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Despite attempts to improve the definitions of ambiguous lineage leukemia (ALAL) during the last 2 decades, general therapy recommendations are missing. Herein, we report a large cohort of children with ALAL and propose a treatment strategy. A retrospective multinational study (International Berlin-Frankfurt-Münster Study of Leukemias of Ambiguous Lineage [iBFM-AMBI2012]) of 233 cases of pediatric ALAL patients is presented. Survival statistics were used to compare the prognosis of subsets and types of treatment. Five-year event-free survival (EFS) of patients with acute lymphoblastic leukemia (ALL)–type primary therapy (80% ± 4%) was superior to that of children who received acute myeloid leukemia (AML)–type or combined-type treatment (36% ± 7.2% and 50% ± 12%, respectively). When ALL- or AML-specific gene fusions were excluded, 5-year EFS of CD19+ leukemia was 83% ± 5.3% on ALL-type primary treatment compared with 0% ± 0% and 28% ± 14% on AML-type and combined-type primary treatment, respectively. Superiority of ALL-type treatment was documented in single-population mixed phenotype ALAL (using World Health Organization and/or European Group for Immunophenotyping of Leukemia definitions) and bilineal ALAL. Treatment with ALL-type protocols is recommended for the majority of pediatric patients with ALAL, including cases with CD19+ ALAL. AML-type treatment is preferred in a minority of ALAL cases with CD19− and no other lymphoid features. No overall benefit of transplantation was documented, and it could be introduced in some patients with a poor response to treatment. As no clear indicator was found for a change in treatment type, this is to be considered only in cases with ≥5% blasts after remission induction. The results provide a basis for a prospective trial.

Introduction:

Purpose:Total body irradiation (TBI) has proved to be the “gold standard” as part of the conditioning regimen before allogeneic hematopoietic stem cell transplantation (HSCT) in pediatric patients with acute lymphoblastic leukemia (ALL). Its superiority over chemo-based conditioning was recently demonstrated in the prospective, international, randomized phase III study, which enrolled 417 patients beyond the age of 4 years transplanted for ALL in complete morphological remission (CR) from either matched sibling (MSD) or matched unrelated donor (MD) (Peters et al, JCO 2021, FORUM study; EudraCT: 2012-003032-22;ClinicalTrials.gov: NCT01949129). The use of either of the two protocol-prespecified chemo-conditioning regimens resulted in significantly worse EFS. Given the unavailability of TBI in some regions/centres and contraindications to TBI in individual patients, we here compare the outcomes of patients who received busulfan (BU) - based regimen vs of those who were given a treosulfan (TREO) - based conditioning in FORUM centres in both randomizing and non-randomizing countries in the years 2013-2018.

Introduction:

No relevant conflicts of interest to declare.

Bleckmann: JazzPharma: Other: financial support of travel costs. Moricke:JazzPharma: Honoraria, Other: financial support of travel costs. Inaba:Arog: Research Funding. Kattamis:Novartis: Honoraria, Research Funding; ApoPharma: Honoraria. Reinhardt:Boehringer Ingelheim: Membership on an entity's Board of Directors or advisory committees; Celgene: Research Funding; Jazz Pharma: Other: Travel Accomodation; Celgene: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees.

Kattamis: Novartis: Research Funding, Speakers Bureau; ApoPharma: Speakers Bureau.

No relevant conflicts of interest to declare.

Transient leukemia (TL) occurs in 5 to 10% of newborns with Down syndrome (DS). In almost all cases it resolves spontaneously within 3 months, but 20–25% of the children develop myeloid leukemia (ML-DS) until the age of 4 years. TL and ML-DS can occur also in children without any clinical signs of Down syndrome, but with constitutional trisomy 21 due to mosaicism. It can be difficult to diagnose TL or ML-DS in these children and the treatment strategies have not been defined.Between 1/2002 and 7/2011, 15 newborns and infants were diagnosed with DS mosaic. Nine of them presented with TL and 8 children suffered from ML-DS; 2 of them with a history of TL (table 1). In children without any stigmata the special morphology and immunophenotype of blasts triggered the screening for GATA1 mutation and trisomy 21 mosaic. Diagnostic work-up was performed according to standard guidelines: morphology, immunophenotyping (IP), cytogenetics and FISH (trisomy 21), molecular genetics (GATA 1 mutation screening). Screening of GATA1 mutations was done with direct sequencing of PCR product (Exon1, Exon2, and Exon3). For monitoring of GATA1 mutant clone qPCR have been used with patient specific TaqMan probes and primers. Mosaic was detected by cytogenetics or FISH in bone marrow, blood and/or fibroblasts.All newborns with TL achieved complete remission (CR). Due to clinical symptoms caused by the leukemic blasts, in 3 children low-dose cytarabine was applied. One patient died due to cardiovascular failure. In all patients GATA 1 mutation was confirmed. Minimal residual disease by qPCR (mutation-specific probes) or immunophenotyping (IP) revealed negativity in 3 out of 3 children monitored (follow-up 2 to 10.1 yrs).Two children with (unknown) trisomy 21 mosaic were diagnosed as acute megakaryoblastic leukemia (AMKL) and treated according the high risk arm of the AML-BFM 2004 including allogeneic stem cell transplantation (one child), GATA1 mutation was identified retrospectively. Both children are alive in CR. Six children with ML-DS were initially treated according the AML-BFM protocol. After ML-DS was confirmed, therapy was continued with the intensity reduced schedule according to the ML-DS 2006 protocol. All children are still in CR (follow-up 1.5 to 6.7 years, median 2.4 yrs). This was confirmed by MRD-monitoring, which achieved negativity after two treatment elements (qPCR <10−4 n=3; IP <10−3 n=6). In one child a distinct refractory myeloid leukemia population (GATA1mut negative/trisomy 21 negative) arose after the 1st induction. Due to treatment refractory, allogenic stem cell transplantation was applied.GATA1 mutated leukemia has to be excluded in all young children with AMKL (<5years old) to prevent overtreatment. Treatment with reduced intensity protocol like ML-DS 2006 seems to be effective and sufficient in children with trisomy 21 mosaic and GATA1 mutated ML-DS.No relevant conflicts of interest to declare.