Childhood Acute Megakaryoblastic Leukemia Research Articles

Gene Alterations In Acute Megakaryoblastic Leukemia (AMKL): a Comparison of AMKL with and without Down Syndrome

AbstractAbstract 875 Introduction:Childhood AMKL has heterogeneous clinical presentations with two major subcategories: AMKL in patients with Down syndrome (DS-AMKL) and AMKL in patients without DS (non-DS-AMKL). Related to DS-AMKL is the transient abnormal myelopoiesis (TAM), observed in neonates with DS, is considered to be a self-limited leukemia in most cases; only 20% of TAM patients develop AMKL within 4 years. The pathogenetic relationship is further illustrated by the presence of somatic mutations of GATA1 gene in children with both TAM and DS-AMKL. However, progression from TAM to AMKL may require acquisition of additional genetic alterations. Furthermore, little is known about the kinds of genetic alterations involved in the pathogenesis of non-DS-AMKL. Patients and methods:To investigate the mechanism of leukemogenesis, we comprehensively analyzed the molecular lesions in childhood AMKL (DS-AMKL, N=24; non-DS-AMKL, N=13; TAM, N=17) using single nucleotide polymorphism array (SNP-array) and mutation analysis of 9 genes, including GATA1, JAK3, JAK2, p53, FLT3, N-RAS, KIT, MPL and ASXL1. The diagnosis of TAM and AMKL was based on morphology, histopathology, the expression of megakaryocyte-specific antigens (CD41, CD42 or CD61) and/or the French-American-British (FAB) classification. The diagnosis of DS was confirmed by conventional cytogenetic analysis. Bone marrow or blood samples were obtained from the patients with TAM and AMKL at diagnosis after obtaining informed consent for banking and molecular analyses from the children's parents. Mutational screen was performed using Sanger sequencing of PCR amplified DNA. A high-density Affymetrix 6.0 SNP-array was used for karyotyping and copy number changes. Results:SNP array analysis revealed somatic gains other than trisomy 21 in 11/11 of DS-AMKL and in 7/12 of non-DS-AMKL, respectively including recurrent duplication of 1q in 4/11 patients with DS-AMKL (Table 1). Deletions were found in 8/11 and 5/12 of DS-AMKL and non-DS-AMKL, respectively. They included del(13p) in 2/11 patients with DS-AMKL and 1/12 with non-DS-AMKL, and del(17p) in 1/11 patients with DS-AMKL and 1/12 with non-DS-AMKL. A hemizygous p53 mutation was found in the DS-AMKL patient with del(17p). Uniparental disomy was found in 2 patients with DS-AMKL. The frequencies of the gene mutations in the DS-AMKL, non-DS-AMKL and TAM patients were distributed as follows: GATA1 (24/24, 1/13, 17/17, respectively), JAK3 (3/24, 1/13, 1/17, respectively), JAK2V617F (1/24, 0/13, 0/17, respectively), p53 (3/24, 0/13, 1/17, respectively), and ASXL1 (0/24, 1/13, 0/17, respectively) (Table 1). Mutations in the other genes were not detected. Two patients with DS-AMKL who had bone marrow samples at the TAM stage did not have additional gene mutations other than GATA1 mutations. Four gene mutations (GATA1, JAK3, JAK2, p53) were found in 1 patient with DS-AMKL, who did not respond to conventional chemotherapy and died of disease progression. The ASXL1 gene mutation was found in 1 patient with non-DS-AMKL who had additional chromosome abnormality t(1;22)(p13;q13) in his leukemic cells. Conclusions:Considering the different patterns of molecular lesions, DS-AMKL needs to be classified into a different category than non-DS-AMKL. Disclosures:No relevant conflicts of interest to declare.

