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  • What is bowel cancer?

    Last reviewed January 2013


    The digestive system

    The bowel is part of the digestive system which is sometimes called the gastrointestinal (GI) tract. The digestive system helps the body to digest food and turn it into energy for the body to use. It also gets rid of remaining solid waste matter (called stools or faeces) from the body. The digestive system starts at the mouth and ends at the anus.


    The bowel has two main parts:

    • Small bowel – takes food from the stomach and absorbs nutrients. It is about five metres long.
    • Large bowel – the colon absorbs salts and water and turns the rest into waste (stools or faeces). It has several sections:
      • Cecum - a pouch at the beginning of the large bowel that receives waste from the small bowel. The appendix is a small tube hanging off the end of the cecum.
      • Colon - the main working area of the large bowel. The colon is divided into four parts (ascending colon, transverse colon, descending colon and sigmoid colon) and stretches from the cecum to the rectum. It is about 1.5 metres long.
      • Rectum - the last 15 to 20 centimetres of the large bowel. The rectum stores waste until it is passed during a bowel motion.
      • Anus - the opening at the end of the digestive tract. The anus has strong sphincter muscles that form a valve. During a bowel motion these muscles relax to release stools from the rectum.

    What is bowel cancer?

    Bowel cancer is cancer in any part of the colon or rectum. Bowel cancer can develop in two ways: it can grow from the inner lining of the bowel or from small growths on the bowel wall called polyps. These mushroom-shaped growths are usually harmless (benign) but may become cancerous over time.

    If untreated bowel cancer can spread (metastasise) deeper into the wall of the bowel. From there it can spread to the lymph nodes (glands).

    Lymph nodes are small, bean-shaped masses that collect and destroy bacteria and viruses in the body. They are part of the body’s lymphatic system which plays an important role in the functioning of the immune system.

    Later bowel cancer can spread to other organs such as the liver or lungs. In most cases it develops fairly slowly and may stay in the bowel for months or years before spreading.

    In this information the colon and rectum together are known
 as the large bowel. The word colorectal is commonly used to describe cancers of the colon or rectum. Bowel cancer is also called colorectal cancer. The terms large intestine, large bowel and colon all refer to the same organ. The term large intestine is not used in this information.

    Symptoms of bowel cancer

    In its early stages bowel cancer often has no noticeable symptoms.

    Symptoms some people may experience include:

    • A change in bowel habits such as the look of stools, 
constipation or smaller, more frequent bowel movements.
    • A feeling of fullness in the bowel or rectum.
    • A feeling that the bowel hasn’t emptied completely after a 
bowel movement.
    • Blood in the stool or on the toilet paper.
    • Unexplained weight loss.
    • Weakness or fatigue.
    • Rectal or anal pain.
    • Feeling very tired or breathless (anaemia). 

    Cancer of the bowel may cause a blockage (bowel obstruction). This causes symptoms such as abdominal pain, feeling bloated, constipation and being sick. 
Many of the symptoms of bowel cancer are common to other large bowel conditions such as haemorrhoids or tears in anal tissue. Some foods or medications can also change bowel habits or cause stools to turn red or black. If you have any of the above symptoms talk to your doctor. 

    How common is it? 

    About one in 17 men and one in 25 women will develop bowel cancer before the age of 75.

    What causes bowel cancer?

    The exact cause of bowel cancer is not known. However some factors increase the chance of developing bowel cancer including:

    • Getting older – bowel cancer more commonly affects people aged 50 and over.
    • Bowel diseases – people who have an inflammatory bowel disease, such as Crohn’s disease or ulcerative colitis, have a significantly increased risk.
    • Lifestyle factors – being overweight, doing little physical activity, a diet high in fat or animal products, alcohol consumption and smoking can play a part.
    • Strong family history – bowel cancer can run in the family. Whether you’re at increased risk depends on who in your family was diagnosed and at what age.
    • Inheriting a rare genetic disorder
    • Polyps in the colon are a risk factor for bowel cancer. If polyps are removed the risk of bowel cancer is reduced.

    Useful websites

    The internet has many useful resources of information although not all websites are reliable. The websites listed below are good sources of reliable information.


    Cancer Council SA www.cancersa.org.au
    Cancer Council Australia www.cancer.org.au
    healthdirect www.healthdirect.gov.au
    Commonwealth Department
of Health and Ageing www.health.gov.au
    Health SA www.healthsa.sa.gov.au
    National Health and Medical Research Council www.nhmrc.gov.au
    Australian Association of Stomal Therapy Nurses www.stomaltherapy.com
    Ostomy NSW www.ostomynsw.org.au
    Continence Foundation of Australia www.continence.org.au
    National Public Toilet Map www.toiletmap.gov.au
    National Cancer Screening Programs www.cancerscreening.gov.au
    Carers SA www.carers-sa.asn.au


    American Cancer Society                                         www.cancer.org                    
    Macmillan Cancer Support                     www.macmillan.org.uk
    US National Cancer Institute  www.cancer.gov

    Information reviewed by:  Karen Barclay, Colorectal Surgeon, The Northern Hospital, Lecturer in Surgery, University of Melbourne, VIC; Carole Arbuckle, Cancer Nurse, Cancer Council VIC; Karen Bowers, Eat it to Beat it Strategy Project Officer, Cancer Council NSW; Darrell Bowyer, Consumer; Rebecca Foot-Connolly, Stomal Therapy Nurse, The Alfred Hospital, VIC; Bernadette Hadfield, Stomal Therapy Nurse, The Alfred Hospital, VIC; Melissa Heagney, Media and Communications Advisor, Cancer Prevention Unit, Cancer Council VIC; Dorothy King, Consumer; and Loreto Pinnuck, Stomal Therapist, Wound Consultant, Paediatric Continence Specialist, Monash Medical Centre, VIC.

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