KRAS and colorectal carcinoma: So far, three fundamental gene categories are considered to be implicated in CRC initiation and progression: firstly, tumor suppressor genes such as APC, DCC, TP53, SMAD2, SMAD4, and CDKN2A; secondly, oncogenes such as KRAS and NRAS, and thirdly, DNA repair genes, including members of the DNA mismatch repair mechanism and MUTYH [3].