Abstract
Introduction: Immunological subtyping and molecular genetic analysis enable risk-adapted treatment of acute lymphoblastic leukemia (ALL). Translocations involving the mixed lingeage leukemia (MLL) gene characterize one poor-prognosis subtype of adult B-lineage precursor ALL correlating with a CD19+/CD10−/cytoplasmic (cy) IgM− immunophenotype (pro-B ALL).Patients and Methods: Immunophenotyping was performed on 2,408 newly diagnosed ALL specimens indentifying pro-B ALL, TdT+/CD19+/CD10−/cyIgM−/surface(S)Ig−; c-ALL, TdT+/CD19+/CD10+/cyIgM−/SIg−; and pre-B ALL, TdT+/CD19+/CD10+/cyIgM+/SIg−. Ambiguous cases of CD10-positivity (5–15% CD10-positivity) were rechecked by a second antibody. BCR-ABL RT-PCR and cytogenetics were performed. CD10-negative blasts also underwent MLL-AF4 RT-PCR. FISH using directly labelled probes for MLL was done in selected cases. Patients were treated according the German Multicenter Adult ALL trials (GMALL) with MLL-rearrangement positive patients treated in the high-risk arm.Results: Immunophenotyping identified 70 CD10-negative pre-B ALL specimens (TdT+CD19+cyIgM+). Fifty-six of these 70 CD10-negative pre-B ALL specimens contained a sufficient amount of blasts for molecular analysis. A total of 46/56 CD10-negative pre-B ALL were assigned to MLL-rearrangement positivity, revealing either MLL-AF4 fusion by RT-PCR (n = 38) or an 11q23/MLL translocation by cytogenetics (n = 4) or FISH (n = 4).Looking at clinical characteristics, MLL-rearrangement-positive patients were characterized by a higher median white blood cell count (P = .0002) and their blasts showed frequently neuroglial antigen 2 chondroitin sulfate proteoglycan (P = .02).Forty CD10− pre-B ALL patients with molecular genetic and/or cytogenetic data were evaluable for the treatment response and outcome. A complete remission (CR) was achieved in 6 of 7 (86%) MLL-rearrangement-negative and in 27 of 33 (82%) MLL-rearrangement-positive patients (P = .06). CR was maintained by 2 of 6 (33.3%) MLL-rearrangement-negative and 7 of 27 (26%) MLL-rearrangement-positive patients. The probability of remission duration after 3 years was 0.37 (± 0.29 SE) in MLL-rearrangement-negative versus 0.28 (± 0.13 SE) in MLL-rearrangement-positive patients contributing essentially to the overall survival at 3 years after diagnosis of 0.15 (± 0.06 SE) in patients with CD10-negative pre-B ALL.Conclusion: Our data identify CD10− cytoplasmic Ig-positive pre-B ALL as a rare (2.2%) but distinct immunosubtype of adult ALL that is characterized by a high MLL rearrangement rate and a worse outcome with conventional intensified treatment strategies.
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