Currently, there is no mandatory DPD deficiency screening prior to fluoropyrimidine-based therapy; however, studies including those by the Group of Clinical Pharmacology in Oncology (GPCO)-UNICANCER and the French Network of Pharmacogenetics (RNPGx) recommend screening for DPD deficiency before fluoropyrimidine-based regimens to prevent the various aforementioned complications [21]. The gene discussed is DPYD; the disease is dihydropyrimidine dehydrogenase deficiency.