TYMS and cancer: Several clinical studies have examined the relationships of clinical response and survival to the tumor expression levels of TS and other enzymes involved in 5FU metabolism, such as dihydropyrimidine dehydrogenase (DPD), thymidine phosphorylase (TP), and orotate phosphoribosyltransferase (OPRT), in patients with cancer who received 5FU-based chemotherapy [9–12].