DPYD and cancer: Dihydropyrimidine dehydrogenase (DPD) deficiency. Deficiency of the DPD enzyme is a relatively rare (3%–5% of cancer patients) autosomal recessive disorder resulting in the ineffective metabolism of 5-FU and capecitabine (Saif, Ezzeldin, Vance, Sellers, & Diasio, 2007).