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.
|Duodenum||The first section of the small bowel; receives food from the stomach.|
|Jejunum||The middle section of the small bowel.|
|Ileum||The final and longest section of the small bowel; transfers waste to the large bowel.|
|Caecum||A pouch that receives waste from the small bowel. The appendix is a small tube hanging off the end of the caecum.|
|Colon||The main working area of the large bowel. Takes up most of the large bowel’s length and has four parts: ascending colon, transverse colon, descending colon and sigmoid colon.|
|Rectum||The last 15–20 cm of the large bowel.|
|Anus||The opening at the end of the digestive tract. During a bowel motion, the muscles of the anus relax to release faeces from the rectum.|
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 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 (glands). These small, bean-shaped masses are part of the body’s lymphatic system. If the cancer advances further, it can spread to other organs, such as the liver or lungs (metastasis).
In most cases, the cancer develops slowly and stays in 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 17,000 people are diagnosed with bowel cancer every year. About one in 19 men and one in 28 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 often has no symptoms. However, some people with bowel cancer do experience persistent symptoms. These can include:
Not everyone with these symptoms has bowel cancer. Other conditions, such as haemorrhoids, diverticulitis (inflammation of pouches in the bowel wall), or tears in the anal canal, and some foods or medications, can also cause these changes.
Short-term changes in bowel function are very common and usually do not indicate a serious problem. However, if you have any of the above symptoms for more than four weeks, see your doctor for a check-up.
The exact cause of bowel cancer is not known. However, some factors increase the chance of developing it.
Risk factors include:
Being physically active, maintaining a healthy weight and eating a high-fibre diet may help protect against bowel cancer.
Although the average age at which bowel cancer is diagnosed is 69 years, about 7% of bowel cancers are in people younger than 50.
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 (5–6%) of bowel cancers.