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Pediatric leukemia presents specific clinical and genetic features from adult leukemia but the underpinning mechanisms of transformation are still unclear. Acute megakaryoblastic leukemia (AMKL) is the malignant accumulation of progenitors of the megakaryocyte lineage that normally produce blood platelets. AMKL is diagnosed de novo , in patients showing a poor prognosis, or in Down syndrome (DS) patients with a better prognosis. Recent data show that de novo AMKL is primarily associated with chromosomal alterations leading to the expression of fusions between transcriptional regulators. This review highlights the most recurrent genetic events found in de novo pediatric AMKL patients and, based on recent functional analyses, proposes a mechanism of leukemogenesis common to de novo and DS–AMKL.

The association between mediastinal germ cell tumors (MGCT) and acute megakaryoblastic (M7) leukemia has been known for many years. We hereby present this review to better characterize the coexistence of these entities as well as the salient features, the treatment options, and the overall prognosis. A search of PUBMED, Medline, and EMBASE databases via OVID engine for primary articles and case reports under keywords "germ cell tumors" and "acute myeloid leukemia" revealed a total of 26 cases in English that reported MGCT and M7 leukemia. The median age at diagnosis of MGCT was 24 (13-36) years. All cases were stage III. All cases of MGCT were of non-seminomatous origin and one case was unclassified. MGCT occurred prior to the diagnosis of leukemia in 46% of cases and concomitantly in 31% of cases. M7 leukemia was never reported prior to the appearance of MGCT. Complex cytogenetics and hyperdiploidy were the most commonly reported cytogenetic abnormalities. In the 23 cases where the treatment regimen was available, platinum-based chemotherapy directed towards management of the germ cell tumors was used initially in 21 cases and leukemia-directed treatment was used initially in 2 cases only. The median time from diagnosis of MGCT to development of M7 leukemia was 5 (2.25-39) months. Median time to death from the initial diagnosis of MGCT was 6 (0.5-60) months. Patients with a history of MGCT are at higher risk of developing M7 leukemia. They need long-term follow-up with a particular attention to the development of hematological malignancies. The overall prognosis remains poor.

Essential thrombocythemia (ET) is a Philadelphia chromosome-negative myeloproliferative neoplasm characterized by sustained thrombocytosis. Its transformation into acute leukemia is a rare event (5% at 20 years). Transformation can be spontaneous or related to therapy. Acute leukemias most often associated with transformation from ET are myeloblastic or myelomonoblastic leukemias. There are very few case reports of ET transforming into acute megakaryoblastic leukemia. Here we report a case of transformation to acute megakaryoblastic leukemia in an elderly female patient who was treated with hydroxyurea for ten years. After 10-years with stable disease she presented and rapidly deteriorated with acute megakaryoblastic leukemia with high JAK2V617F mutant allele burden and high p53 expression. This case provides another example of the poor outcome of acute megakaryoblastic transformation of essential thrombocythemia. Keywords: Essential thrombocythemia, Acute megakaryoblastic leukemia, Transformation

GATA family proteins play essential roles in development of many cell types, including hematopoietic, cardiac, and endodermal lineages. The first three factors, GATAs 1, 2, and 3, are essential for normal hematopoiesis, and their mutations are responsible for a variety of blood disorders. Acquired and inherited GATA1 mutations contribute to Diamond-Blackfan anemia, acute megakaryoblastic leukemia, transient myeloproliferative disorder, and a group of related congenital dyserythropoietic anemias with thrombocytopenia. Conversely, germ line mutations in GATA2 are associated with GATA2 deficiency syndrome, whereas acquired mutations are seen in myelodysplastic syndrome, acute myeloid leukemia, and in blast crisis transformation of chronic myeloid leukemia. The fact that mutations in these genes are commonly seen in blood disorders underscores their critical roles and highlights the need to develop targeted therapies for transcription factors. This review focuses on hematopoietic disorders that are associated with mutations in two prominent GATA family members, GATA1 and GATA2.

International audience; Chimeric transcription factors are a hallmark of human leukemia, but the molecular mechanisms by which they block differentiation and promote aberrant self-renewal remain unclear. Here, we demonstrate that the ETO2-GLIS2 fusion oncoprotein, which is found in aggressive acute megakaryoblastic leukemia, confers megakaryocytic identity via the GLIS2 moiety while both ETO2 and GLIS2 domains are required to drive increased self-renewal properties. ETO2-GLIS2 directly binds DNA to control transcription of associated genes by upregulation of expression and interaction with the ETS-related ERG protein at enhancer elements. Importantly, specific interference with ETO2-GLIS2 oligomerization reverses the transcriptional activation at enhancers and promotes megakaryocytic differentiation, providing a relevant interface to target in this poor-prognosis pediatric leukemia.