Ring/marker chromosome derived from chromosome 7 in childhood acute megakaryoblastic leukemia with monosomy 7

In some cases of childhood acute megakaryoblastic leukemia (AMKL), G-band analysis reveals supernumerary ring/marker chromosomes along with monosomy 7. However, their origin and relevance are poorly understood. We experienced three patients with AMKL, one of whom had Down's syndrome, whose blasts at the first visit exhibited both monosomy 7 and a ring/marker chromosome. For one case, precise molecular-cytogenetic techniques revealed that the ring chromosome was derived from a chromosome 7. It was strongly suggested that the ring chromosome was derived from a chromosome 7 in another case. The ring or one of the 2 marker chromosomes was derived from a chromosome 7 in the other case. All patients responded well to initial induction therapy. While it is not clear whether the ring/marker chromosome 7 affects the long-term prognosis of acute myeloid leukemia with monosomy 7, it may be of prognostic relevance to distinguish pure monosomy 7 from monosomy 7 with a ring/marker chromosome 7. For this purpose, conventional G-banding could be complemented with additional techniques such as spectral karyotyping or fluorescence in situ hybridization, which characterize the aberration in more detail. These methods may be useful for determining the optimal treatment and for elucidating the etiology of AMKL itself.

GATA-2 Reinforces Megakaryocyte Development in the Absence of GATA-1

GATA-2 is an essential transcription factor that regulates multiple aspects of hematopoiesis. Dysregulation of GATA-2 is a hallmark of acute megakaryoblastic leukemia in children with Down syndrome, a malignancy that is defined by the combination of trisomy 21 and a GATA1 mutation. Here, we show that GATA-2 is required for normal megakaryocyte development as well as aberrant megakaryopoiesis in Gata1 mutant cells. Furthermore, we demonstrate that GATA-2 indirectly controls cell cycle progression in GATA-1-deficient megakaryocytes. Genome-wide microarray analysis and chromatin immunoprecipitation studies revealed that GATA-2 regulates a wide set of genes, including cell cycle regulators and megakaryocyte-specific genes. Surprisingly, GATA-2 also negatively regulates the expression of crucial myeloid transcription factors, such as Sfpi1 and Cebpa. In the absence of GATA-1, GATA-2 prevents induction of a latent myeloid gene expression program. Thus, GATA-2 contributes to cell cycle progression and the maintenance of megakaryocyte identity of GATA-1-deficient cells, including GATA-1s-expressing fetal megakaryocyte progenitors. Moreover, our data reveal that overexpression of GATA-2 facilitates aberrant megakaryopoiesis.

Acute megakaryoblastic leukemia in a child with the MLL‐AF4 fusion gene

Mixed-lineage leukemia (MLL) rearrangements are commonly observed in childhood acute lymphoblastic and myeloid leukemia, as well as therapy-related leukemia. However, the occurrence of MLL rearrangements in acute megakaryoblastic leukemia (AMKL) is very rare. We report a pediatric case of AMKL with the MLL-AF4 fusion transcript. MLL-AF4 is derived from t(4;11)(q21:q23) and occurs exclusively in B-cell lineage leukemia. To our knowledge, MLL-AF4 as well as t(4;11)(q21:q23) has not been reported in adult and childhood AMKL. Thus, our case provides new insight into the molecular mechanisms of MLL-AF4-associated leukemia.

Malignancy in Children with Trisomy 21

Patients with Down syndrome (DS) display a unique spectrum of malignancies, with a 10- to 20-fold higher risk of acute leukemias, and a markedly lower incidence of solid tumors. This review discusses the current understanding of the basis for this distinctive pattern of cancer incidence and the clinical and biologic features of the malignant disorders most frequent in DS individuals: transient myeloproliferative disease, acute megakaryoblastic leukemia, and acute lymphoblastic leukemia. We also review distinctive pharmacogenetic issues, highlighting the differential chemosensitivity and toxicity profiles of DS patients compared with the general population, and epidemiologic studies of protective and adverse environmental risk factors for the development of leukemia.

Activating mutations in human acute megakaryoblastic leukemia

AbstractOncogenic activation of tyrosine kinase signaling pathway is recurrent in human leukemia. To gain insight into the oncogenic process leading to acute megakaryoblastic leukemia (AMKL), we performed sequence analyses of a subset of oncogenes known to be activated in human myeloid and myeloproliferative disorders. In a series of human AMKL samples from both Down syndrome and non–Down syndrome patients, mutations were identified within KIT, FLT3, JAK2, JAK3, and MPL genes, with a higher frequency in DS than in non-DS patients. The novel mutations were analyzed using BaF3 cells, showing that JAK3 mutations were activating mutations. Finally, we report a novel constitutively active MPL mutant, MPLT487A, observed in a non–Down syndrome childhood AMKL that induces a myeloproliferative disease in mouse bone marrow transplantation assay.

