Family Medicine Residency Program North Oakland Medical Center Pontiac, Mich
Screening for colorectal cancer has proven to be very successful in reducing mortality by detecting and removing premalignant polyps long before they can turn into cancerous growths. The first and most important step in colorectal cancer screening is assessing whether the patient is at average or increased risk, which determines the appropriate screening test and the age at which screening should begin. Since the majority of cancers develop sporadically in individuals at average risk, screening should begin at age 50, when the incidence begins to rise sharply. Various screening methods are available, including fecal occult blood tests, sigmoidoscopy, double-contrast barium enema, and colonoscopy. Any method can be used for people at average risk, but colonoscopy is the procedure of choice for those at higher risk or with a genetic predisposition. This article provides a detailed screening algorithm for high-risk patients.
Primary care physicians are charged with the responsibility of screening for and treating a wide variety of medical conditions. Colon cancer screening can be life saving. We sought current recommendations from various specialty organizations for the screening of average- and high-risk adults for colorectal cancer. Consensus is difficult, given the sheer number of organizations that have weighed in on the topic. In fact, the Web site for the Canadian Task Force on Preventive Health Care (www.ctfphc.org) lists 40 evidence-based guidelines developers, 10 evidence-based guidelines clearinghouses, and dozens of government organizations, professional societies, search engines, and general reference tools containing guidelines for clinicians. In this review, we focus primarily on guidelines published by the American Gastroenterological Association (AGA),1 the American Cancer Society (ACS),2 and the US Preventive Services Task Force (USPSTF),3 as well as the Cochrane database.4 To grade the recommendations, we use the Strength of Recommendation Taxonomy (SORT) scale, in which “A” denotes consistent and good-quality patient-oriented evidence, and “B” denotes inconsistent or limited-quality patient-oriented evidence.5
Risk Factors Colorectal cancer is the second leading cause of cancer death after lung cancer, accounting for 10% of all cancer deaths.6 A person has about a 6% chance of developing colon cancer in his or her lifetime.6
Increasing age is a major risk factor for sporadic colorectal cancer. Incidence begins to rise significantly between the ages of 50 and 60; 90% of cases occur after age 50.6 People older than age 70 are more likely to present in the early stages of cancer, whereas younger individuals tend to present at later stages with more aggressive disease.7 Women have a slightly higher incidences than men. Both incidence and mortality are higher in blacks than in other racial groups in the United States,6 because they are less likely to present in the early stages of the disease.7 This could be related to their tendency to have a more proximal location of the cancer7 and their later entrance into the health care system. The incidence of colorectal cancer is higher among persons living in developed countries. Family history of colon cancer confers a lifetime risk of 5% to 10%; however, 75% of all colorectal cancers are sporadic.7
Table 1
Risk assessment for colorectal cancer
1. Personal history of colorectal cancer or adenomatous polyps? 2. Personal history of inflammatory bowel disease? 3. Family history of colorectal cancer or an adenomatous polyp? If yes, how many? Was it a first-degree relative (parent, sibling, or child)? At what age was the cancer or polyp first diagnosed? 4. Does the family history suggest any of the genetic syndromes (familial adenomatous polyposis or HNPCC)?
Note: A negative response to all these questions puts a patient in the average-risk category, whereas any positive response puts a patient in the high-risk category. HNPCC = hereditary nonpolyposis colorectal cancer.
Table 2
Colon cancer screening recommendations for average- risk persons aged >50
• FOBT every year • Flexible sigmoidoscopy every 5 years • Double-contrast barium enema every 5 years • Colonoscopy every 10 years
FOBT = fecal occult blood test.
Sources: Reference 1 and Ling BS, Moskowitz MA, Wachs D, et al. Attitudes toward colorectal cancer screening tests. J Gen Intern Med. 2001;16:822-830.
Role of Colorectal Cancer Screening Colorectal cancer usually develops from benign adenomatous polyps over a period of 5 to 15 years.7 Most of these polyps are asymptomatic. Aggressive screening and polypectomy can greatly reduce the risk of developing cancer. This is supported by the reality that in the United States alone, death from colon cancer has dropped by 1.8% annually over the past 15 years,6 probably because of aggressive screening. A 2002 systematic review of the literature showed that screening for colorectal cancer was cost-effective compared with no screening, but the data were insufficient to determine which screening method was best.8 Findings from another study indicated that screening should begin at age 50, based on the low incidence of colorectal cancer in asymptomatic adults aged 40 to 49 years.9
The American Academy of Family Physicians strongly recommends annual screening for all adults aged 50 and older, using annual fecal occult blood testing (FOBT), sigmoidoscopy, or colonoscopy.10 Based on a decrease in the death rate and cost-effectiveness data, screening for colorectal cancer in asymptomatic adults older than 50 years is recommended (SORT: A).
