Hematopoietic neoplasms with 9p24/JAK2 rearrangement: a multicenter study

Fifth Edition of the World Health Organization Classification of Tumors of the Hematopoietic and Lymphoid Tissues: Acute Lymphoblastic Leukemias, Mixed-Phenotype Acute Leukemias, Myeloid/Lymphoid Neoplasms With Eosinophilia, Dendritic/Histiocytic Neoplasms, and Genetic Tumor Syndromes

This manuscript represents a review of lymphoblastic leukemia/lymphoma (acute lymphoblastic leukemia/lymphoblastic lymphoma), acute leukemias of ambiguous lineage, mixed-phenotype acute leukemias, myeloid/lymphoid neoplasms with eosinophilia and defining gene rearrangements, histiocytic and dendritic neoplasms, and genetic tumor syndromes of the 5th edition of the World Health Organization Classification of Tumors of the Hematopoietic and Lymphoid Tissues. The diagnostic, clinicopathologic, cytogenetic, and molecular genetic features are discussed. The differences in comparison to the 4th revised edition of the World Health Organization classification of hematolymphoid neoplasms are highlighted.

Clinical and Therapeutic Intervention of Hypereosinophilia in the Era of Molecular Diagnosis

Hypereosinophilia (HE) presents with an elevated peripheral eosinophilic count of >1.5 × 109/L and is composed of a broad spectrum of secondary non-hematologic disorders and a minority of primary hematologic processes with heterogenous clinical presentations, ranging from mild symptoms to potentially lethal outcome secondary to end-organ damage. Following the introduction of advanced molecular diagnostics (genomic studies, RNA sequencing, and targeted gene mutation profile, etc.) in the last 1-2 decades, there have been deep insights into the etiology and molecular mechanisms involved in the development of HE. The classification of HE has been updated and refined following to the discovery of clinically novel markers and targets in the 2022 WHO classification and ICOG-EO 2021 Working Conference on Eosinophil Disorder and Syndromes. However, the diagnosis and management of HE is challenging given its heterogeneity and variable clinical outcome. It is critical to have a diagnostic algorithm for accurate subclassification of HE and hypereosinophilic syndrome (HES) (e.g., reactive, familial, idiopathic, myeloid/lymphoid neoplasm, organ restricted, or with unknown significance) and to follow established treatment guidelines for patients based on its clinical findings and risk stratification.

Hematological Neoplasms with Eosinophilia

Eosinophils in peripheral blood account for 0.3-5% of leukocytes, which is equivalent to 0.05-0.5 × 109/L. A count above 0.5 × 109/L is considered to indicate eosinophilia, while a count equal to or above 1.5 × 109/L is defined as hypereosinophilia. In bone marrow aspirate, eosinophilia is considered when eosinophils make up more than 6% of the total nuclear cells. In daily clinical practice, the most common causes of reactive eosinophilia are non-hematologic, whether they are non-neoplastic (allergic diseases, drugs, infections, or immunological diseases) or neoplastic (solid tumors). Eosinophilia that is associated with a hematological malignancy may be reactive or secondary to the production of eosinophilopoietic cytokines, and this is mainly seen in lymphoid neoplasms (Hodgkin lymphoma, mature T-cell neoplasms, lymphocytic variant of hypereosinophilic syndrome, and B-acute lymphoblastic leukemia/lymphoma). Eosinophilia that is associated with a hematological malignancy may also be neoplastic or primary, derived from the malignant clone, usually in myeloid neoplasms or with its origin in stem cells (myeloid/lymphoid neoplasms with eosinophilia and tyrosine kinase gene fusions, acute myeloid leukemia with core binding factor translocations, mastocytosis, myeloproliferative neoplasms, myelodysplastic/myeloproliferative neoplasms, and myelodysplastic neoplasms). There are no concrete data in standardized cytological and cytometric procedures that could predict whether eosinophilia is reactive or clonal. The verification is usually indirect, based on the categorization of the accompanying hematologic malignancy. This review focuses on the broad differential diagnosis of hematological malignancies with eosinophilia.

