In a study of 1075 stage I-IV CRC patients by Imamura et al. 23, survival analysis showed that mutations in codon 12, but not codon 13, was associated with a worse prognosis than wild-type KRAS. Similar results were found by Margonis et al. 24 in a study of 512 stage IV CRC patients. This evidence concerns the gene KRAS and colorectal carcinoma.