Background Alpha-synuclein is a member of synuclein family of proteins with unidentified function localized in the cytoplasm, mitochondria of neurons, and presynaptic nerve endings. Although it is found in the Lewy bodies in synucleinopathies and in Alzheimer's disease, the protein could also be considered as a novel marker in diagnosis of diseases related to the hematopoietic system. Methods The current study evaluated alpha-synuclein expression in bone marrow sections obtained from 9 patients with acute myeloblastic leukemia (AML)-M6, 2 patients with AML-M7, and 56 patients with other forms of AML by immunohistochemical (IHC) analysis. Results Seven out of 9 cases with erythroleukemia (66.7%) and 1 of the 2 cases with M7 (50%) were positive. In contrast; the blasts in 2 out of 56 AML cases with non-M6/M7 (3.6%) showed positive staining. Accordingly, alpha-synuclein was positive in normal erythroid precursors and megakaryocytes (if existing) in these cases; while, it was negative in lymphoid and myeloid precursors. Conclusion Alpha-synuclein expression in non-neoplastic and neoplastic erythroid cells and megakaryocytes could be used as a complementary and useful marker for distinction between AML-M6/M7 and other types of AML.

Acute megakaryoblastic leukemia (AMKL) in children without Down syndrome (DS) has an extremely poor outcome with 3-year survival of less than 40%, whereas AMKL in children with DS has an excellent survival rate. Recently, a novel recurrent translocation involving CBFA2T3 and GLIS2 was identified in about 30% of children with non-DS AMKL, and the fusion gene was reported as a strong poor prognostic factor in pediatric AMKL. We report the difficult clinical courses of pediatric patients with AMKL harboring the CBFA2T3-GLIS2 fusion gene.Down sendromu (DS) olmayan çocuklarda akut megakaryoblastik löseminin (AMKL) prognozu çok kötü ve 3 yıllık sağkalım %40’ın altında iken, DS’li çocuklarda AMKL’nin sağkalım oranı mükemmeldir. Yakın zamanda, DS olmayan AMKL’li çocukların yaklaşık %30’unda CBFA2T3 ve GLIS2’yi içeren yeni bir tekrarlayan translokasyon tanımlandı ve füzyon geninin pediatrik AMKL olgularında kötü prognoz ile ilişkili güçlü bir prognostik belirteç olduğu bildirildi. CBFA2T3-GLIS2 füzyon genini taşıyan AMKL tanılı pediatrik hastalarda sorunlu klinik seyri bildiriyoruz.

Objectives: Down syndrome (DS)–associated transient abnormal myelopoiesis (TAM) or acute megakaryoblastic leukemia (AMKL) in monozygotic twins is exceedingly rare and has not been well characterized. Methods: We describe a unique case of monozygotic twins with simultaneous TAM from a triplet pregnancy at 34 weeks’ gestation. Previously reported cases of TAM and DS-AMKL in monozygotic twins have been reviewed to compare with our cases. The current concept of a sequential multistep process in leukemogenesis and disease evolution of TAM into DS-AMKL through the collaboration among trisomy 21, GATA1, and other gene mutations is also reviewed. Results: Distinct GATA1 mutations are identified in our neonate twins with TAM from a triplet pregnancy, whereas precisely identical GATA1 mutations have been detected in all three monozygotic DS twins reported in the literature. Conclusions: Identical GATA1 mutations in cases of monozygotic twins are likely derived from twin-twin transmission. Distinct GATA1 mutations identified in our neonate twins with TAM provide unequivocal evidence of independent intra-utero GATA1 mutations, a completely different mechanism of development of TAM in monozygotic twins from previously reported cases. Interaction of trisomy 21 and GATA1 mutation produces TAM, but additional gene mutations are required for TAM to transform into DS-AMKL.

Acute myeloid leukemia has a rare subtype in French-American-British classification as M7 or acute megakaryoblastic leukemia. Chromosome abnormalities in cases with acute megakaryoblastic leukemia can affect their prognosis. Evaluation of these abnormalities and their impact are not fully elucidated. This case presentation is about 16 months female who has a rare abnormality (trisomy 3) alongside acute megakaryoblastic leukemia. The remarkable point is that her malignancy is as primary or non-Down syndrome acute megakaryoblastic leukemia. The author's suggestion through this case presentation is the necessity of drawing a cytogenetic profile, especially in cases with acute megakaryoblastic leukemia for better treatment strategies.

