Improving Stratification for Children With Late Bone Marrow B-Cell Acute Lymphoblastic Leukemia Relapses With Refined Response Classification and Integration of Genetics

PURPOSE Minimal residual disease (MRD) helps to accurately assess when children with late bone marrow relapses of B-cell precursor (BCP) acute lymphoblastic leukemia (ALL) will benefit from allogeneic hematopoietic stem-cell transplantation (allo-HSCT). More detailed dissection of MRD response heterogeneity and the specific genetic aberrations could improve current practice. PATIENTS AND METHODS MRD was assessed after induction treatment and at different times during relapse treatment until allo-HSCT (indicated in poor responders to induction; MRD >= 10(?3)) for patients being treated for late BCP-ALL bone marrow relapses (n = 413; median follow-up, 9.4 years) in the ALL-REZ BFM 2002 trial/registry (ClinicalTrials.gov identifier: NCT00114348). RESULTS Patients with both good (MRD < 10(-3)) and poor responses to induction treatment reached excellent event-free survival (EFS; 72% v 65%) and overall survival (OS; 82% v 74%). Patients with MRD of 10(-2) or greater after induction had reduced EFS (56%), and their MRD persisted until allo- HSCT more frequently than it did in patients with MRD of 10(-3) or greater to less than 10(-2) (P = .037). Patients with 25% or more leukemic blasts after induction (early nonresponders) had the poorest prognosis (EFS, 22%). Interestingly, patients with MRD of 10(-3) or greater before allo-HSCT (late nonresponders) still had an EFS of 50% and OS of 63%, which in principle justifies allo-HSCT in these patients. From a panel of selected candidate genes, TP53 alterations (frequency, 8%) were the only genetic alteration with independent prognostic value in any MRD-based response subgroup. CONCLUSION After induction treatment, MRD-based treatment stratification resulted in excellent survival in patients with late relapsed BCP-ALL. Prognosis could be further improved in very poor responders by intensifying treatment directly after induction. TP53 alterations can be defined as a novel genetic high-risk marker in all MRD response groups in late relapsed BCP-ALL. Here we identified early and late nonresponders to be considered as events in future trials.