[Emerging concepts in colorectal serrated polyps].

Colorectal serrated polyps are heterogeneous epithelial lesions characterized by a serrated architecture. They include the classical hyperplastic polyps and the much rarer serrated adenomas and mixed polyps. Whereas serrated adenomas are composed of an unequivocal adenomatous epithelium with architectural serrated, mixed polyps include two separate hyperplastic and adenomatous components. During the past few years, another type of serrated polyp with only very subtle proliferation abnormalities has been described. These atypical serrated polyps may occur either sporadically or in the context of colorectal polyposis. Despite their close resemblance to traditional hyperplastic polyps, some authors argued that they should be regarded as authentically neoplastic lesions and have proposed to call them "sessile serrated adenomas". Their malignant potential requires their removal when discovered during colonoscopy. This article reviews the histological features, the endoscopic appearance, the natural history and the molecular phenotype of the different categories of serrated polyps and introduces the concept of "serrated neoplastic pathway" in the development of colorectal cancer.