Risk factors for colorectal cancer

A risk factor is something that increases the risk of developing cancer. It could be a behaviour, substance or condition. Most cancers are the result of many risk factors. But sometimes colorectal cancer develops in people who don’t have any of the risk factors described below.

Most people diagnosed with colorectal cancer are over the age of 50, and the risk increases with age. More men than women develop colorectal cancer. The colorectal cancer incidence rate is highest in North America, northwestern Europe and Australia. Rates are lower in less industrialized countries, including those in Asia, Africa and South America.

Precancerous conditions of the colon or rectum include adenomas and hereditary colorectal syndromes. They aren’t cancer, but they can sometimes become colorectal cancer if they aren’t treated. Some of the risk factors for colorectal cancer may also cause these precancerous condition. Find out more about precancerous conditions of the colon or rectum.

Risk factors are generally listed in order from most to least important. But in most cases, it is impossible to rank them with absolute certainty.

Family history of colorectal cancer

Personal history of colorectal cancer

Familial adenomatous polyposis (FAP)

Lynch syndrome

Polyps in the colon and rectum

Rare genetic conditions

Not being physically active

Overweight or obesity

Alcohol

Smoking

Diet high in red meat

Processed meat

Diet low in fibre

Sedentary behaviour

Inflammatory bowel disease (IBD)

Diabetes

Ashkenazi Jewish ancestry

Personal history of breast, ovarian or uterine cancer

Tall adult height

Cooking meat at high temperatures

Exposure to ionizing radiation

There is convincing evidence that the following factors increase your risk for colorectal cancer.

A family history of colorectal cancer means that one or more close blood relatives have or had colorectal cancer. Some families have more cases of colorectal cancer than would be expected by chance. Sometimes it is not clear whether the family’s pattern of cancer is due to chance, shared lifestyle factors, an inherited (hereditary) factor that has been passed from parents to children through genes or a combination of these factors.

In families with colorectal cancer, the risk is increased if:

• A first-degree relative (such as a parent, sibling or child) has had colorectal cancer. The risk is greater if the first-degree relative had colon cancer than if the first-degree relative had rectal cancer.
• More than one first-degree relative has had colorectal cancer.
• Colorectal cancer was diagnosed in a family member under the age of 50.

If you have had colorectal cancer, you have a higher risk of developing a second colorectal cancer.

FAP is a rare, inherited condition usually caused by a mutation of the adenomatous polyposis coli (APC) gene. FAP causes hundreds to thousands of adenomatous polyps to develop on the inner lining (mucosa) of the colon and rectum. These polyps can develop as early as adolescence. If not treated, the majority of people with FAP will develop colorectal cancer by the age of 40.

Attenuated familial adenomatous polyposis (AFAP) is a subtype of FAP. People with AFAP have fewer adenomatous polyps in the colon than people with FAP, and these polyps tend to develop later in life. Colorectal cancer usually develops in people with AFAP at a later age.

Lynch syndrome (also called hereditary non-polyposis colorectal cancer, or HNPCC) is an inherited condition caused by mutations in the genes that correct mistakes when cells divide and DNA is copied. It causes polyps to develop in the lining of the colon, rectum or both, but not as many polyps as in FAP. Lynch syndrome may be suspected if a person in their mid-40s develops colorectal cancer or has relatives who developed colorectal cancer around that age.

Lynch syndrome can occur as 2 types:

• Type A (Lynch type 1) increases the risk of colorectal cancer only.
• Type B (Lynch type 2) increases the risk of colorectal cancer as well as cancers of the stomach, small intestine, pancreas, kidney, ureter, ovary, uterus, breast, bladder, bile duct and skin.

A personal or family history of polyps in the colon, rectum or both significantly increases the risk of developing colorectal cancer. Colorectal polyps usually start in the inner lining (mucosa) of the colon or rectum. Adenomas (adenomatous polyps) are polyps that have the potential to become cancer.

The risk of developing colorectal cancer from adenomatous polyps is related to the type, size and number of polyps:

• Tubular polyps are common but usually smaller and less likely to become cancerous. Villous polyps are less common but more likely to become cancerous.
• Polyps larger than 1 cm are more likely to be cancerous.
• The more polyps, the more chances that one of the polyps will become cancerous.

The following rare genetic conditions can increase the risk of developing colorectal cancer.

Turcot syndrome is a variant of both Lynch syndrome and FAP. People with Turcot syndrome develop many polyps in the colon that can become cancerous.

MYH-associated polyposis (MAP) is caused by a mutation in the MUTYH DNA repair gene. People with MAP develop many adenomatous polyps in the inner lining (mucosa) of the colon.

Juvenile polyposis syndrome is an inherited condition that causes polyps called hamartomas to develop. Hamartomas are usually non-cancerous, but they have the potential to develop into cancer.

