed by colonoscopy.

If adenomas are confirmed by a pathologist, it is recommended that the patient have regular check-ups by repeated colonoscopy. The frequency of examinations varies, and this needs to be discussed with the doctor who performed the colonoscopy.

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Causes
Current research suggests that bowel cancer is caused by changes to the cells lining the bowel wall. These cells become polyps, which may then develop into cancer cells. These changes may take between 5-10 years to develop and the causes are not completely understood. There are many types of polyps but the most important one to detect and remove is called an adenoma. Environmental and genetic factors may contribute to the development of polyps. Bowel cancer is more common in developed countries, which is thought to be due to the food we eat slowing the transit of stools through the bowel. This increases the exposure to the lining of the bowel by cancer producing substances called carcinogens. So diet can be important. Age, as well as genetic factors which might be inherited, are also important, and research in genetics and molecular biology is increasing our knowledge of these inherited factors.

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Symptoms
Not everyone will have symptoms, and the symptoms may vary.
The most common symptoms to look out for are:
  • A persistent change in bowel habit (looser motions, severe constipation or more frequent visits) for several weeks

  • Bleeding from the bottom for no obvious reason or blood mixed in the stool

  • Abdominal pain, especially if severe and persistent.
Other symptoms to also be aware of include unexplained anaemia causing tiredness or weight loss. Please note that there are a number of other conditions that can cause similar symptoms, however it is always very important to consult your GP for clarification or further tests.

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Risk factors

Although the exact cause of bowel cancer is unknown there are certain factors known to increase your risk, including…

  • Age:
    Bowel cancer tends to affect people aged 50 and over, though younger people can also be at risk. For peace of mind, everyone 50 or over should complete an annual FOB Test and/or have a regular colonoscopy.


  • Family history:
    Bowel cancer risk is increased in people who have significant family history of the disease (parents, children or siblings), especially if they developed bowel cancer or polyps at less than 50 years of age; or if more than one relative on the same side of a family has had the condition.


  • Bowel polyps:
    Abnormal growth of cells on the bowel wall that form a mushroom-like lump: usually only uncovered by a colonoscopy or FOB Test.


  • Diet & Lifestyle:
    Lifestyle issues may be important in reducing the risks such as: regular exercise, maintaining ideal weight and eating a diet low in fat and high in fibre.


  • Inflammatory bowel disease:
    People with a long history of Ulcerative Colitis or Crohn’s Disease, or who have previously had polyps removed, may be at an increased risk.


"Bowel Cancer Risk Test" Take this quick test to determine whether you have any factors that may increase your risk of developing bowel cancer.

PDFPlease click here to download The Cancer Council Victoria's latest Bowel (Colorectal) Cancer Booklet.

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Snapshot
  • Bowel cancer is the most common cause of internal cancer affecting Australian men and women.

  • Bowel cancer affects both men & women almost equally.

  • One in 20 Australians will develop bowel cancer. This increases to one in 10 if an immediate family member has had bowel cancer.

  • Almost 5,000 Australians die each year from bowel cancer

  • One Australian dies every two hours from bowel cancer.

  • A healthy diet & regular exercise can help prevent bowel cancer!

  • Australia has the highest incidence of bowel cancer in the world, but the good news is that more than 90% of people survive bowel cancer if it is detected early and treated before the disease has spread.

  • Currently fewer than 40% of bowel cancers are detected early.

  • If you are over 50, an annual bowel cancer screening test could save your life.
  • More than 90% of bowel cancers are cured if detected and treated at an early stage.
  • 90% of bowel cancers occur over the age of 50 but can occur at any age.
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