Impact of Total Body Irradiation-Based Myeloablative Conditioning Regimens in Patients with Acute Lymphoblastic Leukemia Undergoing Allogeneic Hematopoietic Stem Cell Transplantation: Systematic Review and Meta-Analysis.

Allogeneic hematopoietic cell transplantation (allo-HCT) is a curative treatment option for patients with acute lymphoblastic leukemia (ALL). Both total body irradiation (TBI)-based and chemotherapy only-based myeloablative transplantation conditioning regimens have been applied, but the optimal regimen remains unclear. We performed a systematic review to assess the efficacy of TBI-based versus chemotherapy only-based myeloablative conditioning regimens. We searched PubMed, Embase, and Cochrane databases and meeting abstracts for all studies comparing TBI-based and chemotherapy only-based conditioning regimens in patients who underwent allo-HCT for ALL. Two authors independently reviewed all studies for inclusion and extracted data related to overall survival (OS), progression-free survival (PFS), nonrelapse mortality (NRM), relapse, and acute and chronic graft-versus-host disease (GVHD). Eight studies were included in the final analysis. The overall methodological quality of the included studies was optimal. TBI-based regimens showed evidence of benefit compared with chemotherapy only-based conditioning regimens in terms of relapse (relative risk [RR], 0.82; 95% confidence interval [CI], 0.72 to 0.94; 6 studies, 5091 patients), OS (hazard ratio [HR], 0.76; 95% CI, 0.64 to 0.89; 7 studies, 4727 patients), and PFS (HR, 0.74; 95% CI, 0.63 to 0.85; 7 studies, 4727 patients). The TBI-based regimen did not increase the likelihood of grade II-IV acute GVHD (RR, 1.12; 95% CI, 0.92 to 1.36; 5 studies, 4996 patients) or chronic GVHD (RR, 1.10; 95% CI, 1.00 to 1.21; 5 studies, 4490 patients), or NRM (RR, 0.94; 95% CI, 0.69 to 1.28; 6 studies, 4522 patients). However, TBI-based regimens were associated with an increased risk of grade III-IV acute GVHD (RR, 1.29; 95% CI, 1.01 to 1.63; 3 studies, 3675 patients). A subgroup comparison of patients age ≥16 years showed similar results. This systematic review represents evidence supporting the use of TBI-based conditioning regimen in patients undergoing allo-HCT for ALL who are candidates for myeloablative conditioning, as it offers better OS, PFS, and less relapse with acceptable NRM.