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Background Quantitative measurement of minimal residual disease (MRD) is the “gold standard” for estimating the response to therapy in childhood B‐cell precursor acute lymphoblastic leukemia (BCP‐ALL). Nevertheless, the speed of the MRD response differs for different cytogenetic subgroups. Here we present results of MRD measurement in children with BCP‐ALL, in terms of genetic subgroups with relation to clinically defined risk groups. Methods A total of 485 children with non‐high‐risk BCP‐ALL with available cytogenetic data and MRD studied at the end‐of‐induction (EOI) by multicolor flow cytometry (MFC) were included. All patients were treated with standard‐risk (SR) of intermediate‐risk (ImR) regimens of “ALL‐MB 2008” reduced‐intensity protocol. Results and Discussion Among all study group patients, 203 were found to have low‐risk cytogenetics (ETV6::RUNX1 or high hyperdiploidy), while remaining 282 children were classified in intermediate cytogenetic risk group. For the patients with favorable and intermediate risk cytogenetics, the most significant thresholds for MFC‐MRD values were different: 0.03% and 0.04% respectively. Nevertheless, the most meaningful thresholds were different for clinically defined SR and ImR groups. For the SR group, irrespective to presence/absence of favorable genetic lesions, MFC‐MRD threshold of 0.1% was the most clinically valuable, although for ImR group the most informative thresholds were different in patients from low‐(0.03%) and intermediate (0.01%) cytogenetic risk groups. Conclusion Our data show that combining clinical risk factors with MFC‐MRD measurement is the most useful tool for risk group stratification of children with BCP‐ALL in the reduced‐intensity protocols. However, this algorithm can be supplemented with cytogenetic data for part of the ImR group.

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.

This report presents the results of the assessment of MRD response by multicolor flow cytometry (MFC) with regard to the randomized use of pegylated asparaginase (PEG). In this study, PEG was randomly administered at a dose of 1000 U/m2 on day 3 of induction therapy in children with B-lineage ALL. Methods. Conventional induction therapy consisted of dexamethasone, vincristine, and daunorubicin. MRD data was available in 502 patients who were randomized at the start of induction therapy, standard-risk (SR) patients into three (conventional induction without PEG, induction with additional PEG and with PEG but without daunorubicin) and intermediate-risk (ImR) patients into two groups (with additional PEG and without PEG). Results. The single administration of PEG resulted in a significantly higher proportion of rapid responders, in SR patients even when no anthracyclines were used for induction. In the SR group, the event-free survival of the MFC-MRD fast responders was similar in the PEG− and PEG+ arms (92.0 ± 3.1% vs. 96.2 ± 1.5%, respectively), and the same unfavorable trend was observed for MFC-MRD slow responders (57.5 ± 12.3% vs. 66.7 ± 15.7%, respectively). Results were similar in ImR patients: (94.3 ± 3.2% vs. 95.1 ± 2.4%, for fast responders and 63.3 ± 7.6% vs. 78.1 ± 7.9%, for slow responders in PEG− and PEG+ arms, respectively). However, there is a large difference between the proportion of MFC-MRD slow responders in the PEG− and PEG+ groups (18.3% vs. 5.2% for the SR group and 44.2% vs. 25.0% for the ImR group). Conclusions. Therefore, early use of PEG-ASP not only leads to an accelerated reduction of blasts, but also to an excellent outcome in a significantly larger proportion of patients in both risk groups.