Genotyping of TYMS (5′TRP and 3′UTR), UGT1A1*28, UGT1A9*22 and UGT1A7*3 in metastatic CRC patients treated with irinotecan/5FU shows that the TYMS 3TRP/3TRP genotype is the only independent predictor of tumor response. Here, TYMS is linked to neoplasm.