Cytogenetic/Molecular Findings and Treatment Outcome of Childhood Acute Megakaryoblastic Leukemia. Possible Favorable Effect of High Dose Cytarabine and Stem Cell Transplantation.

Acute megakaryoblastic leukemia (AMKL) is a rare hematological malignancy. Childhood AMKL is classified into three categories including AMKL associated with Down syndrome (AMKL-DS), AMKL with t(1;22)(p13;q13)/RBM15-MKL1, and others. Previous studies have revealed AMKL with t(1;22)(p13;q13) occurs mainly in infant with poor prognosis, and patients with AMKL-DS generally show favorable course, mostly associated with GATA-1 mutation. Appropriate treatment strategy and the role of hematopoietic stem cell transplantation (SCT) remained controversial in childhood AMKL.Cases and Methods: Eleven cases with AMKL were analyzed and reviewed. Cytogenetic analysis was performed with G banding. Expression of RBM15-MKL1 was analyzed with RT-PCR method on seven cases with the material available.Results. The age at onset ranged from 6 months to 2 years and 6 months. Three were males and eight females. Five of 11 cases were AMKL-DS. Three were AMKL with t(1;22)(p13;q13), of which both two cases analyzed express RBM15-MKL1. Translocation at 11q23 was confirmed in two. Preceding MDS had been confirmed in one AMKL-DS and one AMKL with t(1;22)(p13;q13). The treatment differed among the cases; however, the regimens including high dose cytarabine (HD-CA) were utilized as first-line therapy in eight cases out of 11, resulting in long term remission in five. In particular, three AMKL with t(1;22)(p13;q13) attained long term remission with HD-CA containg regimen. Three cases underwent SCT on disease and two of three remain in remission for 7 years and 4 months, respectively. Two poor prognostic AMKL-DS cases had breakpoint at 22q13 where MKL1 resides and at 17p13 where TP53 is localized.Discussion. Childhood AMKL is heterogenous on cytogenetic/molecular aspects. HD-CA containing regimens might have favorable effect even on AMKL with t(1;22)(p13;q13) and the other poor prognostic AMKL. SCT might be effective even for refractory disease.patient characteristicscasesexage at onsetclinical featurekaryotypeRBM15-MKL1treatmentoutcome1M1yDS53, XY, +6, +8, +10, +13, +14, +19, 21NACA18y11mo CR2F1y7mo50, XX, +8, +19, +21, +22−HD-CA11y10mo CR3F6mopreceding MDS46, XX, t(1;22), t(11;14)(q23;q22)NAHD-CA13y10mo CR4F1y5mo48, XX, t(1;22)(p13;q13), +2, +mar+HD-CA12y10mo CR5F2y6mo46, XX, t(9;11;17)(p22;q23;q21)NAHD-CA, SCT10y3mo CR6F1y7moDS47, XX, +21NAHD-CA4y5mo CR7M1y9mo51, XY, t(1;22)(p13;q13), +6, +8, −17, +20, +21, +21, +mar+HD-CA9y8mo CR8M1y11moDS47, XY, der(5)t(1;5)(q21;q33), del(5)(q?), add(9)(q34), +21, add(22)(q13)−HD-CA, SCTinduction failure, 7y8mo CR after SCT on disease9F1y3moDS, preceding TMD and MDS48, XX, +8, +21−CA7y8mo CR10F11moDS45, XX, add(3)(p25), −7, +11, add(11)(p11)X2, −13, der(17)t(13;17)(q12;p13)−CA, HD-CA, SCT7mo Rel after CA, re-induction failure after HD-CA, SCT on disease, 1mo Rel, DOD11F1y11mo46, XX, inv(2)(p23;q37), der(5)t(5;15)(p15;q11)t(6;15)(p11;q26), der(6)t(6;15), del(15)(q11)−HD-CA, SCT6mo Rel after HD-CA, SCT on disease, 4mo CRabbreviations: M, male; F, female; y, year; mo, month; MDS, myelodysplastic syndrome; TMD, transient myeloproliferative disorder; NA, not available; CA, chemotherapeutic regimen containing normal dose of cytarabine; HD-CA, chemotherapeutic regimen containing high dose cytarabine; CR, complete remission; Rel, relapse; and DOD, died of disease

