Nineteen cases of the t(1;22)(p13;q13) acute megakaryblastic leukaemia of infants/children and a review of 39 cases: report from a t(1;22) study group

Myeloid sarcoma with RBM15::MRTFA (MKL1) mimicking vascular neoplasm

Extramedullary involvement of acute myeloid leukemia (AML), aka myeloid sarcoma, is a rare phenomenon in acute megakaryoblastic leukemia with RBM15:: MRTFA(MKL1) fusion, which might mimic non-hematologic malignancies. A 7-month-old infant presented with leukocytosis, hepatosplenomegaly, multiple lymphadenopathies, and a solid mass in the right thigh. Initially, the patient was diagnosed with a malignant vascular tumor regarding the expression of vascular markers from the biopsy of the right thigh lesion that was performed after the inconclusive bone marrow biopsy. The second bone marrow biopsy, which was performed due to the partial response to sarcoma treatment, showed hypercellular bone marrow with CD34 and CD61-positive spindle cell infiltration and > 20% basophilic blasts with cytoplasmic blebs. RNA sequencing of soft tissue biopsy revealed the presence of RBM15::MRTFA(MKL1) fusion. Based on these findings, myeloid sarcoma/AML with RBM15::MRTFA(MKL1) fusion diagnosis was made. AML with RBM15::MRTFA(MKL1) fusion can initially present as extramedullary lesions and might cause misdiagnosis of non-hematologic malignancies.

Liver fibrosis among infants with t(1;22)(p13;q13) acute megakaryoblastic leukemia: a case report and literature review

This case report describes a 2-month-old girl with acute megakaryoblastic leukemia (AMKL) harboring the t(1;22)(p13;q13) translocation, resulting in the RBM15::MRTFA fusion gene. She presented with massive hepatosplenomegaly and liver fibrosis and achieved complete remission with chemotherapy; the liver fibrosis resolved within 2.5 months. After 12 years of follow-up, the patient remained in good health, without relapse. Reviewing the literature on eight additional similar cases of liver fibrosis, this subtype of AMKL predominantly affects female patients below 3 months of age, with a median onset at 6 weeks. High rates of severe complications were observed, with five of nine patients dying within 10 weeks of diagnosis. The authors hypothesized that the proliferation of abnormal megakaryoblasts within the liver leads to the release of profibrotic cytokines, such as TGF-β1, which induces liver fibrosis similar to that observed in transient abnormal myelopoiesis in Down syndrome. Careful monitoring of liver functions and reduced-intensity chemotherapy are recommended for this very young patient population. Nonetheless, long-term survival can be achieved with aggressive supportive care and treatment.

Rare Hematologic Malignancies and Pre-Leukemic Entities in Children and Adolescents Young Adults

There are a variety of rare hematologic malignancies and germline predispositions syndromes that occur in children and adolescent young adults (AYAs). These entities are important to recognize, as an accurate diagnosis is essential for risk assessment, prognostication, and treatment. This descriptive review summarizes rare hematologic malignancies, myelodysplastic neoplasms, and germline predispositions syndromes that occur in children and AYAs. We discuss the unique biology, characteristic genomic aberrations, rare presentations, diagnostic challenges, novel treatments, and outcomes associated with these rare entities.

t(1;7;22)(p13;q21;q13) is a novel 3-way variant of t(1;22)(p13;q13) neonatal acute megakaryoblastic leukemia: A case report

Acute megakaryoblastic leukemia (AMKL) is a rare disease, occurring mostly in infants and young children. The chromosomal translocation t(1;22)(p13;q13), resulting in the RBM15-MKL1 fusion gene, is a recurrent and diagnostic translocation in infants with AMKL. The present case report describes a case of a newborn girl, without Down's syndrome, with congenital AMKL. At birth, the infant had hepatosplenomegaly and the peripheral blood count revealed anemia, thrombopenia and leukocytosis, with 28% blasts. Immunophenotyping demonstrated blasts positive for CD34, CD61 and CD42b. Karyotyping of these blasts (R-banding) showed a hitherto unreported chromosomal translocation, t(1;7;22)(p13;q21;q13), a 3-way variant of the t(1;22)(p13;q13) variant. Fluorescent in situ hybridization analysis confirmed the presence of the RBM15-MKL1 fusion gene.

Immunophenotypic Analysis of Acute Megakaryoblastic Leukemia: A EuroFlow Study

Simple Summary

Acute megakaryoblastic leukemia (AMKL) is a rare and heterogeneous subtype of acute myeloid leukemia (AML). We show that such patients can be identified by flowcytometric immunophenotyping using the standardized EuroFlow panel. AMKL patients show a unique immunophenotypic profile, and among AMKL patients, various subgroups can be distinguished.

