Several measures are currently recommended for colorectal cancer screening, and no single test can be considered ideal (Rex et al, 2000; Smith et al, 2001; Winawer et al, 2003). The options include FOBT (Mandel et al, 1993); flexible sigmoidoscopy (Selby et al, 1992), used alone or in combination with other tests (Lieberman et al, 2001); double-contrast barium enema, often used in combination with flexible sigmoidoscopy; and a more recently discussed approach, "primary" colonoscopy. Firm randomized-trial data support a mortality reduction through the use of FOBT, though significant limitations are conceded, including relatively high false-positive and false-negative rates (Mandel et al, 1993). Nearly as compelling are case-control data showing a mortality advantage of sigmoid-oscopy for lesions within reach of the scope (Selby et al, 1992). No data from well-designed trials have been presented to make a case for double-contrast barium enema in achieving a mortality reduction or definite stage-shift in subjects undergoing the test; long history of use and indirect data combine to support recommendations for its use (Rex et al, 1997; Winawer et al, 2000).
Colonoscopy, while a gold standard for finding colorectal neoplasia and removing precancerous adenomas (Lieberman et al, 2000), has been criticized as excessively expensive and risky for use in routine average-risk screening. It has been shown to carry a mortality advantage when used in high-risk groups, such as subjects at risk for hereditary nonpolyposis colorectal cancer (HNPCC). Figure 7-1 shows illustrative portions of 1 representative set of screening guidelines, that of the National Comprehensive Cancer Network. These guidelines differ in only minor respects from those adopted by the American Cancer Society and the American Gastroenterology Association. Similarly detailed National Comprehensive Cancer Network guidelines exist for familial and genetic high-risk screening (see www.nccn.org for a detailed online presentation).
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