[Nosologic and anatomy pathological study of flat adenoma and associated lesions].

Flat adenomas can be dysplastic from onset, whereas for polyps the risk of malignant transformation increases over time and with the size of the polyp. A dominant autosomal syndrome characterized by the development of flat adenomas has been reported. In a retrospective study of operative specimens from high-risk patients who had surgery for colorectal cancer, the author found that flat adenomas, which had been overlooked at initial evaluation, were a potentially useful phenotype. The mucosa adjacent to the flat adenomas showed hyperplasia and increased proliferation reminiscent of the morphologic abnormalities in aberrant crypts described by Pretlow; the latter have been found to occur rapidly in rats exposed to carcinogens and have also been demonstrated in patients at high risk for colon cancer. Aberrant crypt abnormalities and flat adenomas may be premalignant lesions.