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. 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. 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.