Both decreased expression of deoxycytidine-kinase (dCK) that phosphorylates ara-C prodrug into its active metabolite (ara-C-mono-phosphate, ara-CMP) and increased expression of cytidine-deaminase that dephosphorylates (deactivates) ara-CMP were repeatedly associated with resistance of leukemia or lymphoma cells to araC [65,66,67]. The gene discussed is DCK; the disease is lymphoma.