Form Of Acute Myeloid Leukemia Research Articles

THE TREATMENT FOR RELAPSED AND REFRACTORY FORMS OF ACUTE MYELOID LEUKEMIA

The review focuses on relapse and refractory forms of acute myeloid leukemia, which is a heterogeneous disease and does not have a single universal therapeutic scheme. The paper presents the characteristics of protocols with inclusion of new agents, shows the role of allogenic hematopoietic stem cell transplantation and advances in risk stratification for the treatment for acute myeloid leukemia. The prospects of the therapy personalization based on molecular tests have been determined. The application of more effective induction and post-remission protocols shows a guaranteed reduction in the relapse rate.

Acute megakaryoblastic leukemia associated with trisomy 21 demonstrates a distinct immunophenotype.

Acute megakaryoblastic leukemia (AMKL) is a rare form of acute myeloid leukemia that encompasses three distinct subgroups: children with Down syndrome (DS-AMKL), children without DS (non-DS-AMKL), and adults (adult-AMKL). We hypothesize that the biological differences in the subtypes of AMKL may be reflected in distinct immunophenotypic (IP) features. Our aims were to employ mutiparameter flow cytometry to establish a comprehensive IP spectrum of AMKL in multiple demographic groups and to determine whether the subtypes of AMKL demonstrate distinct immunophenotypes. Thirty-seven AMKL cases were retrieved and subdivided into these three groups. Multiparameter flow cytometry was used to determine and compare the immunophenotypes. Available clinical, cytogenetic, and morphologic data were reviewed to confirm diagnoses. While there is commonality in the expression pattern for a wide range of myelomonocytic markers in these three subtypes of AMKL, blasts in DS-AMKL were more likely to express CD7 and CD11b than those in non-DS-AMKL and adult-AMKL. Furthermore, blasts in DS-AMKL were more likely to express CD13, CD33, and CD36 than non-DS pediatric AMKL, and showed greater CD56 expression compared with adult AMKL. These results indicate that DS-AMKL is related to but immunophenotypically distinct from non-DS-AMKL and adult-AMKL. This distinct immunophenotypic pattern, co-expression of CD7 and CD11b, has practical implications for characterization of AMKL.

Acute Megakaryoblastic Leukemia Associated with Trisomy 21 Demonstrates a Distinct Immunophenotype.

Background: Acute megakaryoblastic leukemia (AMKL) is a rare form of acute myeloid leukemia that encompasses three distinct subgroups, children with Down syndrome (DS-AMKL), children without DS (non-DS-AMKL) and adults (adult-AMKL). We hypothesize that the biological differences in the subtypes of AMKL may be reflected in distinct immunophenotypic (IP) features. Our aims were to employ mutiparameter flow cytometry to establish a comprehensive IP spectrum of AMKL in multiple demographic groups and to determine whether the subtypes of AMKL demonstrate distinct immunophenotypes. Methods: Thirty-seven AMKL cases were retrieved and subdivided into these three groups. Multiparameter flow cytometry was used to determine and compare the immunophenotypes. Available clinical, cytogenetic, and morphologic data were reviewed to confirm diagnoses. Results: While there is commonality in the expression pattern for a wide range of myelomonocytic markers in these three subtypes of AMKL, blasts in DS-AMKL were more likely to express CD7 and CD11b than those in non-DS-AMKL and adult-AMKL. Furthermore, blasts in DS-AMKL were more likely to express CD13, CD33 and CD36 than non-DS pediatric AMKL, and showed greater CD56 expression compared to adult AMKL. Conclusions: These results indicate that DS-AMKL is related to but immunophenotypically distinct from non-DS-AMKL and adult-AMKL. This distinct immunophenotypic pattern, co-expression of CD7 and CD11b, has practical implications for characterization of AMKL. © 2014 Clinical Cytometry Society.

DNA-damage-induced differentiation of leukaemic cells as an anti-cancer barrier.

