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  • Multidisciplinary Symposium — Screening for Cancer: Monday 15 October 2001, 10.20–12.45
  • Open Access

Colon cancer screening

  • 1
Cancer Imaging20152:3

https://doi.org/10.1102/1470-7330.2001.008

©  International Cancer Imaging Society 2001

  • Published:

Keywords

  • Colorectal Cancer
  • Familial Adenomatous Polyposis
  • Fecal Occult Blood Testing
  • Adenomatous Polyp
  • Compute Tomography Colonography

Colorectal cancer is a major health problem worldwide. Last year in the United States alone, more than 130 000 people were diagnosed with colorectal cancer and more than 56 000 died of their disease[1]. Fortunately, this neoplasm is highly suited to screening because of its long preclinical phase, during which it is detectable and curable[2]. Nevertheless, screening programs for colorectal cancer have been only partly successful, owing largely to poor patient compliance with screening recommendations[3,4]. A number of organizations including the World Health Organization (WHO), the American Cancer Society (ACS), the Agency for Health Care Policy and Research (AHCPR), the US Preventive Service Task Force (USPSTF), and the American Gastroenterology Association (AGA) have issued or endorsed guidelines for colorectal cancer screening. This review summarizes the clinical evidence supporting colorectal cancer screening in the average-risk population and in high-risk groups, discusses the advantages and disadvantages of the available screening tests, and outlines the currently recommended guidelines for screening based on risk category.

Average-risk population

Average-risk patients are asymptomatic individuals aged 50 years of age or older who have no personal or family history of colorectal cancer or adenomatous polyps and no history of inflammatory bowel disease. The two most recently published screening recommendations, those of the ACS[5] and AHCPR[6], present guidelines for screening average-risk patients in the form of lists of options (Table 1). The options include annual fecal occult blood test (not included as a stand alone test in the ACS guidelines), flexible sigmoidoscopy every 5 years, annual fecal occult blood test plus flexible sigmoidoscopy every 5 years, double-contrast barium enema every 5 to 10 years, and colonoscopy every 10 years.
Table 1

Recommended options for colorectal cancer screening in asymptomatic, average-risk individuals*

Starting at age 50

 

Annual FOBT†

 

Flexible sigmoidoscopy every 5 years

 

Annual FOBT and sigmoidoscopy every 5 years

 

Colonoscopy every 10 years

 

Double-contrast barium enema every 5–10 years

*Winawer SJ, Fletcher RH, Miller L et al. Colorectal cancer screening: clinical guidelines and rationale. Gastroenterology 1997; 112: 594–642.

†The American Cancer Society does not recommend fecal occult blood testing (FOBT) by itself.

Fecal occult blood testing

Fecal occult blood testing (FOBT) is the safest and least expensive of the currently available screening tests. Three prospective, randomized, controlled trials have demonstrated the effectiveness of FOBT in reducing colorectal cancer mortality by 15% to 33%[7–9]. However, its benefit in reducing colorectal mortality is attributed not only to early cancer detection but also to the incidental discovery and removal of adenomatous polyps at subsequent colonoscopy. Such chance discovery of adenomatous polyps and non-bleeding cancers by colonoscopy has been estimated to account for 16–25% of the colorectal cancer deaths prevented by the use of FOBT[10]. Limitations of FOBT include its relatively low sensitivity for detecting cancers and its inability to detect the vast majority of adenomas[11]. Because colorectal cancers bleed intermittently, 50% or more of patients with colorectal cancer may have a negative test result[11,12]. Thus, to be effective, FOBT must be administered annually or biennially, which makes patient compliance a problem. Furthermore, the positive predictive value of FOBT is only approximately 10%[11,12].

Flexible sigmoidoscopy

Data from two case-control studies support the effectiveness of flexible sigmoidoscopy in reducing colorectal cancer mortality[13,14]. Individuals in these studies who had undergone at least one screening sigmoidoscopy during the previous 10 years had only a 21% to 30% risk of developing fatal colorectal cancer as control subjects. Compared with colonoscopy, flexible sigmoidoscopy is less expensive and has a lower complication rate (approximately one to two perforations per 10 000 examinations)[6,15]. In addition, it requires a less rigorous bowel preparation and does not require sedation. The major disadvantage of flexible sigmoidoscopy, however, is that it examines only a portion of the colon, thereby enabling detection of only approximately 50% of colonic lesions[16,17]. If a polyp is detected by sigmoidoscopy, colonoscopy is still needed to evaluate the entire colon.

