Busulfan-containing conditioning regimens in allogeneic hematopoietic stem cell transplantation for acute lymphoblastic leukemia: A Taiwan observational study.

Background: Allogeneic stem cell transplantation (allo-HSCT) is the ultimate cure for acute lymphoblastic leukemia (ALL).

Aim: This study was performed to compare the outcomes of ALL patients receiving busulfan (Bu) with cyclophosphamide (Cy)-based or total body irradiation (TBI)-based regimen in a Chinese population.

Methods: We enrolled 224 adult patients with ALL who received allo-HSCT at National Taiwan University Hospital between 1997 and 2016.

Results: The median age at transplantation was 33 years. Before allo-HSCT, 75.9% of patients attained first or late complete remission. A total of 141 patients (62.9%) received Bu/Cy-based conditioning, either myeloablative (MA) or reduced-intensity stem cell transplantation (RIST), and 83 patients received a TBI-based regimen (MA-TBI). Patients receiving the MA-Bu regimen had longer relapse-free survival (RFS) than those receiving the MA-TBI regimen (median, 24.1 vs. 6.7 months, p = .044). There was no difference in overall survival (OS, MA-Bu vs. MA-TBI vs. RIST-Bu: 39.4 vs. 28.2 vs. 13.1 months, p = .276), treatment-related mortality (TRM), or incidences of grade 3-4 acute graft-versus-host disease (GvHD). Among patients receiving identical GvHD prophylactic regimens, there was no difference between MA-Bu and MA-TBI groups regarding the incidence of grade 3-4 acute GvHD, grade 2-4, and all-grade chronic GvHD. In subgroup analysis, patients receiving oral busulfan had comparable RFS and OS to the intravenous busulfan group (p = .436 and p = .236, respectively), but a higher TRM (25% vs. 9.8%, p = .016). In the multivariable analysis, disease status before allo-HSCT was the only risk factor impacting RFS and OS.

Conclusion: In summary, patients receiving Bu/Cy-based or TBI-based regimens as conditioning had similar results in terms of OS, TRM, and acute GvHD, whereas the use of myeloablative Bu/Cy resulted in a better RFS. A Bu-based regimen could be an alternative conditioning choice for patients who are ineligible to receive TBI. Prospective and randomized controlled trials are warranted to validate the long-term outcomes.