The epidermal growth factor receptor (EGFR) has become an important target in cancer treatment. In consequence, drugs directed at this and other molecular targets are an increasingly important part of the treatment of numerous tumours. Cetuximab and panitumumab, two monoclonal antibodies that target EGFR, have proved to be effective in metastatic colorectal cancer treatment. However, some patients do not respond to treatment with EGFR inhibitors and, for this reason, interest in the identification of patients most likely to benefit from treatment with these agents has grown considerably. K-Ras, a member of the RAS family of signalling proteins plays an important role in EGFR- mediated regulation of cellular proliferation and survival. Patients with wild-type K-Ras were found to have significantly greater overall survival, progression-free survival and/or response rate compared with patients harbouring K-Ras mutations.