UMPS and neoplasm: Capecitabine is metabolized to 5-FU–the final step occurring inside the tumor–and 5-FU is converted to a phosphorylated metabolite in one of two ways: through direct phosphorylation to fluorouridine monophosphate via orotate phosphoribosyl transferase and in a two-step reaction to fluorodeoxyuridine monophosphate.