KRAS and metastatic colorectal cancer: With the advent of studies showing patients with KRAS exon 2 mutations (Amado et al., 2008; Karapetis et al., 2008), and now extended RAS mutations (KRAS exon 2, 3, 4, and NRAS exon 2, 3, 4) (Douillard et al., 2013; Heinemann et al., 2014), do not derive benefit from treatment with EFGR-targeting monoclonal antibodies, the treatment paradigm for metastatic colorectal cancer (CRC) is shifting to one focused on the molecular subsets of this malignancy.