[Serrated pathway of colorectal carcinogenesis]

The serrated pathway of colorectal carcinogenesis is heterogeneous with respect to its precursor lesions, molecular alterations and its prognosis. The low-risk-subtype of serrated adenocarcinomas is less frequent (<20% of all serrated adenocarcinomas) and characterized by proximal location, BRAF-mutation, high CpG-island methylation with loss of MLH1-expression and MSI-H phenotype. The assumed precursor lesion of this subtype is the sessile serrated adenoma and the 5-year overall survival is >70%. The high-risk-subtype is more frequent (>80% of all serrated adenocarcinomas) and characterized by distal location, KRAS mutation, MSI-L/MSS phenotype, lower CpG-island methylation, and possible p53 accumulation. The assumed precursor lesion is the traditional serrated adenoma and the prognosis is unfavorable (<30% 5-year overall survival). The analysis of MSI status, KRAS and BRAF mutational status and immunohistochemical analyses of hMLH1 and p53 expression enables the distinction between these two subtypes and is therefore clinically relevant, especially since treatment options for the two subtypes may differ in the future.