One-point flow cytometric MRD measurement to identify children with excellent outcome after intermediate-risk BCP-ALL: results of the ALL-MB 2008 study

Background Measurement of minimal residual disease (MRD) with multicolor flow cytometry (MFC) has become an important tool in childhood acute lymphoblastic leukemia (ALL), mainly to identify rapid responders and reduce their therapy intensity. Protocols of the Moscow–Berlin (MB) group use a comparatively low (for standard risk; SR) or moderate (for intermediate risk; ImR) treatment intensity from the onset, based on initial patient characteristics. Recently, we reported that 90% of SR patients—50% B cell precursor (BCP-ALL)—MFC-MRD negative at end of induction (EOI)—had 95% event-free survival (EFS). Methods In the present study, we applied this method to children with initial ImR features. Results In study MB 2008, 1105 children—32% of BCP-ALL patients—were assigned to the ImR group. Of these, 227 were treated in clinics affiliated with MFC laboratories of the MB group network, and included in this MFC-MRD pilot study. A single-point MFC-MRD measurement at the EOI with the threshold of 0.01% identified 65% of patients—20% of all BCP-ALL patients—with EFS of 93.5%. Conclusion Taking both studies together, the combination of clinical parameters and a one-point MRD measurement identifies 70% of BCP-ALL patients with an excellent outcome after low- or moderate-intensity therapy and avoids overtreatment of a significant proportion of patients.