Fecal occult blood testing combined with flexible sigmoidoscopy

The rationale for combining FOBT with flexible sigmoidoscopy is two-fold: (1) approximately half of the cancers missed by FOBT would be detected at sigmoidoscopy, and (2) FOBT is insensitive for detecting adenomas, many of which would be detected at sigmoidoscopy. Nevertheless, there is little direct evidence to support such a combined approach. Furthermore, a large number of colonic adenomas and carcinomas are not within reach of the sigmoidoscope. Although some of these lesions would be detected when a positive sigmoidoscopy leads to a follow-up colonoscopy or barium enema, many of them would be missed, as up to 50% of proximal colonic cancers are not associated with a distal adenoma[18–22].

Colonoscopy

Colonoscopy is the only colorectal cancer screening test that allows evaluation of the entire colon and provides the opportunity to remove polyps and small polypoid cancers at the same time. Although there are no controlled trials demonstrating that screening colonoscopy reduces colorectal cancer incidence or mortality in those at average risk for the disease, indirect evidence for the effectiveness of colonoscopy comes from one case-control study[15] and uncontrolled observational studies[23–25]. The case-control study showed a 40% to 50% reduction in colorectal cancer incidence in individuals who had undergone colonoscopy or polypectomy[15]. A limitation of colonoscopy is that it is incomplete in 5–15% of patients[18,19,26]. In addition, colonoscopy is associated with the highest risk of complications of all screening tests. Perforation occurs in approximately 1 in 1000 colonoscopies, major bleeding occurs in approximately 3 per 1000, and one to three patients undergoing colonoscopy die of complications from the procedure[6,19,26–28].

Barium enema examination

Because of its higher sensitivity than single contrast barium enema, double-contrast barium enema is considered the current radiologic alternative to colonoscopy for colorectal cancer detection. Similar to colonoscopy, barium enema examination is a test that allows evaluation of the entire colon in approximately 90–95% of patients[29–31]. No data are available on the sensitivity of double-contrast barium enema in a screening population. In patients undergoing diagnostic examinations, the reported sensitivity of this test for the detection of cancer is 85–90%[32–34], and the sensitivity for adenomas larger than 1 cm is 75–90%[35,36]. However, recently published data from the National Polyp Study in the United States demonstrated a sensitivity for double-contrast barium enema of only approximately 50% for polyps 1 cm or larger in patients undergoing surveillance after removal of adenomatous polyps[37]. Advantages of double-contrast barium enema compared with colonoscopy are that it is safer (approximately one perforation in 25 000 procedures)[38], less expensive, and does not require sedation. Its major disadvantages are its lower sensitivity and the inability to remove polyps, thus requiring colonoscopy or sigmoidoscopy after positive examinations.

Computed tomography (CT) colonography

CT colonography (also known as ‘virtual colonoscopy’) is a relatively new radiologic procedure that holds promise as a colorectal cancer-screening test, but requires further evaluation. In this study a helically acquired volumetric data set of the abdomen and pelvis is obtained after insufflation of the colon with air or carbon dioxide. The colon can then be viewed with either 2-dimensional or 3-dimensional techniques. The 3-dimensional visualization technique provides a perspective that simulates colonoscopic navigation of the colonic lumen. Prospective studies performed in selected groups of high-risk patients have reported sensitivities with CT colonography of 50% to 91% for polyps 1 cm or larger[39–43]. It is important to note, however, that the results of such studies cannot be generalized to a screening population of average-risk individuals. One potential advantage of CT colonography is the possibility of avoiding rigorous bowel preparation through the use of barium stool tagging and electronic subtraction of stool from the colon prior to diagnostic evaluation of the images[44]. Whether CT colonography will become a viable alternative to colonoscopy for colorectal cancer screening remains to be seen.

Cost-effectiveness

Most studies of the cost-effectiveness of FOBT (every 1 to 2 years), flexible sigmoidoscopy (every 5 years), colonoscopy (every 10 years) and double-contrast barium enema examination (every 5 to 10 years) have shown costs per life-year saved ranging from approximately $2000 to $15 000 for FOBT up to $22 000 for colonoscopy[45–48]. These figures compare favorably with estimates of cost per life-year saved for breast cancer, cervical cancer and hypertension screening programs, which range from approximately $9000 to $50 000[49–50].

