Cytidine deaminase (CDA) has been described in different organisms as a pyrimidine salvage pathway enzyme that catalyzes the hydrolytic deamination of cytidine (Ctd) and dCtd to uridine and dUrd, respectively, and is also capable of deaminating several nucleoside analogues used in cancer treatment, such as decitabine (5′-aza-2′-deoxycytidine) (9), gemcitabine (2′,2′-difluoro-2′-deoxycytidine) (10), or cytarabine (1-β-d-arabinofuranosylcytosine [Ara-C]) (11). This evidence concerns the gene CDA and cancer.