Bowel cancer

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 and is usually called ‘small bowel cancer’ or ‘small intestine cancer’.

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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.

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Who gets bowel cancer?

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.


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 (particularly 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 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.


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 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.

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.


The parts of the bowel

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.

Small bowel

The small bowel is a long tube (4–6 m) that absorbs nutrients from food. Also called the small intestine, it is longer but narrower than the large bowel. It has three main sections:

  • 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.

Large bowel

The large bowel is a tube that absorbs water and salts and turns what is left over into waste (faeces). Also called the large intestine, the large bowel is about 1.5 m long. It has four main sections:

  • 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.

The digestive system

the digestive system

Read more about the large bowel and small bowel

This information was last reviewed in February 2017
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