Putting Prevention into Practice

An Evidence-Based Approach

Screening for Colorectal Cancer


Am Fam Physician. 2010 Apr 15;81(8):1017-1018.

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Case Study

N.P., a 51-year-old man, comes to your office because one of his friends was recently diagnosed with colorectal cancer. He is wondering whether he should be screened too. He has no family history of cancer and no gastrointestinal symptoms. You explain to N.P. that he should be screened for colorectal cancer.

Case Study Questions

  1. Which one of the following is the most appropriate colorectal cancer screening test (or combination of tests) and corresponding testing interval?

    • A. Colonoscopy every five years.

    • B. Computed tomographic (CT) colonography every 10 years.

    • C. High-sensitivity fecal occult blood test (FOBT) every two years.

    • D. Sigmoidoscopy every five years with high-sensitivity FOBT every three years.

    • E. Sigmoidoscopy every five years.

  2. N.P. asks for help choosing a screening method. Which of the following responses would be appropriate?

    • A. Tell him that colonoscopy is the best screening method because of its effectiveness in reducing mortality.

    • B. Explain the risks and benefits of various screening methods and elicit his preference.

    • C. Explain that the risks of colonoscopy can be avoided with sigmoidoscopy or high-sensitivity FOBT.

    • D. Provide information on the local availability and quality of each testing method.

  3. N.P. chooses to have a colonoscopy, and asks whether his 78-year-old mother, who is also your patient, should be screened. Which one of the following responses is consistent with the recommendations of the U.S. Preventive Services Task Force (USPSTF)?

    • A. She should be screened using high-sensitivity FOBT.

    • B. Because of her age, she should be screened at more frequent intervals than persons 75 years and younger.

    • C. She should not be screened routinely for colorectal cancer.

    • D. Regardless of whether she has been screened before, N.P.'s mother should be screened at the recommended intervals throughout her life.

    • E. She should not be screened using colonoscopy because the harms of the test outweigh the benefits in persons her age.


  1. The correct answer is D. The USPSTF recommends screening for colorectal cancer in adults 50 to 75 years of age using colonoscopy, sigmoidoscopy, or high-sensitivity FOBT. Studies show that the optimal intervals for these tests are colonoscopy every 10 years; high-sensitivity FOBT annually; and sigmoidoscopy every five years combined with high-sensitivity FOBT every three years. Sigmoidoscopy every five years without high-sensitivity FOBT is significantly less effective in detecting colorectal cancer than other screening tests. The USPSTF concluded that there is insufficient evidence to determine the net benefit of CT colonography and fecal DNA testing.

  2. The correct answers are B and D. Colonoscopy, sigmoidoscopy, and high-sensitivity FOBT are all effective in reducing mortality. Because these options are variably acceptable to patients, eliciting patient preferences can help ensure that patients seek screening at recommended intervals. A positive test result from screening with FOBT or sigmoidoscopy leads to a diagnostic colonoscopy; therefore, choosing FOBT or sigmoidoscopy is not a guarantee that the patient will avoid a colonoscopy. Ideally, shared decision making between physicians and patients should incorporate information on patient preference and local test quality and availability.

  3. The correct answer is C. Although considerations may warrant screening in particular patients, the USPSTF recommends against routine screening in adults 76 to 85 years of age. For adults in this age group who have not been screened before, the decision whether to screen should be based on health status, competing risks, and patient preference. Although the direct harms of FOBT are minimal, the USPSTF does not endorse a particular screening test in this age group. The USPSTF recommends against colorectal cancer screening in patients 85 years and older because the harms of screening outweigh the benefits.


U.S. Preventive Services Task Force. Screening for colorectal cancer: U.S. Preventive Services Task Force recommendation statement. Ann Intern Med. 2008;149(9):627–637.

Whitlock EP, Lin JS, Liles E, Beil TL, Fu R. Screening for colorectal cancer: a targeted, updated systematic review for the U.S. Preventive Services Task Force. Ann Intern Med. 2008;149(9):638–658.

The case study and answers to the following questions on screening for colorectal cancer are based on the recommendations of the U.S. Preventive Services Task Force (USPSTF), an independent panel of experts in primary care and prevention that systematically reviews the evidence of effectiveness and develops recommendations for clinical preventive services. More detailed information on this subject is available in the USPSTF Recommendation Statement and the evidence synthesis on the USPSTF Web site (http://www.ahrq.gov/clinic/uspstfix.htm). The practice recommendations in this activity are available at http://www.ahrq.gov/clinic/uspstf/uspscolo.htm.



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