Abstract

Acute megakaryoblastic leukemia (AMKL) is a rare and heterogeneous subtype of acute myeloid leukemia (AML). We evaluated the immunophenotypic profile of 72 AMKL and 114 non-AMKL AML patients using the EuroFlow AML panel. Univariate and multivariate/multidimensional analyses were performed to identify most relevant markers contributing to the diagnosis of AMKL. AMKL patients were subdivided into transient abnormal myelopoiesis (TAM), myeloid leukemia associated with Down syndrome (ML-DS), AML—not otherwise specified with megakaryocytic differentiation (NOS-AMKL), and AMKL—other patients (AML patients with other WHO classification but with flowcytometric features of megakaryocytic differentiation). Flowcytometric analysis showed good discrimination between AMKL and non-AMKL patients based on differential expression of, in particular, CD42a.CD61, CD41, CD42b, HLADR, CD15 and CD13. Combining CD42a.CD61 (positive) and CD13 (negative) resulted in a sensitivity of 71% and a specificity of 99%. Within AMKL patients, TAM and ML-DS patients showed higher frequencies of immature CD34+/CD117+ leukemic cells as compared to NOS-AMKL and AMKL-Other patients. In addition, ML-DS patients showed a significantly higher expression of CD33, CD11b, CD38 and CD7 as compared to the other three subgroups, allowing for good distinction of these patients. Overall, our data show that the EuroFlow AML panel allows for straightforward diagnosis of AMKL and that ML-DS is associated with a unique immunophenotypic profile.

t(1;22)(p13;q13) Acute Megakaryoblastic Leukemia Complicated by Hepatic Fibrosis: Antifibrosis Therapy?

BACKGROUND

There is no established effective treatment for patients with t(1;22)(p13;q13) acute megakaryoblastic leukemia (AMKL) and hepatic fibrosis.

OBSERVATION

Here we report the outcomes of 2 t(1;22)(p13;q13) AMKL patients with hepatic fibrosis. One patient died from liver failure despite the control of leukemia. The other patient was successfully treated with reduced-intensity chemotherapy and antifibrosis therapy with tretinoin and α-tocopheryl acetate, the hepatic fibrosis resolved and leukemia was in remission for 3 years.

CONCLUSIONS

Reduced-intensity chemotherapy plus antifibrosis therapy with tretinoin and α-tocopheryl acetate could be a treatment option for these patients with t(1;22)(p13;q13) AMKL and hepatic fibrosis.

Infant Acute Leukemia

Infant acute leukemia is a rare but aggressive disease. Although infant acute leukemia is cytologically and histologically similar to acute leukemia seen in older children and adults, it displays unique and characteristic clinical and genetic characteristics. The features, as well as the extremely young age of the patients, present multiple challenges for treatment. This review focuses on the unique pathology of acute leukemia of infancy, including the genetic characteristics that are specific for these diseases.

Cytogenetics of Pediatric Acute Myeloid Leukemia: A Review of the Current Knowledge

Pediatric acute myeloid leukemia is a rare and heterogeneous disease in relation to morphology, immunophenotyping, germline and somatic cytogenetic and genetic abnormalities. Over recent decades, outcomes have greatly improved, although survival rates remain around 70% and the relapse rate is high, at around 30%. Cytogenetics is an important factor for diagnosis and indication of prognosis. The main cytogenetic abnormalities are referenced in the current WHO classification of acute myeloid leukemia, where there is an indication for risk-adapted therapy. The aim of this article is to provide an updated review of cytogenetics in pediatric AML, describing well-known WHO entities, as well as new subgroups and germline mutations with therapeutic implications. We describe the main chromosomal abnormalities, their frequency according to age and AML subtypes, and their prognostic relevance within current therapeutic protocols. We focus on de novo AML and on cytogenetic diagnosis, including the practical difficulties encountered, based on the most recent hematological and cytogenetic recommendations.

Infant Acute Myeloid Leukemia: A Unique Clinical and Biological Entity

Infant acute myeloid leukemia (AML) is a rare subgroup of AML of children <2 years of age. It is as frequent as infant acute lymphoblastic leukemia (ALL) but not clearly distinguished by study groups. However, infant AML demonstrates peculiar clinical and biological characteristics, and its prognosis differs from AML in older children. Acute megakaryoblastic leukemia (AMKL) is very frequent in this age group and has raised growing interest. Thus, AMKL is a dominant topic in this review. Recent genomic sequencing has contributed to our understanding of infant AML. These data demonstrated striking features of infant AML: fusion genes are able to induce AML transformation without additional cooperation, and unlike AML in older age groups there is a paucity of associated mutations. Mice modeling of these fusions showed the essential role of ontogeny in the infant leukemia phenotype compared to older children and adults. Understanding leukemogenesis may help in developing new targeted treatments to improve outcomes that are often very poor in this age group. A specific diagnostic and therapeutic approach for this age group should be investigated.

RNA-Binding Proteins in Acute Leukemias

Acute leukemias are genetic diseases caused by translocations or mutations, which dysregulate hematopoiesis towards malignant transformation. However, the molecular mode of action is highly versatile and ranges from direct transcriptional to post-transcriptional control, which includes RNA-binding proteins (RBPs) as crucial regulators of cell fate. RBPs coordinate RNA dynamics, including subcellular localization, translational efficiency and metabolism, by binding to their target messenger RNAs (mRNAs), thereby controlling the expression of the encoded proteins. In view of the growing interest in these regulators, this review summarizes recent research regarding the most influential RBPs relevant in acute leukemias in particular. The reported RBPs, either dysregulated or as components of fusion proteins, are described with respect to their functional domains, the pathways they affect, and clinical aspects associated with their dysregulation or altered functions.

Pediatric acute myeloid leukemia: updates on biology, risk stratification, and therapy

PURPOSE OF REVIEW

Despite advances in therapy over the past decades, overall survival for children with acute myeloid leukemia (AML) has not exceeded 70%. In this review, we highlight recent insights into risk stratification for patients with pediatric AML and discuss data driving current and developing therapeutic approaches.

