Chapter 087. Gastrointestinal Tract Cancer (Part 10)

Screening The rationale for colorectal cancer screening programs is that earlier detection of localized, superficial cancers in asymptomatic individuals will increase the surgical cure rate. Such screening programs are important for individuals having a family history of the disease in first-degree relatives. The relative risk for developing colorectal cancer increases to 1.75 in such individuals and may be even higher if the relative was afflicted before age 60. The prior use of proctosigmoidoscopy as a screening tool was based on the observation that 60% of early lesions are located in the rectosigmoid. For unexplained reasons, however, the proportion of...
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Chapter 087. Gastrointestinal Tract Cancer (Part 10) Chapter 087. Gastrointestinal Tract Cancer (Part 10) Screening The rationale for colorectal cancer screening programs is that earlierdetection of localized, superficial cancers in asymptomatic individuals willincrease the surgical cure rate. Such screening programs are important forindividuals having a family history of the disease in first-degree relatives. Therelative risk for developing colorectal cancer increases to 1.75 in such individualsand may be even higher if the relative was afflicted before age 60. The prior use ofproctosigmoidoscopy as a screening tool was based on the observation that 60% ofearly lesions are located in the rectosigmoid. For unexplained reasons, however,the proportion of large-bowel cancers arising in the rectum has been decreasingduring the past several decades, with a corresponding increase in the proportion ofcancers in the more proximal descending colon. As such, the potential for rigidproctosigmoidoscopy to detect a sufficient number of occult neoplasms to makethe procedure cost-effective has been questioned. Flexible, fiberopticsigmoidoscopes permit trained operators to visualize the colon for up to 60 cm,which enhances the capability for cancer detection. However, this technique stillleaves the proximal half of the large bowel unscreened. Most programs directed at the early detection of colorectal cancers havefocused on digital rectal examinations and fecal occult blood testing. The digitalexamination should be part of any routine physical evaluation in adults older thanage 40, serving as a screening test for prostate cancer in men, a component of thepelvic examination in women, and an inexpensive maneuver for the detection ofmasses in the rectum. The development of the Hemoccult test has greatlyfacilitated the detection of occult fecal blood. Unfortunately, even when performedoptimally, the Hemoccult test has major limitations as a screening technique.About 50% of patients with documented colorectal cancers have a negative fecalHemoccult test, consistent with the intermittent bleeding pattern of these tumors.When random cohorts of asymptomatic persons have been tested, 2–4% haveHemoccult-positive stools. Colorectal cancers have been found in with occult blood in their stool. Nonetheless, persons found to have Hemoccult-positive stool routinely undergo further medical evaluation, includingsigmoidoscopy, barium enema, and/or colonoscopy—procedures that are not onlyuncomfortable and expensive but also associated with a small risk for significantcomplications. The added cost of these studies would appear justifiable if thesmall number of patients found to have occult neoplasms because of Hemoccultscreening could be shown to have an improved prognosis and prolonged survival.Prospectively controlled trials showed a statistically significant reduction inmortality from colorectal cancer for individuals undergoing annual screening.However, this benefit only emerged after >13 years of follow-up and wasextremely expensive to achieve, since all positive tests (most of which were false-positive) were followed by colonoscopy. Moreover, these colonoscopicexaminations quite likely provided the opportunity for cancer prevention throughthe removal of potentially premalignant adenomatous polyps since the eventualdevelopment of cancer was reduced by 20% in the cohort undergoing annualscreening. Screening techniques for large-bowel cancer in asymptomatic personsremain unsatisfactory. Compliance with any screening strategy within the generalpopulation is poor. At present, the American Cancer Society suggests fecalHemoccult screening annually and flexible sigmoidoscopy every 5 yearsbeginning at age 50 for asymptomatic individuals having no colorectal cancer riskfactors. The American Cancer Society has also endorsed a total colonexamination (i.e., colonoscopy or double-contrast barium enema) every 10 yearsas an alternative to Hemoccult testing with periodic flexible sigmoidoscopy.Colonoscopy has been shown to be superior to double-contrast barium enema andalso to have a higher sensitivity for detecting villous or dysplastic adenomas orcancers than the strategy employing occult fecal blood testing and flexiblesigmoidoscopy. Whether colonoscopy performed every 10 years beginning afterage 50 will prove to be cost-effective and whether it may be supplanted as ascreening maneuver by sophisticated radiographic techniques (virtualcolonoscopy) remains unclear. More effective techniques for screening areneeded, perhaps taking advantage of the molecular changes that have beendescribed in these tumors. Analysis of fecal DNA for multiple mutationsas ...