Judging the guidelines for colorectal cancer screening

Judging the guidelines for colorectal cancer screening – Editorial

Steven H. Woolf

Family physicians have always liked screening for colorectal cancer, a major cause of cancer morbidity and mortality that, through simple office procedures, can be detected at an early, treatable stage. Despite this interest, we do not see, in family practice or other specialties, the same degree of screening for colorectal cancer as we see for screening of breast cancer (mammography), cervical cancer (Papanicolaou smears) and prostate cancer (prostate-specific antigen testing).

The reasons for this are well known. Patients dislike the available tests for colorectal cancer screening, and many physicians have questioned the scientific evidence that screening improves outcomes and outweighs its potential harm. In its landmark 1989 report, the U.S. Preventive Services Task Force (USPSTF) gave routine colorectal cancer screening a “C” rating (insufficient evidence to make a recommendation),[1] a position reaffirmed in 1991 by the American Academy of Family Physicians in its guidelines on the periodic health examination.[2]

A lot has changed since then, however. In 1992, a case-control study reported that sigmoidoscopy appeared to lower the risk of death from colorectal cancer by 60 percent.[3] One year later, the results of a randomized trial in Minnesota showed that screening with annual fecal occult blood tests could lower the mortality from colorectal cancer by 33 percent.[4] This evidence was compelling enough to convince the USPSTF in 1996 to abandon its neutral policy and recommend colorectal cancer screening.[5] Late last year, the AAFP also endorsed colorectal cancer screening,[6] and two European trials reaffirmed the effectiveness of screening by means of fecal occult blood testing.[7,8] In February 1997, the American Gastroenterological Association (AGA) released new colorectal cancer screening guidelines, prepared under the auspices of the Agency for Health Care Policy and Research and endorsed by the American Cancer Society, the American College of Gastroenterology and other professional groups.[9]

What do these developments and new guidelines mean for family physicians? One message is eminently clear: there is now compelling evidence and there is a strong consensus among professional groups that all persons 50 years of age and older should be offered colorectal cancer screening. Persons with a family history of colorectal cancer may need earlier screening. Given what we now know about the evidence, a failure to offer such testing to our patients is to deny them a preventive measure of proven benefit.

What remains unclear is which screening test(s) to offer. Only two tests — the fecal occult blood test and sigmoidoscopy — have been shown to reduce mortality from colorectal cancer, and only these tests have been recommended by the USPSTF as potential screening options. The new AGA guidelines are noteworthy because they add barium enema radiographic examination and colonoscopy to the list of first-line screening options.

Family physicians, strong proponents of evidence-based health practices, are wise to scrutinize new guidelines to see whether they depart from the evidence and, if so, whether the rationale for doing so is sound. They are justified in asking whether the advocacy of barium enema and colonoscopy screening by the AGA, which is not bound by rules that preclude recommendations for which direct evidence is lacking, reflects the biases of radiologists and gastroenterologists rather than good science.

The fact is, however, that the reason for including barium enema and colonoscopy as screening options has more to do with the pathogenesis of colorectal cancer than with special interests. Current data suggest that essentially all colorectal cancers originate from adenomatous polyps. It follows that removing these polyps will reduce the incidence of new cancers and lower mortality from colorectal cancer. The studies cited above support this hypothesis.

The AGA panel reasoned that it was not the fecal occult blood test and sigmoidoscopy that reduced the incidence of and mortality from colorectal cancer in these studies, but rather it was the interventions (e.g., polypectomy, removal of early-stage cancers) that followed screening. If this is true, and there is little reason to think otherwise, then any test that finds polyps and early cancers should decrease mortality from colorectal cancer. Barium enema and colonoscopy, by offering greater access to proximal lesions and detecting more polyps and earlier cancers than either fecal occult blood testing or sigmoidoscopy, would be expected to be more effective.

This hypothesis has not yet been proven, but it seems reasonable. Patients must undergo colonoscopy and polypectomy for evaluation of abnormal results on fecal occult blood tests and sigmoidoscopy. Indeed, colonoscopy (with a polypectomy) may be the ultimate weapon against colorectal cancer. Or is it?

Which screening test is the best? The answer depends on how “best” is defined: quality of the evidence, potential benefits, safety, cost? In terms of hard evidence of reduced mortality, fecal occult blood testing is the only option supported by a randomized trial. The evidence for sigmoidoscopy consists of case-control studies, and no studies have shown that barium enema or colonoscopy reduces mortality from colorectal cancer. It is for this reason that the USPSTF recommends fecal occult blood testing and sigmoidoscopy but gives a neutral “C” recommendation to barium enema and colonoscopy. Common sense suggests, however, that direct inspection of the whole bowel (by barium enema or colonoscopy) would detect more lesions and offer greater benefit than fecal occult blood tests or sigmoidoscopy. Should common sense supplant the evidence?

