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Am Fam Physician. 2003;67(1):129-130

Case Study

MB is a 51-year-old woman who visits you for a refill of her antihypertensive medication. You review her chart to deliver recommended clinical preventive services and learn that her screenings for lipids, breast cancer, and cervical cancer are current.

Noticing that she has not been screened for colorectal cancer, you inquire about her family history and conduct a pertinent review of systems, both of which are unremarkable.

Case Study Questions

1. According to the U.S. Preventive Services Task Force (USPSTF), which one of the following statements reflects the most appropriate plan to screen MB for colorectal cancer?

  • A. Offer MB a diagnostic test to evaluate for colorectal cancer because she is at high risk.

  • B. Offer MB screening because she is older than 50.

  • C. Offer MB screening at regular intervals until age 70.

  • D. Do not offer screening until MB turns 65.

  • E. Do not offer screening because MB has no risk factors for colorectal cancer.

2. Which of the following methods is recommended by the USPSTF to screen for colorectal cancer?

  • A. Periodic fecal occult blood testing.

  • B. Flexible sigmoidoscopy.

  • C. Colonoscopy.

  • D. Double-contrast barium enema.

  • E. All of the above methods are acceptable.

Answers

1. The answer is B: Colorectal cancer is the fourth most common cancer in the United States and the second leading cause of cancer death.1 The USPSTF strongly recommends that clinicians screen men and women 50 years of age or older for colorectal cancer. In persons at high risk (e.g., those with a first-degree relative who is diagnosed with colorectal cancer before age 60), initiating screening at an earlier age is reasonable. The appropriate age at which colorectal cancer screening should be discontinued is not known. 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.

2. The answer is E: The USPSTF found fair to good evidence that several screening methods are effective in reducing mortality from colorectal cancer. Options include fecal occult blood testing (FOBT), flexible sigmoidoscopy, the combination of FOBT and flexible sigmoidoscopy, colonoscopy, and double-contrast barium enema. However, the quality of evidence, magnitude of benefit, and potential harms vary with each method. The USPSTF found good evidence that periodic FOBT (use of guaiac-based test cards prepared at home by patients from three consecutive stool samples) reduces mortality from colorectal cancer24 and fair evidence that sigmoidoscopy alone or in combination with FOBT reduces mortality.5,6 The USPSTF found no direct evidence that screening colonoscopy is effective in reducing colorectal cancer mortality but did find compelling supportive evidence.7,8 It is not certain whether the potential added benefits of colonoscopy relative to screening alternatives are enough to justify the added risks and inconvenience for patients. Double-contrast barium enema offers an alternative means of examining the entire colon, but the USPSTF found no direct evidence that it reduces mortality. Neither digital rectal examination (DRE) nor the testing of a single stool specimen obtained during DRE is recommended as a screening strategy. Studies have not yet examined clinical outcomes with computed tomographic colography (virtual colonoscopy). The optimal interval for screening depends on the test, and direct evidence exists only for FOBT every one to two years.2,4 Other recommended screening intervals include 10 years for colonoscopy and five years for both sigmoidoscopy and double-contrast barium enema. According to the USPSTF, there are insufficient data to determine which strategy provides the best balance of benefits and potential harms. Studies indicate that screening is likely to be cost effective, regardless of the strategy chosen.9

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