JAK3, JAK2 and GATA1 Mutations in Childhood Acute Megakaryoblastic Leukemia with and without Down Syndrome.

Acute myeloid leukemia (AML) in children with Down syndrome (DS) exhibits unique characteristics, which includes the predominance of megakaryoblastic leukemia (AMKL). In about 10% of DS infants, transient myeloproliferative disorder (TMD) develops and then spontaneously resolves in most cases. However, 20% of TMD cases develop AMKL within 3 years, suggesting that additional genetic alterations might occur during the progression from TMD to AMKL. GATA1 mutations contribute to both the pathogenesis of TMD and AMKL, suggesting that the acquisition of additional genetic alterations might be necessary for the progression from TMD to AMKL. Recently, activating mutations of the JAK3 gene have been found in each of 16 non-DS and 3 DS-AMKL patients. These results suggest that the activating JAK3 mutations are involved in the pathogenesis of AMKL both with and without DS. In this study, we simultaneously analyzed JAK3, JAK2V617F which plays a critical role in the pathogenesis of myeloproliferative disorders and GATA1 mutations in non-DS children with AMKL and in DS children with AMKL or TMD. The study population included 11 non-DS children with AMKL and 20 AMKL and 6 TMD children with DS. After obtaining informed consent from the parents of the children for the purpose of sample banking and molecular analyses, bone marrow (BM) or peripheral blood (PB) samples were obtained from all of the patients with AMKL and TMD at the time of diagnosis. High-molecular weight DNA was extracted from the samples using standard methods. For the screening of the JAK3 mutations, we amplified genomic DNA that corresponded to all 23 exons of the JAK3 gene by using polymerase chain reaction (PCR) that employed 22 primer pairs. Amplified products were subjected to the denaturing HPLC (DHPLC) analysis using a WAVE Maker System (Transgenomic Inc., San Jose, CA). The DHPLC gradients and temperatures were determined using WAVE Maker System software. When heterozygous profiles were identified after a visual inspection of the chromatograms, amplified products were cloned into the pGEM-T Easy vector (Promega, Madison, WI) and sequenced on a DNA sequencer (310; Applied Biosystems, Foster City, CA) using a BigDye terminator cycle sequencing kit (Applied Biosystems). For screening of GATA1 mutations and JAK2V617F mutations, we amplified the genomic DNA that corresponded to exon 2 of GATA1 and exon12 of JAK2 by using PCR that employed 1 primer pair respectively. Amplified products were cloned into the pGEM-T Easy vector and sequenced on a DNA sequencer using a BigDye terminator cycle sequencing kit. Mutations of JAK3 were found in 2 of the DS-AMKL patients and in 1 DS-TMD patient. A573V and A593T substitutions in the JH2 pseudokinase domain along with Q501H substitutions in the JH3 domain were observed in the DS-AMKL patients and an I87T substitution in the JH7 domain of the receptor-binding domain was observed in DS-TMD. In one of the DS-AMKL patients, A573V and A593T substitutions were found in the same allele. GATA1 mutations were observed in 19 of the 20 DS-AMKL patients, in all of the DS-TMD patients and in 1 non-DS-AMKL patient. JAK2V617F mutation was only found in 1 DS-AMKL patient who had also JAK3 mutation (Q501H). The fact that the JAK3 mutations were found in both the AMKL and TMD patients indicates that this is an early event that occurs during the development of AMKL in DS patients and that other genetic changes may contribute to the development of AMKL.

