KRAS and colorectal cancer: Furthermore, activating mutations in KRAS or BRAF occur in approximately 50%–60% of patients with colorectal cancer; these mutations are mutually exclusive and are associated with resistance or decreased response to anti-epidermal growth factor receptor therapy in colorectal cancer (Davies et al, 2002; Fransen et al, 2004; Karapetis et al, 2008).