Interference with DPD activity through methylation of the promoter of the DPYD gene, which encodes the DPD protein, or DPD inhibitors such as 5-ethynyluracil and 5-chloro-2,4-dihydroxypyridine (CDHP) can improve the anti-tumor activity of 5-FU to a greater extent [142–146]. This evidence concerns the gene DPYD and neoplasm.