KRAS and colorectal carcinoma: We can distinguish four main mechanisms of genetic changes in CRC: microsatellite instability (MSI), chromosomal instability (CIN), CpG island methylator phenotype (CIMP), and b-Raf proto-oncogene, serine/threonine kinase (BRAF) or Kirsten rat sarcoma viral oncogene homolog (KRAS) mutations [12].