While we do not know the exact cause of most colorectal cancers, there are certain known risk factors. A risk factor is something that affects a person's chance of getting a disease. Some risk factors, like smoking, can be controlled. Others, such as a person's age, can't be changed. But risk factors don't tell us everything. Having a risk factor, or even several risk factors, does not mean that you will get the disease. And some people who get the disease may not have any known risk factors. Even if a person with colorectal cancer has a risk factor, it is often very hard to know what part that risk factor may have contributed to the cancer.

Researchers have found some risk factors that may increase a person's chance of getting polyps or colorectal cancer.

Risk factors you cannot change

Age: The chances of having colorectal cancer go up after age 50. More than 9 out of 10 people with colorectal cancer are older than 50.

Having had polyps or colorectal cancer before: Some types of polyps increase the risk of colorectal cancer, especially if they are large or if there are many of them. If you have had colorectal cancer (even if it has been completely removed), you are more likely to have new cancers start in other areas of your colon and rectum. The chances of this happening are greater if you had your first colorectal cancer when you were younger.

Having a history of bowel disease: Two bowel diseases, called ulcerative colitis and Crohn's disease, increase the risk of colon cancer. In these diseases, the colon is inflamed over a long period of time. If you have either of these diseases your doctor may want you to have colon screening testing more often. (These diseases are different than irritable bowel syndrome (IBS), which does not carry an increased risk for colorectal cancer.)

Family history of colorectal cancer: If you have close relatives (parents, brothers/sisters, or children) who have had this cancer, your risk might be increased. This is especially true if the family member got the cancer before age 60. People with a family history of colorectal cancer should talk to their doctors about when and how often to have screening tests.

Certain family syndromes: A syndrome is a group of symptoms. The 2 most common inherited syndromes linked with colorectal cancers are familial adenomatous polyposis (FAP) and hereditary non-polyposis colorectal cancer (HNPCC).

If your doctor tells you that you have a condition that makes you or your family members more likely to get colorectal cancer, you will probably need to begin colon cancer testing at a younger age, and you might want to talk about genetic counseling.

Race or ethnic background: Some racial and ethnic groups such as African Americans and Jews of Eastern European descent (Ashkenazi Jews) have a higher colorectal cancer risk. Among Ashkenazi Jews, several gene mutations have been found that lead to an increased risk of colorectal cancer.

Risk factors linked to things you do

Several lifestyle-related factors have been linked to colorectal cancer. In fact, the links between diet, weight, and exercise and colorectal cancer risk are some of the strongest for any type of cancer.

Certain types of diets: A diet that is high in red meats (beef, lamb, or liver) and processed meats such as hot dogs, bologna, and lunch meat can increase your colorectal cancer risk. Cooking meats at very high heat (frying, broiling, or grilling) can create chemicals that might increase cancer risk. Diets high in vegetables and fruits have been linked with a lower risk of colorectal cancer.

Lack of exercise: Getting more exercise may help reduce your risk.

Overweight: Being very overweight increases a person's risk of having and dying from colorectal cancer.

Smoking: Most people know that smoking causes lung cancer, but long-time smokers are more likely than non-smokers to have and die from colorectal cancer. Smoking increases the risk of many other cancers, too.

Alcohol: Heavy use of alcohol has been linked to colorectal cancer.

Diabetes: People with type 2 diabetes have an increased chance of getting colorectal cancer. They also tend to have a worse outlook (prognosis).

Risk factors that are less certain

Night-shift work: One study suggested that working a night shift at least 3 nights a month for at least 15 years might increase the risk of colorectal cancer in women. More research is needed to check out this finding.

Other cancers and their treatment: A recent report on testicular cancer survivors found that these men had a higher rate of colorectal cancer. Men who get radiation therapy for prostate cancer have been reported to have a higher risk of rectal cancer, too.

The American Cancer Society and several other medical organizations recommend earlier testing for people with increased colorectal cancer risk. These recommendations differ from those for people at average risk. For more information, talk with your doctor.

Last Medical Review: 03/05/2008
Last Revised: 05/07/2009