Background Acute myeloid leukemia (AML) is a heterogeneous disease regarding morphology, immunophenotyping, genetic abnormalities, and clinical behavior. The overall survival rate of pediatric AML is 60% to 70%, and has not significantly improved over the past two decades. Children with Down syndrome (DS) are at risk of developing acute megakaryoblastic leukemia (AMKL), which can be preceded by a transient myeloproliferative disorder during the neonatal period. Intensification of current treatment protocols is not feasible due to already high treatment‐related morbidity and mortality. Instead, more targeted therapies with less severe side effects are highly needed. Procedure To identify potential novel therapeutic targets for myeloid disorders in children, including DS‐AMKL and non‐DS‐AML, we performed an unbiased compound screen of 80 small molecules targeting epigenetic regulators in three pediatric AML cell lines that are representative for different subtypes of pediatric AML. Three candidate compounds were validated and further evaluated in normal myeloid precursor cells during neutrophil differentiation and in (pre‐)leukemic pediatric patient cells. Results Candidate drugs LMK235, NSC3852, and bromosporine were effective in all tested pediatric AML cell lines with antiproliferative, proapoptotic, and differentiation effects. Out of these three compounds, the pan‐histone deacetylase inhibitor NSC3852 specifically induced growth arrest and apoptosis in pediatric AML cells, without disrupting normal neutrophil differentiation. Conclusion NSC3852 is a potential candidate drug for further preclinical testing in pediatric AML and DS‐AMKL.

Fusion oncogenes are prevalent in several pediatric cancers, yet little is known about the specific associations between age and phenotype. We observed that fusion oncogenes, such as ETO2–GLIS2, are associated with acute megakaryoblastic or other myeloid leukemia subtypes in an age-dependent manner. Analysis of a novel inducible transgenic mouse model showed that ETO2–GLIS2 expression in fetal hematopoietic stem cells induced rapid megakaryoblastic leukemia whereas expression in adult bone marrow hematopoietic stem cells resulted in a shift toward myeloid transformation with a strikingly delayed in vivo leukemogenic potential. Chromatin accessibility and single-cell transcriptome analyses indicate ontogeny-dependent intrinsic and ETO2–GLIS2-induced differences in the activities of key transcription factors, including ERG, SPI1, GATA1, and CEBPA. Importantly, switching off the fusion oncogene restored terminal differentiation of the leukemic blasts. Together, these data show that aggressiveness and phenotypes in pediatric acute myeloid leukemia result from an ontogeny-related differential susceptibility to transformation by fusion oncogenes. Significance: This work demonstrates that the clinical phenotype of pediatric acute myeloid leukemia is determined by ontogeny-dependent susceptibility for transformation by oncogenic fusion genes. The phenotype is maintained by potentially reversible alteration of key transcription factors, indicating that targeting of the fusions may overcome the differentiation blockage and revert the leukemic state. See related commentary by Cruz Hernandez and Vyas, p. 1653. This article is highlighted in the In This Issue feature, p. 1631

Pediatric non-Down-syndrome acute megakaryoblastic leukemia (non-DS-AMKL) is a heterogeneous subtype of leukemia that has historically been associated with poor prognosis. Until the advent of large-scale genomic sequencing, the management of patients with non-DS-AMKL was very difficult due to the absence of reliable biological prognostic markers. The sequencing of large cohort of pediatric non-DS-AMKL samples led to the discovery of novel genetic aberrations, including high-frequency fusions, such as CBFA2T3-GLIS2 and NUP98-KDM5 A, as well as less frequent aberrations, such as HOX rearrangements. These new insights into the genetic landscape of pediatric non-DS-AMKL has allowed refining the risk-group stratification, leading to important changes in the prognostic scenario of these patients. This review summarizes the most important molecular pathogenic mechanisms of pediatric non-DS-AMKL. A critical discussion on how novel genetic abnormalities have refined the risk profile assessment and changed the management of these patients in clinical practice is also provided.

Various conditions can lead to antenatal hepatosplenomegaly. In addition to commonly known etiologies like hydrops fetalis or viral illnesses, hematologic disorders like congenital leukemia, although rare, should also be ruled out. We present a case of hepatosplenomegaly detected during antenatal screening in a neonate, in whom acute megakaryoblastic leukemia was diagnosed postnatally based on the immunophenotype.

