In an exploratory analysis of NCIC CTG CO.17, Brulé et al demonstrated that a left-sided tumor site (splenic flexure to rectosigmoid colon) is a strong predictive factor for long PFS in patients with refractory, metastatic, and KRAS wild-type (exon 2) colon cancer receiving cetuximab treatment [27]. This evidence concerns the gene KRAS and colonic neoplasm.