Fludarabine and Melphalan Compared with Reduced Doses of Busulfan and Fludarabine Improves Transplant Outcomes in Older MDS Patients.

Reduced-intensity conditioning (RIC) regimens developed to extend allogeneic stem cell transplantation (HSCT) to older patients have resulted in encouraging outcomes. We aimed to compare the two most commonly used RIC regimens, intravenous use of fludarabine with busulfan (FluBu) and fludarabine with melphalan (FluMel), in myelodysplastic syndrome (MDS). Through CIBMTR, we identified 1045 MDS patients aged ≥ 60 years who underwent first HSCT with a matched related or matched (8/8) unrelated donor using RIC. CIBMTR's definition of RIC was used: a regimen that incorporated an intravenous busulfan total dose ≤ 7.2 mg/kg, or a low-dose melphalan total dose of ≤ 150 mg/m2. The two groups, FluBu (n=697) and FluMel (n=448), were comparable for disease and transplant-related characteristics except for the more frequent use of anti-thymocyte globulin or alemtuzumab in the FluBu group (39% vs. 31%). The median age was 67 in both groups. FluMel was associated with a reduced relapse incidence (RI) compared with FluBu, with a 1-year adjusted incidence of 26% vs. 44% (p≤0.0001). Transplant-related mortality (TRM) was higher with FluMel compared with FluBu (26% vs. 16%, p≤0.0001). Since the magnitude of improvement with FluMel in RI was greater than the improvement in TRM with FluBu, disease-free survival (DFS) was improved at 1-year and beyond with FluMel compared with FluBu (48% vs. 40% at 1 year, p=0.02, and 35% vs. 27% at 3 years, p=0.01). Overall survival (OS) was comparable at 1 year (63% vs. 61%, p=0.4) but significantly improved with FluMel compared with FluBu at 3 years (46% vs. 39%, p=0.03). Our results suggest that FluMel is associated with superior DFS compared with FluBu due to reduced RI in older MDS patients.