Janus kinase mutations in the development of acute megakaryoblastic leukemia in children with and without Down's syndrome

Janus kinase mutations in the development of acute megakaryoblastic leukemia in children with and without Down's syndrome

High incidence of CALM-AF10 fusion and the identification of a novel fusion transcript in acute megakaryoblastic leukemia in children without Down's syndrome

High incidence of CALM-AF10 fusion and the identification of a novel fusion transcript in acute megakaryoblastic leukemia in children without Down's syndrome

CD36 (thrombospondin receptor) expression in childhood acute megakaryoblastic leukemia: In vitro drug sensitivity and outcome

The outcome for children with acute megakaryoblastic leukemia (AMKL) remains poor, except for cases associated with Down syndrome (DS). This study compared immunophenotypic and drug sensitivity patterns of childhood AMKL cases with or without DS. All DS-AMKL cases showed high expression of CD36 and were very sensitive to cytarabine and daunorubicin in vitro. In children without DS, high expression of CD36 on AMKL blasts identified a sub-group with immunophenotypic and drug sensitivity patterns similar to that of DS AMKL. Among non-DS AMKL patients, CD36-high cases had a superior outcome compared with CD36-negative cases. CD36 expression in acute myeloid leukemia cases other than AMKL was not associated with increased in vitro drug sensitivity. CD36 expression in AMKL may be an indicator of megakaryoblast maturation and chemotherapy sensitivity.

Clinical and Biological Features of 43 Acute Megakaryoblastic Leukemia (AMKL) in Children: A Comparison of Down Syndrome-AMKL and De Novo AMKL.

AMKL is a rare subtype of acute myelogenous leukemia. In children, AMKL frequently develops in patients with Down syndrome (DS-AMKL). Until now, few large series of childhood AMKL have been reported. We reviewed 43 children with AMKL diganosed between 1987 and 2005 at Nagoya University Hospital and Japanese Red Cross Nagoya First Hospital. The diagnosis of AMKL was established on the basis of cell morphology and was confirmed by the positivity of immunophenotyping against CD41 and CD36. The diagnosis for several patients was also confirmed by platelet peroxidase staining using an electron microscope. The morphology of blast cells was categorized into three groups according to the stage of cell maturation: type 1 = completely undifferentiated blasts; type 2 = intermediately differentiated blasts with characteristic blebs; and type 3 = blasts with dysmegakaryocytopoiesis, including the presence of micromegakaryocytes. Twenty-five patients (58%) had DS-AMKL and 18 (42%) had de novo AMKL. The median age was 20 months (range, 8–38 months) for DS-AMKL and 12 months (range, 2–185 months) for de novo AMKL. The ratio of boys to girls was 1: 0.8 for DS-AMKL and 0.5:1 for de novo AMKL. The initial white blood cell count and lactic dehydrogenase levels were much higher in patients with de novo AMKL than in those with DS-AMKL. The morphology of blast cells in DS-AMKL and de novo AMKL were distributed as follows: type 1 (67%, 57%), type 2 (24%, 43%), and type 3 (9%, 0%), respectively. The results of immunophenotyping in the DS-AMKL and de novo AMKL group, respectively, were as follows: CD41 (88%, 87%), CD7 (96%, 70%), CD33 (84%, 90%), Gly (67%, 0%), and CD34 (70%, 20%). Cytogenetic studies were performed for 23 patients with DS-AMKL and 18 patients with de novo AMKL. Normal karyotype including +21 in DS-AMKL was noted in 5 patients with DS-AMKL and in 1 patient with de novo AMKL. Numerical chromosomal anomalies were common in both groups. Patients with DS-AMKL had +8 (4 patients), additional +21 (1 patient), and −7/del(7q) (6 patients). Patients with de novo AMKL had +8 (5 patients), +21 (7 patients), and −7/del(7q) (2 patients). The specific AMKL-associated translocation such as t (1:22) was noted in 2 patients with de novo AMKL and 3q21q26 was noted in 1 patient with de novo AMKL. In patients with DS-AMKL, 24 of 25 (96%) achieved complete remission. Relapse occurred in 2 patients, and 2 different patients died of cardiac problems. Of the 25 patients with DS-AMKL, 21 (84%) are currently surviving. Of the 18 patients with de novo AMKL, 12 of 17 (71%) patients achieved complete remission. One patient did not receive induction therapy. Thirteen patients received stem cell transplantation (allogeneic, 6; autologous, 7), and 13 of 18 patients (72%) are currently surviving. The estimate of 5-year survival was 83.3% for patients with DS-AMKL and 71.8% for patients with de novo AMKL (p=0.38). Our study shows the diverse heterogeneity of childhood AMKL and the need for subclassification according to megakaryocytic maturation. The blast cells seem more immature in DS-AMKL than in de novo AMKL in terms of morphology and immunophenotyping. The prognosis of DS-AMKL is excellent. Although prognosis of de novo AMKL was very poor in previous studies, our results using stem cell transplantation are promising.

