- The digestive system
- What is bowel cancer?
- How common is bowel cancer?
- What are the symptoms?
- What are the risk factors?
- Can bowel cancer run in families?
- Information reviewed by
The bowel is part of the digestive system, which is also called the gastrointestinal (GI) or digestive tract. 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. This solid waste matter is called faeces (also known as stools when it leaves the body through the anus). The bowel is made up of the small bowel and the large bowel.
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. Cancer of the small bowel is very rare and is usually called ‘small bowel cancer’ or ‘small intestine cancer’.
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 become cancerous (malignant) over time.
If untreated, bowel cancer can grow into the deeper layers of the bowel wall. It can spread from there to the lymph nodes. These small, bean-shaped masses are part of the body’s lymphatic system. If the cancer advances further, it can spread (metastasise) to other organs, such as the liver or lungs.
In most cases, the cancer is confined to the bowel for months or years before spreading.
Bowel cancer is the second most common cancer affecting people in Australia. It is estimated that about 15,000 people are diagnosed with bowel cancer every year. About one in 21 men and one in 30 women will develop bowel cancer before the age of 75. It is most common in people over 50, but it can occur at any age.
In its early stages, bowel cancer may have no symptoms. However, many people with bowel cancer experience symptoms. These can include:
- blood in the stools or on the toilet paper
- a change in bowel habit, such as diarrhoea, constipation or smaller, more frequent bowel movements
- a change in appearance or consistency of bowel movements (e.g. narrower stools or mucus in stools)
- a feeling of fullness or bloating in the abdomen or a strange sensation in the rectum, often during a bowel movement
- feeling that the bowel hasn’t emptied completely after a bowel movement
- unexplained weight loss
- 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), which can cause tiredness and weakness
Not everyone with these symptoms has bowel cancer. Other conditions, such as haemorrhoids, diverticulitis (inflammation of pouches in the bowel wall) or cracks in the anal canal, 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.
Risk factors 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, have a significantly increased risk, particularly if they have had it for more than eight years
- lifestyle factors—being overweight, having a diet high in red meat (particularly processed meats such as salami or ham), drinking alcohol and smoking
- strong family history—a small number of bowel cancers run in families, see below
- 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 cancer may have an increased risk of bowel cancer
- rare genetic disorders—a small number of bowel cancers are associated with an inherited gene
Some factors reduce your risk of developing bowel cancer. These include being physically active, maintaining a healthy weight, cutting out processed meat, cutting down on red meat, reducing alcohol consumption and eating a high-fibre diet.
Sometimes bowel cancer runs in families. If one or more of your close family members (such as a parent or sibling) 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 close relatives on the same side of your family with bowel cancer.
A family history of other cancers, such as endometrial cancer, may also increase your risk of developing bowel cancer.
There are also two rare genetic conditions that occur in some families. These cause a small number (five or six per cent) of bowel cancers.
- Familial adenomatous polyposis (FAP). This condition causes hundreds of polyps to form in the bowel. If polyps caused by FAP are not removed, they may become cancerous.
- Lynch syndrome. Previously known as hereditary non-polyposis colorectal cancer (HNPCC), this syndrome is characterised by a fault in the gene that helps the cell’s DNA repair itself. Having Lynch syndrome increases the risk of developing bowel cancer and other cancers.
If you are concerned about your family risk factors, 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.
This website page was last reviewed and updated November 2018
Information reviewed by: A/Prof Craig Lynch, Colorectal Surgeon and Chair, Lower Gastrointestinal Cancer Service, Peter MacCallum Cancer Centre, VIC; Merran Findlay, Executive Research Lead–Cancer Nutrition, and Oncology Specialist Dietitian, Royal Prince Alfred Hospital, NSW; Jackie Johnston, Palliative Care and Stomal Therapy Clinical Nurse Consultant, St Vincent’s Private Hospital, NSW; A/Prof Susan Pendlebury, Radiation Oncologist, St Vincent’s Clinic, NSW; Jan Priaulx, 13 11 20 Consultant, Cancer Council NSW; A/Prof Eva Segelov, Professor of Oncology, Monash Health and Monash University, VIC; Heather Turner, Consumer; Lynne Wolowiec, Consumer.