United States Preventive Services Task Force
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United States Preventive Services Task Force. Screening for Colorectal Cancer: Recommendations and Rationale: U.S. Preventive Services Task Force. The Internet Journal of Gastroenterology. 2002 Volume 2 Number 1.
Summary of Recomendation
The USPSTF strongly recommends that clinicians screen men and women 50 years of age or older for colorectal cancer.
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 their lower sensitivity, 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 with 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.3 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 prepared at home by patients from three consecutive stool samples and forwarded 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 test results. Neither digital rectal examination (DRE) nor the testing of a single stool specimen obtained during DRE is recommended as an adequate screening strategy for colorectal cancer.
The combination of FOBT and sigmoidoscopy may detect more cancers 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 test 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 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 colorectal cancer screening are likely to be as cost-effective as many other clinical preventive services—less than $30,000 per additional year of life gained.
Epidemiology and Clinical Consequences
Colorectal cancer is the fourth most common cancer in the United States and the second leading cause of cancer death. A person at age 50 has about a 5% lifetime risk of being diagnosed with colorectal cancer and a 2.5% chance of dying from it; 3 the average patient dying of colorectal cancer loses 13 years of life.4
More than 80% of colorectal cancers arise from adenomatous polyps. Although fewer than 1% of adenomatous polyps less than 1 cm will eventually develop into cancer, 10% of adenomatous polyps greater than 1 cm become malignant within 10 years, and about 25% become malignant after 20 years.5 The prevalence of adenomatous polyps increases from 20% to 25% at age 50 to 50% by age 75-80.6
Most colorectal cancers occur in persons at average risk, but 20% occur among patients with specific risk factors, such as those with a family history of colorectal cancer in a first-degree relative. A small proportion (6%) is associated with uncommon genetic syndromes such as familial adenomatous polyposis [FAP] or hereditary nonpolyposis colorectal cancer [HNPCC]. Other persons at increased risk include patients with longstanding ulcerative colitis, persons with previously diagnosed large adenomatous polyps or colorectal cancer, and those with a family history of adenomatous polyps diagnosed before age 60.
Accuracy and Reliability of Screening Tests
The USPSTF reviewed evidence of the effectiveness of the following screening tests for colorectal cancer: DRE, FOBT, sigmoidoscopy, colonoscopy, DCBE, and CT colography, singly and in various combinations.
Effectiveness of Early Detection
When to Start or Stop Screening for Colorectal Cancer
There are few data to determine optimal age for starting or stopping screening. FOBT has been proven effective for persons aged 50-80 and sigmoidoscopy is associated with reduced mortality in persons older than 45. One cost-effectiveness model suggests that beginning screening at age 40 rather than at age 50 would offer less than a 1-day average improvement in life expectancy. Randomized trials suggest that a life expectancy of at least 5 years may be required to realize the benefits of screening.
Potential Harms of Screening
FOBT has few potential harms but false-positive tests
Screening colonoscopy poses higher risks than FOBT or sigmoidoscopy, both because it is a more invasive procedure and because generally it is used with conscious sedation, which may lead to complications. The risks of colonsocopy depend on whether it is used simply for screening and diagnosis, or whether it is also used for therapeutic procedures (eg, removal of polyps). In two studies of screening colonoscopies in more than 5,000 patients, 0.2% to 0.3% had major complications during or immediately after the procedures, the most common being bleeding requiring hospitalization or emergency care.24,25
Risks are higher in therapeutic procedures ( eg, when polypectomy is performed ) than in diagnostic or screening procedures. Rates of perforation for diagnostic procedures in 16 published studies ranged from 0.03% to 0.61%. There are few data on bleeding complications but one study reported no bleeding events in 250 patients.2
The complication rates for therapeutic procedures were higher in some studies: 0.07% to 0.72% for perforations and 0.2% to 2.67% for bleeding. Death was rare (between 1 in 16,000 to 1 in 27,000) and more likely in symptomatic patients with acute problems or those with comorbid conditions. The mortality rate as a result of screening is likely to be on the lower end of this range. Complication rates could increase, however, if widespread adoption of colonoscopy leads to more procedures by less skilled endoscopists. Data are lacking on complications of CT colography.
Patient Preferences and Adherence
Some patients report that they find the FOBT unpleasant or difficult to perform, but 50% to 70% of patients will complete FOBT when advised to by a clinician. A reminder system can increase adherence rates by an average of 14%. Studies conducted in primary care settings have found rates of adherence for sigmoidoscopy to be 25% to 50% for the initial test, but there are no data on adherence to repeat examinations. When given information about screening options and offered the choice of FOBT alone, sigmoidoscopy alone, or both tests together, most patients in an academic internal medicine clinic preferred both tests or FOBT alone; only 8% to 13% preferred sigmoidoscopy alone.26 However, patient adherence to combined testing is lower than it is for sigmoidoscopy or FOBT alone. Patients' acceptance of barium enema screening has not been evaluated.