RECENT FINDINGS

Advances in cytogenetics and molecular profiling, as well as improvements in detection of minimal residual disease after induction therapy, have informed risk stratification, which now relies heavily on these elements. The treatment of childhood AML continues to be based primarily on intensive, conventional chemotherapy. However, recent trials focus on limiting treatment-related toxicity through the identification of low-risk subsets who can safely receive fewer cycles of chemotherapy, allocation of hematopoietic stem-cell transplant to only high-risk patients and optimization of infectious and cardioprotective supportive care.

SUMMARY

Further incorporation of genomic and molecular data in pediatric AML will allow for additional refinements in risk stratification to enable the tailoring of treatment intensity. These data will also dictate the incorporation of molecularly targeted therapeutics into frontline treatment in the hope of improving survival while decreasing treatment-related toxicity.

Prognostic Significance of Complex Karyotypes in Acute Myeloid Leukemia

OPINION STATEMENT

Acute myeloid leukemia (AML) patients with a complex karyotype (CK-AML) show at least 3 unrelated clonal cytogenetic abnormalities with notoriously poor outcome. Such cases fall into either AML with myelodysplasia-related changes or therapy-related AML in the current World Health Organization classification of AML. Allogeneic stem cell transplantation is one of the only treatment modalities that can provide a long-term survival benefit and is recommended as a consolidative treatment in patients who are able to achieve complete remission. Unfortunately, transplantation is also associated with a higher relapse rate and more than half of CK-AML patients relapse from disease within the first 2 years. The probability of achieving remission with traditional induction using cytarabine and daunorubicin or idarubicin ("7 + 3") is so small that investigational therapies should be considered up front in these patients. Less intensive therapeutic backbones, typically using one of the hypomethylating agents, azacitidine or decitabine, minimize toxicity and show a trend toward the improved overall survival. CPX 351 (Vyxeos) is a liposomal formulation of cytarabine and daunorubicin and this encapsulation leads to prolonged exposure to the two drugs. This drug is approved for AML patients with MDS-related changes and therapy-related AML, both of which are frequently associated with complex karyotype. Such patients show improved outcome in trials using this combination. Combination therapy that includes venetoclax (BCL2 inhibitor) with hypomethylating agents may also be appropriate for such patients.

Immunophenotyping of Acute Myeloid Leukemia

Immunophenotyping by multiparameter flow cytometry is a rapid and efficient technique to simultaneously assess and correlate multiple individual cell properties like size and internal complexity along with antigen expression in a population of cells. This method is utilized for rapid characterization of the blasts and classification of acute myeloid leukemia (AML), in both the peripheral blood (PB) and bone marrow (BM). This technique is not only useful in the initial diagnosis but also in monitoring and determining prognosis of the disease through minimal residual disease (MRD) testing. This chapter provides an overview of procedures for specimen processing, staining, and immunophenotyping of AML and describes the principles of data analysis for AML classification and MRD testing.

Clinical implications of molecular markers in acute myeloid leukemia

The recently updated World Health Organization (WHO) Classification of myeloid neoplasms and leukemia reflects the fact that research in the underlying pathogenic mechanisms of acute myeloid leukemia (AML) has led to remarkable advances in our understanding of the disease. Gene mutations now allow us to explore the enormous diversity among cytogenetically defined subsets of AML, particularly the large subset of cytogenetically normal AML. Despite the progress in unraveling the tumor genome, only a small number of recurrent mutations have been incorporated into risk-stratification schemes and have been proven to be clinically relevant, targetable lesions. We here discuss the utility of molecular markers in AML in prognostication and treatment decision making, specifically highlighting the aberrations included in the current WHO classification.

A Novel Variant t(1;22) Translocation - ins(22;1)(q13;p13p31) - in a Child with Acute Megakaryoblastic Leukemia

Patient: Female, 3-month-old

Final Diagnosis: Acute megakaryoblastic leukemia

Symptoms: Abdominal distension • fever

Medication: —

Clinical Procedure: —

Specialty: Pediatrics and Neonatology

[Infant acute leukemia]

If acute leukemia is the most frequent cancer in childhood (33%), it remains a very rare diagnosis in infants less than one year old, e.g. less than 5% of cases. At this age, the frequency of acute lymphoblastic leukemia (ALL) (almost all of B-lineage) is quite similar to the one of myeloblastic forms (AML). Infant leukemia frequently presents with high hyperleucocytosis, major tumoral burden and numerous extra-hematological features, especially in central nervous system and skin. Whatever the lineage, the leukemic cell is often very immature cytologically and immunologically. Rearrangements of the Mixed Lineage Leukemia (MLL) gene, located on band 11q23, are the hallmark of these immature leukemias and confer a particular resistance to conventional approaches, corticosteroids and chemotherapy. The immaturity of infants less than 1-year-old is associated to a decrease of the tolerable dose-intensity of some drugs (anthracyclines, alkylating agents) or asks questions about some procedures like radiotherapy or high dose conditioning regimen, responsible of inacceptable acute and late toxicities. The high level of severe infectious diseases and other high-grade side effects limits also the capacity to cure these infants. The survival of infants less than 1-year-old with AML is only 50% but similar to older children. On the other hand, survival of those with ALL is the same, then quite limited comparing the 80% survival in children over one year. Allogeneic stem cell transplantations are indicated in high-risk subgroups of infant ALL (age below 6 months, high hyperleucocytosis >300.10(9)/L, MLL-rearrangement, initial poor prednisone response). However, morbidity and mortality remain very important and these approaches cannot be extended to all cases. During the neonatal period, the dismal prognosis linked to the high number of primary failures or very early relapses and uncertainties about the late toxicities question physicians about ethics. It is an emergency to propose different strategies (targeted therapies) to these infants with acute leukemia as conventional trials failed to improve outcome.

