Prodrugs of 5-fluorouracil include nucleoside analogues prodrug 5-fluorouridine (colorectal cancer), doxifluridine (5′-deoxy-5-fluorouridine, colorectal, ovarian, melanoma and breast cancer), floxuridine, (gastrointestinal adenocarcinoma), tegafur (FTO, advanced gastric and colorectal cancer), capecitabine (advanced gastric, breast and colorectal cancer), tegafur-uracil (UFT, dihydropyrimidine dehydrogenase (DPD) inhibitor), S-1 (tegafur and 2 enzyme inhibitors (gimeracil (CDHP) and oteracil potassium (OXO)), and BOF-A2 (Figure 1). This evidence concerns the gene DPYD and breast carcinoma.