Bowel cancer (also called colorectal cancer) is cancer in any part of the large bowel (colon or rectum). It may also be called colon cancer or rectal cancer, depending on where in the bowel it is.
Learn more about:
What is bowel cancer?
The cancer starts in the lining of the inner bowel wall (called the mucosa). It usually develops from small growths called polyps. Most polyps are harmless (benign), but some may turn into cancer. Removing polyps during a colonoscopy reduces the risk of bowel cancer.
If untreated, bowel cancer can grow into the deeper layers of the bowel wall. It can also spread to the lymph nodes. If the cancer advances further, it can spread to other organs, such as the liver or the lungs.
The information covered here is on cancer of the large bowel.
The bowel
The bowel is part of the lower gastrointestinal (GI) tract, which is part of the digestive system. The digestive system starts at the mouth and ends at the anus. It helps the body break down food and turn it into energy. It also gets rid of the parts of food the body does not use.
The small bowel (small intestine)
This is a long tube (4–6 m) that absorbs nutrients from food. The small bowel is longer and narrower than the large bowel. It has 3 parts:
- duodenum – top section; receives broken-down food from the stomach
- jejunum – middle section
- ileum – lower, longest section; moves waste into the large bowel.
For more on this, see Small Bowel Cancer.
The large bowel (large intestine)
About 1.5 m long, this tube absorbs water and salts, and turns what is left into solid waste (faeces, stools or poo).
The large bowel has 3 parts:
- caecum – looks like a pouch; it receives waste from the small bowel; the appendix is attached to the caecum (see Appendix Cancer and PMP)
- colon – main, longest section of the large bowel; has 4 parts: ascending colon, transverse colon, descending colon and sigmoid colon
- rectum – the last 15–20 cm of the large bowel.
The anus
This is the opening at the end of the large bowel. During a bowel movement, the anal muscles relax to release faeces (poo). For more on this, see Anal cancer.
The lower digestive system
Less common types of bowel cancer
Most bowel cancers are adenocarcinomas, which start in the tissue lining the large bowel. Rarely, other less common types of cancer can also affect the bowel. These include lymphomas,squamous cell carcinomas, neuroendocrine tumours and gastrointestinal stromal tumours. Cancer can also start in the small bowel (called small bowel cancer or small intestine cancer), or in the appendix, but this is rare. These cancers are not included in this booklet, and may have different treatment. For more information about these less common types of bowel cancers, call Cancer Council 13 11 20.
Who gets bowel cancer?
Bowel cancer is the 4th most common cancer in Australia. Each year, about 15,500 Australians are diagnosed with bowel cancer. It is more common in people over 50, but it can happen at any age. The number of adults under 50 with bowel cancer is increasing, with research yet to give a clear reason for this.
What causes bowel cancer?
Anything that can increase your risk of cancer is called a risk factor. For bowel cancer, these include:
| older age | bowel cancer is most common in people over 50, but the number of younger people being diagnosed is increasing |
| polyps | most polyps can become bowel cancer; having a large number of polyps in the bowel is a strong risk factor |
| dietary factors | a diet that is low in fibre, fruit, vegetables and wholegrains, and high in red and processed meats such as salami, ham and bacon |
| smoking | increases your risk of bowel cancer and bowel polyps |
| drinking alcohol | the less alcohol you drink, the lower your risk. If you choose to drink, follow the Australian Alcohol Guidelines |
| body weight | being above a healthy weight |
| physical inactivity | not moving your body enough. Be active on most days and minimise long periods of sitting |
| strong family history | a small number of bowel cancers and types of polyps run in families |
| other bowel diseases | inflammatory bowel diseases, such as Crohn’s disease or ulcerative colitis, significantly increase risk, particularly if you have had the disease for more than 10 years (IBS does not increase your risk) |
| other cancers | people who have had bowel cancer are more likely to develop a second bowel cancer; some people who have had ovarian cancer or cancer of the uterus, or who have had radiation treatment to the abdomen/pelvis, may also have an increased risk of bowel cancer |
| type 2 diabetes | this may increase your risk of bowel cancer |
| rare genetic disorders | some bowel cancers are linked to an inherited gene or condition (e.g. cystic fibrosis). |
Can bowel cancer run in families?
Sometimes bowel cancer runs in families. The risk of developing bowel cancer may be higher if one or more of your close family members (a parent, brother or sister) has had bowel cancer. The risk is higher if they were diagnosed before the age of 50, or if 2 or more close relatives have had bowel cancer. A family history of some other cancers, such as cancer of the uterus (endometrial cancer), may also increase the risk (see Lynch syndrome, below).
Some people have an inherited faulty gene that increases their risk of developing bowel cancer. These faulty genes are responsible for a small number of bowel cancers in the population.
There are 2 main genetic conditions that occur in some families:
- Lynch syndrome – Less than 5% of bowel cancers are linked to Lynch syndrome, which causes a fault in the gene that helps repair a cell’s DNA. People with Lynch syndrome have an increased risk of developing bowel cancer, cancer of the uterus, and other cancers such as kidney, bladder and ovarian. Bowel cancer may also happen at a younger age than usual. Find out more about Lynch syndrome at Cancer Council Victoria.
- Familial adenomatous polyposis (FAP) – This condition is linked to about 1% of bowel cancers. It causes hundreds of polyps to form in the bowel. If these polyps are not removed, they may become cancerous. If you have a family history, talk to your doctor about regular check-ups or ask for a referral to a family cancer clinic.
If you are worried about your family history, talk to your doctor about having regular check-ups or ask for a referral to a family cancer clinic. To find out more, call Cancer Council 13 11 20.
For an overview of what to expect at every stage of your cancer care, visit Bowel cancer: your guide to best cancer care. This is a short guide to what is recommended, from diagnosis to treatment and beyond.
→ READ MORE: Bowel cancer symptoms
More resources
Prof Alexander Heriot, Colorectal Surgeon and Director Cancer Surgery, Peter MacCallum Cancer Centre, Director, Lower GI Tumour Stream, Victorian Comprehensive Cancer Centre, VIC; Dr Cameron Bell, Gastroenterologist, Royal North Shore Hospital, NSW; Graham Borgas, Consumer; Prof Michael Bourke, Director of Gastrointestinal Endoscopy, Westmead Hospital, The University of Sydney, NSW; Laura Carman, 13 11 20 Consultant, Cancer Council Victoria, VIC; Amanda Connolly, Specialist Bowel Care Nurse, Icon Cancer Centre Windsor Gardens, SA; A/Prof Melissa Eastgate, Operations Director, Cancer Care Services, Royal Brisbane and Women’s Hospital, QLD; Anne Marie Lyons, Stomal Therapy Nurse, Concord Repatriation General Hospital and NSW Stoma Ltd, NSW; Lisa Nicholson, Manager Bowel Care Services, Bowel Cancer Australia, NSW; Stefanie Simnadis, Clinical Dietitian, St John of God Subiaco Hospital, WA; Rafi Sharif, Consumer; Dr Kirsten van Gysen, Radiation Oncologist, The Nepean Cancer and Wellness Centre, NSW; Sarah Williams, Clinical Nurse Consultant, Lower GI, Peter MacCallum Cancer Centre, VIC.
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