Acute megakaryoblastic leukemia in children and adolescents, excluding Down's syndrome: improved outcome with intensified induction treatment

Acute megakaryoblastic leukemia in children and adolescents, excluding Down's syndrome: improved outcome with intensified induction treatment

Acute Megakaryoblastic Leukemia in Children without Down's Syndrome.

Acute megakaryoblastic leukemia (AMKL) in children without Down's syndrome occurs in less than 10% of childhood AML. Data on clinical presentation, immunological and genetic features and treatment strategies are rare.Between 6/1987 and 7/2003 89 children with AMKL (m=46; f=43) were treated according to the AML-BFM trials 87 (n=19), 93 (n=39) and 98 (n=31). AML FAB M7 was centrally confirmed by immunophenotyping (n=86) or immunohistology (n=3). The median age at diagnosis (1.5 yrs) was significantly lower compared to other children with AML (total group n=1,149; median age 7.8 yrs; p<0.004). The percentage of AMKL in the AML-BFM trials was 6%. Children with AMKL presented with anemia (93%), thrombocytopenia (88%) and hepatomegaly (83%). Hyperleukocytosis (> 100,000/μl) was less frequent (13%) compared to other AML subtypes (21%; p<0.0001). Immunophenotyping revealed the co-expression of stem cell antigens such as CD34 (61%) and CD117 (82%), myeloid antigens (CD33/CD13) and megakaryocytic antigens (CD41/CD42/CD61). The aberrant expression of CD7 (92%) was significantly increased (other AML subtypes 29%; p<0.0001). Cytogenetics revealed several aberrations such as t(1;22) (14%), monosomy 7 (12%) and trisomy 8 or 21 (7%), but mostly not isolated.The complete remission rate increased from 58% in study AML-BFM 87 to 77% and 83% in AML-BFM 93 and 98 (p<0.05), respectively. The outcome of all children with AMKL was as follows: 5-year event-free survival (EFS) 40±5%; disease-free survival (DFS) 49±6%; overall survival (OS) 42±6%. Compared to children with high risk (HR)-AML (n=714) treated in the AML-BFM studies, the EFS was similar (40±6% vs. 43±2%; p= 0.44). Due to poor response to relapse treatment, the OS tended to be inferior (AMKL 44±6% vs. HR-AML 52±2%; p=0.13).The treatment intensification in AML-BFM 93 and 98 with high-dose cytarabine and mitoxantrone (HAM) as second induction resulted in a significantly improved EFS (46±6%), DFS (58±7%) and OS (49±6%) compared to AML-BFM 87 (11±7%, 18 ±12%. 21±9%; p<0.009).There was no significant difference of outcome between children treated with chemotherapy only (n=54) or allogeneic stem cell transplantation (alloSCT) in 1st CR (n=13 ) DFS 50±7 vs 37±14; p=0.49; OS 54±7 vs 43±15%; p=0.47).Considering gender, age, WBC, blast percentage, immunophenotype or cytogenetic subgroup (available n=74; 83%) no prognostic factor could be identified. Children with poor response (n=19) or relapse (n=33) had a very unfavorable outcome. Only 5 of these children survived. Two children stayed alive in CR after relapse chemotherapy (follow-up 12.8 and 11.3 years), two after alloSCT (follow-up 1.4 and 2.4 years) and one child was alive with disease after alloSCT and relapse (follow-up 0.6 years). In conclusion, in children with AMKL intensive chemotherapy enabled a remission rate and a long-term survival comparable to other childhood HR-AML. AlloSCT seemed not to improve outcome. Therefore new approaches for the treatment of AMKL in children are needed.

