What are the risk factors for colorectal cancer?

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 at least 50 years old.

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

Some people (about 5% to 10%) who get colorectal cancer have gene changes (mutations) that cause the disease that are inherited (passed on by a parent). Often, these changes lead to cancer that occurs at a younger age than is common. They may also lead to a high risk of cancers other than colorectal cancer. It is important to find families with these gene changes because it lets doctors recommend certain steps, such as screening at a younger age and other preventive measures.

It's important to check your family medical history not just for colon cancer and polyps, but also for any other type of cancer linked to these changes. While cancer in close (first-degree) relatives is of most concern, any history of cancer in more distant relatives is also important. This includes aunts, uncles, grandparents, nieces, nephews, and cousins. People who know they have a family history of cancer or colorectal polyps should discuss this history with their doctor.

They might want to look into genetic counseling to review their family medical tree to see how likely it is that their family is affected by one of these gene change. If so, they can discuss whether or not gene testing is right for them. People who have an abnormal gene can take steps to prevent colon cancer, such as getting screened at an early age.

The 2 most common inherited syndromes linked with colorectal cancers are familial adenomatous polyposis (FAP) and hereditary non-polyposis colorectal cancer (HNPCC). These are both most often caused by a gene change inherited from a parent.

Familial adenomatous polyposis (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. About 1% of all colorectal cancers are due to FAP.

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 the 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.

Type 2 diabetes

People with type 2 (most often non-insulin dependent) diabetes have an increased risk of getting colorectal cancer. Both type 2 diabetes and colorectal cancer share some of the same risk factors (such as excess weight). But even after taking these factors into account, people with type 2 diabetes still have an increased risk. They also tend to have a less good outlook after diagnosis.

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.