Neonatal Acute Megakaryoblastic Leukemia Presenting with Leukemia Cutis and Multiple Intracranial Lesions Successfully Treated with Unrelated Cord Blood Transplantation

Neonatal acute megakaryoblastic leukemia (AMKL) without Down syndrome (DS) is an extremely rare disorder. We report of a one-day-old male infant without DS who developed AMKL with leukemia cutis and right facial nerve palsy. Magnetic resonance imaging of the patient's brain revealed multiple intracranial tumors. A biopsy specimen of the skin lesion was suggestive of AMKL, but the bone marrow leukemic cells were less than 5% of the marrow nucleated cells. The skin and intracranial lesions had spontaneously regressed within one and a half months, but the patient's anemia and thrombocytopenia gradually worsened and the leukemic cells in the bone marrow gradually increased to more than 20% of the nucleated cells. In addition, multiple intracranial lesions reappeared at 72 days of life. We diagnosed the patient with AMKL, and chemotherapy followed by unrelated cord blood transplantation after a reduced-intensity conditioning regimen resulted in sustained complete remission. At present, the patient is well, and he has demonstrated normal development for five years.

The biology of pediatric acute megakaryoblastic leukemia

Acute megakaryoblastic leukemia (AMKL) comprises between 4% and 15% of newly diagnosed pediatric acute myeloid leukemia patients. AMKL in children with Down syndrome (DS) is characterized by a founding GATA1 mutation that cooperates with trisomy 21, followed by the acquisition of additional somatic mutations. In contrast, non-DS-AMKL is characterized by chimeric oncogenes consisting of genes known to play a role in normal hematopoiesis. CBFA2T3-GLIS2 is the most frequent chimeric oncogene identified to date in this subset of patients and confers a poor prognosis.

Neonatal acute megakaryoblastic leukemia mimicking congenital neuroblastoma

We describe a neonate with abdominal distension, massive hepatomegaly, and high serum neuron-specific enolase level suggestive of congenital neuroblastoma. The patient died of pulmonary hemorrhage after therapy. Autopsy revealed that the tumor cells in the liver indicated acute megakaryocytic leukemia with the RBM15-MKL1 fusion gene.

Molecular pathways: induction of polyploidy as a novel differentiation therapy for leukemia

Differentiation therapy has emerged as a powerful way to target specific hematologic malignancies. One of the best examples is the use of all-trans retinoic acid (ATRA) in acute promyelocytic leukemia (APL), which has significantly improved the outcome for patients with this specific form of acute myeloid leukemia (AML). In considering how differentiation therapy could be used in other forms of AML, we predicted that compounds that induce terminal differentiation of megakaryocytes would be effective therapies for the megakaryocytic form of AML, named acute megakaryocytic leukemia (AMKL). We also speculated that such agents would reduce the burden of abnormal hematopoietic cells in primary myelofibrosis and alter the differentiation of megakaryocytes in myelodysplastic syndromes. Using a high-throughput chemical screening approach, we identified small molecules that promoted many features of terminal megakaryocyte differentiation, including the induction of polyploidization, the process by which cells accumulate DNA to 32N or greater. As the induction of polyploidization is an irreversible process, cells that enter this form of the cell cycle do not divide again. Thus, this would be an effective way to reduce the tumor burden. Clinical studies with polyploidy inducers, such as aurora kinase A inhibitors, are under way for a wide variety of malignancies, whereas trials specifically for AMKL and PMF are in development. This novel form of differentiation therapy may be clinically available in the not-too-distant future. Clin Cancer Res; 19(22); 6084-8. ©2013 AACR.

An unusual case of Philadelphia chromosome-positive chronic myelogenous leukemia with trisomy 19 presenting with megakaryoblastosis and myelofibrosis

Initial identification of chronic myelogenous leukemia is very important since targeted therapy leads to life-saving remission. Rarely, chronic myelogenous leukemia presents with an unusual picture, making the diagnosis challenging. We describe such a case of chronic myelogenous leukemia in blast crisis in a previously healthy 61-year-old woman. The patient presented with fever, myalgias, and night sweats and was first worked up for an infectious etiology. Because of persistent anemia, a bone marrow biopsy was performed that revealed fibrosis with increased megakaryoblasts. Even though initial cytogenetic studies could not be performed because of "dry tap" aspirate, persistent efforts for cytogenetic studies were made, including a "squeeze preparation" from the core biopsy, which revealed t(9;22)(q34;q11.2) and trisomy 19. The patient was treated with tyrosine kinase inhibitors, chemotherapy, and subsequently an allogeneic stem cell transplant. She is in persistent remission. This case illustrates a complex presentation of chronic myelogenous leukemia and provides an overview of morphologic cues and the importance of performing cytogenetic studies that led to the diagnosis.

Utility of a multiplex reverse transcriptase-polymerase chain reaction assay (HemaVision) in the evaluation of genetic abnormalities in Korean children with acute leukemia: a single institution study

Purpose

In children with acute leukemia, bone marrow genetic abnormalities (GA) have prognostic significance, and may be the basis for minimal residual disease monitoring. Since April 2007, we have used a multiplex reverse transcriptase-polymerase chain reaction tool (HemaVision) to detect of GA.

Methods

In this study, we reviewed the results of HemaVision screening in 270 children with acute leukemia, newly diagnosed at The Catholic University of Korea from April 2007 to December 2011, and compared the results with those of fluorescence in situ hybridization (FISH), and G-band karyotyping.

