KRAS and cancer: According to the COSMIC database (the Catalogue Of Somatic Mutations In Cancer), a majority (approximately 90–95%) of KRAS-activating mutations occur in codons 12 (p.G12A, p.G12C, p.G12D, p.G12R, p.G12S, and p.G12V) or 13 (p.G13D) of exon 2, whereas less common mutations occur in exon 3 and exon 4.