Cytidine deaminase status as a marker of response to azacytidine treatment in MDS and AML patients

Summary Azacitidine (Aza) is a mainstay of treatment for patients with acute myeloid leukaemia (AML) ineligible for induction chemotherapy and other high‐risk myelodysplastic syndromes (MDS). Only half of patients respond, and almost all will eventually relapse. There are no predictive markers of response to Aza. Aza is detoxified in the liver by cytidine deaminase (CDA). Here, we investigated the association between CDA phenotype, toxicity and efficacy of Aza in real‐world adult patients. Median overall survival (OS) was 15 months and 13 months in AML and high‐risk MDS patients respectively. In addition, our data suggest that delaying Aza treatment was not associated with lack of efficacy and should not be considered a signal to switch to an alternative treatment. Half of the patients had deficient CDA activity (i.e.