Whereas patients with a high CDA activity suffer from less adverse events following treatment with cytidine analogues, they are also at higher risk for disease progression due to a lack of efficacy as shown for dF-dC with pancreatic cancer [257], decitabine/azacitidine with myelodysplastic syndrome (MDS) [256], and ara-C with acute myeloid leukaemia (AML) [258,259]. Here, CDA is linked to myelodysplastic syndrome.