KRAS and colorectal carcinoma: Consistent with this idea, although it has been well established that activating mutations in codons 12, 13 and 61 of KRAS are all considered drivers of acquired resistance to anti-EGFR mAbs in metastatic CRC patients17,20,26, there appears to be an unexplained preponderance of codon 61 mutations in patients with anti-EGFR refractory disease, mutations which are seldom observed in patients prior to the initiation of therapy21,27.