Screening for Colorectal Cancer: Recommendation and Rationale

Summary of the Recommendation

The U.S. Preventive Services Task Force (USPSTF) strongly recommends that clinicians screen all men and women 50 years of age or older for colorectal cancer. This is a grade A recommendation. (See Appendix Table 1 for a description of the USPSTF classification of recommendations.)

The USPSTF found fair to good evidence that several screening methods are effective in reducing mortality from colorectal cancer. The USPSTF concluded that the benefits from screening substantially outweigh potential harms, but the quality of evidence, magnitude of benefit, and potential harms vary with each method.

The USPSTF found good evidence that periodic fecal occult blood testing (FOBT) reduces mortality from colorectal cancer and fair evidence that sigmoidoscopy alone or in combination with FOBT reduces mortality. The USPSTF did not find direct evidence that screening colonoscopy is effective in reducing colorectal cancer mortality rates; efficacy of colonoscopy is supported by its integral role in trials of FOBT, extrapolation from sigmoidoscopy studies, limited case–control evidence, and the ability of colonoscopy to inspect the proximal colon. Double-contrast barium enema offers an alternative means of whole-bowel examination, but it is less sensitive than colonoscopy and there is no direct evidence that it is effective in reducing mortality rates. The USPSTF found insufficient evidence that newer screening techniques (for example, computed tomographic colography) are effective in improving health outcomes. (See Appendix Table 2 for a description of the USPSTF classification of levels of evidence.)

There are insufficient data to determine which screening strategy is best in terms of the balance of benefits and potential harms or cost-effectiveness. Studies reviewed by the USPSTF indicate that colorectal cancer screening is likely to be cost-effective (<$30 000 per additional year of life gained) regardless of the strategy chosen.

It is unclear whether the increased accuracy of colonoscopy compared with alternative screening methods (for example, the identification of lesions that FOBT and flexible sigmoidoscopy would not detect) offsets the procedure's additional complications, inconvenience, and costs.

Clinical Considerations

Potential screening options for colorectal cancer include home FOBT, flexible sigmoidoscopy, the combination of home FOBT and flexible sigmoidoscopy, colonoscopy, and double-contrast barium enema. Each option has advantages and disadvantages that may vary for individual patients and practice settings. The choice of specific screening strategy should be based on patient preferences, medical contraindications, patient adherence, and available resources for testing and follow-up. Clinicians should talk to patients about the benefits and potential harms associated with each option before selecting a screening strategy.

The optimal interval for screening depends on the test. Annual FOBT offers greater reductions in mortality rates than biennial screening but produces more false-positive results. A 10-year interval has been recommended for colonoscopy on the basis of evidence regarding the natural history of adenomatous polyps. Shorter intervals (5 years) have been recommended for flexible sigmoidoscopy and double-contrast barium enema because of the lower sensitivity of these methods, but there is no direct evidence with which to determine the optimal interval for tests other than FOBT. Case–control studies have suggested that sigmoidoscopy every 10 years may be as effective as sigmoidoscopy performed at shorter intervals.

The USPSTF recommends initiating screening at 50 years of age for men and women at average risk for colorectal cancer, based on the incidence of cancer above this age in the general population. In persons at higher risk (for example, those with a first-degree relative who receives a diagnosis of colorectal cancer before 60 years of age), initiating screening at an earlier age is reasonable.

Expert guidelines exist for screening very high-risk patients, including those with a history suggestive of familial polyposis or hereditary nonpolyposis colorectal cancer or those with a personal history of ulcerative colitis (1). Early screening with colonoscopy may be appropriate, and genetic counseling or testing may be indicated for patients with genetic syndromes.

The appropriate age at which colorectal cancer screening should be discontinued is not known. Screening studies have generally been restricted to patients younger than 80 years of age, with colorectal cancer mortality rates beginning to decrease within 5 years of initiating screening. Yield of screening should increase in older persons (because of higher incidence of colorectal cancer), but benefits may be limited as a result of competing causes of death. Discontinuing screening is therefore reasonable in patients whose age or comorbid conditions limit life expectancy.

Proven methods of FOBT screening use guaiac-based test cards that patients prepare at home from three consecutive stool samples and forward to the clinician. Whether patients need to restrict their diet and avoid certain medications is not established. Rehydration of the specimens before testing increases the sensitivity of FOBT but substantially increases the number of false-positive results. Neither digital rectal examination nor the testing of a single stool specimen obtained during digital rectal examination is recommended as an adequate screening strategy for colorectal cancer.

The combination of FOBT and sigmoidoscopy may detect more cases of cancer and more large polyps than either test alone, but the additional benefits and potential harms of combining the two tests are uncertain. In general, FOBT should precede sigmoidoscopy because a positive result is an indication for colonoscopy, obviating the need for sigmoidoscopy.

Colonoscopy is the most sensitive and specific test for detecting cancer and large polyps but is associated with higher risks than other screening tests for colorectal cancer. These include a small risk for bleeding and risk for perforation, primarily associated with removal of polyps or with biopsies performed during screening. Colonoscopy also usually requires more highly trained personnel, overnight bowel preparation, sedation, and longer recovery time (which may necessitate transportation for the patient). It is not certain whether the potential added benefits of colonoscopy relative to screening alternatives are large enough to justify the added risks and inconvenience for all patients.

Initial costs of colonoscopy are higher than the costs of other tests. Estimates of cost-effectiveness, however, suggest that, from a societal perspective, compared with no screening, all methods of screening for colorectal cancer are likely to be as cost-effective as other clinical preventive services—less than $30 000 per additional year of life gained. The brief review of the evidence that is normally included in USPSTF recommendations is available in the complete Recommendation and Rationale statement on the USPSTF Web site (http://www.preventiveservices.ahrq.gov).

Recommendations of Others

The American Cancer Society recommends screening people at average risk for colorectal cancer beginning at 50 years of age by 1) FOBT annually, 2) flexible sigmoidoscopy every 5 years, 3) annual FOBT plus flexible sigmoidoscopy every 5 years, 4) double-contrast barium enema every 5 years, or 5) colonoscopy every 10 years (2). The American Cancer Society does not recommend digital rectal examination as a stand-alone screening test for colorectal cancer. Similar recommendations are issued by the American College of Surgeons, the American College of Obstetricians and Gynecologists, and the American Academy of Family Physicians (3-5). The American Gastroenterological Association, as part of a consortium of related professional organizations, also issues similar recommendations, which are currently being updated (1). The American College of Physicians–American Society of Internal Medicine does not have current guidelines on screening. The Canadian Task Force on Preventive Health Care concludes that there is good evidence to recommend annual or biennial FOBT and fair evidence to recommend sigmoidoscopy as part of the periodic health examination in average-risk adults after 50 years of age; evidence is insufficient to recommend for or against colonoscopy or combined FOBT and sigmoidoscopy (6).