Peutz-Jeghers syndrome is an inherited condition that involves a mutation of the STK11 gene. People with Peutz-Jeghers syndrome often develop hamartomas in the digestive tract. Peutz-Jeghers syndrome is also associated with a higher than average risk of developing other types of cancer, including breast, pancreatic, stomach, ovarian, lung and small intestine cancers.

Hereditary mixed polyposis syndrome (HMPS) is an inherited condition that causes many different types of polyps to grow. The most common type of polyp to grow is a hamartoma.

Cowden syndrome and Bannayan-Riley-Ruvalcaba syndrome are part of a group of disorders that have a mutation in the PTEN gene, which is usually a tumour suppressor gene. People with a PTEN mutation have a higher risk of developing non-cancerous and cancerous tumours, including colorectal cancer.

People who are not physically active have a higher risk for developing colorectal cancer.

Colorectal cancer occurs more often in people who are overweight or obese than in those who have a healthy weight. Having a higher body mass index (BMI) increases the risk in both men and women, although men seem to be most at risk.

Drinking alcohol increases your risk for developing colorectal cancer. Alcohol increases the risk for both men and women, but the effect appears to be stronger for men. The less alcohol you drink, the lower your cancer risk.

Find out more about how to limit alcohol.

Smoking tobacco increases the risk of developing colorectal cancer. It appears that the risk increases with both the length of time a person smokes and the amount smoked.

Eating a diet high in red meat (beef, pork, lamb and goat) increases the risk of developing colorectal cancer. The risk increases with the amount of red meat in a person’s diet.

Processed meats are meats preserved by smoking, curing, salting or adding preservatives such as nitrates or nitrites. Eating processed meats increases the risk of developing colorectal cancer, and the risk increases with the amount eaten.

Eating a diet low in fibre increases the risk of colorectal cancer. The evidence shows that eating foods containing dietary fibre protects against colorectal cancer.

Higher amounts of sedentary behaviour (sitting for long periods of time) are linked to a higher risk for colorectal cancer, particularly cancer in the distal colon and rectum.

IBD is a disease in which the lining of the digestive tract becomes inflamed, causing sores and bleeding. Ulcerative colitis and Crohn’s disease are the 2 most common types of IBD. Ulcerative colitis increases the risk for colorectal cancer more than Crohn’s disease. The risk increases with the length of time you have IBD and how much of the colon is affected by IBD.

People who have type 2 diabetes have higher rates of colorectal cancer. There is an association because 2 of the risk factors for developing diabetes – physical inactivity and overweight or obesity – are also risk factors for colorectal cancer.

Jewish people of Eastern European descent (Ashkenazi Jews) have a higher than average risk of developing colorectal cancer. This group tends to have a specific mutation in the APC gene that increases the risk. This genetic mutation isn’t common among other ethnic groups.

Women who have had breast, ovarian or uterine cancer have a greater chance of developing colorectal cancer. This higher risk may be due to common risk factors including Peutz-Jeghers syndrome, Ashkenazi Jewish ancestry, Lynch syndrome or some other genetic syndromes.

Several studies show that being tall is a risk factor for colon cancer, but probably not for rectal cancer. Researchers think this higher risk may be due to the influence of growth and puberty hormones.

Cooking meat (including beef, pork and poultry) and fish at high temperatures (such as well done, fried, broiled or barbecued) creates chemicals called heterocyclic amines (HCAs). Some HCAs are associated with a higher risk of developing colorectal cancer.

Fat from meat, poultry or fish dripping onto hot coals or stones creates other potentially cancer-causing substances called polycyclic aromatic hydrocarbons (PAHs). PAHs are added to food by smoke and flare-ups. Some PAHs are linked with a higher risk of developing colorectal cancer.

People who have been exposed to ionizing radiation, such as during atomic bomb explosions in Japan, have a higher risk of developing colorectal cancer, mainly colon cancer. People who have been treated with radiation therapy for a previous cancer are at greater risk for colorectal cancer.

The following factors have been linked with colorectal cancer, but there is not enough evidence to show for sure that they are risk factors. More research is needed to clarify the role of these factors for colorectal cancer.

Asbestos is a group of minerals that occur naturally. Asbestos has been widely used in building materials and many industries. It is known to cause cancer in people. Long-term and frequent exposure to asbestos might cause colorectal cancer.

Cystic fibrosis is a genetic condition that affects glands that make mucus and sweat, which can affect how well the lungs and digestive tract function. A large study that followed people with cystic fibrosis for 20 years showed that they may have an increased risk of developing colorectal cancer.

Significant research shows that there is no link between laxatives and a higher risk for colorectal cancer.

To make the decisions that are right for you, ask your healthcare team questions about risks.