The serrated pathway of neoplasia: new insights into an evolving concept

Twenty years ago, the only known pathway of colorectal carcinoma was the adenoma-carcinoma sequence; while profoundly important, this pathway does not account for all cases of colorectal carcinoma. Today the serrated pathway is recognized as an alternative pathway to colorectal carcinoma. The signature features of the serrated pathway include sessile serrated adenomas, microsatellite instability, and the potentially rapid conversion to malignancy. The family of histologically serrated lesions also encompasses traditional serrated adenoma and variants such as the filiform serrated adenoma, serrated epithelial change/dysplasia, and, potentially, colonic perineurioma. This review highlights key morphologic and molecular concepts in the serrated pathway of neoplasia, and discusses how recent insights can inform clinical management decisions.