Congenital leukemia is rare disease with an incidence of one to five cases per million births. Transient abnormal myelopoiesis (TAM), also called transient myeloproliferative disorder, is a pre-leukemia disorder that may occur in Down syndrome (DS) or non-DS infants. TAM may enter spontaneous remission; however, continual monitoring is required, as this disorder has been observed to develop into acute megakaryoblastic leukemia in 16-30% of cases. In the literature, 16 cases of TAM in non-DS infants have been reported. The case presented in the current study is, to the best of our knowledge, the first case of an Italian non-DS newborn presenting with clinical manifestations of acute leukemia at five days after birth, exhibiting a normal karyotype, trisomy 21 only in blast cells, and spontaneous remission. Chromosomal analyses on peripheral blood cells, bone marrow cells and dermal fibroblasts were conducted using a G-banding technique, and fluorescence in situ hybridization (FISH) was used to identify the critical regions of DS. Amplification of GATA binding protein 1 (GATA1) exon 2 genomic DNA was performed using polymerase chain reaction. Cytogenetic analysis of 50 peripheral blood cells and dermal fibroblasts from the patient revealed a normal karyotype: 46, XX. Conversely, cytogenetic analysis of the patient's bone marrow revealed an abnormal karyotype 47, XX+21. In order to investigate this result, FISH was performed, which identified the presence of three signals in 70% of the cells and two signals in 30% of bone marrow cells. GATA1 sequencing revealed the substitution of a single base (c.150delG) in exon 2. Seven months after the initial analysis, FISH and cytogenetic analyses of the stimulated/unstimulated peripheral blood cells and bone marrow cells were performed, revealing that each exhibited diploid signals, as observed in a normal karyotype.

Acute erythroid leukemia (FAB-M6) and acute megakaryoblastic leukemia (FAB-M7) exhibit closely related properties in cells regarding morphology and the gene expression profile. Although allogeneic hematopoietic stem cell transplantation (allo-HSCT) is considered the mainstay of the treatment for both subtypes of leukemia due to their refractoriness to chemotherapy and high rates of relapse, it remains unclear whether allo-HSCT is curative in such cases due to their scarcity. We retrospectively examined the impact of allo-HSCT in 382 patients with M6 and 108 patients with M7 using nationwide HSCT data and found the overall survival (OS) and relapse rates of the M6 patients to be significantly better than those of the M7 patients after adjusting for confounding factors and statistically comparable with those of the patients with M0/M1/M2/M4/M5 disease. Consequently, the factors of age, gender, performance status, karyotype, disease status at HSCT and development of graft-vs.-host disease predicted the OS for the M6 patients, while the performance status and disease status at HSCT were predictive of the OS for the M7 patients. These findings substantiate the importance of distinguishing between M6 and M7 in the HSCT setting and suggest that unknown mechanisms influence the HSCT outcomes of these closely related subtypes of leukemia. © 2016 Elsevier Ltd., Embargo Period 12 months

Acute megakaryocytic leukemia is a rare form of acute myeloid leukemia that carries a poor prognosis. As most cases of osteolytic lesions are due to plasma cell and myeloid malignancies, maintaining a broad differential directly influences clinical course. We document a 45-year-old patient with progressive constitutional symptoms, osteolytic bone lesions in the setting of hypercalcemia, who developed acutely worsening pancytopenia. The diagnosis of myeloid sarcoma with megakaryocytic differentiation was made after obtaining tissue from osteolytic bone that stained strong for CD34. Immunohistochemical testing underscores the importance of how serologic and urine testing remains limited and can delay early diagnosis in this disease. Keywords: myelofibrosis; AML; acute panmyelosis; acute megakaryoblastic leukemia (Published: 25 April 2016) Citation: Journal of Community Hospital Internal Medicine Perspectives 2016, 6 : 30327 - http://dx.doi.org/10.3402/jchimp.v6.30327

Context Acute megakaryoblastic leukemia (AMKL) is a rare myeloid leukemia, occurring in 1%–5% of all adult acute myeloid leukemia (AML) cases. AMKL is characterized by a leukemic blast population positive for factor VIII, CD41a, CD42b, and/or CD61 with extensive myelofibrosis. Although various cytogenetic abnormalities are commonly reported, the association between constitutional trisomy 21 and AMKL has been of particular interest, because of the near universal presence of GATA1 mutation in such cases. Objective and Design We report a case of AMKL in an adult presenting with extensive bone marrow necrosis in which cytogenetic studies revealed three copies of chromosome 21 as part of a complex karyotype; however, sequencing of the GATA1 gene revealed no mutation. Results The patient was an adult male who presented with extensive bone marrow necrosis, making definitive diagnosis difficult. Autopsy studies using a multimodality approach identified AMKL with a complex karyotype, including trisomy 21. Sanger sequencing of the GATA1 gene showed a germline configuration without a mutation. Conclusions To our knowledge, this is the first reported case of an adult with AMKL with acquired trisomy 21 in which the GATA1 mutation was investigated and the second reported case of AMKL presenting with extensive bone marrow necrosis. We will present a diagnostic approach to AMKL in which extensive bone marrow necrosis renders examination of the bone marrow difficult. Furthermore, we will examine the absence of the GATA1 mutation in a case of AMKL with trisomy 21 in an adult.

