DPYD and cancer: To further identify the molecular mechanism of 5-FU resistance in the generated chemo-resistant cancer cells, we investigated the expression level of five genes involved in drug metabolism such as, thymidylate synthase (TS), thymidine kinase (TK), dihydrofolate reductase (DHFR) and the folylpolyglutamate synthetase (FPGS) implicated in 5-FU anabolism and dihydropyrimidine dehydrogenase (DPD), the key enzyme of 5-FU catabolism33.