Minimal residual disease is an important predictive factor of outcome in children with relapsed ‘high-risk’ acute lymphoblastic leukemia

The aim of the study was to analyze the impact of minimal residual disease (MRD) after reinduction therapy on the outcome of children with relapsed ‘high-risk’ acute lymphoblastic leukemia (ALL). Sixty patients with isolated or combined marrow relapse were studied. All patients belonged to the S3 or S4 groups, as defined by the Berlin–Frankfurt–Münster stratification for relapsed ALL. MRD was studied by real-time quantitative PCR after the first, second and third chemotherapy course (time points 1 (TP1), 2 (TP2) and 3 (TP3), respectively). MRD results, not used for treatment refinement, were categorized as negative (NEG MRD), positive not-quantifiable (POS-NQ MRD) when MRD level was below quantitative range (a level