Busulfan with 400 centigray of total body irradiation and higher dose fludarabine: An alternative regimen for hematopoietic stem cell transplantation in pediatric acute lymphoblastic leukemia

Background Hematopoietic stem cell transplantation can be curative for children with difficult‐to‐treat leukemia. The conditioning regimen utilized is known to influence outcomes. We report outcomes of the conditioning regimen used at the Alberta Children's Hospital, consisting of busulfan (with pharmacokinetic target of 3750 μmol*min/L/day ±10%) for 4 days, higher dose (250 mg/m2) fludarabine and 400 centigray (cGy) of total body irradiation. Procedure This retrospective study involved children receiving transplant for acute lymphoblastic leukemia (ALL). It compared children who fell within the target range for busulfan with those who were either not measured or were measured and fell outside this range. All other treatment factors were identical. Results Twenty‐nine children (17 within target) were evaluated. All subjects engrafted neutrophils with a median [interquartile range] time of 14 days [8–30 days]. The cumulative incidence of acute graft‐versus‐host disease was 44.8% [95% confidence interval, CI: 35.6%–54.0%], while chronic graft‐versus‐host disease was noted in 16.0% [95% CI: 8.7%–23.3%]. At 2 years, the overall survival was 78.1% [95% CI: 70.8%–86.4%] and event‐free survival was 74.7% [95% CI: 66.4%–83.0%]. Cumulative incidence of relapse was 11.3% [95% CI: 5.1%–17.5%]. There were no statistically significant differences in between the group that received targeted busulfan compared with the untargeted group. Conclusion Our conditioning regiment for children with ALL resulted in outcomes comparable to standard treatment with acceptable toxicities and significant reduction in radiation dose. Targeting busulfan dose in this cohort did not result in improved outcomes.