Risk Assessment The first step in screening for colorectal cancer is to determine the patient’s risk level, which can be accomplished with a few simple questions (Table 1). It is important to keep in mind that even though colorectal cancer is more likely to develop in individuals at high risk, most cases occur in those at average risk. Therefore, ongoing screening as outlined in Table 2 is important.
Screening Methods FOBT Annual FOBT reduces colorectal cancer mortality by 15% to 33%.11-13 Although the sensitivity of a single FOBT is low (30%-50%), repeated annual testing can detect as many as 92% of cancers.12 The most commonly used FOBT is the guaiac card (eg, Hemoccult II Sensa). The guaiac-impregnated filter paper turns blue when exposed to heme and hydrogen peroxide (a developer solution). The sensitivity of the test is about 90%.14 False-positive results can occur if the patient has eaten certain foods, including turnips, broccoli, horseradish, cantaloupe, or red meat containing heme. Aspirin and nonsteroidal antiinflammatory drugs (NSAIDs) can cause gastric irritation and bleeding that can also cause false-positive results, although a recent study suggests that these medications do not increase the false-positive rate.15
False-negative results are possible in patients taking more than 500 mg/day of vitamin C, which interferes with guaiac oxidation. Some experts favor avoiding NSAIDs for 7 days and vitamin C (in supplements or citrus fruits) and red meat for 3 days before testing. Studies have shown that a restricted diet does improve the performance of the more sensitive guaiac-based tests, but telling patients to avoid only red meat can enhance adherence.13,16 Rehydration of specimens can make the test more sensitive but is no longer recommended, since it increases the chances of false-positive results.
Table 3
Screening recommendations, by family history of colon cancer or adenomatous polyps
History 1st-degree relative with colorectal cancer or adenomatous polyp diagnosed at age <60 or 2 or more 1st-degree relatives diagnosed with colorectal cancer at any age
1st-degree relative with colorectal cancer or adenomatous polyp diagnosed at age >60 or 2 or more 2nd-degree relatives with colorectal cancer
2nd- or 3rd-degree relative with colorectal cancer
Recommendation Screening colonoscopy at age 40, or 10 years younger than the earliest age at diagnosis in patient's family, whichever comes first, then repeated every 5 years
Screen as average-risk persons, but beginning at age 40
Screened as average-risk persons
Immunochemical tests (hemagglutination and latex agglutination), which measure antibodies to human hemoglobin, are highly specific for fecal blood. These tests are unaffected by diet but are not widely used because they are more expensive and require special handling of specimens since, for example, hemoglobin antigenicity can be lost at room temperature.17
A major drawback of FOBT is that because most polyps and cancers bleed intermittently, many go undetected. One study showed that even when FOBT was combined with flexible sigmoidoscopy, at least 24% of cancers were missed.18 In addition, most people who have a positive FOBT will not have neoplasia and thus will endure the discomfort, cost, and risk of colonoscopy without any benefit.4 Compliance with FOBT is low, further limiting its usefulness.
The AGA, the USPSTF, and the ACS recommend offering yearly screening with FOBT using a guaiac-based test with dietary restriction or an immunochemical test without dietary restriction.1,3,19 Two samples from each of 3 consecutive stools should be examined without rehydration. Patients with a positive test on any specimen should be followed up with colonoscopy (SORT: B).
Sigmoidoscopy A 60-cm sigmoidoscope can examine up to the splenic flexure and identify about one half of all colonic lesions. Screening with flexible sigmoidoscopy reduces mortality from distal colorectal cancer by about 60%.20 The procedure can be performed in the physician’s office with minimal patient preparation (ie, using an enema the previous night and a few hours before the procedure). Sedation is unnecessary, since the examination generally causes only mild cramping. Sigmoidoscopy should be followed by colonoscopy in patients with risk factors including age older than 65, villous histology in distal adenomas, multiple distal adenomas, positive family history of colorectal cancer, and polyps more than 1 cm in size (since they are assumed to be adenomas).21,22 The AGA and ACS recommend offering flexible sigmoidoscopy every 5 years (SORT: B).
