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Colorectal cancer (CRC) is the second leading cause of cancer death in America. Approximately 130,000 Americans are diagnosed each year and 55,000 die annually. Without preventive action, about 6% of Americans will develop CRC sometime in their lives. The genetic events leading to CRC are rapidly becoming understood. Benign polyps (adenomas) are clearly the precursor lesion of almost all colon and rectal cancers, and adenomas are usually present for several years before they develop into cancer. The same methods used to detect CRC at an early curable stage can be used to find and remove adenomatous polyps, and therefore actually prevent cancer.
The following guidelines were developed and published in 1997 by the American Cancer Society and endorsed by the American Gastroenterological Association, the American Society for Colon and Rectal Surgeons, and the American College of Gastroenterology. Please keep in mind the fact that these guidelines were developed as recommendations for general public policy based, in part, upon cost/benefit analysis. Some individuals may be best served by a different approach, and some don’t fit neatly into one of the defined categories. Therefore each individual should discuss these guidelines with his or her physician to determine the best approach based on each individual health situation.
Persons at Average Risk
Approximately 70 – 80% of all CRC occur in people at "average" risk. This category includes all individuals without any of the risk factors outlined below. Basically, it includes all individuals without known gastrointestinal problems or family history of colon cancer. In this group, screening should begin at about age 50 with:
- Annual fecal occult blood testing and flexible sigmoidoscopy every 5 years, or
- Examination of the entire colon by colonoscopy every 10 years or barium enema every 5 years.
Examination of the entire colon offers more protection but is more costly and inconvenient.
Persons at Moderate Risk
Approximately 15 – 20% of CRC occur in people at moderate risk. This category includes people with one of the following:
- 1st degree relative with CRC acquired below age 60
- 2 relatives with CRC at any age
- prior colon adenomas or cancer
- history of breast or endometrial cancer
- Peutz-Jeghers syndrome
These people should have complete screening of the colon with either colonoscopy or combination sigmoidoscopy plus barium enema at diagnosis, 1 to 3 years after removal of a polyp or cancer, and every 5 years thereafter.
Persons at High Risk
Hereditary Nonpolyposis Colon Cancer (HNPCC): This is classically defined by 3 or more family members with colon cancer, across generations, at least two of whom are first degree relatives, with at least one cancer occurring below age 50. However, other variants of this pedigree exist. Individuals with genetic mutations that lead to HNPCC are also at increased risk for cancer of the ovary, uterus, ureter, pancreas, and stomach. These individuals should have screening colonoscopy every 1 to 2 years, as well as periodic screening for uterine and ovarian tumors. Treatment with nonsteroidal anti-inflammatory drugs (NSAIDs) may be considered. Refer to "Role of Medical Therapy" below. For more information about HNPCC see web site for the International Collaborative Group on HNPCC.
Longstanding Ulcerative Colitis or Crohn’s Colitis: Individuals with longstanding ulcerative colitis should have screening colonoscopy and biopsy every 1 to 2 years. For more information, please refer to patient information "Ulcerative Colitis" and "Crohn’s Disease" at this web site.
Familial Adenomatous Polyposis (FAP): This is a genetic condition that afflicts 1 in 10,000 people. People with this condition develop hundreds of polyps and will almost certainly develop CRC unless the colon is removed. Colectomy should be done after puberty. Refer to "Role of Genetic Testing" below.
Role of Medical Therapy
Epidemiologic studies suggest that longterm use of anti-inflammatory drugs such as aspirin are associated with reduced incidence of colon cancer. There is accumulating evidence that the newer anti-inflammatory drugs such as Celebrex (cox – 2 inhibitors), which have fewer side effects, may have a more specific effect at inhibiting the development of colon polyps and cancer. The optimal age to start NSAIDs, the effective dose, and the best NSAID are unknown. In addition, the risks of NSAIDs and cost-effectiveness of a chemoprevention program must be considered. It is important to keep in mind that these drugs have side effects, and, in individuals with a low risk of cancer, it is not clear that the benefit outweighs the risk. Therefore, NSAIDs are not presently recommended solely for the prevention of colon cancer. However, persons with HNPCC may be the most likely to receive benefit. The results of clinical trials on this subject are awaited.
Role of Diet
Western diets, which are relatively high in fat and low in fiber compared to diets in the third world, seem to be associated with an increased risk of colon cancer. However, the exact relationship between diet and cancer is not known. If there are elements of diet that increase the risk of cancer, it may take decades for the damage to take place. There are good reasons for most Americans to increase fiber intake and reduce fat, but there are better ways to protect oneself against colon cancer.
Role of Genetic Testing
An asymptomatic member of an HNPCC family has a 50% chance of inheriting the gene from an affected parent. Detection of a mutation in an affected individual permits genetic testing of other family members. However, a negative test in a family member does not exclude the possibility of an inherited genetic defect. Therefore, in most circumstances, the result of genetic testing does not change the screening recommendations.
The specific gene that causes FAP has been identified. About 1/3 of affected individuals have no family history and therefore represent new mutations. If the mutant gene in an affected family member can be found, then other family members should be tested. |
