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The utility of flexible sigmoidoscopy as a screening tool for colon cancer.

Colorectal cancer (CRC) afflicts approximately 140,000 people annually in the United States, with fewer than half of the cancers being detected at an early stage when the rate of cure with surgery and adjunctive chemotherapy and radiation treatments is highest (Solomon & McLeod, 1993). CRC is the second leading cause of cancer death in the United States and it comprised more than 15% of all cancercare expenditures in the Medicare program between 1974 and 1981 (Byers & Gorsky, 1992). In an effort to reduce the financial burden, the American Cancer Society (ACS) currently recommends instituting a screening program that includes annual fecal occult blood testing (FOBT) beginning at age 40 and flexible sigmoidoscopy every 3 to 5 years beginning at age 50 (Wayne, Cath, 8c Pamies, 1995). Currently, there is a great deal of controversy surrounding the utility of flexible sigmoidoscopy (FS) as a screening tool for CRC, with the recommendation that colonoscopy is more sensitive and cost-effective. Although colonoscopy is more sensitive for polyps that are smaller than 10 mm in diameter and will detect lesions beyond the 60-cm reach of the sigmoidoscope, it is not advocated as a screening tool because it fails to meet three important criteria for screening tests, specifically (a) it is expensive, (b) there is a general lack of resources and trained personnel available to perform colonoscopy in asymptomatic patients, and (c) there is significant risk involved in colonoscopy (Lieberman, 1991). The application of a screening test is a complex process that involves many issues, including the timing of the test, the population to be screened, cost, patient accepmce of the test, and safety (Lieberman, 1994). In evaluating the above factors relevant to research data that we presently available, the ACS continues to recommend FS as the screening test for CRC (Lieberman, 1994). The crux of the argument against FS is the belief by some that neoplasms are moving further up the bowel. In one study, one third of the neoplasms detected on colonoscopy were found beyond the 6 k m reach of the flexible sigmoidoscope (Wayne et al., 1995). According to Lieberman (1994), the ACS is adhering to its present recommendation for screening using FS based on data from two recent casecontrol studies (Atkin, Morson, & Cuzick, 1992; Selby, Friedman, Quesenberry, & Weiss, 1992) show a reduction in mortality ranging from 70% to 79% (Selby et al., 1992) to 45% (Atkin et al., 1992). The wide range in mortality reduction was dependent on the anatomic location of the tumor; up to one third of the tumors occurred beyond the reach of the 6 k m sigmoidoscope (Wayne et al., 1995). Lieberman (1994) suggested that the use of FS would provide protection against 40% to 50% of proximal lesions that are associated with synchronous lesions in the sigmoid colon, the discovery of which would lead to a full examination of the colon. The flexible sigmoidoscopic examination has high sensitivity for detecting early cancers and adenomas (Ransohoff & Lang, 1993); polyps larger than 5 mm are rarely missed (Lieberman, 1994). The natural history of CRC is a multistage process that occurs over a 5to 10-year period, with evidence strongly suggesting that most CRCs arise from preexisting polyps (Toribara 8c Sleisenger, 1995). Using a 60cm flexible sigmoidoscope, a trained examiner can reach the descending colon and can detect 2 to 3 times as many neoplasms as one can using the rigid sigmoidoscope. The cost of FS is relatively low since no sedation is required. The sensitivity and specificity are high and its safety, ease of performance, and demonstrated benefit in reducing the incidence of CRC and the mortality from CRC within the 60-cm reach of the sigmoidoscope, as well as the long-term protective effect based on the natural history of the disease, make FS an integral part of the screening program for asymptomatic individuals of average risk (Toribara & Sleisenger,