KRAS and carcinoma: Mutations in codons 59 and 117 occur with the same frequency as in codon 61.[44] Mutations in the K-ras oncogene are thought to occur at an early stage in the adenoma-carcinoma sequence, with the frequency of mutations increasing with the size of the adenoma.[40] The frequency of mutations in the K-ras oncogene has been reported to vary between 20 and 60%.[4, 5]