Even though we do not know the exact cause of most colorectal cancers, it is possible to prevent many colorectal cancers.

Screening

Regular colorectal cancer screening or testing is one of the most powerful weapons for preventing colorectal cancer. Screening is the process of looking for cancer in people who have no symptoms of the disease.

From the time the first abnormal cells start to grow into polyps, it usually takes about 10 to 15 years for them to develop into colorectal cancer. Regular screening can, in many cases, prevent colorectal cancer altogether. This is because some polyps, or growths, can be found and removed before they have the chance to turn into cancer. Screening can also result in finding colorectal cancer early, when it is highly curable.

People who have no identified risk factors (other than age) should begin regular screening at age 50. Those who have a family history or other risk factors for colorectal polyps or cancer, such as inflammatory bowel disease, should talk with their doctor about starting screening at a younger age and/or getting screened more frequently. (See the American Cancer Society screening guidelines in the next section, "Can colorectal polyps and cancer be found early?")

Genetic testing, screening, and treatment for those with a strong family history

People with a strong family history of colorectal polyps or cancer should consider genetic counseling to review their family medical tree and determine whether genetic testing may be right for them. If needed, this can help them decide about getting screened and treated at an early age.

Before getting genetic testing, it's important to know ahead of time what the results may or may not tell you about your risk. Genetic testing is not perfect, and in some cases the tests may not be able to provide solid answers. This is why meeting with a genetic counselor before testing is crucial in deciding whether or not testing should be done.

Genetic tests can help determine if members of certain families have inherited a high risk for developing colorectal cancer due to syndromes such as familial adenomatous polyposis (FAP) or hereditary non-polyposis colorectal cancer (HNPCC). Without genetic testing, all members of a family known to have an inherited form of colorectal cancer should be screened early and frequently. If genetic testing is done for a known mutation within a family, those members who are found not to have inherited the mutated gene may be able to be screened with the same frequency as people at average risk.

When looking at whether testing might be appropriate, a genetic counselor will try to get a detailed view of your family history. For example, doctors have found that many families with HNPCC tend to have certain characteristics:

• at least 3 relatives have colorectal cancer
• one should be a first-degree relative (parent, sibling, or child) of the other 2 relatives
• at least 2 successive generations are involved
• at least 1 relative had their cancer when they were younger than age 50

These are called the Amsterdam criteria. If these hold true for your family, then you might want to seek genetic counseling. But even if your family history satisfies the Amsterdam criteria, it doesn't always mean you have HNPCC. Only about half of families who meet the Amsterdam criteria have HNPCC. The other half do not, and although their colorectal cancer rate is about twice as high as normal, it is not as high as that of people with HNPCC. On the other hand, many families with HNPCC do not meet the Amsterdam criteria.

A second set of criteria, called the revised Bethesda guidelines, are used to determine whether a person with colorectal cancer should have his or her cancer tested for genetic changes that are seen with HNPCC. These criteria include at least one of the following:

• The person is younger than 50 years.

• The person has or had a second colorectal cancer or another cancer (endometrial, stomach, pancreas, small intestine, ovary, kidney, ureters, or bile duct) that is associated with HNPCC.

• The person is younger than 60 years and the cancer has certain characteristics seen with HNPCC when viewed under the microscope or with other lab tests.

• The person has a first-degree relative younger than 50 who was diagnosed with colorectal cancer or another cancer often seen in HNPCC carriers (endometrial, stomach, pancreas, small intestine, ovary, kidney, ureters, or bile duct).

• The person has 2 or more first- or second-degree relatives who had colorectal cancer or an HNPCC-related cancer at any age.

If a person with colorectal cancer has any of the Bethesda criteria, genetic testing is advised to look for an inherited HNPCC-associated gene mutation. Still, most people who meet the Bethesda criteria do not have HNPCC.

Not all families with HNPCC meet any of the criteria listed. Doctors should be suspicious of HNPCC in families with colorectal cancer and other cancers associated with this syndrome, including endometrial cancer, ovarian cancer, stomach cancer, small bowel cancer, pancreas cancer, bile duct cancer, or cancer of the lining of the kidney or the ureters.

The lifetime risk of developing colorectal cancer for people with HNPCC may be as high as 80%. In families known to carry an HNPCC gene mutation, doctors recommend that family members who have tested positive for the mutation and those who have not been tested should start colonoscopy screening during their early 20s to remove any polyps and find any cancers at the earliest possible stage (see the section, "Can colorectal polyps or cancer be found early?"). People known to carry one of the gene mutations may also be offered the option of removal of most of the colon.