Self-renewal is the hallmark feature both of normal stem cells and cancer stem cells. Since the regenerative capacity of normal haematopoietic stem cells is limited by the accumulation of reactive oxygen species and DNA double-strand breaks, we speculated that DNA damage might also constrain leukaemic self-renewal and malignant haematopoiesis. Here we show that the histone methyl-transferase MLL4, a suppressor of B-cell lymphoma, is required for stem-cell activity and an aggressive form of acute myeloid leukaemia harbouring the MLL-AF9 oncogene. Deletion of MLL4 enhances myelopoiesis and myeloid differentiation of leukaemic blasts, which protects mice from death related to acute myeloid leukaemia. MLL4 exerts its function by regulating transcriptional programs associated with the antioxidant response. Addition of reactive oxygen species scavengers or ectopic expression of FOXO3 protects MLL4(-/-) MLL-AF9 cells from DNA damage and inhibits myeloid maturation. Similar to MLL4 deficiency, loss of ATM or BRCA1 sensitizes transformed cells to differentiation, suggesting that myeloid differentiation is promoted by loss of genome integrity. Indeed, we show that restriction-enzyme-induced double-strand breaks are sufficient to induce differentiation of MLL-AF9 blasts, which requires cyclin-dependent kinase inhibitor p21(Cip1) (Cdkn1a) activity. In summary, we have uncovered an unexpected tumour-promoting role of genome guardians in enforcing the oncogene-induced differentiation blockade in acute myeloid leukaemia.

Thrombo-hemorrhagic deaths in acute promyelocytic leukemia

Acute promyelocytic leukemia (APL) has become the most curable form of acute myeloid leukemia after the advent of all-trans retinoic acid (ATRA). However, early deaths (ED) mostly due to the disease-associated coagulopathy remain the major cause of treatment failure. In particular, hemorrhagic events account for 40-65% of ED and several prognostic factors have been identified for such hemorrhagic deaths, including poor performance status, high white blood cell (WBC) count and coagulopathy. Occurrence of thrombosis during treatment with ATRA may be associated with differentiation syndrome (DS) or represent an isolated event. Some prognostic factors have been reported to be associated with thrombosis, including increased WBC or aberrant immunophenotype of leukemic promyelocytes. Aim of this review is to report the incidence, severity, possible pathogenesis and clinical manifestations of thrombo-haemorrhagic deaths in APL.

DNMT3A and IDH mutations in acute myeloid leukemia and other myeloid malignancies: associations with prognosis and potential treatment strategies

The development of effective treatment strategies for most forms of acute myeloid leukemia (AML) has languished for the past several decades. There are a number of reasons for this, but key among them is the considerable heterogeneity of this disease and the paucity of molecular markers that can be used to predict clinical outcomes and responsiveness to different therapies. The recent large-scale sequencing of AML genomes is now providing opportunities for patient stratification and personalized approaches to treatment that are based on individual mutational profiles. It is particularly notable that studies by The Cancer Genome Atlas and others have determined that 44% of patients with AML exhibit mutations in genes that regulate methylation of genomic DNA. In particular, frequent mutation has been observed in the genes encoding DNA methyltransferase 3A (DNMT3A), isocitrate dehydrogenase 1 (IDH1) and isocitrate dehydrogenase 2 (IDH2), as well as Tet oncogene family member 2. This review will summarize the incidence of these mutations, their impact on biochemical functions including epigenetic modification of genomic DNA and their potential usefulness as prognostic indicators. Importantly, the presence of DNMT3A, IDH1 or IDH2 mutations may confer sensitivity to novel therapeutic approaches, including the use of demethylating agents. Therefore, the clinical experience with decitabine and azacitidine in the treatment of patients harboring these mutations will be reviewed. Overall, we propose that understanding the role of these mutations in AML biology will lead to more rational therapeutic approaches targeting molecularly defined subtypes of the disease.

New frontiers of target therapy in oncology: acute promyelocytic leukemia

SUMMARY By introduction of all-trans retinoic acid (ATRA) in de novo acute promyelocytic leukemia (APL) an revolution in therapy of this disease has been made. The rate of molecular complete remissions (CR) have been doubled compared to conventional chemotherapy with anthracyclines ranging from 90% to 95%. Consolidation therapy is required in order to reduce the risk of early relapse. Maintenance therapy is recommended as it further reduces the risk of relapse, especially in high-risk patients. The relapse rate in APL is relatively high, about 30% and is the most common within three years of starting the treatment. Another agent, arsenic trioxide (ATO) is the optimal drug that achieves high CR rate in relapsed, approximately 80% and hematopoietic stem cell transplantation (HSCT) may prolong the overall survival in patients with APL. ATRA and ATO have become a paradigm of targeted therapy, and APL is a paradigm of curable disease, at least in comparison to other forms of acute myeloid leukemia (AML).

Myeloid sarcoma: a rare case of an orbital mass mimicking orbital pseudotumor requiring neurosurgical intervention.

