Outcomes after relapse of childhood B-acute lymphoblastic leukemia (B-ALL) are poor, and optimal therapy is unclear. Children's Oncology Group study AALL0433 evaluated a new platform for relapsed ALL. Between March 2007 and October 2013 AALL0433 enrolled 275 participants with late bone marrow or very early isolated central nervous system (iCNS) relapse of childhood B-ALL. Patients were randomized to receive standard versus intensive vincristine dosing; this randomization closed due to excess peripheral neuropathy in 2010. Patients with matched sibling donors received allogeneic hematopoietic cell transplantation (HCT) after the first three blocks of therapy. The prognostic value of minimal residual disease (MRD) was also evaluated in this study. The 3-year event free and overall survival (EFS/OS) for the 271 eligible patients were 63.6% + 3.0% and 72.3% + 2.8% respectively. MRD at the end of Induction-1 was highly predictive of outcome, with 3-year EFS/OS of 84.9 + 4.0% and 93.8 + 2.7% for patients with MRD <0.1%, vs. 53.7 + 7.8% and 60.6 + 7.8% for patients with MRD ≥0.1% (p<0.0001). Patients who received HCT vs. chemotherapy alone had an improved 3-year disease-free survival (77.5 + 6.2% vs. 66.9 + 4.5%, p=0.03) but not OS (81.5 + 5.8% for HCT vs. 85.8 + 3.4% for chemotherapy, p=0.46). Patients with early iCNS relapse fared poorly, with a 3-year EFS/OS of 41.4% + 9.2% and 51.7% + 9.3%, respectively. Infectious toxicities of the chemotherapy platform were significant. The AALL0433 chemotherapy platform is efficacious for late bone marrow relapse of B-ALL, but with significant toxicities. The MRD threshold of 0.1% at the end of Induction-1 was highly predictive of outcome. The optimal role for HCT for this patient population remains uncertain. This trial is registered at clinicaltrials.gov (NCT# 00381680).
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