TYMP and neoplasm: In 2013, Kilburn et al. [136] conducted a phase I study using a 3+3 dose-escalation design to determine the MTD and DLT of capecitabine, an oral fluoropyrimidine carbamate converted to 5-fluorouracil (5-FU) by thymidine phosphorylase, an enzyme preferentially expressed in various tumor types [137].