Background/purpose Although Down syndrome (DS) patients have a higher risk of developing transient myeloproliferative disorder (TMD) and acute leukemia, very little data is available on long-term outcome in Taiwanese patients. The current study was designed to determine the clinical characteristics and treatment outcome of DS patients with TMD or acute leukemia (AL). Methods In 25 consecutive DS patients with TMD or AL enrolled from 1990 to 2012, clinical manifestations and treatment protocols were investigated and GATA1 (GATA binding protein 1) mutations were identified. Among 16 DS-acute myeloid leukemia (DS-AML) patients, clinical outcomes were compared between survivors and nonsurvivors. Results Most of our DS patients had TMD (32%), acute megakaryoblastic leukemia (24%), or acute erythromegakaryoblastic leukemia (16%). The median follow-up time was 22.5 months (1–230 months). The age was younger and the hemoglobin (Hb) level and platelet count were higher in TMD patients than in leukemia patients. Among DS-AML patients, the Hb level was higher in survivors than nonsurvivors (8.8 ± 2.7 g/dL vs. 5.8 ± 2.4 g/dL; p = 0.044) and the age was older in relapsed patients than in nonrelapsed patients (43.8 ± 18 months old vs. 21.6 ± 8.6 months old; p = 0.025). The 3-year overall survival (OS) rate was 44%, higher in patients receiving appropriate chemotherapy than in those receiving inadequate treatment (63.6% vs. 0%, p = 0.001), and higher in those diagnosed with TMD or AL after 2008 than before 2008 (33.3% vs. 75%; p = 0.119). Conclusion Outcome in DS-AML patients is optimal if appropriate treatment is provided. With modification of the treatment strategy in 2008, OS increased in Taiwan.

Ataxia telangiectasia mutated (ATM) is a tumor suppressor gene, and its somatic inactivation plays a role in the pathogenesis of lymphoid malignancies. However, the role of ATM in patients with myeloid malignancies is still unknown. We herein report a case of acute megakaryoblastic leukemia (AMKL) with ATM gene deletion. An 84-year-old Japanese woman presenting with a pale face and pancytopenia was admitted to our institution and diagnosed to have AMKL with ATM gene deletion. She was treated with intravenous azacitidine. The azacitidine treatment was effective for approximately 1 year. Somatic inactivation of the ATM gene may therefore be involved in the pathogenesis of AMKL.

MicroRNAs (miRNAs) are non-coding RNAs involved in post-transcriptional regulation of gene expression. In many cancers, up- or downregulation of different miRNAs is reported. In acute myeloid leukemia, upregulation of miR-92a-3p was reported in human in vitro studies. We performed blockage of miR-29a-3p in human acute megakaryoblastic leukemia cell line (M-07e) by using locked nucleic acid (LNA) and cell proliferation; apoptosis and necrosis were assessed. At different time points after LNA-anti-miR92a-3p transfection, miR-92a-3p quantitation was assessed by qRT-real-time PCR, MTT assay and annexin/propidium iodide staining were performed. The data were processed using the ANOVA test. At all three time points, the expression of miR-92a-3p was lower in the LNA-anti-miR group compared with the control groups. Cell viability between LNA-Anti-miR and the control group was statistically significant. Blockage of miR-92a-3p was associated with increment of the ratio of apoptotic cells in the LNA-anti-miR group was higher than the other group. The ratio of necrotic cells in the LNA-antimiR group was higher than the other groups. These assessments indicate that miR-92a-3p blockage can decrease the viability of M-07e cells, which is mainly due to induction of apoptosis and necrosis. Our findings could open up a path to a miRNA based therapeutic approach for treatment of acute megakaryoblastic leukemia.

Acute megakaryoblastic leukemia (AMKL) is a rare disease accounting for 7%–10% of acute myeloid leukemia (AML) in children. It is uncommon in children without Down syndrome (DS). Orbital chloroma is usually associated with AML M2, M4, and M5. Herein, we report the case of a 22-month-old female who was diagnosed to have AMKL with orbital chloromas and without DS. Morphology and the initial panel of immunophenotyping were inconclusive and the presence of orbital chloromas added to the ambiguity. The presence of CD61 expression and marrow fibrosis supported by hyperdiploidy helped us clinch the diagnosis. Hence, comprehensive analysis of morphology, immunophenotyping, and cytogenetics is warranted to make an accurate diagnosis of AMKL.

