Impact of Conditioning Regimen in Allogeneic Hematopoetic Stem Cell Transplantation for Children with Acute Myelogenous Leukemia beyond First Complete Remission: A Pediatric Blood and Marrow Transplant Consortium (PBMTC) Study

Total body irradiation (TBI)-based conditioning regimens for pediatric patients with acute myelogenous leukemia (AML) beyond first complete remission (CR1) are controversial. Because the long-term morbidity of busulfan (Bu)-based regimens appears to be lower, determining efficacy is critical. We retrospectively evaluated 151 pediatric patients with AML beyond CR1, comparing outcomes in 90 patients who received a TBI-based conditioning regimen and 61 patients who received a Bu-based conditioning regimen. There were no differences between the 2 groups with respect to age, sex, duration of CR1, time from most recent remission to transplantation, or donor source. The probability of relapse at 2 years also did not differ between the 2 groups (26% and 27%, respectively; P=.93). No significant difference in event-free survival (EFS) (P=.29) or overall survival (OS) (P=.11) was noted between the 2 groups. These findings were supported by a multivariate analysis in which TBI was not associated with improved EFS (hazard ratio [HR]=1.17; 95% confidence interval [CI]=0.66-2.10; P=.58) or OS (HR=1.42; 95% CI=0.76-2.64; P=.27). Shorter CR1 and receiving an HLA-mismatched transplant adversely affected EFS and OS in this cohort. Our study provides no evidence of an advantage to using TBI in children with AML beyond CR1. A prospective, randomized study is needed to confirm these results.