The RAS-RAF-MAPK pathway is a key signal transduction pathway in many cancers including CRC and was investigated in the current study by examining the mutations status of KRAS, NRAS, BRAF and MAP2K4. In the context of flat colorectal lesions this pathway is still controversial, since it has been reported that KRAS mutations would be uncommon in flat adenomas [13], [14], while later studies claimed the opposite [16] or did not detect a difference with polypoid lesions [15], [32]. This evidence concerns the gene MAP2K4 and colorectal carcinoma.