Is codon 13 KRAS mutation biologically different from codon 12 mutation

The introduction into clinical practice of KRAS mutational status for selection of patients has dramatically improved the results from use of anti-EGFR monoclonal antibodies cetuximab or panitumumab for metastatic colorectal cancer. More refined selection of patients by means of other molecular alterations, for example BRAF, PIK3CA, and NRAS has enabled further increases in responses to first-line and other therapy for metastatic disease. Elucidation of differences among specific subtypes of KRAS mutations affecting sensitivity, and identification of other mechanisms by which tumor cell resistance is acquired, revealing "druggable" molecular targets to overcome resistance, are clearly a priority of clinical research. Recent data have revealed potentially different activity of the G13D KRAS mutation in conferring resistance to cetuximab. This review examines the most recent evidence available on codon 13 mutation in metastatic colorectal cancer, including both preclinical and available clinical data, indicating differences between codon 13 and other KRAS mutations and analyzing its prognostic and predictive use in EGFRtargeted therapy.