Flat adenomas are found commonly at colonoscopy throughout the world. Similarly, small, flat submucosally invasive cancers have been described worldwide but are relatively rare, accounting for 5% to 10% of all cancers detected at colonoscopy. Although there appears to be no difference in frequency of non-polypoid colorectal neoplasms between East and West, considerable variation has been reported by individual studies, probably because of lack of consistency when defining a flat lesion. Flat elevated lesions are the most common type of flat lesion and do not appear to have a greatly increased risk of harboring invasive malignancy; however, flat lesions with depression have a significant risk of malignancy and are probably the precursor lesions for most small, flat, or ulcerating cancers.
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