Bowel cancer

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. Cancer of the small bowel is very rare – it is called small bowel cancer or small intestine cancer. For information on its treatment and management, call 13 11 20.

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. 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. The National Bowel Cancer Screening Program aims to improve early detection.

Learn more about:

• Who gets bowel cancer?
• What causes bowel cancer?
• Can bowel cancer run in families?
• The bowel

Who gets bowel cancer?

Bowel cancer is the third most common cancer affecting people in Australia. It is estimated that about 15,250 people are diagnosed with bowel cancer every year. About one in 21 men and one in 31 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.

What causes bowel cancer?

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 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.

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, and 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.

Can bowel cancer run in families?

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 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.

If you are concerned 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.

The bowel

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 m) 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; 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; transfers waste matter to the large bowel.

The large bowel (large intestine)

This tube is about 1.5 m 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; the appendix is a small tube hanging off the end of the caecum
• colon – the main working area of the large bowel, the colon 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.

The anus

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. For more on this, see Anal cancer.

The lower digestive system