TYMS and cancer: After entering the cell, 5FU prevents cancer growth through converting to several active metabolites: Fluoro-deoxyuridine-monophosphate (FdUMP), Fluoro-deoxyuridine-triphosphate (FdUTP), and Fluoro-uridine-triphosphate (FUTP), which inhibit thymidylate synthase (TS) and block RNA and DNA synthesis [2].