Screening recommendations (Table 1)

Recommended options for colorectal cancer screening of asymptomatic individuals of average risk include the following (beginning at age 50): annual FOBT (if positive, examine entire colon with colonoscopy or double-contrast barium enema examination), flexible sigmoidoscopy every 5 years (followed by colonoscopy if adenomatous polyp or cancer found), annual FOBT and sigmoidoscopy every 5 years, colonoscopy every 10 years, or double-contrast barium enema examination every 5–10 years. It should be noted that the American Cancer Society does not endorse the option of FOBT by itself because of the relatively low mortality reductions that have been associated with its use[5].

High-risk population

Individuals at increased risk for colorectal cancer are those with: (1) a personal or family (first degree relative) history of colorectal cancer or adenoma; (2) longstanding ulcerative or Crohn’s colitis; or (3) a genetic predisposition to a hereditary polyposis or nonpolyposis syndrome. Individuals with a single first-degree relative with colorectal cancer have a risk of developing colorectal cancer approximately 1.7 times that of the general population[51]. In addition, cancers tend to occur at an earlier age in this population. First-degree relatives of patients with adenomas have a similar increased risk of colorectal cancer[52,53]. Patients with long-standing ulcerative colitis are at increased risk for colorectal cancer, particularly those with pancolitis and early age of onset of their disease[54]. Colorectal cancer in this group of patients is thought to develop in areas of mucosal dysplasia. Patients with longstanding Crohn’s colitis are also at increased risk for colorectal cancer, but the risk is lower than that associated with ulcerative colitis[55]. Familial adenomatous polyposis coli (FAP) is a disease that results from inherited or acquired defects in the APC gene located on the fifth chromosome. Patients with this disease develop numerous polyps throughout the colon, which results in a 100% risk of colorectal cancer if the colon is not removed. Hereditary nonpolyposis colorectal cancer (HNPCC) is an autosomal dominant disorder that results in a familial predisposition to multiple cancers. The colon cancers typically occur at a young age, are often located in the right colon, and may be associated with extracolonic neoplasms[56].

Screening recommendations (Table 2)

For individuals with first-degree relatives with colorectal cancer or an adenomatous polyp, the screening recommendations are the same as for the average risk population, except that screening should begin at age 40. (Patients with a personal history of colorectal cancer or adenomatous polyp are not included in this discussion, as they fall under the category of surveillance rather than screening.) The recommendation for patients with FAP is to receive genetic counseling (and possibly genetic testing to determine if the patient is a gene carrier) and to undergo flexible sigmoidoscopy annually beginning at puberty. The recommendation for patients with HNPCC is to receive genetic counseling (and possibly genetic testing) and to undergo colonoscopy every 1–2 years beginning at age 20–30, with annual colonoscopies beginning at age 40. The recommendation for patients with longstanding ulcerative colitis is to undergo colonoscopy with biopsies looking for dysplasia every 1–2 years beginning 8 years after diagnosis for pancolitis and beginning 15 years after diagnosis for left-sided disease. However, there is no direct evidence that this practice reduces colorectal cancer mortality in these patients and none that it is more effective than colectomy based on extent and duration of disease[6]. Surveillance for colorectal cancer is not currently recommended for patients with Crohn’s colitis[57].
Table 2

Recommendations for colorectal cancer screening in individuals at increased risk*

First-degree relative with colorectal cancer or adenomatous polyp(s): same as for average risk individual, but begin at age 40

Family history of FAP

 

Genetic counseling (consider genetic testing)

 

Annual flexible sigmoidoscopy beginning at puberty if gene carrier or indeterminate

Family history of HNPCC

 

Genetic counseling (consider genetic testing)

 

Colonoscopy every 1–2 years beginning at age 20–30, annually beginning at age 40

History of inflammatory bowel disease

 

Consider colonoscopy surveillance for dysplasia every 1–2 years beginning after 8 years of disease for pancolitis and after 15 years of disease for left-sided colitis

*Winawer SJ, Fletcher RH, Miller L et al. Colorectal cancer screening: clinical guidelines and rationale. Gastroenterology 1997; 112: 594–642.

FAP, familial adenomatous polyposis; HNPCC, hereditary nonpolyposis colorectal cancer.

