The transformation of 2'-deoxyurindylate (dUMP) to 2'-deoxythymidylate (dTMP) is essential in driving the synthesis of DNA and purines in cells. Thymidylate synthase catalyzes the conversion of dUMP to dTMP, which is a precursor of thymidine triphosphate (TTP), one of the four deoxyribonucleotides required for DNA synthesis. After administration into the body, tegafur is converted into the active antineoplastic metabolite, fluorouracil (5-FU). In tumour cells, 5-FU undergoes phosphorylation to form the active anabolites, including 5-fluorodeoxyuridine monophosphate (FdUMP). FdUMP and reduced folate are bound to thymidylate synthase leading to formation of a ternary complex which inhibits DNA synthesis. In addition, 5-fluorouridine-triphosphate (FUTP) is incorporated into RNA causing disruption of RNA functions.

Indicated for the treatment of cancer usually in combination with other biochemically modulating drugs.
Indicated in adults for the treatment of advanced gastric cancer when given in combination with Cisplatin.
Indicated for the first-line treatment of metastatic colorectal cancer with Uracil and calcium folinate.