[Molecular pathology of colorectal cancer]

In recent years, several predictive and prognostic biomarkers have been established in colorectal cancer (CRC). The RAS-mutation status is widely applied in the daily routine diagnostic as predictive biomarker for treatment with EGFR-inhibitors. A BRAF- mutation has no predictive value in this context. The detection of high-grade microsatellite instability (MSI-H) is a predictive biomarker for response to 5-Fluoruracil-monotherapy. Prognostic biomarkers in CRC are the MSI-status and the mutational status of BRAF. According to the current WHO classification poorly and undifferentiated CRC and MSI-associated special morphological subtypes are molecular graded depending on their MSI-status. The detection of a BRAF-mutation in the context of microsatellite stability (MSS) is associated with a very poor prognosis and thus represents the most aggressive molecular subtype of CRC. In patients with positive Bethesda criteria a stepwise immunohistochemical and molecular diagnostic scheme is proposed.