Authors’ Affiliations

(1)
Mallinckrodt Institute of Radiology, Washington University School of Medicine, St Louis, Missouri, USA

References

  1. Greenlee RT, Murray P, Bolden S, Wingo PA. Cancer statistics: 2000. CA Cancer J Clin 2000; 50: 7–33.View ArticlePubMedGoogle Scholar
  2. Bond JH. Screening guidelines for colorectal cancer. Am J Med 1999; 106(1A) 7S–10S: 75–105.View ArticlePubMedGoogle Scholar
  3. Vernon SW. Participation in colorectal cancer screening: a review. J Natl Cancer Inst 1997; 89: 1406–23.View ArticlePubMedGoogle Scholar
  4. Centers for Disease Control. Screening for colorectal cancer — United States, 1997. MMWR 1999; 48: 116–121.Google Scholar
  5. Byers T, Levin B, Rothenberger D. American Cancer Society guidelines for screening and surveillance for early detection of colorectal polyps and cancer: update 1997. American Cancer Society Detection and Treatment Advisory Group on Colorectal Cancer. CA Cancer J Clin 1997; 47: 154–60.View ArticlePubMedGoogle Scholar
  6. Winawer SJ, Fletcher RH, Miller L et al. Colorectal cancer screening: clinical guidelines and rationale. Gastroenterology 1997; 112: 594–642.View ArticlePubMedGoogle Scholar
  7. Mandel JS, Bond JH, Church TR et al. Reducing mortality from colorectal cancer by screening for fecal occult blood. Minnesota Colon Cancer Control Study. N Engl J Med 1993; 328: 1365–71.View ArticlePubMedGoogle Scholar
  8. Kronborg O, Fenger C, Olsen J et al. Randomized study of screening for colorectal cancer with faecal-occult-blood test. Lancet 1996; 348: 1467–71.View ArticlePubMedGoogle Scholar
  9. Hardcastle JD, Chamberlain JO, Robinson MHE et al. Randomized controlled trial of faecal-occult-blood screening for colorectal cancer. Lancet 1996; 348: 1472–7.View ArticlePubMedGoogle Scholar
  10. Ederer F, Church TR, Mandel JS. Fecal occult blood screening in the Minnesota study: role of chance detection of lesions. J Natl Cancer Inst 1997; 89: 1423–8.View ArticlePubMedGoogle Scholar
  11. Ahlquist DA, Wieand HS, Moertel CG et al. Accuracy of fecal occult blood screening for colorectal neoplasia: a prospective study using Hemoccult and HemoQuant tests. JAMA 1993; 269: 1262–7.View ArticlePubMedGoogle Scholar
  12. Allison JE, Tekawa IS, Ransom LJ et al. A comparison of fecal occult-blood tests for colorectal-cancer screening. N Engl J Med 1996; 334: 155–9.View ArticlePubMedGoogle Scholar
  13. Selby JV, Friedman GD, Quesenberry CPJ et al. A case-control study of screening sigmoidoscopy and mortality from colorectal cancer. N Engl J Med 1992; 326: 653–7.View ArticlePubMedGoogle Scholar
  14. Newcomb PA, Norfleet RG, Storer BE et al. Screening sigmoidoscopy and colorectal cancer mortality. J Natl Cancer Inst 1992; 84: 1572–5.View ArticlePubMedGoogle Scholar
  15. Muller AD, Sonnenberg A. Prevention of colorectal cancer by flexible endoscopy and polypectomy: a case-control study of 32 702 veterans. Ann Intern Med 1995; 123: 904–10.View ArticlePubMedGoogle Scholar
  16. Selby JV, Friedman GD. US preventative task force. Sigmoidoscopy in the periodic health examination of asymptomatic adults. JAMA 1989; 261: 594–601.View ArticlePubMedGoogle Scholar
  17. Selby JV, Friedman GD, Collen MF. Sigmoidoscopy and mortality from colorectal cancer: the Kaiser Permanente Multiplastic Evaluation study. J Clin Epidemiol 1988; 41: 427–34.View ArticlePubMedGoogle Scholar
  18. Lieberman DA, Smith FW. Screening for colon malignancy with colonoscopy. Am J Gastroenterol 1991; 86: 1775–80.Google Scholar
  19. Rex DK, Lehman GA, Hawes RH et al. Screening colonoscopy in symptomatic average-risk persons with negative fecal occult blood tests. Gastroenterology 1991; 100: 64–7.PubMedGoogle Scholar
