CDHP competitively inhibits dihydropyrimidine dehydrogenase (DPD), the enzyme that degrades the majority of 5-FU, approximately 180 times more effectively than uracil, which is a component of Tegafur-Uracil (UFT), and it was reported that S-1 had a significantly higher antitumor effect than UFT in various cancers 10. The gene discussed is DPYD; the disease is cancer.