A Phase II Multicenter Study of the Addition of Azacitidine to Reduced-Intensity Conditioning Allogeneic Transplant for High-Risk Myelodysplasia (and Older Patients with Acute Myeloid Leukemia): Results of CALGB 100801 (Alliance)

Relapse remains the major cause of death in older patients transplanted for acute myeloid leukemia (AML) in first complete remission or for patients with advanced myelodysplastic syndrome (MDS) at any age. Conventional myeloablative conditioning followed by allogeneic blood or marrow transplantation is associated with significantly less relapse compared with reduced-intensity conditioning when performed in younger patients with AML or MDS, but the toxicity of this approach in older patients is prohibitive. We hypothesized that pharmacokinetic targeting to optimize busulfan (BU) exposure, combined with the administration of azacitidine (AZA) post-transplant would mitigate the risk of relapse while reducing nonrelapse mortality and ultimately improve progression-free survival (PFS). On this phase II multicenter study, 63 patients (40 unrelated donors and 23 matched related donors) received a uniform conditioning regimen consisting of fludarabine i.v. (days –7 to –3), BU targeted to a daily area under the curve (AUC) of 4000 μM/min (days –6 to –3) after the administration of a 25-mg/m² i.v. test dose on 1 day between days –14 to –9, and antithymocyte globulin (days –6, –5, and –4 (2 doses for matched related donors and 3 for matched unrelated donors only). Beginning on days +42 to +90, all patients were planned to receive up to 6 monthly cycles of AZA at 32 mg/m² subcutaneously for 5 days. The median age was 62 years (range, 44 to 74); 13 had AML and 50 had MDS; 87% of patients were within 20% of the target AUC based on a validation sample. Forty-one patients (65%) started AZA at a median of 61 days (range, 43 to 91) post-transplant, and 17 patients (41%) completed all 6 cycles of AZA. The cumulative incidence of nonrelapse mortality at 2 years was 33.4% (95% confidence interval [CI], 22%-45%). The cumulative incidence of relapse was 25% (95% CI, 15%-37%) at 2 years. With a median follow-up of 58.9 months, the estimated PFS probability at 2 years and 5 years after transplantation was 41.2% (80% CI, 33.9%-49.9%) and 26.9% (80% CI, 20.4%-35.5%), respectively, for the entire group with a median PFS of 15.8 months (95% CI, 6.7 to 28.3). The probability of overall survival at 2 and 5 years was 45.7% (95% CI, 34.9%-59.9%) and 31.2% (95% CI, 21.3% to 45.8%), respectively, for the entire group with a median overall survival of 19.2 months (95% CI, 8.7 to 37.5). In summary, we demonstrated the feasibility of a novel reduced-intensity conditioning regimen with test dose BU targeted to an AUC of 4000 μM/min. The feasibility of AZA in this setting appears to be limited if applied to an unselected population of older hematopoietic stem cell transplantation recipients. (ClinicalTrials.gov Identifier: NCT01168219.)