Vorinostat Does Not Improve Outcome in Patients with Acute Myeloid Leukemia and High Risk Myelodysplasia Treated with Azacitidine: Results of the UK Trials Acceleration Programme Ravva Trial

Introduction:

Azacitidine (AZA) represents a significant advance in the treatment of adults with acute myeloid leukaemia (AML) (Dombret et al Blood 2016 126:291-9) and myelodysplasia (MDS) (Fenaux et al Lancet Oncol 2009) 10:223-32) ineligible for intensive chemotherapy. However complete response (CR) rates remain modest and disease progression is almost inevitable. Consequently, additional agents which improve the clinical activity of AZA and other hypomethylating agents are urgently required. Pre-clinical and Phase II studies have identified the potential of co-administration of histone deacteylase inhibitors, notably vorinostat (VOR), with AZA as a strategy to improve its clinical activity. We have therefore compared outcomes after AZA monotherapy or combined AZA and VOR in a prospective randomized trial in adults with high risk AML and MDS.

Patients and Methods: 259adults with AML or high risk MDS deemed ineligible for intensive chemotherapy were randomized to receive either AZA (75 mg/m²) x 7 days every 28 days or AZA in combination with VOR 300 mg bd days 3-9 po for a minimum of 6 cycles. Patients were assessed for response, using modified Cheson criteria, after 3 and 6 cycles of therapy. Patients who achieved a major clinical response (CR, CRi or PR) were eligible to receive continued treatment until loss of response, toxicity or death. Major response after 6 cycles and overall survival (OS) were co-primary endpoints. 219 patients had AML (newly diagnosed n= 108) and 44 had MDS (newly diagnosed n= 30).

Results: Co-administration of VOR did not increase either the major response rate at 6 months compared with AZA monotherapy (33% AZA v 37% AZA+VOR, OR (95% CI)=1.2 (0.7,2.0), p=0.55) or improve OS (1 year OS AZA 43% versus AZA/VOR 44%, HR (95% CI)=1.06 (0.8, 1.4), p=0.68). No benefit of addition of VOR was observed in any patient subgroup. In multivariate analysis of the study population, a low presentation white blood count (p=0.029) and a diagnosis of MDS vs AML (p=0.0048) was associated with significantly improved survival, whilst disease status (CR v advanced disease) (p=0.023) and low presentation white blood count (p=0.034) significantly improved major response rates. Presentation karyotype was not predictive of either survival or response. Both adverse events (AE) and serious adverse events (SAE) were balanced between treatment arms with 64 and 89 patients in the AZA arm experiencing AE and SAEs respectively versus 75 and 97 in the combination arm respectively.

Discussion: To our knowledge this is the largest randomized study of epigenetic therapy in AML and MDS. We conclude that the addition ofVOR to AZA therapy does not increase either major response rates or overall survival in patients with AML and high risk MDS. Alternative therapeutic strategies with the potential to increase response to AZA are required in this patient population.