Colon cancer (also called bowel cancer) is cancer of the large intestine, or colon. Cancer of the last 6 inches of the colon is referred to as rectal cancer. Together, they are often referred to as colorectal cancer.
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%.
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 (~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 Scan does not identify such rare and highly familial cancer genes, including APC, MLH1, MSH2, MSH6, and PMS2.
To date, six common genetic variants have been found that increase the risk of developing colorectal cancer. These variants are located in the SMAD7 gene on chromosome 18, in the CRAC1 gene on chromosome 15, 2 variants on chromosome 8 (one in the EIF3H gene and the other close to POU5F1P1) and variants on chromosomes 10 and 11.
The deCODEme Genetic Scan identifies the six variants listed above and provides interpretation of the associated risk of development of colorectal cancer in individuals of European descent. For individuals of East Asian origin, the deCODEme Genetic Scan provides interpretation of colorectal cancer risk associated with two variants; on chromosome 8 (close to POU5F1P1) and a variant in the SMAD7 gene on chromosome 18. At the present time data is not available to support risk asessments for individuals of other ethnicities for the variants listed above.
risk factors
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.
prevention and treatment
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.
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:
- Yearly fecal occult blood test (FOBT) or fecal immunochemical test (FIT).
- Flexible sigmoidoscopy every 5 years.
- Yearly FOBT or FIT, plus flexible sigmoidoscopy every 5 years.
- Double-contrast barium enema every 5 years.
- 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
You can find more information about colorectal cancer by talking with your doctor and visiting these Web sites:
American Cancer Society
Cancer Help UK
Centers for Disease Control and Prevention
Medline Plus Article on Colorectal Cancer
National Cancer Institute
OncoLink