Myeloid/lymphoid neoplasms with eosinophilia and tyrosine kinase fusion genes: A workshop report with focus on novel entities and a literature review including paediatric cases

Myeloid/lymphoid neoplasms with eosinophilia (M/LN-eo) and tyrosine kinase (TK) gene fusions are a rare group of haematopoietic neoplasms with a broad range of clinical and morphological presentations. Paediatric cases have increasingly been recognised. Importantly, not all appear as a chronic myeloid neoplasm and eosinophilia is not always present. In addition, standard cytogenetic and molecular methods may not be sufficient to diagnose M/LN-eo due to cytogenetically cryptic aberrations. Therefore, additional evaluation with fluorescence in-situ hybridisation and other molecular genetic techniques (array-based comparative genomic hybridisation, RNA sequencing) are recommended for the identification of specific TK gene fusions. M/LN-eo with JAK2 and FLT3-rearrangements and ETV6::ABL1 fusion were recently added as a formal member to this category in the International Consensus Classification (ICC) and the 5th edition of the WHO classification (WHO-HAEM5). In addition, other less common defined genetic alterations involving TK genes have been described. This study is an update on M/LN-eo with TK gene fusions with focus on novel entities, as illustrated by cases submitted to the Bone Marrow Workshop, organised by the European Bone Marrow Working Group (EBMWG) within the frame of the 21st European Association for Haematopathology congress (EAHP-SH) in Florence 2022. A literature review was performed including paediatric cases of M/LN-eo with TK gene fusions.

Clinical Validation of FusionPlex RNA Sequencing and Its Utility in the Diagnosis and Classification of Hematologic Neoplasms

Recurrent gene rearrangements result in gene fusions that encode chimeric proteins, driving the pathogenesis of many hematologic neoplasms. The fifth edition World Health Organization classification and International Consensus Classification 2022 include an expanding list of entities defined by such gene rearrangements. Therefore, sensitive and rapid methods are needed to identify a broad range of gene fusions for precise diagnosis and prognostication. In this study, we validated the FusionPlex Pan-Heme panel analysis using anchored multiplex PCR/targeted RNA next-generation sequencing for routine clinical testing. Furthermore, we assessed its utility in detecting gene fusions in myeloid and lymphoid neoplasms. The validation cohort of 61 cases demonstrated good concordance between the FusionPlex Pan-Heme panel and other methods, including chromosome analysis, fluorescence in situ hybridization, RT-PCR, and Sanger sequencing, with an analytic sensitivity and specificity of 95% and 100%, respectively. In an independent cohort of 28 patients indicated for FusionPlex testing, gene fusions were detected in 21 patients. The FusionPlex Pan-Heme panel analysis reliably detected fusion partners and patient-specific fusion sequences, allowing accurate classification of hematologic neoplasms and the discovery of new fusion partners, contributing to a better understanding of the pathogenesis of the diseases.

Guide to the Diagnosis of Myeloid Neoplasms: A Bone Marrow Pathology Group Approach

OBJECTIVES

The practicing pathologist is challenged by the ever-increasing diagnostic complexity of myeloid neoplasms. This guide is intended to provide a general roadmap from initial case detection, often triggered by complete blood count results with subsequent blood smear review, to final diagnosis.

METHODS

The integration of hematologic, morphologic, immunophenotypic, and genetic features into routine practice is standard of care. The requirement for molecular genetic testing has increased along with the complexity of test types, the utility of different testing modalities in identifying key gene mutations, and the sensitivity and turnaround time for various assays.

RESULTS

Classification systems for myeloid neoplasms have evolved to achieve the goal of providing a pathology diagnosis that enhances patient care, outcome prediction, and treatment options for individual patients and is formulated, endorsed, and adopted by hematologists/oncologists.

CONCLUSIONS

This guide provides diagnostic strategies for all myeloid neoplasm subtypes. Special considerations are provided for each category of testing and neoplasm category, along with classification information, genetic testing requirements, interpretation information, and case reporting recommendations based on the experience of 11 Bone Marrow Pathology Group members.