FOBT and sigmoidoscopy The main purpose of combining the 2 tests is that sigmoidoscopy can detect cancer in the distal colon, whereas FOBT can detect it in the proximal colon. A nonrandomized trial showed a 43% reduction in colorectal cancer mortality when both tests were used compared with sigmoidoscopy alone.23
The AGA recommends offering screening with FOBT every year combined with flexible sigmoidoscopy every 5 years. When both tests are performed, FOBT should be done first, since a positive result is an indication for colonoscopy, obviating the need for sigmoidoscopy (SORT: B).
Double-contrast barium enema
Figure—Colorectal cancer screening guidelines for high-risk persons. HNPCC = hereditary nonpolyposis colorectal cancer.
Also known as air-contrast barium enema, double-contrast barium enema is sometimes the procedure of choice when colonoscopy is contraindicated because of comorbid medical conditions. It allows evaluation of the entire colon, is relatively safe, and can detect colorectal cancer and polyps almost as well as colonoscopy or flexible sigmoidoscopy.24 However, some small polyps may be missed, and false-positive results can occur because of stool, air, and other mucosal irregularities, requiring unnecessary follow-up colonoscopy.25 There appear to be no published studies that evaluated the effectiveness of double-contrast barium enema in reducing colorectal cancer deaths. Combining flexible sigmoidoscopy with double-contrast barium enema is not recommended, since it does not increase the detection rate significantly and unnecessarily adds to the cost and patient inconvenience.
In average-risk patients, the AGA and ACS recommend offering double-contrast barium enema as a screening option every 5 years (SORT: B).
Colonoscopy Colonoscopy permits direct visualization of the entire colon and is the most sensitive and specific method available for the detection of colonic polyps and cancers. It has the added benefit of allowing the removal of lesions during the examination. This is the test of choice for further evaluation of a patient with a positive FOBT or sigmoidoscopic report of a polyp or cancer. Colonoscopy has been shown to reduce the mortality rate from colorectal cancer.26 However, a recent study found that 50% of patients referred for colonoscopy never followed through, and only 40% knew there were other screening tests available.27 Adherence may improve with better physician-patient communication, counseling to help resolve logistic problems, and improved referral and scheduling.27
Its disadvantages are higher cost, inconvenience (bowel preparation with saline cathartic), need for intravenous sedation, and risk of colon perforation (albeit very rare).
The AGA and ACS recommend offering colonoscopy every 10 years (SORT: B). The ACS now considers colonoscopy to be the preferred screening test.
Table 4
Medicare coverage for colon cancer screening
Medicare beneficiaries are entitled to regular colon cancer screening, with reimbursement for: • Annual FOBT • Flexible sigmoidoscopy once every 4 years for average-risk persons • Screening colonoscopy once every 10 years for average-risk individuals • Screening colonoscopy once every 2 years for high-risk individuals
FOBT = fecal occult blood test.
Table 5
Clinical criteria for hereditary nonpolyposis colorectal cancer
Amsterdam II criteria 1. At least 3 relatives with an HNPCC-associated tumor (colorectal, endometrial, small bowel, ureter, or renal pelvis cancer) 2. 1 affected patient is a 1st-degree relative of the other 2 3. >2 successive generations are affected 4. >1 case diagnosed before age 50 5. Familial adenomatous polyposis has been excluded 6. Tumors verified by pathologic examination
Bethesda criteria 1. Cancer in the family that fulfill Amsterdam II criteria 2. 2 HNPCC-related cancers, including synchronous and metachronous colorectal cancer or associated extracolonic cancers 3. Colorectal cancer and a 1st-degree relative with colorectal cancer and/or HNPCC-related extracolonic cancer and/or colorectal adenoma; 1 of the cancers diagnosed at age <45, and the adenoma diagnosed at age <40 4. Colorectal cancer or endometrial cancer diagnosed at age <45 5. Right-sided colorectal cancer with an undifferentiated pattern (solid/cribriform) on histopathology diagnosed at age <45 6. Signet ring cell-type colorectal cancer diagnosed at age <45 7. Adenomas diagnosed at age <40
Sources: Vasen HF, Watson P, Mecklin JP, et al. New clinical criteria for hereditary nonpolyposis colorectal cancer (HNPCC, Lynch syndrome) proposed by the International Collaborative group on HNPCC. Gastroenterology. 1999;116:1453-1456. Rodriguez-Bigas MA, Boland CR, Hamilton SR, et al. A National Cancer Institute Workshop on Hereditary Nonpolyposis Colorectal Cancer Syndrome: meeting highlights and Bethesda guidelines. J Natl Cancer Inst. 1997;89:1758-1762.