  20. Kadakia SC, Wrobleski CS, Kadakia AS et al. Prevalence or proximal colonic polyps in average-risk asymptomatic patients with negative fecal occult blood test and flexible sigmoidoscopy. Gastrointest Endosc 1996; 44: 112–7.View ArticlePubMedGoogle Scholar
  21. Lemmel TG, Haseman JH, Rex DK et al. Neoplasia distal to the splenic flexure in patients with proximal colon cancer. Gastrointest Endosc 1996; 44: 109–11.View ArticlePubMedGoogle Scholar
  22. Imperiale TF, Wagner DR, Ching YL, Larkin GN, Rogge JD, Ransohoff DF. Risk of advanced proximal neoplasms in asymptomatic adults according to the distal colorectal findings. N Engl J Med 2000; 343: 169–74.View ArticlePubMedGoogle Scholar
  23. Winawer SJ, Zauber AG, Ho MN et al. Prevention of colorectal cancer by colonoscopic polypectomy. N Engl J Med 1977; 329: 1977–81.View ArticleGoogle Scholar
  24. Jøgensen OD, Kronborg O, Fenger C. The Funen adenoma follow-up study: Incidence and death from colorectal carcinoma in an adenoma surveillance program. Scand J Gastroenterol 1993; 28: 869–74.View ArticleGoogle Scholar
  25. Rex DK. Colonoscopy: a review of its yield for cancer and adenomas by indication. Am J Gastroenterol 1995; 3: 353–65.Google Scholar
  26. Godreau CJ. Office-based colonoscopy in a family practice. Fam Pract Res J 1992; 12: 313–20.PubMedGoogle Scholar
  27. Jentschura D, Raute M, Winter J et al. Complications in endoscopy of the lower gastrointestinal tract: therapy and prognosis. Surg Endosc 1994; 8: 672–6.View ArticlePubMedGoogle Scholar
  28. Waye JD, Lewis BS, Yessayan S. Colonoscopy: a prospective report of complications. J Clin Gastroenterol 1992; 15: 347–51.View ArticlePubMedGoogle Scholar
  29. Bloomfield JA. Reliability of barium enema in detecting colonic neoplasia. Med J Austr 1981; 1: 631–3.Google Scholar
  30. Jaramillo E, Slezak P. Comparison between double-contrast barium enema and colonoscopy to investigate lower gastrointestinal bleeding. Gastrointest Radiol 1992; 17: 81–3.View ArticlePubMedGoogle Scholar
  31. Brewster NT, Grieve DC, Saunders JH. Double-contrast barium enema and flexible sigmoidoscopy for routine colonic investigation. Br J Surg 1994; 8: 445–7.View ArticleGoogle Scholar
  32. Rex DK, Rahmani EY, Haseman JH et al. Relative sensitivity of colonoscopy and barium enema for detection of colorectal cancer in clinical practice. Gastroenterology 1997; 112: 17–23.View ArticlePubMedGoogle Scholar
  33. Fork FT, Lindstrom C, Ekelund G. Double contrast examination in carcinoma of the colon and rectum: a prospective clinical series. Acta Radiol 1983; 24: 177–88.View ArticleGoogle Scholar
  34. Johnson DC, Carlson HC, Taylor WE et al. Barium enema of carcinoma of the colon: sensitivity of double- and single-contrast studies. Am J Radiol 1983; 140: 1143–9.Google Scholar
  35. Fork FT. Double contrast enema and colonoscopy in polyp detection. Gut 1981; 22: 971–7.PubMed CentralView ArticlePubMedGoogle Scholar
  36. Steine S, Stordahl A, Lunde OC et al. Double-contrast barium enema versus colonoscopy in the diagnosis of neoplastic disorders: aspects of decision-making in general practice. Fam Pract 1993; 10: 288–91.View ArticlePubMedGoogle Scholar
  37. Winawer SJ, Stewart ET, Zauber AG et al. A comparison of colonoscopy and double-contrast barium enema for surveillance after polypectomy. N Engl J Med 2000; 342: 1766–72.View ArticlePubMedGoogle Scholar
  38. Blakeborough A, Sheridan MB, Chapman AH. Complications of barium enema examinations: a survey of UK consultant radiologists 1992–1994. Clin Radiol 1992; 52: 142–8.View ArticleGoogle Scholar