Genetic counseling and testing is also available for those at risk of FAP. Their lifetime risk of developing colorectal cancer is near 100%, and in most cases it develops before the age of 40. People who test positive for the gene change linked to FAP should start colonoscopy during their teens (see the section, "Can colorectal polyps or cancer be found early?"). Most doctors recommend they have their colon removed when they are in their 20s to prevent cancer from developing.

Diet, exercise, and body weight

People can lower their risk of developing colorectal cancer by managing the risk factors that they can control, such as diet and physical activity.

Diets high in vegetables and fruits have been linked with lower risk of colon cancer. Diets high in processed and/or red meats have been linked with a higher risk. The American Cancer Society recommends that you eat a healthy diet, with an emphasis on plant sources. This includes the following:

• Choose foods and beverages in amounts that help achieve and maintain a healthy weight.
• Eat 5 or more servings of a variety of vegetables and fruits each day.
• Choose whole grains rather than processed (refined) grains.
• Limit your intake of processed and red meats.

Avoiding excessive alcohol intake may also help lower your risk of colorectal cancer. The American Cancer Society recommends no more than 1 drink per day for women or 2 per day for men.

Physical activity is another area that people can control. The American Cancer Society recommends at least 30 minutes, preferably 45 to 60 minutes, of physical activity on 5 or more days of the week. Taking part in moderate or vigorous activity for at least 45 minutes on 5 or more days of the week may lower your risk for colorectal cancer even more.

Obesity raises the risk of colon cancer in both men and women, but the link seems to be stronger in men. The American Cancer Society recommends that people try to maintain a healthy weight throughout life by balancing what they eat with physical activity. If you are overweight, you can ask your doctor about a weight loss plan that will work for you.

For more information about diet and physical activity, refer to the separate document, American Cancer Society Guidelines for Nutrition and Physical Activity for Cancer Prevention.

Vitamins, calcium, and magnesium

Some studies suggest that taking a daily multi-vitamin containing folic acid, or folate, may lower colorectal cancer risk, but not all studies have found this. More research is needed in this area.

Some studies have suggested that vitamin D, which you can get from sun exposure, in certain foods, or in a vitamin pill, can lower colorectal cancer risk. Because of concerns that excessive sun exposure can cause skin cancer, most experts do not recommend this as a way to lower colorectal cancer risk at this time.

Other studies suggest that increasing calcium intake may lower colorectal cancer risk. Calcium is important for a number of health reasons aside from possible effects on cancer risk. However, because of the possible increased risk of prostate cancer with high calcium intake, it may be wise for men to limit their daily calcium intake to less than 1,500 mg per day until further studies are done.

Calcium and vitamin D may work together to reduce colorectal cancer risk, as vitamin D aids in the body's absorption of calcium. Still, not all studies have found that supplements of these nutrients reduce risk.

A few studies have looked at a possible link between a diet high in magnesium and reduced colorectal cancer risk. Some, but not all, of these studies have found a link, especially among women. More research is needed to determine if this link exists.

Non-steroidal anti-inflammatory drugs

Many studies have found that people who regularly use aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen (Motrin, Advil) and naproxen (Aleve), have a lower risk of colorectal cancer and adenomatous polyps. Most of these studies looked at people who took these medicines for reasons such as to treat arthritis or prevent heart attacks. Other, stronger studies have provided evidence that aspirin can prevent the growth of polyps in people who were previously treated for early stages of colorectal cancer or who previously had polyps removed.

But NSAIDs can cause serious or even life-threatening side effects such as bleeding from stomach irritation, which may outweigh the benefits of these medicines for the general public. For this reason, experts do not recommend NSAIDs as a cancer prevention strategy for people at average risk of developing colorectal cancer.

The value of these drugs for people at increased colorectal cancer risk is being actively studied. Celecoxib (Celebrex) has been approved by the US Food and Drug Administration for reducing polyp formation in people with familial adenomatous polyposis (FAP). This drug may cause less bleeding in the stomach than other NSAIDs, but it may increase the risk of heart attacks and strokes. A similar drug, rofecoxib (Vioxx), was taken off the market because too many people who took it had heart attacks and strokes.

Because aspirin or other NSAIDs can have serious side effects, check with your doctor before starting to take any of them on a regular basis.

Female hormones

Hormone replacement therapy (HRT) consisting of estrogen and progesterone may reduce the risk of developing colorectal cancer in postmenopausal women, although cancers found in women on HRT may be at a more advanced stage. HRT also lowers the risk of developing osteoporosis (bone thinning). But it can also increase some risks, including those of heart disease, blood clots, and breast and uterine cancers.

The decision whether or not to use HRT should be based on a careful discussion of the possible benefits and risks with your doctor.

Some studies have found that the use of oral contraceptives (birth control pills) may lower the risk of colorectal cancer in women. More research is needed to confirm this link.

Last Medical Review: 05/18/2009
Last Revised: 05/18/2009