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, does not mean that you will get the disease. And some people who get colorectal cancer 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 played in the development of the disease.
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
Inflammatory bowel diseases, like ulcerative colitis and Crohn's disease, increase the risk of colon cancer. In these diseases, the colon is inflamed over a long time. If you have one 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 increase colorectal cancer risk.)
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 at a younger age. 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).
Familial adenomatous polyposis (FAP): FAP is caused by changes (mutations) a gene that a person inherits from his or her parents. About 1% of all colorectal cancers are due to FAP.
People with FAP typically get hundreds or thousands of polyps in their colon and rectum, most often in their teens or as early adults. Cancer often starts in one or more of these polyps as early as age 20. By age 40, almost all people with this disorder will have cancer if surgery to remove the colon is not done.
Hereditary non-polyposis colon cancer (HNPCC): HNPCC (also known as Lynch syndrome) accounts for about 3% to 5% of all colorectal cancers. It can be caused by inherited changes in a number of different genes that normally help repair DNA damage.
The cancers that occur as a part of this syndrome also happen when people are fairly young. People with HNPCC may also have polyps, but they only have a few, not hundreds as in FAP. The lifetime risk of colorectal cancer in people with this condition may be as high as 80%. Women with this condition also have a very high risk of getting cancer of lining of the uterus. Other cancers are also linked with 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 most likely need to begin colon cancer testing at a younger age, and you might want to think 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
Some 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 (like 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, fruits, and whole grains have been linked with a lower risk of colorectal cancer, but fiber supplements do not seem to help.
Lack of exercise
Getting more exercise may help reduce your risk.
Being overweight
Being very overweight (or obese) 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 get colorectal cancer. Smoking also increases the risk of many other cancers.
Alcohol use
Heavy use of alcohol has been linked to colorectal cancer. Men should limit their use to no more than 2 drinks a day and women no more than one.
Type 2 diabetes
People with type 2 diabetes have an increased chance of getting colorectal cancer. They also tend to have a worse outlook (prognosis).
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.
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