Objective. A rare case of myeloid sarcoma (MS), previously referred to as granulocytic sarcoma or chloroma, is presented. Representing a unique form of acute myeloid leukemia (AML), MS may rarely occur in adults. Even rarer, MS may occur as the initial presentation of AML. Methods. We report a singular and illustrative case of an orbital pseudotumor mimicking mass in a 65-year-old male as the initial presentation of AML. Results. Neurosurgical intervention was required to establish the definitive diagnosis via right modified orbitofrontozygomatic craniotomy as well as to decompress the optic canal, superior orbital fissure, and orbit. Conclusion. Postoperatively, he reported decreased pain and improvement of his vision. Further examination revealed decreased proptosis and improved extraocular mobility. Pathological findings demonstrated MS. We review the literature and discuss the neurosurgical relevance of MS as the initial presentation of AML.

New Variant Translocation (8;9;21)(q22;p24;q22) in a Patient with Granulocytic Sarcoma Concurrent with Acute Myeloid Leukemia

Granulocytic sarcoma is a form of acute myeloid leukemia which may occur in any anatomical site. Isolated pancreatic granulocytic sarcoma is however, extremely rare. Translocation t(8;21) is the most common cytogenetic abnormality found in leukemia patients with granulocytic sarcoma and is associated with a relatively good prognosis when treated with chemotherapy. Variants of the t(8;21) are uncommon and account for approximately 3% to 4% of acute myeloid leukemia associated with t(8;21) and are rarely described in acute myeloid leukemia cases associated with granulocytic sarcoma. We report here a patient with acute myeloid leukemia and a novel variant t(8;9;21)(q22;p24;q22) with suspected granulocytic sarcoma in pancreas. A dual-color fluorescence in situ hybridization analysis with RUNX1T1 and RUNX1 probes, revealed the presence of an RUNX1/RUNX1T1 fusion signal in this translocation. To the best of our knowledge, a variant of t(8;21) in GS was rarely described and the involvement of the 9q22 region is the first time described here even in isolated AML-M2. We conclude that further accumulation of similar cases is needed and that genetic exploring of variants of t(8;21) may be helpful for a better understanding of molecular pathogenetic mechanism.

Role of Epigenetic Readers in Pathogenesis and Therapy of Acute Leukemias

Acute myeloid leukemia (AML) is an aggressive hematological malignancy with a dismal survival rate of less than 30 percent and is thus a disease where novel therapeutics are urgently required. AML is highly heterogeneous at both the molecular and clinical level. However, recurrent themes of altered transcriptional and epigenetic control are evident from sequencing and mechanistic studies. Recently, critical epigenetic regulators have surfaced as mediators of leukemogenesis and potential therapeutic targets in AML and other hematological malignancies. We and others have recently demonstrated that the Bromodomain and Extra Terminal (BET) protein family of transcriptional adapter proteins are required for transformation by MLL-fusion proteins, where they facilitate the localization of aberrant transcriptional complexes to chromatin at genes critical for leukemogenesis. Furthermore, we and others have demonstrated that small molecule inhibitors, such as I-BET151 and JQ1, of the protein-protein interactions between these proteins and acetylated lysine residues in histone tails are effective in pre-clinical models of MLL leukemias. We have recently extended studies of BET inhibition to other forms of AML using I-BET151 and found a range of sensitivities across a panel of AML cell lines and patient samples with common recurrent mutations. These cell lines also demonstrate a common cellular response to MLL-fusion leukemias, with induction of apoptosis and G1/0 arrest, suggesting that similar transcriptional programs may be targeted. In further investigating this, we identified a common transcriptional program downregulated in sensitive leukemia subtypes. In addition, using diagnostic gene expression profiles, we also demonstrate that this program can classify AML patients, suggesting that the program may provide predictive biomarkers and potentially identify those patients most likely to respond to BET inhibitions. Focusing on the most common mutation in AML, mutations of the nucleophosmin gene (NPM1c mutations), we present evidence to suggest that wild-type NPM1 has an inhibitory influence on BRD4, which is relieved upon NPM1c mutation and cytosplasmic dislocation. NPM1c mutation allows upregulation of the core transcriptional program facilitating leukemia development, and this program is abrogated by I-BET therapy. Finally, we demonstrate the efficacy of I-BET151 in human cell lines, a unique murine model, and in primary patient samples of NPM1c AML. Taken together, we have used BET inhibitors as a laboratory tool to dissect out mechanisms of aberrant transcriptional control in AML. Furthermore our pre-clinical evaluation supports clinical trials of BET inhibitors across multiple AML subtypes and identifies potential predictive biomarkers of sensitivity and response to inform these studies. Disclosures:No relevant conflicts of interest to declare.

