The cold (non-radiolabeled) clofarabine (CFA) was approved by the Food and Drug Administration (FDA) in 2004 for the treatment of pediatric refractory acute lymphoblastic leukemia (ALL) [2], and it is a substrate of deoxycytidine kinase (dCK), which is a target of several other anti-cancer pro-drugs such as gemcitabine and decitabine. The gene discussed is DCK; the disease is acute lymphoblastic leukemia.