Results

Among the 270 children (153 males, 117 females), 187 acute lymphoblastic leukemia and 74 acute myeloid leukemia patients were identified. Overall, GA was detected in 230 patients (85.2%). HemaVision, FISH, and G-band karyotyping identified GA in 125 (46.3%), 126 (46.7%), and 215 patients (79.6%), respectively. TEL-AML1 (20.9%, 39/187) and AML1-ETO (27%, 20/74) were the most common GA in ALL and AML, respectively. Overall sensitivity of HemaVision was 98.4%, with false-negative results in 2 instances: 1 each for TEL-AML1 and MLL-AF4. An aggregate of diseasesspecific FISH showed 100% sensitivity in detection of GA covered by HemaVision for actual probes utilized. G-band karyotype revealed GA other than those covered by HemaVison screening in 133 patients (49.3%). Except for hyperdiplody and hypodiploidy, recurrent GA as defined by the World Health Organizationthat were not screened by HemaVision, were absent in the karyotype.

Conclusion

HemaVision, supported by an aggregate of FISH tests for important translocations, may allow for accurate diagnosis of GA in Korean children with acute leukemia.

Hemophagocytosis by leukemic megakaryoblasts in acute myeloid leukemia (megakaryoblastic) with t(1;22)(p13;q13);RBM15-MKL1

Acute megakaryoblastic leukemia is a rare variant of acute myeloid leukemia, whereby leukemic blasts display characteristic morphologic and phenotypic features indicating megakaryocytoid differentiation. A distinct entity characterized by the t(1;22)(p13;q13) translocation, resulting in the RBM15-MKL1 fusion oncogene, has been recently recognized. This is predominantly a disease afflicting infants and displays characteristic clinical features. We present a case of acute megakaryoblastic leukemia with t(1;22)(p13;q13) along with a discussion of the current understanding of the molecular biology of RBM15-MKL1. This case also displayed striking and unusual morphologic appearances including extensive hemophagocytosis by leukemic blasts, which has not been previously reported for this particular type of leukemia.

Normal and malignant megakaryopoiesis

Megakaryopoiesis is the process by which bone marrow progenitor cells develop into mature megakaryocytes (MKs), which in turn produce platelets required for normal haemostasis. Over the past decade, molecular mechanisms that contribute to MK development and differentiation have begun to be elucidated. In this review, we provide an overview of megakaryopoiesis and summarise the latest developments in this field. Specially, we focus on polyploidisation, a unique form of the cell cycle that allows MKs to increase their DNA content, and the genes that regulate this process. In addition, because MKs have an important role in the pathogenesis of acute megakaryocytic leukaemia and a subset of myeloproliferative neoplasms, including essential thrombocythemia and primary myelofibrosis, we discuss the biology and genetics of these disorders. We anticipate that an increased understanding of normal MK differentiation will provide new insights into novel therapeutic approaches that will directly benefit patients.

A comparative analysis of molecular genetic and conventional cytogenetic detection of diagnostically important translocations in more than 400 cases of acute leukemia, highlighting the frequency of false-negative conventional cytogenetics

In this study, we correlated the results of concurrent molecular and cytogenetic detection of entity-defining translocations in adults with acute leukemia to determine the frequency of cryptic translocations missed by conventional cytogenetics (CC) and of recurrent, prognostically relevant translocations not detectable by multiplex reverse transcriptase-polymerase chain reaction (MRP). During a 5.5-year period, 442 diagnostic acute leukemia specimens were submitted for MRP-based detection of 7 common recurrent translocations: t(8;21), t(15;17), inv(16), t(9;22), t(12;21), t(4;11), and t(1;19), with a detection rate of 15.2% (67/442). CC was performed in 330 (74.7%) of 442 cases. In 7 of these 330 cases, CC missed the translocation detected by MRP. In 50 additional cases, CC revealed 1 of the MRP-detectable translocations (all were also MRP positive), yielding a false-negative rate of 12% (7/57) for the CC assay. The remaining 140 of 190 cases with clonal cytogenetic changes harbored abnormalities that were not targeted by the MRP assay, including 8 that define specific acute myeloid leukemia entities. This study revealed the frequent occurrence of false-negative, entity-defining CC analysis and highlighted the complementary nature of MRP and CC approaches in detecting genetic abnormalities in acute leukemia.

Acute megakaryoblastic leukemia with a four-way variant translocation originating the RBM15-MKL1 fusion gene

Acute megakaryoblastic leukemia (AMKL) with t(1;22)(p13;q13) is a subset of acute myeloid leukemia (AML) representing <1% of all cases and about 70% of pediatric AMKL in the first year of life. We present a case of a 7-month-old female in whom the bone marrow karyotype showed the derivative chromosome der(22)t(1;22)(p13;q13). The RBM15-MKL1 fusion transcript was detected by RT-PCR and confirmed by sequencing analyses. FISH analyses revealed the presence of the four-way translocation t(1;22;17;18)(p13;q13;q22;q12).

Biology, risk stratification, and therapy of pediatric acute leukemias: an update

PURPOSE

We review recent advances in the biologic understanding and treatment of childhood acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML), identify therapeutically challenging subgroups, and suggest future directions of research.

METHODS

A review of English literature on childhood acute leukemias from the past 5 years was performed.