Investigation Of p210 Bcr-Abl Rhogef Activity In The Progression Of Chronic Myelogenous Leukemia

The Philadelphia chromosome is formed by a balanced, reciprocal translocation that pairs sequences from BCR on Chromosome 22 with sequences from ABL on Chromosome 9 and results in the production of the constituitively active tyrosine kinase Bcr-Abl. Depending on the location of the breakpoint within BCR, three different sizes of Bcr-Abl can be produced (i.e., p190, p210 and p230) and they are associated with different clinical outcomes. The larger p210 form is observed in greater-than 95% of chronic myelogenous leukemia [CML], while the diminutive p190 is present in approximately 2/3 of Philadelphia-positive acute lymphoblastic leukemia [ALL]. Although both the p210 and p190 forms contain the same portion of Abl, importantly, they differ only in the amount of Bcr which is retained at the amino terminus. We previously identified a functional domain within the Bcr sequences preserved by p210, but not by p190, which demonstrates a constitutive Rho GTPase-specific guanine nucleotide exchange factor [RhoGEF] activity. To determine the contribution of this region to p210 Bcr-Abl-related disease progression in CML, we therefore introduced a single amino acid substitution [S509A] into this construct which abrogated its activity and then compared this mutant to the p210 and p190 variants in a murine bone marrow transplantation model. While all of the mice eventually developed myeloproliferative disease, those transplanted with either p210 Bcr-Abl S509A or p190 Bcr-Abl displayed a more rapid onset than the mice transplanted with p210 Bcr-Abl (within 12 vs. 23 days of transplantation, respectively). Interestingly, this reduced disease latency is associated with erythroid hyperplasia in the absence of anemia and expansion of megakaryocyte-erythrocyte progenitor, common myeloid progenitor and granulocyte-macrophage progenitor populations, which results in a phenotype that is similar to the M6 form of acute myeloid leukemia. This phenotype is also readily transplantable into secondary recipients, indicating that it is a true element of the malignancy and not a reactive process. Taken together, these results support a model wherein the RhoGEF activity of p210 Bcr-Abl actively regulates disease progression by downregulating the self-renewal of myeloid progenitors. While our animal studies indicate that the Bcr region plays a significant role in disease progression, to the best of our knowledge, this has yet to be evaluated using clinically derived mutations. Recently, the RhoGEF domain of p210 Bcr-Abl was reported to be mutated and/or partially deleted in tumors obtained from several CML blast crisis patients and a p210 Bcr-Abl-positive ALL patient. These findings suggest that the RhoGEF domain of p210 Bcr-Abl may in fact be actively involved in the aggressiveness of primary specimens as well. In order to determine the consequences of the reported mutations, we therefore examined their effects on disease progression using a murine bone marrow transplant model. Disclosures:No relevant conflicts of interest to declare.

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.

Treatment of acute promyelocytic leukemia with arsenic trioxide: clinical results and open questions

Acute promyelocytic leukemia (APL) is a rare form of acute myeloid leukemia. The specific translocation t(15;17), which results in the fusion gene PML–RARA is the diagnostic and pathomechanistic hallmark of APL. By combination, treatment consisting of the differentiating agent all-trans retinoic acid (ATRA), which targets this molecular lesion, and cytotoxic chemotherapy, cure can be achieved in over 70% of patients. Recently, arsenic trioxide (ATO) has emerged to be the most active single agent in the treatment of APL. Previous studies employing ATO in relapse settings reported average complete remission rates of 85% and a mean overall survival of over 60%. In recent approaches installing ATO in first-line treatment, ATO-induced response rates comparable to previous combination regimen. The results of these newer studies indicate that the backbone of chemotherapy can be dramatically reduced or completely replaced by ATO and ATRA with similar or even better outcome.