In terms of safety, the best test is the fecal occult blood test, followed by flexible sigmoidoscopy and barium enema, with colonoscopy posing the highest complication rate (about one perforation per 1,000 procedures). In terms of costs, there is no clear winner. While colonoscopy is the most costly (in total dollars spent per person screened), it also detects more polyps and prevents more cancers, thereby enhancing its cost-effectiveness. In fact, the cost-effectiveness ratios of an four procedures fall within an acceptable range.[10]

Because no single screening option is clearly superior to another, the AGA panel recommends giving patients the option of making their own choice. The latest position statement from the AAFP also advocates giving patients options. Tailoring the decision to patient preferences, rather than using the same screening test for all patients, is important for several reasons. First, the “best choice” for any one patient depends on the relative importance the patient assigns to potential benefit, scientific proof and safety. Recent research has shown that patients, once properly informed about the options for colorectal cancer screening, have markedly different attitudes about which test they prefer.[11] What is best for one patient may not be best for another.

Second, empowering patients to make their own choices and to select a test that suits their preferences may boost compliance rates. The fact that flexible sigmoidoscopy finds more polyps than the fecal occult blood test is irrelevant if the patient will refuse sigmoidoscopy. On the other hand, the fact that fecal occult blood testing is less expensive is immaterial if the patient is unwilling to comply with the diet or is put off by specimen collection. Even though colonoscopy may find more polyps than barium enema, barium enema may be the best test if the patient prefers it over endoscopy.

Offering patients options, rather than following a uniform screening policy with all patients, is not without its problems. Busy family physicians lack the time for long discussions. Flow sheets and reminder systems to ensure the delivery of preventive services work best when guidelines are simple and consistent. The new AGA guidelines require a discussion of four or five options, not just one or two. How can this be done in a busy office? Will the potential gains in patient compliance afforded by multiple options be lost because clinicians themselves cannot comply?

Helpful solutions to these problems are on the way. In addition to time-management techniques like delegating the explanation of options to other office staff, clinicians soon will be able to prescribe print and video materials that help patients make informed choices about screening for colorectal cancer and other difficult options, such as screening for prostate cancer, treatment for benign prostatic hyperplasia and hormone replacement therapy.[12]

In the meantime, we should begin by changing our attitudes about screening for colorectal cancer. Just as a woman’s preventive care is incomplete without giving attention to Pap smears and breast cancer screening, patients age 50 and older should not leave the office without some plan for colorectal cancer screening. Whether one uses the fecal occult blood test, sigmoidoscopy or another test is less important than ensuring that screening occurs. More than 130,000 Americans died last year from colorectal cancer, and now we can do something about it. Let’s get started.


[1.] U.S. Preventive Services Task Force. Guide to clinical preventive services. Baltimore: William & Wilkins, 1989.

[2.] Age charts for periodic health examination. Kansas City, Mo.: American Academy of Family Physicians, 1991.

[3.] Selby JV, Friedman GD, Quesenberry CP Jr, Weiss NS. A case-control study of screening sigmoidoscopy and mortality from colorectal cancer. N Engl J Med 1992;326:653-7.

[4.] Mandel JS, Bond JH, Church TR, Snover DC, Bradley GM, Schuman LM, Ederer F. Reducing mortality from colorectal cancer by screening for fecal occult blood. Minnesota Colon Cancer Control Study. N Engl J Med 1993;328:1365-71. (Published erratum appears in N Engl J Med 1993;329:672.)

[5.] U.S. Preventive Services Task Force. Guide to clinical preventive services. Baltimore: William & Wilkins, 1996.

[6.] Summary of policy recommendations for periodic health examination. In: AAFP Reference Manual. Kansas City, Mo.: American Academy of Family Physicians, 1996-1997.

[7.] Kronborg O, Fenger C, Olsen J, Jorgensen OD, Sondergaard O. Randomised study of screening for colorectal cancer with faecal-occult-blood test. Lancet 1996;348:1467-71.

[8.] Hardcastle JD, Chamberlain JO, Robinson MH, Moss SM, Amar SS, Balfour TW, et al. Randomised controlled trial of faecal-occult-blood screening for colorectal cancer. Lancet 1996;348:1472-7.

[9.] Winawer SJ, Fletcher RH, Miller L, Godlee F, Stolar MH, Mulrow CD, et al. Colorectal cancer screening and surveillance: clinical guidelines, evidence and rationale. Gastroenterology 1997;112:594-642.

[10.] Wagner JL, Tunis S, Brown M, Ching A, Almeida R. Cost-effectiveness of colorectal cancer screeing in average-risk adults. In: Young G, Rozen P, Levin B, eds. Prevention and early detection of colorectal cancer. London: Sanders, 1996.

[11.] Leard LE, Savides TJ, Ganiats TG. Patient preferences for colorectal cancer screening. J Invest Res (accepted).

[12.] Kasper JF, Mulley AG Jr, Wennberg JE. Developing shared decision-making programs to improve the quality of care. QRB Qual Rev Bull 1992;18:183-90.

Dr. Woolf is professor of family practice at the Medical College of Virginia-Virginia Commonwealth University and served as science advisor to the U.S. Preventive Services Task Force. Dr. Ganiats is associate professor and chief of the Division of Family Medicine at the University of California-San Diego School of Medicine. Drs. Ganiats and Woolf were members of the expert panel on colorectal cancer screening.

COPYRIGHT 1997 American Academy of Family Physicians

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