RESULTS

Contemporary treatments have resulted in 5-year event-free survival rates of approximately 80% for childhood ALL and almost 60% for pediatric AML. The advent of high-resolution genome-wide analyses has provided new insights into leukemogenesis and identified many novel subtypes of leukemia. Virtually all ALL and the vast majority of AML cases can be classified according to specific genetic abnormalities. Cooperative mutations involved in cell differentiation, cell cycle regulation, tumor suppression, drug responsiveness, and apoptosis have also been identified in many cases. The development of new formulations of existing drugs, molecularly targeted therapy, and immunotherapies promises to further advance the cure rates and improve quality of life of patients.

CONCLUSION

The application of new high-throughput sequencing techniques to define the complete DNA sequence of leukemia and host normal cells and the development of new agents targeted to leukemogenic pathways promise to further improve outcome in the coming decade.

MAL/SRF complex is involved in platelet formation and megakaryocyte migration by regulating MYL9 (MLC2) and MMP9

Megakaryoblastic leukemia 1 (MAL) is a transcriptional coactivator of serum response factor (SRF). In acute megakaryoblastic leukemia, the MAL gene is translocated and fused with the gene encoding one twenty-two (OTT). Herein, we show that MAL expression increases during the late differentiation steps of neonate and adult human megakaryopoiesis and localized into the nucleus after Rho GTPase activation by adhesion on collagen I or convulxin. MAL knockdown in megakaryocyte progenitors reduced the percentage of cells forming filopodia, lamellipodia, and stress fibers after adhesion on the same substrates, and reduced proplatelet formation. MAL repression led to dysmorphic megakaryocytes with disorganized demarcation membranes and alpha granules heterogeneously scattered in the cytoplasm. Gene expression profiling revealed a marked decrease in metalloproteinase 9 (MMP-9) and MYL9 expression after MAL inhibition. Luciferase assays in HEK293T cells and chromatin immunoprecipitation in primary megakaryocytes showed that the MAL/SRF complex directly regulates MYL9 and MMP9 in vitro. Megakaryocyte migration in response to stromal cell-derived factor 1, through Matrigel was considerably decreased after MAL knockdown, implicating MMP9 in migration. Finally, the use of a shRNA to decrease MYL9 expression showed that MYL9 was involved in proplatelet formation. MAL/SRF complex is thus involved in platelet formation and megakaryocyte migration by regulating MYL9 and MMP9.

c-Myc is a target of RNA-binding motif protein 15 in the regulation of adult hematopoietic stem cell and megakaryocyte development

RNA-binding motif protein 15 (RBM15) is involved in the RBM15-megakaryoblastic leukemia 1 fusion in acute megakaryoblastic leukemia. Although Rbm15 has been reported to be required for B-cell differentiation and to inhibit myeloid and megakaryocytic expansion, it is not clear what the normal functions of Rbm15 are in the regulation of hematopoietic stem cell (HSC) and megakaryocyte development. In this study, we report that Rbm15 may function in part through regulation of expression of the proto-oncogene c-Myc. Similar to c-Myc knockout (c-Myc-KO) mice, long-term (LT) HSCs are significantly increased in Rbm15-KO mice due to an apparent LT-HSC to short-term HSC differentiation defect associated with abnormal HSC-niche interactions caused by increased N-cadherin and beta(1) integrin expression on mutant HSCs. Both serial transplantation and competitive reconstitution capabilities of Rbm15-KO LT-HSCs are greatly compromised. Rbm15-KO and c-Myc-KO mice also share related abnormalities in megakaryocyte development, with mutant progenitors producing increased, abnormally small low-ploidy megakaryocytes. Consistent with a possible functional interplay between Rbm15 and c-Myc, the megakaryocyte increase in Rbm15-KO mice could be partially reversed by ectopic c-Myc. Thus, Rbm15 appears to be required for normal HSC-niche interactions, for the ability of HSCs to contribute normally to adult hematopoiesis, and for normal megakaryocyte development; these effects of Rbm15 on hematopoiesis may be mediated at least in part by c-Myc.

Hypercalcemia in pediatric acute megakaryocytic leukemia: case report and review of the literature

Hypercalcemia has been described as a possible complication of many pediatric malignancies. Here, we report an 8-month-old non-Down syndrome infant with acute megakaryocytic leukemia and severe hypercalcemia at presentation. A review of the literature reveals that this is the first case of hypercalcemia complicating acute megakaryocytic leukemia reported in the pediatric literature. His initial workup, and the course of management and outcome, is described in detail. Though the etiology of this complication remains unclear, our experience suggests that early institution of chemotherapy along with supportive care is the best treatment for control of hypercalcemia.

Acute megakaryoblastic leukaemia (AMKL) in children: a comparison of AMKL with and without Down syndrome

To characterize childhood acute megakaryoblastic leukaemia (AMKL), we reviewed 45 children with AMKL diagnosed between 1986 and 2005 at Nagoya University Hospital and Japanese Red Cross Nagoya First Hospital. Twenty-four patients (53%) had AMKL associated with Down syndrome (DS-AMKL) and 21 (47%) had non-DS-AMKL. The median age of the DS-AMKL patients was 21 months (range, 8-38 months) and that of non-DS-AMKL patients was 15 months (range, 2-185 months). The morphology of blast cells was categorized into three groups according to the stage of megakaryocyte maturation. The blast cells were more immature in DS-AMKL than in non-DS-AMKL in terms of morphology and immunophenotyping. Cytogenetic abnormalities of leukaemic cells were classified into seven categories: normal karyotype including constitutional trisomy 21 in DS-AMKL; numerical abnormalities only; t(1;22)(p13;q13); 3q21q26 abnormalities; t(16;21)(p11;q22); -5/del(5q) and/or -7/del(7q); and other structural changes. The outcome of children with either DS-AMKL or non-DS-AMKL is excellent. The 10-year overall survival estimate was 79% [95% confidence interval (CI): 54-90] for DS-AMKL and 76% (95% CI: 58-91) for non-DS-AMKL (P = 0.81) with a median follow-up of 78 months (range, 20-243 months). Our study shows the diverse heterogeneity of childhood AMKL and the need for subclassification according to cytogenetic and morphological features.

