Comparison of melphalan- And busulfan-based myeloablative conditioning in children undergoing allogeneic transplantation for acute myeloid leukemia or myelodysplasia

Background: The optimal conditioning regimen for alloHCT in children with myeloid malignancies remains undefined. Procedure: We performed a retrospective review of children undergoing alloHCT for AML and MDS over a 10-year period (2008-2018) at our institution, comparing the outcomes of recipients of either a myeloablative busulfan- or reduced toxicity mel/thio-based conditioning regimen. Results: A total of 49 patients underwent alloHCT for AML/MDS (mel/thio, N = 21; busulfan, N = 28). Mel/thio recipients were selected due to pretransplant comorbidities. Recipients of mel/thio were more likely to have t-AML, and less likely to have MRD <0.1% at the time of alloHCT (57.1% vs 82.1%). Graft failure was more common in busulfan recipients; engraftment kinetics were similar between groups. Sinusoidal obstructive syndrome was diagnosed in 21% of busulfan and no mel/thio recipients (P =.03). One patient in each group died from TRM. Relapse incidence was comparable (mel/thio—29% vs busulfan—32%); however, relapse occurred significantly later in recipients of mel/thio conditioning (median d + 396 vs d + 137; P =.01). As a result, there was a trend toward improved OS at 1 and 3 years in mel/thio recipients (95% vs 74%, P =.06; and 75% vs 50%, P =.11; respectively). Conclusion: In our single institution, when compared to myeloablative busulfan-based conditioning, use of a mel/thio-based reduced toxicity regimen resulted in comparable outcomes, despite higher risk patient and disease characteristics. Mel/thio recipients had both more comorbidities and higher risk disease profile, which did not translate into higher rates of either TRM or relapse.