Recommendations for People at Increased Risk Persons with a family history of colon cancer or adenomatous polyps are at increased risk for cancer and should be screened according to current recommendations (Table 3). Screening guidelines for all those at high risk of colon cancer are outlined in the algorithm (Figure).
A history of colorectal cancer The chances of developing additional colorectal cancer increases after the first occurrence, apart from a recurrence of the original cancer. Thus, patients should have a colonoscopic examination either preoperatively or 2 to 3 months after tumor resection to rule out synchronous neoplasms and then surveillance colonoscopy 6 months later. If surveillance examination reveals a normal colon, subsequent colonoscopy should be offered after 3 years, and if it is still normal, every 5 years.1
A history of adenomatous polyps The schedule for follow-up colonoscopy depends on pathology and the number of adenomas found at colonoscopy. Short-interval colonoscopy is advised for patients with a history of numerous adenomas, malignant adenocarcinomas, large sessile adenomas, or an initial incomplete colonoscopy. An interval of 3 years is advised for patients with advanced or multiple adenomas (ie, >3 adenomas) and an interval of 5 years for patients with 1 or 2 small adenomas (ie, <1-cm tubular adenomas).1
Because aging is a major risk factor for colon cancer, familiarity with Medicare coverage for colon cancer screening is important (Table 4). Medicare coverage for each test reflects the currently accepted screening guidelines and may therefore change if the screening guidelines change.
Genetic predisposition A small percentage of all colorectal cancers are caused by germline genetic mutations. Therefore, it is important to screen for colorectal cancer in all patients who have more than one family member affected, a family member who was affected at an early age (<50 years), a personal or family history of multiple polyps, or a personal or family history of multiple extracolonic malignancies. The AGA recommends screening colonoscopy starting at age 40, or 10 years before the youngest age at diagnosis in the patient’s family, whichever is earlier. Colonoscopy can then be repeated every 5 years.1
Familial adenomatous polyposis is a genetic condition caused by a mutation in the APC gene on chromosome 5. Affected individuals develop hundreds of colorectal polyps, and colorectal cancer is inevitable if the colon is not removed. Persons with this disorder should have annual sigmoidoscopy beginning at age 10 to 12, according to the AGA.1 Genetic counseling and testing should be offered to patients with familial adenomatous polyposis to assess the risk in relatives and to consider colectomy.
Hereditary nonpolyposis colorectal cancer (HNPCC) is an inherited genetic condition caused by mutations in mismatch repair genes located on chromosome 2, 3, or 7. HNPCC increases the risk of developing colorectal cancer as well as other cancers, including endometrial, ovarian, renal, hepatobiliary, gastric, and small intestinal. HNPCC is classically defined as colorectal cancer in 3 or more family members (2 of whom are first-degree relatives of the third member), involving at least 2 generations, and with at least one person diagnosed before the age of 50. Individuals suspected of having this disorder should have colonoscopy every 1 to 2 years beginning at age 20 to 25 years, or 10 years before the youngest age at colon cancer diagnosis in the family, whichever is earlier.1 Genetic testing should be offered to first-degree relatives of persons with a known mismatch repair gene mutation and to those who meet any 1 of the first 3 Bethesda guidelines criteria (Table 5). Since HNPCC also increases susceptibility to endometrial cancer, women should be screened with endometrial aspiration or ultrasound starting at age 25 to 35 years.
Inflammatory bowel disease In patients with longstanding, extensive inflammatory bowel disease, surveillance colonoscopy with systematic biopsies should be performed to assess the extent of disease. Colonoscopy is commonly performed after 8 years of diagnosis of the disease in patients with pancolitis and after 15 years in those with left-sided colitis. Follow-up colonoscopies are recommended every 1 to 2 years thereafter.1
New Tests Virtual colonoscopy This computer-enhanced spiral computed tomography scan allows visualization of the entire colon after bowel preparation and air insufflation. Sensitivity and specificity are about 90% and 72%, respectively, for polyps larger than 1 cm.28 Virtual colonoscopy is a safe and noninvasive procedure.29 It rivals conventional colonoscopy and exceeds double-contrast barium enema in sensitivity for colorectal polyps.30,31
Virtual colonoscopy has some significant advantages over conventional colonoscopy. It is a noninvasive test that is rapid and requires no sedation. However, it has certain drawbacks that keep conventional colonoscopy as the gold standard method for colon cancer screening. Sensitivity is reduced for polyps smaller than 1 cm, and the texture and color details of the colonic mucosa are not seen. Biopsy specimens cannot be obtained, and the test is expensive and associated with radiation exposure.28,32
Despite its limitations, virtual colonoscopy could lead to increased patient compliance and cancer detection, resulting in less colon cancer. However, virtual colonoscopy is not yet ready for widespread screening outside the research setting, pending improvements in the technology, clinical studies of performance in average-risk patients, and a better understanding of its costs.
