What is bowel cancer?
Bowel cancer is cancer in any part of the large bowel (colon or rectum). It is sometimes known as colorectal cancer and might also be called colon cancer or rectal cancer, depending on where it starts in the bowel.
Bowel cancer grows from the inner lining of the bowel (mucosa). It usually develops from small growths on the bowel wall called polyps. Most polyps are harmless (benign), but some polyps develop into cancer over time. Polyps can be removed during a colonoscopy to prevent them becoming cancerous.
If untreated, bowel cancer can grow into the deeper layers of the bowel wall and can spread from there to the lymph nodes. If the cancer advances further, it can spread to other organs, such as the liver or lungs.
The bowel is part of the lower gastrointestinal 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 metres) that absorbs nutrients from food. It is longer but narrower than the large bowel. It has three parts:
- duodenum – the first section of the small bowel, which receives broken-down food from the stomach
- jejunum – the middle section of the small bowel
- ileum – the final and longest section of the small bowel, which transfers waste matter to the large bowel.
The large bowel (large intestine)
This tube is about 1.5 metres long. It absorbs water and salts, and turns what is left over into solid waste matter (known as faeces, stools or poo when it leaves the body). The large bowel has three parts:
- caecum – a pouch that receives waste from the small bowel
- colon – the main working area of the large bowel that takes up most of the large bowel's length
- rectum – the last 15–20 centimetres of the large bowel.
This is the opening at the end of the bowel. During a bowel movement, the anal muscles relax to release faeces. Anal cancer is treated differently to bowel cancer.
Your guide to best cancer care
A lot can happen in a hurry when you’re diagnosed with cancer. The guide to best cancer care for bowel cancer can help you make sense of what should happen. It will help you with what questions to ask your health professionals to make sure you receive the best care at every step.
Please note: work is currently underway to refresh the guide to best cancer care for bowel cancer.
Read the guide
How common is bowel cancer?
Bowel cancer is the third most common cancer affecting people in Australia. It is estimated that about 15,500 people are diagnosed with bowel cancer every year. It is most common in people over 50, but it can occur at any age.
Less common types of bowel cancer
About 9 out of 10 bowel cancers are adenocarcinomas, which start in the glandular tissue lining the 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), but this is rare.
Learn more about small bowel cancer
In its early stages, bowel cancer may have no symptoms. This is why screening is important to increase the chance of an early diagnosis. However, many people with bowel cancer do experience symptoms, which can include:
- blood in faeces (poo) or on the toilet paper
- a change in bowel habit, such as diarrhoea, constipation or smaller, more frequent bowel movements
- a change in the look of faeces (e.g. narrower or with mucus)
- a feeling of fullness or bloating in the abdomen (belly) or a strange sensation in the rectum, often during a bowel movement
- a feeling that the bowel hasn’t emptied completely
- losing weight for no obvious reason
- weakness or fatigue
- rectal or anal pain
- a lump in the rectum or anus
- abdominal pain or swelling
- a low red blood cell count (anaemia or iron deficiency), which can cause tiredness and weakness
- a blockage in the bowel.
Not everyone with these symptoms has bowel cancer. Other conditions, such as haemorrhoids, diverticulitis, inflammatory bowel disease or an anal fissure, can also cause these changes.
Changes in bowel function are common and often do not indicate a serious problem. However, any amount of bleeding is not normal, and you should see your doctor for a check-up.
The exact cause of bowel cancer is not known. However, research shows that people with certain risk factors are more likely to develop bowel cancer. These include:
- older age – most people with bowel cancer are over 50, and the risk increases with age.
- polyps – having a large number of polyps in the bowel.
- bowel diseases – people who have an inflammatory bowel disease, such as Crohn's disease or ulcerative colitis, particularly if they have had it for more than eight years.
- lifestyle factors – being overweight, having a diet high in red meat or processed meats such as salami or ham, drinking alcohol and smoking.
- strong family history – a small number of bowel cancers run in families.
- other diseases – people who have had bowel cancer once are more likely to develop a second bowel cancer. Some people who have had ovarian or endometrial (uterine) cancer may have an increased risk of bowel cancer.
- rare genetic disorders – a small number of bowel cancers are associated with an inherited gene.
Reducing your risk
Some things reduce your risk of developing bowel cancer, including:
- being physically active
- maintaining a healthy weight
- cutting out processed meat
- cutting down on red meat
- drinking less alcohol
- not smoking
- eating wholegrains, dietary fibre and dairy foods.
Talk to your doctor about whether you should take aspirin, which has been shown to reduce the risk of developing bowel cancer.
Learn more about preventing cancer
Sometimes bowel cancer runs in families. If one or more of your close family members have had bowel cancer, it may increase your risk. This is especially the case if they were diagnosed before the age of 55, or if there are two or more close relatives on the same side of your family with bowel cancer. A family history of other cancers, such as endometrial (uterine) cancer, may also increase your risk of developing bowel cancer.
Some people have an inherited faulty gene that increases their risk of developing bowel cancer. These faulty genes cause a small number (about 5–6%) of bowel cancers. There are two main genetic conditions that occur in some families:
- Familial adenomatous polyposis (FAP) – This condition causes hundreds of polyps to form in the bowel. If these polyps are not removed, they may become cancerous.
- Lynch syndrome – This syndrome is characterised by a fault in the gene that helps the cell's DNA repair itself.
Your general practitioner (GP) will organise the first tests to assess your symptoms, or further tests if you have had a positive screening test. If these tests do not rule out cancer, you will usually be referred to a specialist, such as a colorectal surgeon or a gastroenterologist, who will arrange further tests.
If bowel cancer is diagnosed, the specialist will consider treatment options. Often these will be discussed with other health professionals at what is known as a multidisciplinary team (MDT) meeting.
During and after treatment you will see a range of health professionals, which may include a genetic counsellor, stomal therapy nurse, medical oncologist, dietician and psychologist, who specialise in different aspects of your care.
Understanding Bowel Cancer
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Expert content reviewers:
A/Prof David A Clark, Colorectal Surgeon, Royal Brisbane and Women’s Hospital, and The University of Queensland, QLD, and The University of Sydney, NSW; A/Prof Siddhartha Baxi, Radiation Oncologist and Medical Director, GenesisCare Gold Coast, QLD; Dr Hooi Ee, Specialist Gastroenterologist and Head, Department of Gastroenterology, Sir Charles Gairdner Hospital, WA; Annie Harvey, Consumer; A/Prof Louise Nott, Medical Oncologist, Icon Cancer Centre, Hobart, TAS; Caley Schnaid, Accredited Practising Dietitian, GenesisCare, St Leonards and Frenchs Forest, NSW; Chris Sibthorpe, 13 11 20 Consultant, Cancer Council Queensland; Dr Alina Stoita, Gastroenterologist and Hepatologist, St Vincent’s Hospital Sydney, NSW; Catherine Trevaskis, Gastrointestinal Cancer Specialist Nurse, Canberra Hospital, ACT; Richard Vallance, Consumer.
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The information on this webpage was adapted from Understanding Bowel Cancer - A guide for people with cancer, their families and friends (2021 edition). This webpage was last updated in June 2021.