Studies examining the relative discomfort of barium enema and colonoscopy have produced inconsistent results. In one study of patients in a population with considerable previous screening experience, 38% preferred colonoscopy to other methods. The acceptability and feasibility of CT colography have not been examined.
Cost and Cost-effectiveness
Among 6 high-quality cost-effectiveness analyses examining only direct costs, the average cost-effectiveness ratio values for screening adults older than 50 with each of the major strategies were under $30,000 per life-year saved (Year 2000 dollars).2 Studies varied as to which strategy was most cost-effective, however.
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.27 The American Cancer Society does not recommend DRE 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.28,29,30 The American Gastroenterological Association, as part of a consortium of related professional organizations, also issues similar recommendations, which are currently being updated.3 The American College of Physicians--American Society of Internal Medicine does not have current guidelines on screening.5 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 age 50 years; evidence is insufficient to recommend for or against colonosopy or combined FOBT and sigmoidscopy.31
Corresponding Author: Alfred O. Berg, MD, MPH, Chair, U.S. Preventive Services Task Force, c/o David Atkins, MD, MPH, Chief Medical Officer, Center for Practice and Technology Assessment, Agency for Healthcare Research and Quality, 6010 Executive Boulevard, Suite 300, Rockville, MD 20852. (301) 594-4016, fax (301) 594-4027, E-mail, email@example.com
Members of the U.S. Preventive Services Task Force are Alfred O. Berg, MD, MPH, Chair, USPSTF (Professor and Chair, Department of Family Medicine, University of Washington, Seattle, WA); Janet D. Allan, PhD, RN, CS, Vice-chair, USPSTF (Dean and Professor, School of Nursing, University of Texas Health Science Center, San Antonio, TX); Paul S. Frame, MD (Tri-County Family Medicine, Cohocton, NY, and Clinical Professor of Family Medicine, University of Rochester, Rochester, NY); Charles J. Homer, MD, MPH (Executive Director, National Initiative for Children's Healthcare Quality, Boston, MA); Mark S. Johnson, MD, MPH (Associate Professor of Clinical Family Medicine and Chairman Department of Family Medicine, University of Medicine and Dentistry of New Jersey-New Jersey Medical School); Jonathan D. Klein, MD, MPH (Associate Professor of Pediatrics and of Community and Preventive Medicine, University of Rochester School of Medicine); Tracy A. Lieu, MD, MPH (Associate Professor, Department of Ambulatory Care and Prevention, Harvard Pilgrim Health Care and Harvard Medical School, Boston, MA); Cynthia D. Mulrow, MD, MSc (Professor of Medicine, University of Texas Health Science Center, Audie L. Murphy Memorial Veterans Hospital, San Antonio, TX); C. Tracy Orleans, PhD (Senior Scientist, The Robert Wood Johnson Foundation, Princeton, NJ); Jeffrey F. Peipert, MD, MPH (Director of Research, Women and Infants' Hospital, Providence, RI); Nola J. Pender, PhD, RN (Professor and Associate Dean for Research, School of Nursing, University of Michigan, Ann Arbor, MI); Albert L. Siu, MD, MSPH (Professor of Medicine, Chief of Division of General Internal Medicine, and Medical Director of the Primary Care and Medical Services Care Center, Mount Sinai School of Medicine and The Mount Sinai Medical Center); Steven M. Teutsch, MD, MPH (Senior Director, Outcomes Research and Management, Merck & Company, Inc., West Point, PA); Carolyn Westhoff, MD, MSc (Associate Professor of Obstetrics, Gynecology and Public Health, Department of Obstetrics and Gynecology, Columbia University College of Physicians and Surgeons, New York, NY); and Steven H. Woolf, MD, MPH (Professor of Family Medicine, Department of Family Practice, and Professor, Department of Preventive and Community Medicine, Virginia Commonwealth University, Fairfax, VA).
Explanations of the current ratings and of the strength of overall evidence are given in Appendix A and Appendix B, respectively. The complete information on which this statement is based, including evidence tables and references, is available in the summary of the evidence and the Systematic Evidence Review2 on this topic, which can be obtained through the USPSTF Web site (http://www.ahrq.preventiveservices.gov), through the National Guideline Clearinghouse (www.guideline.gov), and in print through the AHRQ Publications Clearinghouse (phone, 800-358-9295; e-mail, firstname.lastname@example.org).
David Atkins, MD, MPH, Chief Medical Officer, U.S. Preventive Services Task Force, Agency for Healthcare Research and Quality, Center for Practice and Technology Assessment, 6010 Executive Boulevard, Suite 300, Rockville, MD 20852. tel (301) 594-4016, fax (301) 594-4027, email@example.com
Reprints are available from the AHRQ Web site at http://www.ahrq.gov/clinic/uspstfix.htm, through the National Guideline Clearinghouse (http://www.guideline.gov), or in print through the AHRQ Publications Clearinghouse (1-800-358-9295).
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U.S. Preventive Services Task Force: Recommendations and Ratings
The Task Force grades its recommendations according to one of 5 classifications (A, B, C, D, I) reflecting the strength of evidence and magnitude of net benefit (benefits minus harms):