Introduction Development of Acute megakaryoblastic leukemia in Down syndrome children (DS-AMKL) is a multi-step process. Acquired GATA1s mutation during fetal hematopoiesis is responsible of a transient myeloproliferative disorder (TMD) characterized by an accumulation of megakaryoblasts. Although most of TMD regress around birth, some TMD can progress from the initial GATA1s clone to AMKL through the acquisition of additional mutations, including in (i) the cohesin complex (i.e: SMC3), (ii) the JAK/STAT signaling pathway, such as MPL and (iii) the polycomb repressive complex 2 (EZH2). How these mutations cooperate to deregulate megakaryocyte (MK) differentiation and to induce a full-blown AMKL, along with the precise role of trisomy 21 (T21) during this transformation process remain unclear. Because modeling of DS-AMKL is particularly difficult in mice, we performed a step-wise introduction of GATA1s, a gain of function mutation of MPL (MPLW515K) and a heterozygous loss of function mutation in a cohesin (SMC3), separately or in combination, in T21 and isogenic disomic 21 (Dis21) human induced Pluripotent Stem Cells (iPSCs). Methods Trisomy 21 iPSCs were kindly provided by M. Weiss (Memphis, TN). CRISPR/Cas 9 genome editing of GATA1 or SMC3 allowed the generation of GATA1s T21, SMC3+/- T21 and GATA1s SMC3+/- T21 iPSC clones. CRISPR/Cas9-mediated knock-in of MPLW515K was performed in T21 GATA1s iPSCs. The subsequent T21 GATA1sMPLW515K/W515Kclones were selected as well as a revertant Dis21 GATA1sMPLW515K/W515Kclone. Finally, SMC3 insertion/deletion were obtained in isogenic T21 and Dis21 GATA1s MPLW515K/W515K SMC3+/-iPSCs clones. Hematopoietic differentiation was induced in 2D cultures in presence of a matrix and a cocktail of cytokines followed by a MK differentiation with SCF and TPO. MK differentiation was studied by clonogenic assays, flow cytometry, confocal microscopy and ultrastructural studies. Gene expression analyses were performed by RNA-seq on highly purified MK from all genotypes. Results GATA1s alone blocked MK maturation characterized by a persistent CD34 expression, an accumulation of abnormal large granules, a defect in the development of demarcation membranes (DMS), and a marked decrease in proplatelet formation. The typical GATA1s MK were large megakaryoblasts with numerous large granules and rare DMS. However, GATA1s alone had no effect on the clonogenic activity in CFU-MK assays and MK numbers. The introduction of the MPLW515K mutation did not modify this phenotype either in Dis21 or T21 GATA1s MK, but induced a complete TPO independence. SMC3+/- alone enhanced the MK maturation allowing the generation of a higher number of proplatelets-generating MK. Importantly, the combination of GATA1s and SMC3+/- mutations had a marked cooperative effect that worsened the MK maturation defect, led to the generation of abnormal megakaryoblasts with only a pre-DMS and resulted in enhanced proliferation and ploidization both in Dis21 and T21 iPSCs. Interestingly, the proliferation was markedly higher in T21 clones compared to Dis21 counterparts. RNA-seq and GSEA analyses showed that T21 GATA1s SMC3+/- mutant MK exhibited transcriptional signatures consistent with a dramatic decrease in the expression of maturation genes, including GATA1 target genes, while DNA replication gene markers were increased compared with GATA1s alone. T21 GATA1s MPLW515K/W515K SMC3+/- MK were enriched for AMKL signatures as compared to isogenic Dis21 GATA1sMPLW515K/W515K SMC3+/- MK. Ongoing ATAC-seq analyses will define the consequence of the different mutations on chromatin accessibility. Conclusion Using iPSC modeling, we analyzed in a human cell-context the consequences of the different combination of mutations associated with DS-AMKL that would be difficult to model using human primary cells. Our data demonstrate that GATA1s expression cooperates with SMC3+/- to enhance proliferation of megakaryoblasts from T21 iPSCs and isogenic Dis21 iPSCs hence reproducing the abnormalities observed in DS-AMKL. T21 is not directly involved in the MK differentiation defects but rather give a proliferative advantage supporting its role in leukemia development. Disclosures No relevant conflicts of interest to declare.

