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What is Bowel Cancer?

Bowel Cancer, also known as colorectal cancer, is a cancer of the lining of the colon or rectum. It is the number two cancer killer in Australia with one person dying every two hours.

Cancer of the large bowel (colon and rectum) is the most commonly diagnosed internal cancer in Australia. The large bowel is a muscular tube one to two metres in length. The rectum is the last 15cm of the large intestine, and this leads to the anal canal, which is around three centimetres long and leads to the outside of the body.


  • Australia has one of the highest rates of bowel cancer in the world.
  • Over 14,000 men and women Australians are diagnosed annually.
  • In Victoria, over 1,300 die annually – more than 3 times the state’s road toll.
  • Bowel cancer affects men and women of all ages, almost equally.
  • Risk increases with age.
  • 1 in 12 Australians will develop bowel cancer in their lifetime.
  • While 90% of bowel cancers occur in those 50 and over – around 1,000 younger Australians are diagnosed annually.
  • Screening every 1-2 years can reduce the risk of dying from bowel cancer by up to 33%.

How bowel cancer develops

Most bowel cancers start as wart-like growths, on the wall of the bowel called polyps. Polyps are usually harmless (benign) but can become cancerous over time. The polyps associated with bowel cancer are termed ‘adenomatous polyps’ or simply adenomas.  Patients who are found to have adenomas are considered at risk of developing bowel cancer.


If untreated, bowel cancer can spread (or metastasise) deeper into the wall of the bowel, or invade nearby organs.  From there, it can spread through the body via the bloodstream and the lymph system.

Lymph nodes are small, oval-shaped organs that are found throughout the body. They are an important part of the immune system and help your body recognise and fight germs, infections, and other foreign substances.

Over time, bowel cancer can spread to other organs of the body, such as the liver or lungs, via the lymph nodes.  

When bowel cancer is diagnosed early, there is an excellent chance of being completely cured.  If the disease is widespread throughout the body, it may be impossible to cure, but the disease may still be controllable.

Causes of Bowel Cancer

The exact cause of bowel cancer is unknown.  Current research suggests that a combination of genetic or inherited factors, plus environmental influences are the most likely causes.

Researchers believe that bowel cancer is caused by changes in 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’.

Bowel cancer is more common in developed countries. A high animal-fat, highly processed diet may be associated with an increased incidence of bowel cancer, and an increased amount of dietary fibre may reduce the incidence.

Risk Factors

While the exact causes of bowel cancer are unknown, there are known risk factors for an increased chance of developing the disease. 

These include:

  • Age
    Most bowel cancers occur in people over the age of 50, but no age group is immune.
  • Family history
    The lifetime risk of bowel cancer for the average Australian is one in 12.  This risk doubles if a first-degree relative (parents, children or siblings) develops bowel cancer, especially if they developed bowel cancer or polyps younger than age 50; or if more than one relative on the same side of a family has had the condition.
  • Inflammatory bowel disease
    People with a long-standing history of Ulcerative Colitis  or Crohn’s Colitis, have an increased risk of developing bowel cancer.
  • Hereditary bowel conditions
    There are two rare bowel conditions that can run in families and a small percentage of bowel cancers are caused by these inherited genetic conditions:
  1. Familial adenomatous polyposis (FAP) is an inherited condition where the lining of the bowel contains hundreds of polyps. It is a rare condition but people who are affected by the disease, if untreated, will develop bowel cancer.
  2. Hereditary non-polyposis colorectal cancer (HNPCC), also known as Lynch syndrome, is an inherited condition and is characterised by early age of onset of bowel cancer. The children of those affected with Lynch Syndrome have a 50% chance of inheriting the same condition.
  • Polyps
    Polyps are a risk factor for bowel cancer.  If polyps are removed, the risk of bowel cancer is significantly reduced.
  • Diet & Lifestyle
    Lifestyle issues may be important in reducing the risk of bowel cancer.  Obesity, lack of exercise, a diet high in fat and low in fibre can increase the risk of many cancers, including bowel cancer.  Consuming alcohol and smoking can also increase risk.


Bowel cancer can occur without any obvious warning signs.  Not everyone will have symptoms, and the symptoms can vary. 

If you have any of the following common signs or symptoms, you should see your doctor who may suggest further testing:

  • Persistent change in bowel habits
    Keep an eye out for diarrhoea, constipation, change of appearance or narrowing of the stool that continues for more than a few weeks.
  • Blood in the stool (bowel motion)
    Bleeding from your bottom, dark stools or blood in the stool should always be investigated.   Sometimes blood in the stool can be present, but invisible to the naked eye. 
  • Abdominal bloating or cramping abdominal pain
    If you notice abdominal bloating or cramping abdominal pain, or a lump or swelling in your abdomen, talk to your doctor who might suggest further testing.
  • Unexplained weight loss or loss of appetite
    Weakness, fatigue and breathlessness for no apparent reason.

There are other bowel conditions that can cause similar symptoms to these, such as haemorrhoids, bowel infections or inflammatory bowel disease. Some medications and foods can also change the colour of the stool (red or black) or change usual bowel habits.  

If you do experience any of these symptoms, regardless of your age, it is important to consult your GP so the cause can be found.

Getting screened & Prevention

Australia has one of the highest rates of bowel cancer in the world. Yet it is also one of the most preventable cancers.

Reducing known lifestyle risk factors and undergoing regular bowel screening are vital tools in reducing the risk of developing bowel cancer.


Treatment for cancers in both the colon and the rectum are different, and the type of treatment received depends on a number of factors including:

  • the size and position of the cancer
  • whether or not it has spread to other parts of the body
  • age and general health
  • any personal requirements or concerns