Imaging findings of upper abdominal involvement by acute megakaryoblastic leukaemia

Acute megakaryoblastic leukaemia (AMKL), a relatively rare type of acute myeloid leukaemia, is characterized by frequent involvement of the liver, spleen and lymph nodes in addition to myelofibrosis in children. Diagnosis is difficult both clinically and pathologically, and the hepatic or lymph node involvement is not uncommonly misinterpreted as solid tumour. We report the imaging findings of upper abdominal involvement by AMKL in an infant. The hepatic lesion, initially suspected to be hepatoblastoma, showed a distinctive appearance on MRI suggesting its infiltrative nature. With the association of splenic lesion and lymphadenopathy, the imaging findings were considered indicative of a haematological disorder.

Acute megakaryoblastic leukemia mimicking small round cell tumor with novel t(1;5)(q21;p13)

Acute megakaryoblastic leukemia is a relatively rare form of acute leukemia that has heterogeneous blast morphology and karyotypic abnormalities. An 8-month-old boy with a retroperitoneal mass was diagnosed as having acute megakaryoblastic leukemia that initially presented as small round cell tumor of childhood. Bone marrow aspiration showed syncytial groups of atypical medium sized cells with scant cytoplasm and fine nuclear chromatin. Retroperitoneal mass biopsy showed several lymph nodes with cohesive clusters of neoplastic cells that demonstrated expression of Factor VIII. Flow cytometric analysis of the second bone marrow aspiration showed CD 61 positivity. Karyotypic analysis of bone marrow cells showed a novel translocation, (1;5)(q21;p13).

Cytogenetic features of acute lymphoblastic and myeloid leukemias in pediatric patients with Down syndrome: an iBFM-SG study

Children with Down syndrome (DS) have a markedly increased risk of acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML). To identify chromosomal changes cooperating with +21 that may provide information on the pathogenesis of these leukemias, we analyzed 215 DS-ALLs and 189 DS-AMLs. Unlike previous smaller series, a significant proportion of DS-ALLs had the typical B-cell precursor ALL abnormalities high hyperdiploidy (HeH; 11%) and t(12;21)(p13;q22) (10%). The HeH DS-ALLs were characterized by gains of the same chromosomes as non–DS-HeH, suggesting the same etiology/pathogenesis. In addition, specific genetic subtypes of DS-ALL were suggested by the significant overrepresentation of cases with +X, t(8;14)(q11;q32), and del(9p). Unlike DS-ALL, the common translocations associated with non–DS-AML were rare in DS-AML, which instead were characterized by the frequent presence of dup(1q), del(6q), del(7p), dup(7q), +8, +11, del(16q), and +21. This series of DS leukemias—the largest to date—reveals that DS-ALL is a heterogeneous disorder that comprises both t(12;21) and HeH as well as DS-related abnormalities. Furthermore, this analysis confirms that DS-AML is a distinct entity, originating through other genetic pathways than do non–DS-AMLs, and suggests that unbalanced changes such as dup(1q), +8, and +21 are involved in the leukemogenic process.

Hepatic involvement in congenital acute megakaryoblastic leukemia: a case report with emphasis on the liver pathology findings

We report the case of a 4-week-old infant diagnosed with acute megakaryoblastic leukemia with the t (1;22) (p13, q13) who presented with ascites caused by massive infiltration of hepatic sinusoids by leukemic cells. The bone marrow by microscopy and flow cytometry and the peripheral blood smear did not initially show the presence of blasts. Marrow fibrosis appeared after infiltrative disease in the liver and liver fibrosis. We describe the microscopic liver findings and associated clinical presentation that, in the absence of bone marrow involvement, can be difficult to diagnose as leukemia. Few cases have been reported in the medical literature with the liver as the primary site of involvement in congenital leukemia. Awareness of this unusual clinical presentation and of the characteristic liver pathology may facilitate the pathologic diagnosis.

Cytogenetic anomalies in hyaline vascular Castleman disease: report of two cases with reappraisal of histogenesis

The pathogenesis of hyaline vascular Castleman disease (HVCD) is poorly understood. Although generally considered reactive in nature, a subset of cases has been shown to harbor focal proliferations of stromal cells, such as follicular dendritic cell (FDC) and angiomyoid proliferations. We report two typical cases of HVCD with cytogenetic anomalies: one was t(1;22)(qter;q13) and the other was t(7;8)(q37.3;q12) in cultured stromal cells, as demonstrated by conventional cytogenetic analysis. The cultured cells were immunoreactive for smooth muscle actin but negative for CD21, CD31, and CD34, and ultrastructurally possessed thin filaments (5-7.5 nm) with dense bodies, and pinocytotic vesicles, characteristic of smooth muscle cells. The lack of monoclonality of lymphoid cells in lesional tissues by immunohistochemical and molecular analyses also supports the origin of these anomalies from the stromal cells, most likely myoid cells. Moreover, the absence of overt stromal proliferations suggests that cytogenetic changes in stromal cells of HVCD precede histologic evidence of stromal overgrowth, which may account for the occurrence of angiomyoid proliferations arising in some cases of HVCD. Further studies with more cases are needed to decipher whether part or even most of HVCD cases bear genetic changes in the beginning of the disease without morphologically stromal overgrowth.

