Beyond the genes altered sequentially as part of the of the adenoma–carcinoma sequence such as the oncogenes, APC and KRAS, and tumor suppressor genes, TP53 and deleted in colorectal carcinoma (DCC), a significant proportion of colorectal cancers display high degrees of microsatellite instability (MSI) as a result of defects in genes involved in the DNA mismatch repair (MMR) pathway such as MLH1, MSH2, MSH6, and PMS2 [5]. Here, KRAS is linked to colorectal carcinoma.