Antifolates currently in use for cancer treatment inhibit dihydrofolate reductase (DHFR), that converts 7,8-dihydrofolate (DHF) into tetrahydrofolate (THF), the glycinamide ribonucleotide formyltransferase (GARFT) that uses 10-formyl-THF during the synthesis of purines, and thymidylate synthase (TS) that catalyzes the conversion of 2-deoxyuridine monophosphate (dUMP) into dTMP (8). This evidence concerns the gene DHFR and cancer.