Cytogenetics in the management of myeloproliferative neoplasms, mastocytosis and myelodysplastic/myeloproliferative neoplasms: Guidelines from the Group Francophone de Cytogénétique Hématologique (GFCH)

Myeloproliferative neoplasms, mastocytosis, myeloid/lymphoid neoplasms with hypereosinophilia and tyrosine kinase gene fusions, and myelodysplastic/myeloproliferative neoplasms are clonal hematopoietic cancers that, with the exception of certain entities, have an indolent course. In addition to their increasingly important role in the diagnosis of these entities, as shown by the recent classification of hematolymphoid tumors in the 5th edition of the World Health Organization and the International Consensus Classification of myeloid neoplasms and acute leukemias, identification of the profile of acquired genetic abnormalities is essential for adapting patient management and early detection of patients at high risk of progression. Alongside molecular abnormalities, cytogenetic abnormalities play an important role in the diagnosis, prognosis and follow-up of these diseases. Here, we review the recent literature on the impact of chromosomal abnormalities in these different entities and provide updated cytogenetic recommendations and guidelines for their management.

Sustained Response to Ruxolitinib of Eosinophilia-Associated Myeloproliferative Neoplasm with Translocation t(8;9)(p21;p24)

The translocation t(8;9) produces the fusion gene PCM1-JAK2, resulting in the continuous activation of the JAK2 tyrosine kinase. Myelodysplastic/myeloproliferative neoplasms are the most common disease with t(8;9)/PCM1-JAK2. Individuals with this abnormality have similar features, and JAK2 kinase inhibitor (ruxolitinib) is an effective treatment of the condition. The long-term remission results of ruxolitinib are varied. It is important to determine the response to ruxolitinib. Here, we describe a patient who has been diagnosed with eosinophilia-associated myeloproliferative neoplasm with t(8;9)(p21;p24). This patient has achieved sustained response for >1 year since the administration of ruxolitinib.

Clinicopathologic characteristics, genetic features, and treatment options for acute lymphoblastic leukemia with JAK2 rearrangement-A 10-case study and literature review

JAK2 rearrangement (JAK2-R) in acute lymphoblastic leukemia (ALL) is rare and often categorized as B-ALL with BCR::ABL1-like features based on the World Health Organization classification. We report 10 patients with JAK2-R ALL, 9 males and 1 female, with a median age 40.5 years. Eight patients presented with marked leukocytosis (median WBC, 63 × 10 ⁹/L) and hypercellular (>95%) bone marrow with increased lymphoblasts (72%-95%). There was no evidence of bone marrow fibrosis or hypereosinophilia. Immunophenotypic analysis showed 9 B-cell and 1 T-cell neoplasms. Using fluorescence in situ hybridization (FISH) and RNA sequencing analysis, JAK2 partners were identified for 7 cases and included PCM1 (n=4), ETV6 (n=2) and BCR (n=1). All patients received upfront polychemotherapy. Additionally, 2 patients received ruxolitinib, 2 received allogeneic stem cell transplant, and 1 received CAR-T therapy. The 1- and 3-year overall survival rates were 55.6% and 22.2%, respectively. A literature review identified 24 B-ALL and 4 T-ALL cases with JAK2-R reported, including 16 males, 6 females and 6 gender not stated. Many JAK2 partner-genes were reported with the most common being PAX5 (n=7), ETV6 (n=4), BCR (n=3) and PCM1 (n=2). Survival data or 13 reported cases showed 1- and 3-year overall survival rates of 41.7% and 41.7%, respectively. In summary, JAK2-R ALL occurs more often in adult males, are mostly of B-cell lineage, and associated with an aggressive clinical course. Absence of eosinophilia and bone marrow fibrosis and no evidence of preexisting/concurrent JAK2-R myeloid neoplasms distinguish JAK2-R ALL from other myeloid/lymphoid neoplasms with eosinophilia and JAK2-R.

