DPYD and metastatic neoplasm: The rationale of a metronomic chemotherapy strategy based on the combination of UFT and CTX derives in part from their synergistic antitumor activity in mouse models of advanced metastatic disease [19] and also because of evidence that CTX may alter the expression of enzymes such as thymidylate synthase (TS) and dihydropyrimidine dehydrogenase (DPD) in tumor cells in such a way as to render them more sensitive to 5-FU [20].