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Screening for Colorectal Cancer

All people who are 50 or older should be screened for colorectal cancer; the screening method should be discussed with each patient.

The third U.S. Preventive Services Task Force (USPSTF) has been releasing new and updated guidelines during the past year (guidelines homepage; Journal Watch May 15 2001; Journal Watch Jul 19 2002).

USPSTF 3 concludes each of its guidelines with a recommendation, graded as follows:

A -- The intervention is strongly recommended.

B -- The intervention is recommended.

C -- The USPSTF makes no recommendation for or against the intervention.

D -- The intervention is not routinely recommended.

I -- Evidence is insufficient to recommend for or against the intervention.

The 1996 USPSTF recommendation regarding colorectal cancer (CRC) screening was based on reductions in CRC mortality in a randomized trial of annual home fecal occult blood testing (FOBT), which showed 4.6 fewer CRC deaths per 1000 people screened, and in 2 nonrandomized studies of sigmoidoscopy (1 with, and 1 without, FOBT). At that time, the USPSTF recommended FOBT, sigmoidoscopy, or both for screening. Since that time, colonoscopy (during which the entire colon is evaluated) has become more popular as a screening option: It is indicated at longer intervals than are other screening tests (every 10 years); observational studies have suggested mortality benefit; and analyses consistently have shown it to be cost-effective, despite its higher initial cost. Double-contrast barium enema is a less sensitive alternative. With respect to CRC mortality, the current USPSTF systematic review identified the following data:

• barium enema -- no evidence;
  
• digital rectal examination -- a case-control study found no benefit;
  
• FOBT -- 3 new reports of randomized trials showed benefit (decreased mortality) for both rehydrated and unrehydrated biennial home FOBT cards;
  
• sigmoidoscopy -- a small randomized trial showed a nonsignificant decrease in mortality;
  
• colonoscopy -- a case-control study showed a significant decrease in mortality.
  

Adverse effects include inconvenience with FOBT; bleeding in 2.5% and perforation in <0.01% of sigmoidoscopy examinations; and perforation in 0.029% to 0.61% and death in 1/3000 to 1/30,000 colonoscopy examinations.

Based on this evidence, the USPSTF strongly recommends that clinicians screen all people who are 50 or older for colorectal cancer. Recommendation: A

The USPSTF states that the data are insufficient to determine which screening strategy is best. Specifically, the task force could not determine whether the likely increased accuracy of colonoscopy is offset by the procedure's additional complications, inconvenience, and costs.

Comment: The recommendation to screen for colorectal cancer is clear -- which test to choose and how often to do it are less clear. Despite the absence of a specific recommendation, the USPSTF notes that "fair-to-good" evidence of efficacy exists only for FOBT and sigmoidoscopy. The USPSTF points out several facts: Sigmoidoscopy, performed every 10 years, might be as effective as the same procedure performed every 5 years; annual FOBT yields greater reductions in mortality but more false positives than does biennial testing; and screening benefits are seen within 5 years (so people as old as 80 should be screened, but testing could be discontinued if life expectancy is <5 years). Information on evidence for efficacy, risk for complications, inconvenience, and costs should be made available to patients during selection of a screening strategy. At the time of publication, the full text of the original articles was available at http://www.ahrq.gov/clinic/3rduspstf/colorectal/colorr.htm, http://www.ahrq.gov/clinic/3rduspstf/colorectal/colosum1.htm, and http://www.ahrq.gov/clinic/3rduspstf/colorectal/colocost1.htm free of charge.

— Richard Saitz, MD, MPH

Published in Journal Watch General Medicine August 13, 2002

Citation(s):

U.S. Preventive Services Task Force. Screening for colorectal cancer: Recommendation and rationale. Ann Intern Med 2002 Jul 16; 137:129-31.

• Original article (Subscription may be required)
• Medline abstract (Free)

Pignone M et al. Screening for colorectal cancer in adults at average risk: A summary of the evidence for the U.S. Preventive Services Task Force. Ann Intern Med 2002 Jul 16; 137:132-41.

• Original article (Subscription may be required)
• Medline abstract (Free)

Pignone M et al. Cost-effectiveness analyses of colorectal cancer screening: A systematic review for the U.S. Preventive Services Task Force. Ann Intern Med 2002 Jul 16; 137:96-104.

• Original article (Subscription may be required)
• Medline abstract (Free)