Colon Cancer Prevention

Colon cancer prevention strategies fall into three major categories: (a) identification and removal of precursor and early lesions, (b) dietary alterations, and (c) chemoprevention. Disease prevention falls into primary and secondary modalities. Primary prevention is defined as prevention of disease by some active intervention before the disease occurs. The second form of disease prevention is called secondary prevention, which involves detecting a disease before it is symptomatic and implementing an intervention to prevent the clinical manifestations of the disease, such as by removing a colonic adenoma thereby preventing its progression to adenocarcinoma.

If an improvement in colon cancer survival is to occur, increased efforts need to focus on primary prevention as well as on early detection and removal of premalignant and malignant lesions. Since epidemiologic, animal, and biochemical studies suggest that diets high in total calories and fat and low in various dietary fibers, vegetables, and micronutrients associate with an increased incidence of colorectal cancer, one
primary means of prevention would be dietary education and diet modification. There are no data on the efficacy of this approach; therefore, most attention has focused on early detection of colonic neoplasms and chemoprevention.

TABLE 14.5 Screening Options of Patients at Average Risk for Colorectal Cancer

Screening Method	Interval	Consequences of a Positive Test
Fecal occult blood testing	Annual	Colonoscopy
Flexible sigmoidoscopy	Every 5 years	Polypectomy for distal polyps; possibly colonoscopy
Combined FOBT and sigmoidoscopy	FOBT annually, sigmoidoscopy every 5 years
Colonoscopy	Every 10 years	Polypectomy; surgery for cancers or lesions that are not endoscopically resectable
Double-contrast barium enema	Every 5 years	Colonoscopy
FOBT, fecal occult blood testing.

Screening for Colorectal Adenomas and Carcinomas

Early Detection of Colorectal Cancer

The beneficial effects of early adenoma detection and removal were initially reported by Gilbertson in 1974 (122). Several more recent trials based on sigmoidoscopy or colonoscopy have reported a significant reduction in mortality as a result of screening (123,124,125). Case control studies indicate a reduction in the mortality rate from distal colorectal cancers in the magnitude of 60% to 85% (126). All studies indicate that the cancers detected have a more favorable stage when the patients are in a screening program (127). The reduction in cancer mortality results from (a) identification of early curable cancers, (b) identification and removal of premalignant polyps, and (c) the benefits of subsequent surveillance.

Screening recommendations vary depending on whether a patient falls into a high- or average-risk category. Therefore, asymptomatic individuals should have their risk evaluated to include an analysis of inherited syndromes, personal history of adenomas, or colorectal cancer and IBD (126,127).

Screening of Average-risk Populations

In 1995, an expert panel was assembled by the U.S. Agency for Health Care Policy and a consortium of gastroenterological societies to prepare clinical guidelines for colorectal cancer screening. The panel’s initial report was published in 1997 (128) and later updated in 2003 (128). Screening for colorectal carcinoma is recommended for all persons aged 50 and older using one of several possible strategies: fecal occult blood testing (FOBT), flexible sigmoidoscopy, a combination of FOBT and sigmoidoscopy, colonoscopy, and double-contrast barium enema (Table 14.5). The rationale for presenting patients with a number of screening options lies in the fact that no single test is of unequivocal superiority to the others, and giving patients a choice of methodologies may increase the likelihood that screening will occur.

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