Serrated Polyps of Colon and Rectum: a Clinicopathologic Review

In the past decade, there have been significant changes in the classification and nomenclature of colorectal polyps. Previously, only two groups of lesions were widely recognized, the adenoma and the hyperplastic polyp. Adenomas were considered the only precursor of colorectal cancer, and hyperplastic polyps were considered innocent with no malignant potential. However, recent discoveries about molecular pathways of colorectal cancers have significantly changed our understanding of these neoplasms. Serrated polyps-previously uniformly called hyperplastic polyps-are now known to comprise a heterogeneous family of neoplasms united by their characteristic saw tooth morphology but differing in many important ways, including their malignant potential and molecular profile. This group of neoplasms includes both hyperplastic polyps and the more recently recognized serrated adenomas. Serrated adenomas can be subdivided into the traditional serrated adenoma and the sessile serrated adenoma/polyp. Both of these lesions show characteristic molecular changes, which differ from traditional colorectal adenomatous polyps. In this review, we will discuss the morphologic features of serrated colorectal lesions, the molecular alterations that characterize them, and their role in colorectal cancer development. The English literature regarding the new nomenclature will be reviewed and the key diagnostic points will be recorded. This large group of polyps has recently been better classified which needs specific attention by pathologists, gastroenterologists and even surgeons.