Stool DNA tests In this technique, DNA shed in the stool is tested for the presence of genetic changes associated with the pathogenesis of colon cancer. The test has a sensitivity and specificity of 91% and 93%, respectively.33
Conclusion Colorectal cancer is one of only a few preventable cancers. Screening for colorectal cancer is one of the most successful preventive care measures in modern medical practice. Beginning at age 50, men and women who are at average risk should undergo screening. Persons at high risk should begin screening earlier and be screened more frequently. Unfortunately, colorectal cancer screening is fraught with adherence problems. Better monitoring of patient referral and improved communication between physicians and patients may enhance adherence.
Self-assessment test 1. Which of these statements about colorectal cancer is NOT true? A. People older than 70 years often present with more aggressive disease than younger patients B. Blacks have a higher incidence and mortality rate than Hispanics C. Three fourths of the cancers are sporadic D. It usually develops from benign adenomatous polyps over 5 to 15 years
2. Consumption of which of the following items can cause false-negative FOBT results? A. Red meat B. Aspirin >300 mg/day C. Cantaloupe D. Vitamin C >600 mg/day
3. All these are recommended screening for average-risk persons, except: A. Annual FOBT B. Flexible sigmoidoscopy every 5 years C. Double-contrast barium enema every 10 years D. Colonoscopy every 10 years
4. Which of these recommendations is appropriate for someone with HNPCC? A. Annual sigmoidoscopy beginning at age 10 to 12 years B. Colonoscopy every 1 to 2 years beginning at age 20 to 25 years C. Colonoscopy every 5 years D. Sigmoidoscopy every 3 years
5. All the following patients should begin screening at age 40 years, except: A. Men with a first-degree relative with adenomatous polyp diagnosed at age 55 years B. Women with 2 first-degree relatives diagnosed with colorectal cancer at age 60 years C. Women with a first-degree relative diagnosed with colorectal cancer at age 62 years D. Men with a second-degree relative diagnosed with colorectal cancer
References 1. Winawer SJ, Fletcher RH, Miller L, et al. Colorectal cancer screening: clinical guidelines and rationale [published corrections appear in Gastroenterology. 1997;112:1060 and 1998;114:635]. Gastroenterology. 1997;112:594-642.
2. Smith RA, Cokkinides V, Eyre HJ. American Cancer Society guidelines for the early detection of cancer, 2005. CA Cancer J Clin. 2005; 55:31-44.
3. US Preventive Services Task Force. Screening for colorectal cancer: recommendation and rationale. Ann Intern Med. 2002;137:129-131.
4. Towler BP, Irwig L, Glasziou P, et al. Screening for colorectal cancer using the faecal occult blood test, Hemoccult. Cochrane Database Syst Rev. 2005;4. Available at www.cochrane.org/reviews/en/ab001216.html
5. Ebell MH, Siwek J, Weiss B, et al. Strength of recommendation taxonomy (SORT): a patient-centered approach to grading evidence in the medical literature. Am Fam Physician. 2004;69:548-556.
6. American Cancer Society. Cancer Facts and Figures 2005. Atlanta, Ga: American Cancer Society; 2005.
7. Rudy DR, Zdon MJ. Update on colorectal cancer. Am Fam Physician. 2000;61: 1759-1770,1773-1774.
8. Pignone M, Saha S, Hoerger T, et al. Cost-effectiveness analyses of colorectal cancer screening: a systematic review for the US Preventive Services Task Force. Ann Intern Med. 2002;137:96-104.
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13. Hardcastle JD, Chamberlain JO, Robinson MH, et al. Randomised controlled trial of faecal-occult-blood screening for colorectal cancer. Lancet. 1996;348: 1472-1477.
14. Church TR, Ederer F, Mandel JS. Fecal occult blood screening in the Minnesota study: sensitivity of the screening test. J Natl Cancer Inst. 1997;89: 1440-1448.
