Stratification
All patients were stratified at diagnosis according to conventional risk criteria, allocating patients aged > 10 years, T or pro-B cell-immunophenotype (CD10 negative) or with a white blood cell count > 25/nl to the HR arm and all others to the low-risk (LR) arm. A second stratification was applied at EOI which included the state of cytomorphological remission and the results of in vivo treatment response (MRD) as well as the molecular and cytogenetic result. Patients with a KMT2A -rearrangement or a hypodiploid karyotype were additionally stratified to the HR arm. Within the LR and HR arm, patients were allocated to receive either a treatment reduction, standard treatment or treatment intensification based on their MRD result. All HR patients with a persisting high MRD-level at EOI (B-lineage-ALL: MRD ≥ 10-3 at day 29, T-lineage-ALL: MRD ≥ 10-3 at day 29 and day 43) were stratified to the HR-I treatment arm.
Patients presenting with a persistence of leukemic blasts ≥ 5 % upon microscopic cytomorphological evaluation of the bone marrow with a corresponding MRD result at EOI were classified as induction treatment failure.