AKT collaborates with ERG and Gata1s to dysregulate megakaryopoiesis and promote AMKL

The requirement that leukemic GATA1 mutations be present in cells harboring trisomy 21 led to the discovery that overexpression of ERG drives aberrant megakaryopoiesis. Given that constitutive PI3K/AKT signaling is a frequent component of hematologic malignancies and the relationship between AKT and Notch in this lineage, we studied the cross talk between AKT signaling and ERG in megakaryopoiesis. We discovered that constitutive AKT signaling is associated with a dramatic increase in apoptosis of WT MKs, but that overexpression of ERG blocks AKT-induced death. We further found that Gata1 mutations protect megakaryocytes from activated AKT-induced apoptosis. As a consequence, however, the enhanced signaling inhibits differentiation of Gata1 mutant, but not WT, megakaryocytes. Gata1 mutant cells that overexpress ERG with hyperactive AKT are characterized by diminished FOXO1/3a expression and an increased dependency on the c-Jun pathway similar to that seen in AMKL cell lines, AML with knockdown of FOXO3a, or AML with expression of myrAKT. Additionally, we found that the AKT allosteric inhibitor MK2206 caused reduced cell viability and proliferation of AMKL cell lines. The contribution of aberrant AKT signaling during the ontogeny of DS-TMD/AMKL indicates that AKT is a therapeutic target in this form of AML.

Treatment of acute erythroleukemia with Azacitidine: A case series

Acute erythroleukemia (AEL) is a rare form of acute myeloid leukemia (AML) often associated with a poor prognosis. It is more frequent in elderly patients, limiting the use aggressive therapies. Azacitidine is a hypomethylating agent with recognized efficacy in high risk myelodysplasia and AML in the elderly. Here we report 5 cases of AEL treated with Azacitidine. The cohort included 4 men and 1 woman, median age 70. One patient had been refractory to intensive chemotherapy, the others received Azacitidine as first line. Treatment was well tolerated. Four patients achieved transfusion independence. Two patients achieved complete remission and 1 achieved partial remission. After a median follow up time of 20 months, the median survival of the cohort was 20 months. Three patients died of disease progression. These results confirm the therapeutic value of Azacitidine in AEL.

A retrospective study of absence of expression of HLA-DR in acute myeloid leukaemia

Aims To investigate whether absence of expression of HLA-DR on myeloblasts has a predictive value in the diagnosis of acute pro-myelocytic leukaemia (APML) and other subtypes of acute my-eloid leukaemia (AML). Background From 2000 to 2008, 142 new cases of AML were diagnosed in Tasmania, of which 10–20% are expected to be of the APML subtype according to the Tasmania Cancer Registry. APML has one of the worst prognoses among the AML subtypes on presentation, however with rapid diagnosis and treatment it is the most curable form of AML. Methods The immunophenotype results from the Flow Cytom-etry Department of the Royal Hobart Hospital (RHH) of all patients diagnosed with AML in Tasmania from 2000 to 2008 was reviewed and patients were categorised into respective French-American-British classification (FAB) AML subtypes using this data. Confirmation of true APMLs were obtained from the cytoge-netics department of the RHH. Results A total of 110 patients were diagnosed with AML based upon flow cytometry results. There were nine suspected with APML, of which four were confirmed to be APML by cytogenetics. HLA-DR expression was negative on 18 patients, of which only one was an APML. In fact nine (50%) were classified as M2. Conclusions Preliminary results suggest that absence of expression of HLA-DR does not correlate with a diagnosis of APML; rather it may suggest a diagnosis of AML with maturation (M2).

All-trans retinoic acid in the treatment of pediatric acute promyelocytic leukemia

Acute promyelocytic leukemia (APL) is a rare form of acute myeloid leukemia with specific epidemiological, pathogenetic and clinical features. Its frequency varies widely among nations, with a decreased incidence among ‘Nordic’ origin populations. The molecular hallmark of the disease is the presence of a balanced reciprocal translocation resulting in the PML/RAR-α gene fusion, which represents the target of the all-trans retinoic acid (ATRA) therapy. The introduction of ATRA in conjunction with anthracyclines marked a turning point in the treatment of APL, previously associated with a significant morbidity and mortality. Nowadays the standard front-line therapy for pediatric APL includes ATRA in every phase of the treatment, resulting in a complete remission rate of 90–95%. Here we provide an overview of the role of ATRA in the treatment of pediatric APL, summarizing the most relevant clinical results of recent decades and investigating future therapeutic perspectives for children with APL.

Remission maintenance in acute myeloid leukemia: impact of functional histamine H2 receptors expressed by leukemic cells

Post-consolidation immunotherapy with histamine dihydrochloride and interleukin-2 has been shown to improve leukemia-free survival in acute myeloid leukemia in a phase III trial. For this study, treatment efficacy was determined among 145 trial patients with morphological forms of acute myeloid leukemia as defined by the French-American-British classification. Leukemia-free survival was strongly improved in M4/M5 (myelomonocytic/monocytic) leukemia but not in M2 (myeloblastic) leukemia. We also analyzed histamine H(2) receptor expression by leukemic cells recovered from 26 newly diagnosed patients. H(2) receptors were typically absent from M2 cells but frequently expressed by M4/M5 cells. M4/M5 cells, but not M2 cells, produced reactive oxygen species that triggered apoptosis in adjacent natural killer cells. These events were significantly inhibited by histamine dihydrochloride. Our data demonstrate the presence of functional histamine H(2) receptors on human AML cells and suggest that expression of these receptors by leukemic cells may impact on the effectiveness of histamine-based immunotherapy.

