Epidemiology of colorectal polyps
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The prevalence of colorectal adenomatous polyps varies widely from country to country. Among asymptomatic, average-risk patients, adenoma prevalence averages approximately 10% in sigmoidoscopy studies and more than 25% in colonoscopy studies, whereas the prevalence of colorectal cancer among these patients is less than 1%. These data may change in the future due to the advent of new technological approaches and, in particular, chromo- and magnifying endoscopy as well as confocal laser endoscopy. The cumulative incidence of new adenomas within 3 years after normal endoscopy averages about 7% by flexible sigmoidoscopy and 27% by colonoscopy. As far as risk factors for colorectal adenomas are concerned, several data are now available on the potential role of various diet items. Tobacco smoking may be important in the early stages of adenoma formation, but not necessarily in the later stages. Alcohol consumption elevates the risk of adenomatous colorectal polyps and this seems increased by ADH3 polymorphism. Another gene–environment relationship of interest in colorectal tumorigenesis may be based on folate’s effects on K-ras mutations.