DPYS and diabetes mellitus: Past clinical investigations have proposed that deficiency of, either dihydropyrimidine dehydrogenese or dihydropyrimidinase, is a pharmacogenetic disorder associated with 5-FU toxicity (Milano et al., 1999[34]; van Kuilenburg, 2004[41]; van Kuilenburg et al., 2003[42]), but the activities of these 5-FU catabolic enzymes in the cancer patients with diabetes are still not fully understood.