Cyclophosphamide (Cy) combined with total-body irradiation (TBI) or with busulfan (Bu) are currently the most common myeloablative regimens used in allogeneic stem-cell transplantation (alloSCT) in adults with acute myelogenous leukemia (AML). Intravenous (IV) Bu has more predictable bioavailability and a safer toxicity profile than the oral formulation. Comparative studies of outcomes have been performed between oral Bu/Cy and Cy/TBI, but there have been no comparative trials in the era of IV Bu.

We performed a retrospective registry-based study comparing outcomes of patients with AML in first or second remission after alloSCT from sibling donors who underwent IV Bu/Cy (n = 795) or Cy/TBI (n = 864) conditioning.

Engraftment rate was 98% and 99% after IV Bu/Cy and Cy/TBI, respectively. Grade 2 to 4 acute graft-versus-host disease (GVHD) was significantly lower in the IV Bu/Cy compared with Cy/TBI group (P < .001). Similarly, chronic GVHD was significantly lower in the IV Bu/Cy compared with Cy/TBI group (P = .003). Cumulative incidence of 2-year nonrelapse mortality (NRM; ± standard deviation [SD]) was 12% ± 1% in the IV Bu/Cy group and 15% ± 2% in the Cy/TBI group (P = .14), and 2-year relapse incidence (RI; ± SD) was 26% ± 3% and 21% ± 1%, respectively (P = .012). Leukemia-free survival (LFS) rate (± SD) was 61% ± 2% after IV Bu/Cy and 64% ± 2% after Cy/TBI (P = .27). In multivariable analysis, adjusting for differences between both groups, patients who received IV Bu/Cy had lower acute and chronic GVHD, higher RI, and a trend toward lower NRM. LFS was not statistically different between the two conditioning regimens.

This retrospective study shows that final outcomes after myeloablative conditioning using IV Bu/Cy were not statistically different from those after Cy/TBI.