Comparison of reduced-intensity conditioning regimens in patients with acute lymphoblastic leukemia > 45 years undergoing allogeneic stem cell transplantation-a retrospective study by the Acute Leukemia Working Party of EBMT

The optimal reduced-intensity conditioning (RIC) for patients with acute lymphoblastic leukemia (ALL) undergoing allogeneic hematopoietic stem cell transplantation (allo-HSCT) remains unclear. We retrospectively analyzed 417 patients > 45 years with ALL in first complete remission who underwent a matched sibling or unrelated allo-HSCT and compared outcomes between fludarabine/busulfan (FLUBU, n = 127), fludarabine/melphalan (FLUMEL, n = 190), and fludarabine-TBI (FLUTBI, n = 100) conditioning. At 2 years, there were no differences between the groups in terms of cumulative incidence (CI) of relapse (40% for FLUBU vs 36% for FLUMEL vs 41% for FLUTBI, p = 0.21); transplant-related mortality (TRM) (18% for FLUBU, 22% for FLUMEL, 14% for FLUTBI, p = 0.09); overall survival (55% for FLUBU, 50% for FLUMEL, 60% for FLUTBI, p = 0.62) or leukemia-free survival (43% for FLUBU, 42% for FLUMEL, 45% for FLUTBI, p = 0.99), but GVHD-relapse-free survival was significantly lower in the FLUTBI group than FLUBU and FLUMEL group (18% vs 35% vs 28%, p = 0.02). However, this difference was lost in the multivariate analysis when adjusted for the in vivo T-cell depletion. Finally, the FLUMEL regimen was shown to be an independent risk factor for a higher TRM (HR 1.97, 95% CI 1.05-3.72, p = 0.04). We conclude that the three most popular RIC regimens yield similar transplant outcomes.