What are the risk factors?

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.