Discovery of imatinib-responsive FIP1L1-PDGFRA mutation during refractory acute myeloid leukemia transformation of chronic myelomonocytic leukemia

Acute myeloid leukemia with a novel AKAP9::PDGFRA fusion transformed from essential thrombocythemia: A case report and mini review

Acute myeloid leukemia (AML) is a heterogeneous hematological malignancy associated with various combinations of gene mutations, epigenetic abnormalities, and chromosome rearrangement-related gene fusions. Despite the significant degree of heterogeneity in its pathogenesis, many gene fusions and point mutations are recurrent in AML and have been employed in risk stratification over the last several decades. Gene fusions have long been recognized for understanding tumorigenesis and their proven roles in clinical diagnosis and targeted therapies. Advances in DNA sequencing technologies and computational biology have contributed significantly to the detection of known fusion genes as well as for the discovery of novel ones. Several recurring gene fusions in AML have been linked to prognosis, treatment response, and disease progression. In this report, we present a case with a long history of essential thrombocythemia and hallmark CALR mutation transforming to AML characterized by a previously unreported AKAP9::PDGFRA fusion gene. We propose mechanisms by which this fusion may contribute to the pathogenesis of AML and its potential as a molecular target for tyrosine kinase inhibitors.

Myeloid sarcoma: An overview

Myeloid Sarcoma (MS) is a high grade, hematological malignancy defined as an extramedullary tumor mass of myeloid blasts with or without maturation that effaces tissue architecture. It is a highly heterogenous condition that represents a variety of myeloid neoplasms. This heterogeneity of MS, together with its rarity, have greatly hampered our understanding of the condition. Diagnosis requires tumor biopsy, which should be accompanied by bone marrow evaluation for medullary disease. It is presently recommended that MS be treated similar to AML. Additionally, ablative radiotherapy and novel targeted therapies may also be beneficial. Genetic profiling has identified recurrent genetic abnormalities including gene mutations associated with MS, supporting its etiology similar to AML. However, the mechanisms by which MS homes to specific organs is unclear. This review provides an overview of pathogenesis, pathological and genetic findings, treatment, and prognosis. Improving the management and outcomes of MS patients requires a better understanding of its pathogenesis and its response to various therapeutic approaches.

Bone Marrow Mesenchymal Stem Cell-Derived miR-29b Promotes the Progression of Acute Myeloid Leukemia

This study investigates the effect of low miR-29b expression derived from bone marrow mesenchymal stem cells (BMSC) on AML. miR-29b expression in acute leukemia drug resistant cell line as K562/ADM was detected with RT-PCR. Cell proliferation was tested with MTT assay and apoptosis was analyzed by flow cytometry. The correlation between miR-29b and PDGFRα level was analyzed. miR-29b expression was reduced after si-miR-29b transfection. PDGFRα expression was increased by the low miR-29b expression in AML cells so as to prompt the progression of AML. Cell proliferation in K562/ADM was increased after miR-29b expression was reduced and quantity of apoptosis was decreased. There was a correlation of miR-29b and PDGFRα in the staging of AML (P <0.05). In conclusion, AML could be aggravated by the low miR-29b expression possibly through regulating PDGFRα, resulting in increased drug tolerance.

Chronic Myelomonocytic Leukemia: Hematopathology Perspective

Our understanding of chronic myelomonocytic leukemia (CMML) has evolved tremendously over the past decade. Large-scale sequencing studies have led to increased insight into the genomic landscape of CMML and clinical implications of these changes. This in turn has resulted in refined and improved risk stratification models, which to date remain versatile and subject to remodeling, as new and evolving studies continue to refine our understanding of this disease. In this article, we present an up-to-date review of CMML from a hematopathology perspective, while providing a clinically practical summary that sheds light on the constant evolution of our understanding of this disease.

Laboratory Evaluation and Pathological Workup of Neoplastic Monocytosis - Chronic Myelomonocytic Leukemia and Beyond

PURPOSE OF REVIEW

Monocytosis is a distinct but non-specific manifestation of various physiologic and pathologic conditions. Among hematopoietic stem cell neoplasms, depending on the criteria used for disease classification, monocytosis may be a consistent and integral component of diseases such as chronic myelomonocytic leukemia or acute myeloid leukemia with monocytic differentiation, or it may represent an inconsistent finding that often provides a clue to the underlying genetic changes driving the neoplasm. The purpose of this review is to provide the readers with a laboratory-based approach to neoplastic monocytosis.