15. Kahi CJ, Imperiale TF. Do aspirin and nonsteroidal anti-inflammatory drugs cause false-positive fecal occult blood test results? A prospective study in a cohort of veterans. Am J Med. 2004;117: 837-841.
16. Rozen P, Knaani J, Samuel Z. Eliminating the need for dietary restrictions when using a sensitive guaiac fecal occult blood test. Dig Dis Sci. 1999;44:756-760.
17. Young GP, St John DJ, Winawer SJ, et al. Choice of fecal occult blood tests for colorectal cancer screening: recommendations based on performance characteristics in population studies: a WHO (World Health Organization) and OMED (World Organization for Digestive Endoscopy) report. Am J Gastroenterol. 2002;97:2499-2507.
18. Lieberman DA, Harford WV, Ahnen DJ, et al, for the Veterans Affairs Cooperative Study Group 380. One-time screening for colorectal cancer with combined fecal occult-blood testing and examination of the distal colon. N Engl J Med. 2001;345:555-560.
19. Rozen P, Knaani J, Samuel Z. Performance characteristics and comparison of two immunochemical and two guaiac fecal occult blood screening tests for colorectal neoplasia. Dig Dis Sci. 1997;42:2064-2071.
20. Selby JV, Friedman GD, Quesenberry CP Jr, et al. A case control study of screening sigmoidoscopy and mortality from colorectal cancer. N Engl J Med. 1992;326: 653-657.
21. Wallace MB, Kemp JA, Trnka YM, et al. Is colonoscopy indicated for small adenomas found by screening flexible sigmoidoscopy? Ann Intern Med. 1998;129:273-278.
22. Atkin WS, Morson BC, Cuzick J. Long-term risk of colorectal cancer after excision of rectosigmoid adenomas. N Engl J Med. 1992; 326:658-662.
23. Winawer SJ, Flehinger BJ, Schottenfeld D, et al. Screening for colorectal cancer with fecal occult blood testing and sigmoidoscopy. J Natl Cancer Inst. 1993;85:1311-1318.
25. Scheitel SM, Ahlquist DA, Wollan PC, et al. Colorectal cancer screening: a community case-control study of proctosigmoidoscopy, barium enema radiography, and fecal occult blood test efficacy. Mayo Clin Proc. 1999;74:1207-1213.
26. O’Leary BA, Olynyk JK, Neville AM, et al. Cost-effectiveness of colorectal cancer screening: comparison of community-based flexible sigmoidoscopy with fecal occult blood testing and colonoscopy. J Gastroenterol Hepatol. 2004;19: 38-47.
27. Denberg TD, Melhado TV, Coombes JM, et al. Predictors of nonadherence to screening colonoscopy. J Gen Intern Med. 2005;20:989-995.
28. Yee J, Akerkar GA, Hung RK, et al. Colorectal neoplasia: performance characteristics of CT colonography for detection in 300 patients. Radiology. 2001;219:685-692.
29. Pickhardt PJ, Choi JR, Hwang I, et al. Computed tomographic virtual colonoscopy to screen for colorectal neoplasia in asymptomatic adults. N Engl J Med. 2003;349: 2191-2200.
30. Ferrucci JT. CT colonography for colorectal cancer screening: lessons from mammography. AJR Am J Roentgenol. 2000;174:1539-1541.
31. Johnson CD, Toledano AY, Herman BA, et al, for the American College of Radiology Imaging Network A6656. Computerized tomographic colonography: performance evaluation in a retrospective multicenter setting. Gastroenterology. 2003;125:688-695.
32. Morrin MM, LaMont JT. Screening virtual colonoscopy—ready for prime time? [editorial]. N Engl J Med. 2003;349:2261-2264.
33. Ahlquist DA, Skoletsky JE, Boynton KA, et al. Colorectal cancer screening by detection of altered human DNA in stool: feasibility of a multitarget assay panel. Gastroenterology. 2000;119:1219-1227.
Practice points
• Increasing age is a major risk factor for sporadic colorectal cancer, with 90% of cases occurring in patients older than 50 years.
• Persons at average risk should undergo screening for colorectal cancer beginning at age 50. Those at high risk require more frequent screening.
• FOBT should be done annually, along with flexible sigmoidoscopy every 5 years. A positive FOBT or sigmoidoscopy is an indication for colonoscopy.
• Colonoscopy is the most sensitive and specific screening test. It should be done every 10 years.
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