Radiation-Free myeloablative allogeneic hematopoietic stem cell transplantation for adult acute lymphoblastic leukemia: A comparison of outcomes between patients with and without central nervous system involvement

For patients with acute lymphoblastic leukemia (ALL) undergoing allogeneic hematopoietic stem cell transplantation (allo-HSCT), total body irradiation (TBI) has been particularly advocated as a part of the conditioning regimen in case of extramedullary involvement in sanctuary sites such as the central nervous system (CNS), to ensure greater tissue penetration. In resource-limited countries lacking TBI facilities; however, ALL patients undergo radiation-free myeloablative conditioning, though its impacts on post-HSCT outcomes of the patients with pre-HSCT CNS involvement have not been analyzed. In this 14-year series of 278 adult (> 18 y) ALL patients undergoing TBI-free busulfan/cyclophosphamide conditioning allo-HSCT, we found that the long-term probabilities of overall survival, disease free survival, relapse and non-relapse mortality were not significantly different between CNS-involved and CNS-spared patients. Moreover, there was no statistically significant difference in the incidence of post-HSCT CNS relapse between CNS-involved and CNS-spared patients. Pre-HSCT cranial radiation therapy (CRT) showed no significant preventive effect on the likelihood of post-HSCT CNS relapse. Through multivariable regression analysis, grade III-IV acute graft-versus-host disease (GvHD), extensive chronic GvHD and post-HSCT relapse were ascertained as independent determinants of mortality (Adj.R2 = 53.9 %, F(12,265) = 28.1, P < 0.001), while other parameters including Philadelphia translocation, pre-HSCT CNS involvement and CRT were found to have no independent effect. Although this study was not an attempt to compare TBI-based vs. non-TBI conditioning, the TBI-free myeloablative allo-HSCT was shown to be feasible and an option for adult ALL patients with CNS involvement, considering the comparable outcomes between patients with and without CNS involvement.