Risk Factors

Risk factors for colorectal cancer that can be controlled include:

• Being overweight/obese: People who are obese are about 30% more likely to develop colorectal cancer than normal-weight people. A person with a body mass index (BMI) of 30 or more is generally considered obese. A person with a BMI equal to or more than 25 is considered overweight. There are many BMI calculators available online to help you calculate your BMI. Please note that BMI is not a perfect measurement, and other factors (such as waist size) should also be taken into consideration.
• Certain types of diet: Diets high in red and processed meats, fat, refined grains (e.g. white rice, white flour) and high-calorie beverages are associated with a higher risk for developing colorectal cancer.
• Smoking: Smoking is a risk factor for all cancers and many other serious diseases. Smokers are around 18% more likely to develop colorectal cancer than non-smokers.
• Drinking alcohol: Moderate to heavy alcohol consumption is associated with 1.2- to 1.5-fold increased risk of cancers of the colon and rectum compared with no alcohol consumption.

Risk factors for colorectal cancer that you cannot control include:

• Ageing: Like most cancers, colorectal cancer is much more common as people get older (e.g. 50 and over). However, colorectal cancer does also appear to be increasing in those under the age of 50.
• Previous history of colorectal polyps: Individuals who have previously been diagnosed and treated for colorectal polyps are at increased risk for developing colorectal cancer in the future. Women who have had cancer of the ovary, uterus or breast have a higher-than-average risk of developing colorectal cancer.
• Inflammatory bowel disease (IBD) such as Crohn’s disease or ulcerative colitis: People with IBD are at an increased risk of developing colorectal cancer, primarily as a result of chronic intestinal inflammation.
• Certain inherited genetic syndromes: About 5–10% of people who develop colorectal cancer have inherited changes (mutations) in their genes (the functional units of our genetic material, also known as DNA) that can lead to them getting the disease. These are often associated with people having colorectal cancer at a younger age than average. The most common hereditary conditions leading to colorectal cancer are:
  • Lynch syndrome: This is the most common hereditary syndrome leading to colorectal cancer and is also known as Hereditary Non-Polyposis Colorectal Cancer (HNPCC). It accounts for about 3–5% of all colorectal cancers. The lifetime risk of colorectal cancer in people with this condition is 20–70%.
  • Familial adenomatous polyposis (FAP): About 1% of all colorectal cancers are caused by mutations in the APC (Adenomatous polyposis coli) gene. It causes hundreds or thousands of small polyps in the large bowel. If the polyps are not treated, one or more of them will almost certainly develop into cancer, usually by the age of 40. To prevent this, many people affected by FAP decide to have surgery to remove the large bowel. There are three different sub-types of FAP, known as attenuated FAP or AFAP, Gardner syndrome and Turcot syndrome.