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While smoking, obesity, and a diet poor in fruits and vegetables play a contributory role to the development of colorectal cancer, it has been estimated that up to 30% may be due to genetic factors.

Avoiding smoking, and maintaining a regular exercise program and a healthy diet may prevent or delay the development of colorectal cancer.

It has been estimated that up to 30% of colorectal cancers may be due to genetic factors

A common cancer among men and women

Colorectal cancer is the fourth most common cancer in males and females in the Unites States and worldwide, and it is the second leading cause of cancer death in the US. The average risk that an individual in the US will develop colorectal cancer in their lifetime is 6%.

Up to 30% of cases may be due to genetic factors

Individuals with a first-degree relative (sibling, parent, or child) with colorectal cancer are twice as likely to develop the disease as the general population. The risk is greater if a relative is diagnosed at an early age (younger than 60 years) or if more than one relative has been diagnosed with the disease. It has been estimated that up to 30% of colorectal cancers may be due to genetic factors.

A fraction of cases are due to rare genetic mutations

A fraction (~5%) of colorectal cancer cases occur in families with multiple cases of the disease. An example of such a condition is multiple polyposis of the colon, where the inner surface of the colon is covered with thousands of polyps. In some instances, these cases are known to be caused by specific mutations in genes that substantially increase the risk of the disease. Individuals belonging to such families should seek counselling about preventive measures.

Please note that the deCODEme genetic scans do not identify such rare and highly familial cancer genes, including APC, MLH1, MSH2, MSH6, and PMS2.

Common genetic variants are associated with colorectal cancer risk

Several genetic variants have been identified that increase the risk of developing colorectal cancer. The number of variants included in the deCODEme Genetic Scan for each ethnic group are listed in the table below. These variants are used to provide our customers with a personalized interpretation of their genetic risk for developing colorectal cancer. See what your genetic test results could look like

	Number of Variants Measured
European ancestry	8
East Asian ancestry	2

At present, the necessary scientific information to interpret the genetic risk for individuals of other ethnicities is not available. This information will be added as soon as it becomes available and we are assured of its quality.

Are you at risk for colorectal cancer?

Some people are more likely to develop colorectal cancer than others. The major risk factors are:

• Age: More than 90 percent of patients are diagnosed over the age of 50.
• Polyps: Colorectal tumors often arise from polyps in the colon. Such polyps are common in people over 50 but only some polyps will become cancerous.
• Chronic inflammatory diseases of the bowel: Individuals with ulcerative colitis or Crohn’s disease have an increased risk of developing colorectal cancer.
• Diet and lifestyle: Some studies suggest that high-fat diets with low levels of fiber, calcium, and folate may increase the risk of colorectal cancer. It has also been suggested that people with diets poor in fruit and vegetables, those who smoke, and those who are obese may have an increased risk of the disease.
• Genetics: Individuals with a first-degree relative (sibling, parent, or child) with colorectal cancer are twice as likely to develop the disease as the general population. The risk is greater if a relative is diagnosed at an early age (younger than 60 years) or if more than one relative has been diagnosed with the disease. It has been estimated that up to 30% of colorectal cancers may be due to genetic factors.

Some risk factors can be avoided

Some risk factors for developing colorectal cancer can be avoided, others cannot. Avoiding the controllable risk factors, like smoking, and maintaining a regular exercise program and a healthy diet may prevent or delay the development of some types of cancer.

Screening guidelines for colorectal cancer

If abnormal tissue, polyps, or colorectal cancer are caught early, there is a higher chance of preventing development of disease or curing the disease while it is in its early stages. For this reason, the American Cancer Society recommends that, beginning at age 50, all individuals should follow 1 of 5 testing schedules:

1. Yearly fecal occult blood test (FOBT) or fecal immunochemical test (FIT).
2. Flexible sigmoidoscopy every 5 years.
3. Yearly FOBT or FIT, plus flexible sigmoidoscopy every 5 years.
4. Double-contrast barium enema every 5 years.
5. Colonoscopy every 10 years.

Positive tests should be followed-up with a colonoscopy. Furthermore, people who have been diagnosed with inflammatory bowel disease or have a strong family history of colorectal cancer should talk to their doctor about starting colorectal cancer screening earlier and/or undergoing screening more often. The prognosis is strongly associated with how advanced the disease is at diagnosis; if the cancer is caught early, cure rates are high. Therefore, colorectal cancer screening presents an opportunity for early cancer detection and cancer prevention.

More information on colorectal cancer

You can find more information about colorectal cancer by talking with your doctor and visiting these Web sites:

• American Cancer Society on Colorectal Cancer
• Cancer Help UK
• Cancer symptoms from Caring.com – Helping you help your parents
• Centers for Disease Control and Prevention
• Medline Plus Article on Colorectal Cancer
• National Cancer Institute
• OncoLink

This content was last reviewed on February 15, 2012.

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