Purpose We aimed to identify relapse predictors in children with a B-cell precursor acute lymphoblastic leukemia (ALL) and an intrachromosomal amplification of chromosome 21 (iAMP21), a novel genetic entity associated with poor outcome. Patients and Methods We screened 1,625 patients who were enrolled onto the Austrian and German ALL–Berlin-Frankfurt-Münster (ALL-BFM) trials 86, 90, 95, and 2000 with ETV6/RUNX1-specific fluorescent in situ hybridization probes, and we identified 29 patient cases (2%) who had an iAMP21. Minimal residual disease (MRD) was quantified with clone-specific immunoglobulin and T-cell receptor gene rearrangements. Results Twenty-five patients were good responders to prednisone, and all achieved remission after induction therapy. Eleven patients experienced relapse, which included eight who experienced relapse after cessation of front-line therapy. Six-year event-free and overall survival rates were 37% ± 14% and 66% ± 11%, respectively. Results of MRD analysis were available in 24 (83%) of 29 patients: nine (37.5%) belonged to the low-risk, 14 (58.5%) to the intermediate-risk, and one (4%) to the high-risk group. MRD results were available in 8 of 11 patients who experienced a relapse. Seven occurred among the 14 intermediate-risk patients, and one occurred in the high-risk patient. Conclusion The overall and early relapse rates in the BFM study were lower than that in a previous United Kingdom Medical Research Council/Childhood Leukemia Working Party study (38% v 61% and 27% v 47%, respectively), which might result from more intensive induction and early reintensification therapy in the ALL-BFM protocols. MRD values were the only reliable parameter to discriminate between a low and high risk of relapse (P = .02).
Modulation of antigen expression in B-cell precursor acute lymphoblastic leukemia during induction therapy is partly transient: Evidence for a drug-induced regulatory phenomenon. Results of the AIEOP-BFM-ALL-FLOW-MRD-Study Group