Irradiation free conditioning regimen is associated with high relapse rate in Egyptian patients with acute lymphoblastic leukemia following allogeneic hematopoietic stem cell transplantation

Background Allogeneic hematopoietic stem cell transplantation (Allo-HSCT) is a curative treatment for adult patients with acute lymphoblastic leukemia (ALL). Cyclophosphamide plus total body irradiation (TBI/Cy) or plus busulfan (Bu/Cy) is a widely used pre-transplant conditioning regimen for ALL. We retrospectively compared the overall survival (OS), disease-free survival (DFS), and other transplant outcomes of allo-HSCT in 119 adult patients with ALL who received an HLA-matched sibling allo-HSCT using TBI-based versus non-TBI-based conditioning regimens. Patients were divided into two groups by their conditioning regimen: TBI/Cy or Bu/Cy. Results Median OS was 11 months in the TBI/Cy group and 6.2 months in the Bu/Cy group. Median DFS was 11.1 months in the TBI group versus 6.8 months in the Bu group, without a statistically significant difference. A higher risk of relapse was observed with the Bu/Cy regimen (HR 2.709, CI 95% 1.106 to 6.638,p= 0.029). Patients who received a transplant in >= CR2 were associated with poor DFS. Conclusion Despite the high relapse rate in the non-TBI regimen (Bu/Cy), both regimens had no statistically significant differences in OS, DFS, and NRM. Additional prospective studies are indeed warranted to evaluate the long-term outcomes of radiation-free regimens, including oral and intravenous busulfan, and compare these regimens with TBI-based ones.