Flat and depressed colorectal neoplasms.

An increasing body of literature is available showing the existence of flat and depressed colorectal neoplasms in Western countries. The appreciation that colorectal neoplasms may present as flat or depressed lesions has important implications, as the risk of adenocarcinoma in depressed lesions has been found to be markedly higher than in flat or protruding lesions of similar size. There is concern that flat or depressed colorectal neoplasms might be easily missed during a colonoscopy and subsequently diagnosed as cancer within a few years after a clearing examination. In this review, we appraise advances in the study of flat and depressed colorectal cancers based on the English literature published in 2000 and subsequently, with emphasis on their epidemiology, diagnosis, and therapy.