Other enzymes involved in the metabolism and degradation of 5-FU, such as Thymidine phosphorylase (TP), uridine phosphorylase (UP), orotate phosphoribosyl transferase (OPRT) and dihydropyrimidine dehydrogenase (DPD), are correlated with sensitivity of CRC cells to 5-FU. This evidence concerns the gene UPP1 and colorectal carcinoma.