A Novel Pit Pattern Identifies the Precursor of Colorectal Cancer Derived From Sessile Serrated Adenoma

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OBJECTIVES:Sessile serrated adenomas (SSAs) are known to be precursors of sporadic colorectal cancers (CRCs) with microsatellite instability (MSI), and to be tightly associated withBRAFmutation and the CpG island methylator phenotype (CIMP). Consequently, colonoscopic identification of SSAs has important implications for preventing CRCs, but accurate endoscopic diagnosis is often difficult. Our aim was to clarify which endoscopic findings are specific to SSAs.METHODS:The morphological, histological and molecular features of 261 specimens from 226 colorectal tumors were analyzed. Surface microstructures were analyzed using magnifying endoscopy. Mutation inBRAFandKRASwas examined by pyrosequencing. Methylation ofp16,IGFBP7,MLH1andMINT1, -2, -12and -31was analyzed using bisulfite pyrosequencing.RESULTS:Through retrospective analysis of a training set (n=145), we identified a novel surface microstructure, the Type II open-shape pit pattern (Type II-O), which was specific to SSAs withBRAFmutation and CIMP. Subsequent prospective analysis of an independent validation set (n=116) confirmed that the Type II-O pattern is highly predictive of SSAs (sensitivity, 65.5%; specificity, 97.3%).BRAFmutation and CIMP occurred with significant frequency in Type II-O-positive serrated lesions. Progression of SSAs to more advanced lesions was associated with further accumulation of aberrant DNA methylation and additional morphological changes, including the Type III, IV and V pit patterns.CONCLUSIONS:Our results suggest the Type II-O pit pattern is a useful hallmark of the premalignant stage of CRCs with MSI and CIMP, which could serve to improve the efficacy of colonoscopic surveillance.

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