However, apart from potentially coexisting secondary malignancies, the KRAS mutation mosaicism found in one heterogeneously differentiated CRC (#43, Figures 1 and 2) may explain the discordant results concerning this trait in primary CRCs and metastases reported previously [12, 13, 22] and underlines the necessity for diligent clinical and histological characterization of any atypical tumour manifestation in mCRC to prevent misleading results with negative impact on anti-EGFR targeted therapies. This evidence concerns the gene EGFR and colorectal carcinoma.