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The detection of flat and depressed colorectal lesions: which endoscopic imaging approach?

The secondary prevention of colorectal cancer (CRC) assumes that early detection and resection of precursor lesions disrupts the adenoma– carcinoma sequence and halts progression to invasive neoplastic disease. The adenoma– carcinoma sequence has until now formed the rationale for endoscopic therapies directed at reducing the incidence of CRC. The fact that snare polypectomy of exophytic lesions fails to prevent progression to carcinoma in up to 24% of cases has prompted reevaluation of the prevalence and clinicopathologic significance of flat and depressed colorectal lesions in Western population cohorts. Such lesions, although well-described in the Japanese literature, have only recently been reported in Western population cohorts. Debate has continued regarding their prevalence, anatomic localization, histopathologic characteristics, and proposed imaging modality of choice. Within this perspective, we summarize the key data pertinent to recently described endoscopic diagnostic modalities and detail their clinical applicability both for the detection of flat neoplastic lesions occurring in the “sporadic” patient cohort, familial polyposis syndromes, and chronic ulcerative colitis.