These drugs were initially proved to be effective only in a subgroup of metastatic colorectal cancer (mCRC) carrying a wild-type KRAS gene in codons 12 and 13 of exon 2 [3–5] and in 2009 received the European Medicines Agency (EMA) approval for this molecularly selected group of mCRC patients. This evidence concerns the gene KRAS and metastatic colorectal cancer.