Cetuximab was approved by the FDA for K-Ras wild-type, EGFR-positive, metastatic colorectal cancer (i) in combination with FOLFIRI as a first-line treatment, (ii) in combination with irinotecan in patients who are refractory to irinotecan-based chemotherapy, and (iii) as a single agent in patients who have failed oxaliplatin- and irinotecan-based chemotherapy or who are intolerant to irinotecan. Here, KRAS is linked to metastatic colorectal cancer.