Chromosomal translocations of the Nucleoporin 98 gene (NUP98) are associated with multiple hematopoietic malignancies. In particular, NUP98 rearrangements can be found in up to 6.6% of de novo cases of pediatric AML. Specific subpopulations of pediatric AML appear to be even more enriched for NUP98 fusions, with over 16% of cytogenetically normal pediatric AML patients and 15% of non-Down syndrome acute megakaryoblastic leukemia (AMKL) patients harboring these fusions. Clinically, the NUP98-KDM5A fusion is associated with erythroid and megakaryocytic leukemias while the NUP98-NSD1 fusion is associated with myelomonocytic leukemias. When NUP98 fusions are present in AML, they confer a poor prognosis. To better characterize the role of these fusions in human hematopoiesis, we used cord blood CD34+ (cb-CD34+) hematopoietic stem and progenitor cells (HSPCs) as an in vitro model system. We transduced cb-CD34+ HSPCs with NUP98-NSD1, NUP98-KDM5A, or empty vector control and studied the effects on cell proliferation and differentiation in liquid culture media containing cytokines (IL-6, FLT3-Ligand, SCF, TPO, and SR1 (an aryl hydrocarbon receptor antagonist)). NUP98-NSD1 and NUP98-KDM5A fusions increase the proliferation rate in liquid culture by three-fold and 19-fold, respectively (p Citation Format: Ryan Hiltenbrand, Jonathan Miller, Jeffery Klco. Cord blood CD34+ HSPCs: An in vitro model system for characterizing NUP98 fusions [abstract]. In: Proceedings of the AACR Special Conference on the Advances in Pediatric Cancer Research; 2019 Sep 17-20; Montreal, QC, Canada. Philadelphia (PA): AACR; Cancer Res 2020;80(14 Suppl):Abstract nr B34.

In this study, we aimed to characterize the molecular mechanisms of two very rare subtypes of AML: acute megakaryoblastic leukemia (AMKL) and acute panmyelosis with myelofibrosis (APMF). Our goal is to describe the clinical-pathologic features of APMF and explore the genomic landscape AMKL to further understand these rare malignancies. We identified 35 patients diagnosed with AMKL (n=27) and APMF (n=8) at Mayo Clinic between 1995 and 2015 by retrospective chart review. For 10 of the AMKL patients, tissue was available for whole-exome sequencing and was analyzed in comparison to a published AML reference population. The median overall survival was shorter in patients with AMKL (3.9 months, 95% CI 1.7-7.4) than in patients with APMF (14.3 months, 95% CI 0.7-NE, p = 0.026,). For both AMKL and APMF, patients who underwent allogeneic hematopoietic stem cell transplantation had better overall survival (14.3 months, 95% CI 1.9-NE) compared to those not undergoing transplantation (4.6 months, 95% CI 1.5-7.4, p = 0.003). Patients with AMKL presented more frequently with splenomegaly, with higher peripheral blood blast counts, and with higher serum lactate dehydrogenase concentrations. 9 out of 10 AMKL patients with available tissue for sequencing demonstrated variants in 22 of 35 AML driver genes, with JAK2 V617F as the most common mutation. Although our small study numbers preclude firm conclusions, it does reflect the rarity of these AML subtypes. Furthermore, inferior survival in AMKL (compared to APMF) was reflected in its proliferative disease features such as splenomegaly, high blast counts, and high lactate dehydrogenase. Interestingly, the presence of JAK2 V617F variants in 40% of the interrogated samples was higher than expected. Although JAK2 is a known molecular driver in myeloproliferative neoplasms, it is actually very rare in de novo AML (~1%). Despite improved survival with allogeneic stem cell transplant, we can conclude that treatment outcomes for AMKL and APMF with standard-of-care therapy were sobering and that patients with these rare AML subtypes should undergo molecular evaluation to qualify them for clinical trials with novel targeted therapies. Citation Format: Marissa Li, Moritz Binder, Basma Basha, Ben Zhang, Alejandro Ferrer, Yuanhan Liu, Mrinal Patnaik, David Viswanatha, Naseema Gangat. Acute megakaryoblastic leukemia is associated with poor overall survival and enriched in JAK2 variants [abstract]. In: Proceedings of the AACR Special Conference on the Evolving Landscape of Cancer Modeling; 2020 Mar 2-5; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2020;80(11 Suppl):Abstract nr B03.

Children with Down syndrome (DS) are found to have an increased risk of developing various hematological disorders. Particularly, they have an increased predisposition to acute leukemia, predominantly the myeloid type known as myeloid leukemia of Down syndrome (ML-DS). The major morphological subtype is acute megakaryoblastic leukemia. Approximately 10% of the neonates with DS show a unique disorder known as transient leukemia or transient abnormal myelopoiesis (TAM). Their clinical and morphological features are indistinguishable from acute myeloid leukemia (AML); however, they regress spontaneously within the first few months of life. Here we present a series of four cases with different hematological conditions in children with DS. Of the four cases, two presented with AML-M7, one with TAM, and one case was diagnosed as AML-M2 subtype. This case series highlights the spectrum of hematological disorders in children with DS. Although the majority of the case studies show that TAM and AML-M7 are strongly associated with DS, this case series brings to focus that other AML subtypes may occur as well.

