Alan P. Venook, MD, is Professor of Clinical Medicine and Associate Chief, Division of Medical Oncology, University of California, San Francisco. Results of the phase III CRYSTAL study reported in 2008 by Van Cutsem et al confirmed that in first-line treatment of metastatic epidermal growth factor receptor (EGFR)-positive colorectal cancer (CRC), response to FOLFIRI plus cetuximab (as compared with FOLFIRI alone) occurs mainly in patients with wild-type KRAS-carrying tumors. As a result, KRAS mutational...