Detection of positive EGFR expression by immunostaining does not reliably predict clinical outcome in patients receiving cetuximab; however, mutations in the genes of the signaling effectors downstream of EGFR, such as KRAS, are central to the progression of CRC and have emerged as important predictive markers of resistance to cetuximab treatment (Siena et al, 2009). This evidence concerns the gene KRAS and colorectal carcinoma.