KRAS and metastatic colorectal cancer: The OPUS and CRYSTAL trials evaluated the benefit of adding cetuximab in patients with metastatic colorectal cancer (mCRC) to the FOLFOX4 and FOLFIRI regimens, respectively, both concluding with the same postulate, specifically that patients with KRAS exon 2 tumor mutations do not show any benefit from adding cetuximab to the chemotherapy regimen unlike patients with wild type KRAS (18, 19).