KRAS and colorectal carcinoma: The CRYSTAL trial demonstrated the efficacy of cetuximab, in combination with a FOLFOX or FOLFIRI regimen, only in patients with CRC negative for KRAS or NRAS mutations [44,80,82] The RAS mutation is also a negative predictive marker for panitimumab biological therapy [83], except in the case of the G13D KRAS mutation, which has been associated with a positive response to the anti-EGFR antibody, comparable to that of patients with a KRAS wild-type tumor [84,85].