Our systematic review supports the effectiveness of screening as a means of reducing colorectal cancer mortality. For biennial FOBT, 3 high-quality RCTs have shown disease-specific mortality rate reductions of 15 percent to 21 percent over 8 to 13 years. Annual FOBT with rehydrated slides appears to produce larger reductions in mortality rates (33 percent in one trial). Case-control studies have shown that sigmoidoscopy and possibly colonoscopy are also associated with decreased death from colorectal cancer. The combined strategy of FOBT and sigmoidoscopy was supported by one nonrandomized trial showing a borderline statistically significant 43 percent reduction in mortality rates when FOBT was added to rigid sigmoidoscopy(4). This strategy was also supported by indirect evidence showing increased yield with both tests compared with FOBT alone. DCBE has not been studied as extensively as other methods for screening; further data are required in screening populations.
Although colorectal cancer screening is supported by strong direct and indirect evidence, no trials have compared different screening strategies head-to-head using colorectal cancer incidence or mortality rates as the endpoint of interest. Some groups have interpreted recent evidence showing the superior single-test accuracy of colonoscopy as proving its broader superiority and have recommended it as the procedure of choice for screening. However, these analyses have not always considered differences in yield over time, complications, and real-world performance, which may not always favor colonoscopy(62,63). One possibility would be to perform a trial of colonoscopy. However, the cost of such a trial, particularly if colonoscopy were to be compared to other screening modalities rather than to no screening, would be quite high, and many years of followup would be required. In the face of good general evidence supporting screening but uncertainty about the most effective method for doing so, providers and patients may benefit from discussing the pros and cons of the different methods and incorporating patients' preferences in the decision about how to screen(64).
Several areas of colorectal cancer screening and prevention warrant additional research. One is the critical need to learn more about adherence to screening among informed patients. Furthermore, we need better data on the real-world complication rates of colonoscopic screening and polypectomy, including whether complications become more or less likely as procedure volume increases. DCBE should be studied in a screening population. The accuracy of novel screening techniques, including virtual colonoscopy and genetic stool tests (or other novel noninvasive tests) should be evaluated in screening populations.
Additional means of prevention, including chemopreventive agents such as nonsteroidal anti-inflammatory drugs, calcium, or estrogen also warrant further study. Behavioral factors, including physical activity, dietary fat, dietary fiber, and fruit and vegetable consumption, appear to be related to colorectal cancer incidence; further research would clarify whether these relationships are causal or the result of uncontrolled confounding.
Despite its apparent effectiveness, colorectal cancer screening is currently underused by age-eligible adults. The multiple reasons for low utilization include patient-, provider-, and system-specific barriers(65). Effective colon cancer screening requires ongoing efforts to ensure test ordering and adherence. Screening with FOBT, for example, may require offering annual testing to 500 to 1,000 people for 10 years to prevent one death from colorectal cancer(2). Although this level of effort may seem inefficient or low in yield, the potential benefit is large and the costs per person are small. To achieve high rates of screening in real-world settings rather than in trials, which focused strictly on one aspect of preventive care, colorectal cancer screening must be integrated with other care needs, including other preventive services.
Several strategies have shown effectiveness in raising screening rates in primary care settings over the short term. Effective strategies include reminder systems, patient decision aids, and special screening clinics(66). Further research is needed to determine whether such systems can maintain their effect over time and to identify novel means of reaching people at risk who currently are not served, or are underserved, by the existing health care system.
We acknowledge the assistance of David Atkins, M.D., M.P.H., of the Agency for Healthcare Research and Quality, and Eve Shapiro, managing editor to the USPSTF (under contract to the Agency for Healthcare Research and Quality). We extend our appreciation as well to Research Triangle Institute-University of North Carolina Evidence-based Practice Center staff, Sonya Sutton, BSPH, Sheila White, and Loraine Monroe all of RTI, and Carol Krasnov of the University of North Carolina at Chapel Hill Cecil G. Sheps Center for Health Services Research.
Contract support: This study was developed by the Research Triangle Institute-University of North Carolina Evidence-based Practice Center under contract to the Agency for Healthcare Research and Quality (Contract No. 290-97-0011), Rockville, MD.
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[a] Michael Pignone, M.D., M.P.H.: Department of Medicine and Cecil Sheps Center for Health Services Research, University of North Carolina-Chapel Hill, Chapel Hill, NC.
[b] Melissa Rich, M.D.: Gastroenterology, UNC at Chapel Hill, Chapel Hill, NC
[c] Steven M. Teutsch, M.D., M.P.H.: Merck & Co., Inc., West Point, PA
[d] Alfred O. Berg, M.D., M.P.H.: Chair, US Preventive Services Task Force, Department of Family Medicine, University of Washington, Seattle, WA
[e] Kathleen N. Lohr, Ph.D.: RTI, Research Triangle Park, NC
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Source: U.S. Preventive Services Task Force. Chemoprevention of breast cancer: summary of the evidence. Ann Intern Med 2002;137:132-41.
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Internet Citation:
Pignone M, Rich M, Teutsch SM, Berg AO, Lohr KN. Screening for Colorectal Cancer in Adults at Average Risk: Summary of the Evidence for the U.S. Preventive Services Task Force. Originally in Annals of Internal Medicine 2002;137:132-41. Agency for Healthcare Research and Quality, Rockville, MD. http://www.ahrq.gov/clinic/3rduspstf/colorectal/colosum1.htm
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