RECENT FINDINGS

In-depth elucidation of the genomic landscape of myeloid neoplasms within the past few years has broadened our understanding of monocytosis and its implications for diagnosis and prognosis. Genetic findings also shed light on potential disease response - or lack thereof - to various therapeutic agents used in the setting of myeloid neoplasms. In this review, we provide our approach to diagnose neoplastic monocytosis in the context of case-based studies while incorporating the most recent literature on this topic.

GZD824 as a FLT3, FGFR1 and PDGFRα Inhibitor Against Leukemia In Vitro and In Vivo

GZD824 is a novel third-generation BCR-ABL inhibitor. It entered Phase II clinical trials in China and Phase Ib clinical trials in USA in 2019 for treatment of patients with resistant chronic myeloid leukemia (CML). We found that at concentrations below 10 nM, GZD824 significantly suppresses FLT3, FGFR1 and PDGFRα kinase activities and inhibits their signal pathways in MV4-11^Flt3-ITD, KG-1^{FGFR1OP2-FGFR1} and EOL-1^{FIP1L1-PDGFRa} leukemia cells. It selectively inhibits the growth of MV4-11^Flt3-ITD, KG-1^{FGFR1OP2-FGFR1} and EOL-1^{FIP1L1-PDGFRa} cells, and also effectively suppresses the growth of Ba/F3-FLT3-ITD cells harboring F691I and other mutations with IC₅₀ values <10 nM. GZD824 induces G0/G1 phase arrest and apoptosis in MV4-11, KG-1 and EOL-1 cells and activates cleavage of caspase-3 and PARP. In MV4-11, Ba/F3-ITD-F691I and KG-1 mouse xenograft models, GZD824 at 10 or 20 mg/kg, q2d, p.o. almost completely eradicates tumors. It also inhibits the viability of primary leukemic blasts from a FLT3-ITD positive AML patient but not those expressing native FLT3. Thus GZD824 suppresses leukemia cells of FLT3-ITD-driven AML and other hematologic malignancies driven by FGFR1 or PDGFRa, and it may be considered to be a novel agent for the treatment of leukemia.

Defining the Boundary Between Myelodysplastic Syndromes and Myeloproliferative Neoplasms

In this article we provide a practical and comprehensive review of myeloid neoplasms with overlapping myelodysplastic (MDS) and myeloproliferative (MPN) features, with emphasis on recent updates in classification, particularly the utility of morphologic, cytogenetic, and molecular findings in better defining and classifying these disease entities. We provide the reader with a summary of the most recent developments and updates that have helped further our understanding of the genomic landscape, clinicopathologic features, and prognostic elements of myeloid neoplasms with MDS/MPN features.

Recent Updates on Chronic Myelomonocytic Leukemia

PURPOSE OF REVIEW

The goal of this review is to provide a practical and comprehensive update on changes in the classification of chronic myelomonocytic leukemia (CMML) and a summary of the most recent developments in our understanding of its genomic landscape, prognostic models, and therapeutic approaches.

RECENT FINDINGS

The 2017 revision of the World Health Organization (WHO) classification includes substantial changes to the subclassification CMML. The clinical utility of the newly revised subclassification scheme is discussed. In addition, we provide an overview of the genetic changes involved in the pathogenesis of CMML and discuss the clinical utility of the more recently developed molecularly integrated prognostic models and their management and therapeutic implications. Finally, we provide an overview of the currently available treatment options for patients with CMML. The classification of CMML as well as our understanding of its genomic landscape and optimal treatment approaches has advanced significantly over the past decade but remains in flux.

Proposed diagnostic criteria for classical chronic myelomonocytic leukemia (CMML), CMML variants and pre-CMML conditions

Chronic myelomonocytic leukemia (CMML) is a myeloid neoplasm characterized by dysplasia, abnormal production and accumulation of monocytic cells and an elevated risk of transforming into acute leukemia. Over the past two decades, our knowledge about the pathogenesis and molecular mechanisms in CMML has increased substantially. In parallel, better diagnostic criteria and therapeutic strategies have been developed. However, many questions remain regarding prognostication and optimal therapy. In addition, there is a need to define potential pre-phases of CMML and special CMML variants, and to separate these entities from each other and from conditions mimicking CMML. To address these unmet needs, an international consensus group met in a Working Conference in August 2018 and discussed open questions and issues around CMML, its variants, and pre-CMML conditions. The outcomes of this meeting are summarized herein and include diag nostic criteria and a proposed classification of pre-CMML conditions as well as refined minimal diagnostic criteria for classical CMML and special CMML variants, including oligomonocytic CMML and CMML associated with systemic mastocytosis. Moreover, we propose diagnostic standards and tools to distinguish between 'normal', pre-CMML and CMML entities. These criteria and standards should facilitate diagnostic and prognostic evaluations in daily practice and clinical studies in applied hematology.

