KRAS and colorectal cancer: BRAF and K-ras mutations are frequently found to be mutually exclusive in colorectal cancer [5,18] and both genes harbour the majority of mutations in distinct hotspots: BRAF at codons 463-468 [19] and 600 [18,19] and K-ras at codons 12 and 13 [20] and also, but more infrequently, at codon 61 [21].