S-1 (TS-1, Taiho Pharmaceutical) is an oral fluorouracil derivative consisting of tegafur (a prodrug that converts cells to fluorouracil), gemelacil (a dihydropyrimidine dehydrogenase inhibitor that degrades fluorouracil), and oteracil (inhibits phosphorylation of fluorouracil in the gastrointestinal tract), which can be converted into 5-Fu for anti-tumor effect (12). The gene discussed is DPYD; the disease is neoplasm.