Eosinophilia in acute myeloid leukemia: Overlooked and underexamined

The presence of eosinophilia in acute myeloid leukemia (AML) suggests an underlying core binding factor (CBF) lesion, a platelet derived growth factor (PDGFR) translocation, or another rare translocation (such as ETV6-ABL1). Each of these cytogenetic entities carries unique diagnostic, prognostic, and therapeutic implications. CBF AML is most common and as such, its treatment is more clearly established, consisting of intensive induction chemotherapy followed by cytarabine based consolidation. Due in large part to its intrinsic chemo-sensitivity, CBF AML is associated with relatively high rates of remission and survival. PDGFR mediated AML is comparatively rare, and as such, diagnostic and treatment paradigms are not as well defined. Early identification of PDGFR translocations is essential, as they confer profound imatinib sensitivity which may, in many instances, spare the need for chemotherapy. Prompt recognition of such lesions requires a strong index of suspicion, and as such these diagnoses are often initially overlooked. Unfortunately, many cases of PDGFR associated AML, particularly those with other concurrent cytogenetic abnormalities, demonstrate treatment emergent imatinib resistance. Such patients continue to present a challenge, even with the advent of novel tyrosine kinase inhibitors (TKIs). Patients with rare translocations such as ETV6-ABL1 are not well described however seem to follow an aggressive clinical course, with limited response to imatinib, and poor outcomes. This review examines the significance of eosinophilia in the context of AML, with respect to its presentation, pathology, and cytogenetics, and with special attention to appropriate evaluation and treatment.

Identification of a novel PDGFRA point mutation at p.P6L as a potential molecular target of imatinib in an eosinophilia patient showing genetic heterogeneity

Eosinophilia is a severe disease with increased eosinophil count. The transcript of FIP1L1-PDGFRA fusion gene is a genetic biomarker of clonal eosinophilia screened routinely by reverse transcript PCR (RT-PCR) during diagnosis. Another significant genetic biomarker is the PDGFRA gene alone as some of its mutations are targets of imatinib. In this study, we identified a patient who had typical symptoms of Eosinophilia but had no response to the first-line treatment of hormonotherapy. This patient also showed bone rupture and eosinophil bone infiltration, which are extremely rare among all known eosinophilia patients. We identified the FIP1L1-PDGFRA fusion gene via RT-PCR and Sanger sequencing. Using next generation sequencing (NGS), we detected point mutations in PDGFRA, MYOM2, and ASXL3. The patient then received imatinib therapy, leading to the complete disappearance of FIP1L1-PDGFRA fusion gene and mutated MYOM2. The level of PDGFRA point mutation was also decreased from pre-treatment: 57.86% down to 42.99% at 6 months and to 38.80% at one-year after treatment. The level of ASXL3 mutations did not change significantly. To the best of our knowledge, this is the first case in which the point mutation of PDGFRA has been identified at p.P6L in exon 2, likely making it sensitive to imatinib and thus should be further studied as a potential new molecular target of imatinib therapy.

Eosinophil-rich tissue infiltrates in chronic myelomonocytic leukemia patients

Chronic myelomonocytic leukemia (CMML) is a clonal hematopoietic disorder that associates dysplastic and proliferative features. Tissue inflammatory disorders occur in a fraction of CMML patients during the course of their disease. Here, we describe the occurrence of eosinophil-rich tissue inflammation, including eosinophilic pneumonia, chondritis, and cystitis, in CMML patients. Whole exome sequencing of leukemic cells did not identify a recurrent genetic abnormality among these three patients who were clinically improved by local or oral corticosteroids. Hypomethylating drugs were subsequently added in two of them, allowing decreasing corticosteroid doses and further treating their hematopoietic malignancy.

Refractory myeloid sarcoma with a FIP1L1-PDGFRA rearrangement detected by clinical high throughput somatic sequencing

Next generation sequencing (NGS) is increasingly being used clinically to characterize the molecular alterations found in patients’ tumors. These testing results have the potential to affect clinical care by guiding therapeutic approaches based upon genotype. NGS based testing approaches have a distinct advantage over provider-ordered single gene testing in that they can detect unexpected, yet clinically important genetic changes. Here, we illustrate this principle with the case of a 33-year-old man with myeloid sarcoma that was refractory to six different chemotherapeutic regimens. Our clinical NGS assay detected an unanticipated FIP1L1-PDGFRA rearrangement in his tumor. The patient was immediately placed on Imatinib therapy to which he responded, and remains in remission 10 months after the rearrangement was initially detected.