Flow cytometric minimal residual disease measurement accounting for cytogenetics in children with non‐high‐risk acute lymphoblastic leukemia treated according to the ALL‐MB 2008 protocol

Abstract 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.