Biology, clinical, and hematologic features of acute megakaryoblastic leukemia in children.

To assess the incidence, clinical features at presentation, hematologic, immunophenotypic, and cytogenetic characteristics of AMKL in children we prospectively studied 834 consecutive non selected children with newly diagnosed acute leukemia (AL) admitted to the Hematology Department at the Instituto Nacional de Pediatría (INP), Mexico, D.F. We found 682 cases (81.8%) with a typical ALL immunophenotype, and the remaining 152 (18.2%) were considered to have AML. In 29 of the 152 patients with AML studied, a diagnosis of AMKL was established. These 29 cases represented 19.1% of the cases of AML and 3.48% of the total cases of AL during the time span covered by the study. Twenty-four percent of the cases occurred in infants 2 years old or younger and 41.4% occurred in children 41 months of age or younger. In contrast, in only 18.6% of the patients with AML (M0-M6), the diagnosis was established before 42 months of age and in 17% before their second year of life. Clinical presentation was not strikingly different than that observed in patients with other types of AML, and the time interval from onset of symptoms to diagnosis was also similar, though in a small subset of patients, the clinical course was characterized by a chronic slowly progressive disorder extending over weeks or months resembling smoldering leukemia or chronic myelofibrosis with agnogenic myeloid metaplasia. Bone marrow (BM) fibrosis was a constant features in our patients; 75% of the patients studied showed this complication at the time of diagnosis. Some rather unusual findings in this study were intense skeletal pains from multiple osteolytic lesions, the presence of soft-tissue tumor, and the presence of cohesive scanty clusters of primitive-looking blast cells in BM aspirates. Several interesting cytogenetic findings in our study were t(1;22)(p13;q13) in a 14-year-old boy, t(9;22)(q34;q11) in one patient, and monosomy 7 in two patients. Another important finding in our study was the clinical association with colonic adenocarcinoma in one patient, an association that to our knowledge has not been reported previously. In conclusion, our data suggest that the incidence of AMKL in Mexico might be higher than those reported in Caucasian white pediatric population, and that biologic and cytogenetic profile may differ from those of western countries, but more studies are needed to corroborate cytogenetic heterogeneity, ethnic and geographic diversity. Early onset of the disease, low WBC counts, slight thrombocytopenia or normal platelet counts, and BM fibrosis were characteristic distinctive features of at least half of the patients with this subtype of AML.

Biology and outcome of childhood acute megakaryoblastic leukemia: a single institution's experience

To describe the clinical and biologic features of pediatric acute megakaryoblastic leukemia (AMKL) and to identify prognostic factors, experience at St Jude Children's Research Hospital was reviewed. Of 281 patients with acute myeloid leukemia treated over a 14-year period, 41 (14.6%) had a diagnosis of AMKL. Six patients had Down syndrome and AMKL, 6 had secondary AMKL, and 29 had de novo AMKL. The median age of the 22 boys and 19 girls was 23.9 months (range, 6.7-208.9 months). The rate of remission induction was 60.5%, with a 48% rate of subsequent relapse. Patients with Down syndrome had a significantly higher 2-year event-free survival (EFS) estimate (83%) than did other patients with de novo AMKL (14%) or with secondary AMKL (20%; P < or =.038). Among patients who had de novo AMKL without Down syndrome, 2-year EFS was significantly higher after allogeneic bone marrow transplantation (26%) than after chemotherapy alone (0%; P =.019) and significantly higher when performed during remission (46%) than when performed during persistent disease (0%; P =.019). The 5-year survival estimates were significantly lower for de novo AMKL (10%) than for other forms of de novo AML (42%; P <.001). Treatment outcome is very poor for patients with AMKL in the absence of Down syndrome. Remission induction is the most important prognostic factor. Allogeneic transplantation during remission offers the best chance of cure; in the absence of remission, transplantation offers no advantage over chemotherapy alone. (Blood. 2001;97:3727-3732)