Cornelia de Lange Syndrome (CdLS) is a rare autosomal dominant developmental disorder characterized by a distinctive facial dysmorphism and variable developmental anomalies including prenatal and postnatal growth delay, microcephaly, intellectual disability, upper limb anomalies and hirsutism. CdLS

Several conventions have been established in order to define and characterize Mixed Phenotype Acute Leukemia (MPAL). However, megakaryocytic markers have not been included in the definition of MPAL neither in the European Group for the Immunological Characterization of Leukemias (EGIL) proposal nor in any of the WHO Classification of Tumors issues. We report four pediatric acute leukemia (AL) cases (prevalence: 0.18%) with megakaryoblasts co-expressing the T-specific antigen CD3 (cytoplasmic), together with a very homogeneous antigen profile of immature cells and other lymphoid traits. In one case, the presence of epsilon CD3 mRNA was confirmed as well on sorted CD34+ blasts. All four cases were infants, and two of them disclosed trisomy 21 in the blast population (not constitutional) without being children with Down Syndrome. They were homogeneously treated with AML schemes, achieving all four CR. However, 3 patients relapsed early. Only one patient is alive and remain disease-free, with a long follow-up. Even though cyCD3 was the only T cell marker expressed, its specificity entails the consideration of these cases as a new subtype of MPAL Megakaryoblastic/T, keeping this in mind when designing diagnostic panels. Detection and report of these cases are necessary so as to further characterize them in order to define the most appropriate treatment.

The RUNX1-EVI1 gene generated by the t(3;21) translocation encodes a chimeric transcription factor and is a causative gene in the development of de novo acute megakaryoblastic leukemia and leukemic transformation of hematopoietic stem cell tumors. Heterozygous RUNX1-EVI1 knock-in mice die in utero due to hemorrhage in the central nervous system and spinal cord and complete abolishment of definitive hematopoiesis in the fetal liver. On the other hand, the chimeric knock-in mouse develops acute megakaryoblastic leukemia. We created another mouse model of RUNX1-EVI1 using transplantation of retrovirus-infected bone marrow cells. Some mice transplanted with RUNX1-EVI1-expressing bone marrow cells developed acute megakaryoblastic leukemia within eight months, and the other non-leukemic mice showed thrombocytosis at around a year. In the non-leukemic mice, dysplastic megakaryocytes proliferated in the bone marrow and frequently infiltrated into the spleen, which was not associated with marrow fibrosis. In the leukemic mice, their tumor cells were positive for c-kit and CD41, and negative for TER119. Although they were negative for platelet peroxidase in the electron microscopic analysis, they had multiple centrioles in the cytoplasm, which are characteristic of megakaryocytes that undergo endomitosis. The leukemic cells were serially transplantable, and gene-expression analyses using quantitative RT-PCR arrays revealed that they showed significantly elevated expression of stem cell, primitive hematopoietic cell and endothelial cell-related genes compared with normal bone marrow cells. All these data suggested that RUNX1-EVI1 caused dysplastic hematopoiesis or leukemia of the megakaryocytic lineage and endowed gene expression profiles distinctive of immature hematopoietic cells.

International audience; We report the outcome of 27 children with de novo acute megakaryoblastic leukemia (AMKL) (excluding Down syndrome) enrolled in the French multicenter prospective study ELAM02 (2005-2011). There was no difference in gender, initial leukocyte count, CNS involvement, and complete remission rate (88.9%), as compared to other acute myeloid leukemia (AML) subtypes. AMKL patients had a significantly poorer outcome (5-year overall survival 54% [CI 95% 33%-71%] than children with other AML subtypes (5-year overall survival 73% [CI 95% 68%-77%] p = 0.02). Gender, age, CNS leukemia, hyperleukocytosis, complete remission or cytogenetic subgroups were not significant prognostic factors of disease-free survival. AMKL (excluding Down syndrom) remains an AML subgroup with inferior outcome.

Individuals with Down syndrome (DS) have a markedly increased risk of developing unique myeloid proliferations such as transient abnormal myelopoiesis (TAM) and myeloid leukemia associated with Down syndrome (ML-DS) [1, 2]. These proliferations occur in the first 3 years of life and are a result of several transforming genetic events that arise during the fetal and newborn period. The initial event, an additional chromosome 21, leads to increased megakaryocytic proliferation in the fetal liver. Subsequent mutation of GATA-binding protein 1 (GATA1) results in the development of TAM. Further acquisition of additional mutations of epigenetic regulators and common signaling pathways such as JAK family kinases, MPL, and multiple RAS pathway genes leads to the transformation to MS-DS [3].