Use of Colonoscopy to Screen Asymptomatic Adults For Colorectal Cancer
abstracts & commentary
Synopsis: These reports reinforce the growing suspicion among physicians that in recommending flexible sigmoidoscopy to screen persons for colorectal cancer, we are promoting a suboptimal approach.
Sources: Lieberman DA, et al. N Engl J Med 2000;343:162-168; Imperiale TF, et al. N Engl J Med 2000;343:169-174.
The New England Journal of Medicine recently published two studies with similar objectives whose results are of critical importance to clinicians and patients alike. The first paper, by Lieberman and colleagues, reports the results of a study carried out at 13 Veterans Affairs medical centers between February 1994 and January 1997, which had as its objectives "to determine the prevalence and location of colonic neoplasia in asymptomatic patients, the risk of proximal advanced neoplasia in patients with and in those without neoplasia in the distal colon, and the likelihood that advanced proximal neoplasia would be detected on the basis of the presence of an adenoma in the distal colon." The study enrolled 3196 men between the ages of 50 and 75 years, of whom 97.7% underwent colonoscopy to the cecum. Of this group, all were asymptomatic, 13.9% had a family history of colorectal cancer, and the remaining were free of apparent risk factors.
Imperiale and colleagues report the results of consecutive colonoscopic examination of 1994 asymptomatic Eli Lilly employees (59% men), aged 50 years or older, who were studied between September 1995 and December 1998, of whom 97% underwent colonoscopy to the cecum. The primary objective of this study was "to determine the relative risk of advanced proximal neoplasia in patients with distal polyps, either hyperplastic or neoplastic, as compared with persons with no distal polyps." A secondary objective was to determine the risk of large proximal neoplasms (³ 10 mm in diameter) according to distal findings. No participant had clinical evidence to suspect colon cancer/polyps nor any prior personal history of same. The proportion of this population that had a family history of colon cancer/polyps is not reported.
The Veterans Administration study detected one or more adenomas of any type or invasive cancer in 1171 (37.5%) patients. Of these, 329 (10.5%) had lesions which were considered "advanced" (³ 10 mm diameter adenoma, villous features, high-grade dysplasia, or invasive cancer), of which 228 were in the distal colon and 128 were in the proximal colon. Of the patients with advanced proximal colon lesions, 51.4% had no adenoma detected in the distal colon. The risk of having an advanced neoplasia increased according to age and family history. If colonoscopy had been reserved only for patients in whom lesions had been detected in the distal colon (splenic flexure or below), 62.1% of advanced colonic neoplasia would have been missed.
The study by Imperiale et al detected the combination of hyperplastic polyps, tubular adenomas and advanced neoplasms in the distal colon of 21.6% and in the proximal colon of 15.4% of patients. The prevalence of advanced proximal neoplasia increased from 1.5% in the absence of distal polyps to 4%, 7.1%, and 11.5% in the presence of distal hyperplastic polyps, tubular adenomas, and advanced neoplasms, respectively. Of the patients with advanced proximal neoplasia, 46% had no polyps in the distal colon. Male sex and age were associated with an increased risk of neoplasia.
Comment by Michael K. Rees, MD, MPH
The 1996 Preventive Services Task Force Guide To Clinical Preventive Services lists fecal occult-blood test and sigmoidoscopy as acceptable methods of screening for colon cancer. The American College of Physicians-American Society of Internal Medicine and the British Medical Journal Publishing Group 2000 Clinical Evidence (a compendium of evidence on the effects of common clinical interventions) does not include reference to colorectal cancer screening due to a lack of randomized, clinical, controlled trials. Influenced by the arbitrary dictates of Medicare and the various other payors of health care costs, it is the current practice of almost all U.S. physicians to recommend colonoscopy as a diagnostic—not screening—procedure reserved for patients presenting with rectal bleeding/guiac positive stools, discovery of polyps on screening proctosigmoidoscopy, or a personal or family history of colon cancer/polyps. Now—finally—we are presented with two excellent studies—both of which convincingly demonstrate that there is scant reason to continue to rely on screening of the distal colon as a method of deciding who is at risk for cancer of the proximal colon.
In an accompanying editorial, Podalsky comments: "These two new reports reinforce the growing suspicion among physicians that in recommending flexible sigmoidoscopy to screen persons for colorectal cancer, we are promoting a suboptimal approach. The failure of insurance companies to cover the costs of colonoscopic screening is no longer acceptable." Not only is it no longer acceptable, in my recent experience, it is no longer uniformly practiced. Although maintaining an unacceptable silence, I now find that "when recommended by your primary care physician," several managed care companies in the Boston area do now pay for "screening" colonoscopy.
Proctosigmoidoscopy is an irrational procedure that provides a false sense of security and can no longer be tolerated. By advising patients to refuse to accept anything less than colonoscopy, the informed public will soon accomplish what a compliant medical profession has failed to do, insurance payment for periodic examination of the entire colon of asymptomatic persons older than 50 years. Patients can also be encouraged to undergo the procedure without anesthesia, which will lessen its cost by permitting its delivery in lower overhead facilities.
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