Induction of the Erythropoietin Receptor Gene and Acquisition of Responsiveness to Erythropoietin by Stem Cell Factor in HML/SE, a Human Leukemic Cell Line

HML/SE is a cytokine-dependent cell line established from childhood acute megakaryoblastic leukemia. Granulocyte-macrophage colony-stimulating factor or stem cell factor (SCF) alone could stimulate proliferation of HML/SE cells, however interleukin-3, interleukin-6, granulocyte colony-stimulating factor and thrombopoietin could not. Although erythropoietin (EPO) alone stimulated neither proliferation nor differentiation of HML/SE cells, it did stimulate proliferation of HML/SE cells and production of hemoglobin in the presence of SCF. SCF activated the human EPO receptor promoter and induced EPO receptor gene expression. Given these results, we speculate that HML/SE cells acquired responsiveness to EPO via the EPO receptor induced by SCF. Mutation analysis of putative transcription factor binding sites in the human EPO receptor promoter suggested that Sp1, rather than the GATA-1 binding site, contributed to the induction of the hEPOR gene. Although it is well documented that hematopoietic stem cells and primitive progenitors require both an early-acting cytokine and a lineage-specific cytokine to differentiate to a certain lineage, related mechanisms are not well understood. HML/SE may serve as an excellent model system to analyze functions of early-acting cytokine SCF and lineage-specific cytokine EPO related to proliferation and differentiation of hematopoietic stem cells.

Expression of MDR-1/P-glycoprotein in childhood acute megakaryoblastic leukemia cells.

Multidrug resistance is a major clinical problem in chemotherapy of malignant disease. Acute megakaryoblastic leukemia (AMKL) is a rare form of childhood leukemia, and is often more resistant to many anticancer chemotherapeutic drugs compared to other types of childhood leukemia. There have been reports of the increased expression in hematologic malignancy of multidrug resistant (mdr-1) gene, which encodes for a transmembrane glycoprotein P-glycoprotein that acts as an efflux pump for structurally unrelated chemotherapeutic drugs. We investigated the malignant cells of 15 newly diagnosed childhood AMKL patients by immunocytochemical analysis and found P-glycoprotein expression in all samples from these patients. RNA prepared from five patients at the time of presentation confirmed the expression of mdr-1 specific message in all cases by Northern blot analysis. These results imply that malignant cells from all childhood AMKL might express the mdr-1/P-glycoprotein.

Acute megakaryoblastic leukemia in children and adolescents: a retrospective analysis of 24 cases.

In order to characterize the clinical, cytogenetic, and outcome features of childhood acute megakaryoblastic leukemia (AMKL), we reviewed 24 cases; 14 were identified among 150 consecutive newly diagnosed acute myelogenous leukemia (AML) patients at St. Jude Children's Research Hospital, and 10 were cases referred to the National Institute of Cancer in Rio de Janeiro, Brazil. There were 5 Down syndrome patients and one patient with chronic myeloid leukemia (Ph+) in blastic crisis. Twelve patients had significant hepatosplenomegaly. Leukemic cell morphology and cytochemistry were consistent with the M7 classification in 17 cases, and all cases tested expressed megakaryocytic surface antigens. AMKL patients were significantly younger than other AML patients (P = 0.0001) and had poorer responses to therapy (P = 0.03, univariate analysis only). Ten of 24 failed induction, and only 5 are disease-free at 6 months to 4.5+ years. We conclude that AMKL usually affects young children, frequently producing marked organomegaly. It comprises approximately 10% of pediatric AML cases, and responds poorly to intensive AML therapies.

Induction of Complete Remission in a Case of Drug-resistant Childhood Acute Megakaryoblastic Leukemia by Combination of G-CSF and Chemotherapy

Induction of Complete Remission in a Case of Drug-resistant Childhood Acute Megakaryoblastic Leukemia by Combination of G-CSF and Chemotherapy