  39. Hara AJ, Johnson CD, Reed JE et al. Detection of colorectal polyps with CT colography: initial assessment of sensitivity and specificity. Radiology 1997; 205: 59–65.View ArticlePubMedGoogle Scholar
  40. Fenlon HM, Nunes DP, Schroy PC et al. A comparison of virtual and conventional colonoscopy for the detection of colorectal polyps. N Engl J Med 1999; 341: 1496–503.View ArticlePubMedGoogle Scholar
  41. Kay CL, Kulling D, Hawes HR, Young JWR, Cotton PB. Virtual endoscopy — comparison with colonoscopy in the detection of space-occupying lesions of the colon. Endoscopy 2000; 32: 226–32.View ArticlePubMedGoogle Scholar
  42. Rex DK, Vining D, Kopecky KK. An initial experience with screening for colon polyps using spiral CT with and without CT colography (virtual colonoscopy). Gastrointest Endosc 1999; 50: 309–13.View ArticlePubMedGoogle Scholar
  43. Yee J, Akerkar GA, Hung RK et al. Colorectal neoplasia: performance characteristics of CT colonography for detection in 300 patients. Radiology 2001; 219: 685–92.View ArticlePubMedGoogle Scholar
  44. Callstrom MR, Johnson CD, Fletcher JG et al. CT colonography without cathartic preparation: feasibility study. Radiology 2001; 219: 693–8.View ArticlePubMedGoogle Scholar
  45. Eddy DM. Screening for colorectal cancer. Ann Intern Med 1990; 113: 373–84.View ArticlePubMedGoogle Scholar
  46. Glick S, Wagner JL, Johnson CD. Cost-effectiveness of double-contrast barium enema in screening for colorectal cancer. Am J Radiol 1998; 170: 629–36.Google Scholar
  47. Gyrd-Hansen D. Fecal occult blood tests: a cost-effectiveness analysis. Int J Technol Asses Health Care 1998; 14: 290–301.View ArticleGoogle Scholar
  48. Whynes DK, Nielson AR, Walker AR et al. Fecal occult blood screening for colorectal cancer: is it cost-effective? Health Econ 1998; 7: 21–9.View ArticlePubMedGoogle Scholar
  49. Garber AM, Phelps CE. Economic foundation of cost-effectiveness analysis. J Health Econ 1997; 16: 1–31.View ArticlePubMedGoogle Scholar
  50. Brown ML, Fintor L. Cost-effectiveness of breast cancer screening: preliminary results of a systematic review of the literature. Breast Cancer Res Treat 1993; 25: 113–8.View ArticlePubMedGoogle Scholar
  51. Fuchs CS, Giovannucci EL, Colditz G. A prospective study of family history and the risk of colorectal cancer. N Engl J Med 1994: 331: 1669–74.View ArticlePubMedGoogle Scholar
  52. Ahsan H, Neugut AI, Garbowski CG et al. Family history of colorectal adenomatous polyps and increased risk for colorectal cancer. Ann Intern Med 1998; 128: 900–5.View ArticlePubMedGoogle Scholar
  53. Winawer SJ, Zauber AG, Gerdes H et al. Risk of colorectal cancer in the families of patients with adenomatous polyps. National Polyp Study Workgroup. N Engl J Med 1996; 334: 82–7.View ArticlePubMedGoogle Scholar
  54. Ekbom A, Helmick C, Zack M et al. Ulcerative colitis and colorectal cancer. A population-based study. N Engl J Med 1990; 323: 1228–33.View ArticlePubMedGoogle Scholar
  55. Ekbom A, Helmick C, Zack M et al. Increased risk of large-bowel cancer in Crohn’s disease with colonic involvement. Lancet 1990; 336: 357–9.View ArticlePubMedGoogle Scholar
  56. Vasen HF, Wijnen JT, Menko FH et al. Cancer risk in families with hereditary non-polyposis colorectal cancer diagnosed by mutation analysis. Gastroenterology 1996; 110: 1020–7.View ArticlePubMedGoogle Scholar
  57. Helm JF, Sandler RS. Colorectal cancer screening. Med Clin N Am 1999; 83: 1403–22.View ArticlePubMedGoogle Scholar

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