Abstract 4867: Identification of an inv(16)-encoded CBFA2T3-GLIS2 fusion protein in 34% of non-infant acute megkaryoblastic leukemias: A report from the Pediatric Cancer Genome Project

Abstract Acute Megakaryoblastic Leukemia (AMKL) accounts for ∼10% of childhood acute myeloid leukemia (AML). Although AMKL patients with Down syndrome (DS-AMKL) have an excellent 5 year event-free survival (EFS), non-DS-AMKL patients have an extremely poor outcome with a 3 year EFS < 40%. To define the landscape of mutations that occur in non-DS-AMKL, we performed transcriptome sequencing on diagnostic blasts from 14 cases. Our results identified chromosomal rearrangements resulting in the expression of novel fusion transcripts in 12/14 cases. Remarkably, in 7/14 cases, we detected an inversion on chromosome 16 [inv(16)(p13.3;q24.3)] that resulted in the juxtaposition of CBFA2T3, a member of the ETO family of transcription factors, next to GLIS2 resulting in a CBFA2T3-GLIS2 chimeric gene encoding an in frame fusion protein. GLIS2 is a member of the GLI family of transcription factors that mediate sonic hedgehog (SHH) signaling and has been demonstrated to play a role in regulating expression of GLI target genes. Evaluation of a recurrency cohort of 52 samples including 24 additional pediatric cases and 28 adult cases revealed 6 additional pediatric samples carrying the fusion for an overall frequency of 34% in pediatric AMKL. To gain insight into the mechanism whereby CBFA2T3-GLIS2 promotes leukemogenesis, we introduced the fusion into murine hematopoietic cells and assessed its effect on in vitro colony replating as a surrogate measure of self-renewal. Cells transduced with a mCherry expressing retrovirus failed to form colonies after the 2nd replating. By contrast, expression of either wild-type GLIS2 or CBFA2T3-GLIS2 resulted in a marked increase in the self-renewal capacity, with colony formation persisting through 12 replatings. Immunophenotypic analysis of the CBFA2T3-GLIS2 expressing colonies revealed evidence of megakaryocytic differentiation. GLI transcription factors modulate expression of multiple downstream targets including components of BMP, WNT, and SHH pathways. To interrogate these pathways as potential contributors to the enhanced self-renewal capacity, we conducted luciferase reporter assays and found that CBFA2T3-GLIS2 functioned as a strong activator of the BMP responsive element. Furthermore, expression of CBFA2T3-GLIS2 in Drosophila resulted in ectopic expression of endogenous dpp, the fly homolog of BMP4, and conferred a dpp gain of function phenotype. Taken together these data identify a novel inv(16)-encoded CBFA2T3-GLIS2 fusion protein as a recurrent driver mutation in ∼35% of non-infant pediatric non-DS-AMKLs. The alteration of a key transcriptional regulator within the SHH signaling pathways in a substantial percentage of pediatric AMKL raises the possibility that inhibition of this pathway or downstream activated pathways may have a therapeutic benefit in this aggressive form of AML. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4867. doi:1538-7445.AM2012-4867

Clinical and Pathologic Features of Secondary Acute Promyelocytic Leukemia

Acute promyelocytic leukemia (APL) is a relatively common form of acute myeloid leukemia (AML) that has an excellent prognosis. In contrast, secondary acute myeloid leukemias, including therapy-related AML and AML with myelodysplasia-related changes, have a relatively poor prognosis. We identified 9 cases of APL at our institution in which there was a history of chemotherapy, radiotherapy, chronic immunosuppression, or antecedent myelodysplastic syndrome. The clinical and pathologic findings in these cases of secondary APL were compared with the clinical and pathologic findings in cases of de novo APL. We found that secondary and de novo APL had abnormal promyelocytes with similar morphologic and immunophenotypic features, comparable cytogenetic findings, comparable rates of FMS-like tyrosine kinase mutations, and similar rates of recurrent disease and death. These data suggest that secondary APL is similar to de novo APL and, thus, should be considered distinct from other secondary acute myeloid neoplasms.