Translocation (6;17)(q23;q11.2): a novel cytogenetic abnormality in congenital acute myeloid leukemia?

Congenital leukemia occurring within 4 weeks of birth is extremely rare and, excluding transient neonatal myeloproliferation associated with Down syndrome, makes up approximately 1% of childhood leukemias. It is usually seen as acute myeloid leukemia (AML), most frequently French-American-British (FAB) types M4 and M5. Recurrent cytogenetic abnormalities have been reported in this group, and in approximately one third of cases the MLL gene at 11q23 is involved. These patients generally have a poor prognosis. We present a case of congenital leukemia (AML FAB type M1) with an acquired translocation between chromosomes 6 and 17.

RBM15-MKL1 (OTT-MAL) fusion transcript in an adult acute myeloid leukemia patient

The t(1;22)(p13;q13) is a nonrandom chromosomal abnormality in acute leukemia with the fusion oncogene, RBM15-MKL1 (OTT-MAL), identified recently. However, this abnormality has been described only in infants and young children with acute megakaryoblastic leukemia (AMKL). We report a 59-year-old male patient with the diagnosis of acute myeloid leukemia, subtype M1, who harbors an abnormal chromosome +der(1)t(1;22)(p13;q13). The RBM15-MKL1 (OTT-MAL) fusion transcript was also confirmed by the reverse transcriptase-polymerase chain reaction. This unusual abnormality is rare in adult cases of leukemia, and in children it is restricted to AMKL. This report is accompanied by a review of the literature on the t(1;22)(p13;q13).

Cytogenetics in acute leukemia

Cytogenetic analyses in acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) have revealed a great number of non-random chromosome abnormalities. In many instances, molecular studies of these abnormalities identified specific genes implicated in the process of leukemogenesis. The more common chromosome aberrations have been associated with specific laboratory and clinical characteristics, and are now being used as diagnostic and prognostic markers guiding the clinician in selecting the most effective therapies. Specific chromosome aberrations and their molecular counterparts have been included in the World Health Organization classification of hematologic malignancies, and together with morphology, immunophenotype and clinical features are used to define distinct disease entities. However, the prognostic importance of less frequent recurrent aberrations in AML and ALL, both primary and secondary, is still to be determined. This review summarizes current views on clinical relevance of major cytogenetic findings in adult AML and ALL.

Classical and molecular cytogenetic abnormalities and outcome of childhood acute myeloid leukaemia: report from a referral centre in Israel

The incidence of cytogenetic abnormalities in childhood de novo acute myeloid leukaemia (AML) and its prognostic significance was assessed in an Israeli paediatric referral centre. Cytogenetic analysis was successful in 86 of 97 children (< 20 years of age) diagnosed between 1988 and 2002 with de novo AML. Fluorescence in situ hybridization analysis detected new information in 11 of them, leading to reassignment in cytogenetic group classification. The incidence of the various cytogenetic subgroups was as follows: normal - 9%; t(11q23) - 22%; t(8;21) - 13%; t(15;17) - 8%; inv(16) - 3.4%; abn(3q) - 4.6%; 7/7q-(sole or main) - 5.8%; del(9q)(sole) and +21(sole) - 4.6% each; t(8;16) - 2.3%; t(6;9), t(1;22), +8(sole) - 1.1% each; and miscellaneous - 18%. The overall survival (OS) and event-free survival (EFS) (4 years) for 94 patients treated with the modified Berlin-Frankfürt-Münster (BFM) AML protocols (non-irradiated) were 59.9% (SE = 5%) and 55.7% (SE = 5%), respectively, and for the favourable t(8;21), t(15;17) and inv(16), OS was 60% (SE = 15%), 83% (SE = 15%) and 100% respectively. For the normal group it was 62% (SE = 17%), miscellaneous 64% (SE = 12%), t(11q23) 44.6% (SE = 11%) and of the -7/7q-, del(9q)(sole) or t(6;9), none had survived at 4 years. The incidence of cytogenetic subgroups in the Israeli childhood AML population and their outcome were similar to other recently reported paediatric series. Cytogenetic abnormalities still carry clinical relevance for treatment stratification in the context of modern chemotherapy.

Classification of acute leukemias

Because of the increasing recognition of the importance of genetic events to the diagnosis and treatment of the acute leukemias, the proposed new World Health Organization (WHO) classification incorporates genetic aberrations and immunology as major defining features in addition to morphology. In a hierarchal approach, genetic changes have precedence in the acute myeloid leukemias and immunology and genetic changes have precedence in the acute lymphoblastic leukemias. Four major groups of acute myeloid leukemia are recognized: 1) Acute myeloid leukemias with recurrent genetic abnormalities, 2) Acute myeloid leukemia with multilineage dysplasia, 3) Acute myeloid leukemias, therapy related, and 4) Acute myeloid leukemia not otherwise categorized. Two types of acute lymphoblastic leukemia are recognized based on immunologic characteristics: precursor B lymphoblastic leukemia/lymphoma and precursor T lymphoblastic leukemia/lymphoma. Precursor B acute lymphoblastic leukemia/lymphoma is subclassified into prognostic genetic groups. Biphenotypic leukemia is recognized as a form of acute leukemia of ambiguous lineage.

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.