The Combination of JAK2V617F Allele Burden and WT1 Expression can Be Helpful in Distinguishing the Subtype of MPN Patients

INTRODUCTION

Classical Philadelphia-negative myeloproliferative neoplasm (MPN) includes Essential Thrombocythemia (ET), Polycythemia Vera (PV) and Primary Myelofibrosis (PMF). The JAK2V617F mutation is part of the major criteria for diagnosis of MPN. WT1 is reported to be highly overexpressed in most hematological malignancy. Our aim was to explore the combination value of JAK2V617F allele burden and WT1 expression in distinguishing the subtype of MPN patients.

METHODS

Allele specific real-time quantitative fluorescence PCR (AS-qPCR) was conducted to detect JAK2V617F allele burden. WT1 expression was assessed by RQ-PCR. Our study is a retrospective study.

RESULTS

JAK2V617F allele burden and WT1 expression were different in MPN subgroups. The expression of WT1 in PMF and PV is higher than in ET. JAK2V617F allele burden in PMF and PV is also higher than in ET. ROC analysis indicated that combination of JAK2V617F allele burden and WT1 expression to discriminate ET and PV, ET and PMF, PV and PMF is 0.956, 0.871, 0.737 respectively. Furthermore, their ability to distinguish ET patients with high Hb levels from PV patients with high platelet counts is 0.891.

CONCLUSIONS

Our data revealed that combination of JAK2V617F allele burden and WT1 expression is useful in distinguishing the subtype of MPN patients.

Updates on eosinophilic disorders

This review addresses changes and updates in eosinophilic disorders under the International Consensus Classification (ICC). The previous category of myeloid/lymphoid neoplasm with eosinophilia (M/LN-eo) and a specific gene rearrangement is changed to M/LN-eo with tyrosine kinase gene fusions to reflect the underlying genetic lesions. Two new members, M/LN-eo with ETV6::ABL1 fusion and M/LN-eo with various FLT3 fusions, have been added to the category; and M/LN-eo with PCM1::JAK2 and its genetic variants ETV6::JAK2 and BCR::JAK2 are recognized as a formal entity from their former provisional status. The updated understanding of the clinical and molecular genetic features of PDGFRA, PDGFRB and FGFR1 neoplasms is summarized. Clear guidance as to how to distinguish these fusion gene-associated disorders from the overlapping entities of Ph-like B-acute lymphoblastic leukemia (ALL), de novo T-ALL, and systemic mastocytosis is provided. Bone marrow morphology now constitutes one of the diagnostic criteria of chronic eosinophilic leukemia, NOS (CEL, NOS), and idiopathic hypereosinophilia/hypereosinophilic syndrome (HE/HES), facilitating the separation of a true myeloid neoplasm with characteristic eosinophilic proliferation from those of unknown etiology and not attributable to a myeloid neoplasm.

International Consensus Classification of Myeloid Neoplasms and Acute Leukemias: integrating morphologic, clinical, and genomic data

The classification of myeloid neoplasms and acute leukemias was last updated in 2016 within a collaboration between the World Health Organization (WHO), the Society for Hematopathology, and the European Association for Haematopathology. This collaboration was primarily based on input from a clinical advisory committees (CACs) composed of pathologists, hematologists, oncologists, geneticists, and bioinformaticians from around the world. The recent advances in our understanding of the biology of hematologic malignancies, the experience with the use of the 2016 WHO classification in clinical practice, and the results of clinical trials have indicated the need for further revising and updating the classification. As a continuation of this CAC-based process, the authors, a group with expertise in the clinical, pathologic, and genetic aspects of these disorders, developed the International Consensus Classification (ICC) of myeloid neoplasms and acute leukemias. Using a multiparameter approach, the main objective of the consensus process was the definition of real disease entities, including the introduction of new entities and refined criteria for existing diagnostic categories, based on accumulated data. The ICC is aimed at facilitating diagnosis and prognostication of these neoplasms, improving treatment of affected patients, and allowing the design of innovative clinical trials.

JAK2 Alterations in Acute Lymphoblastic Leukemia: Molecular Insights for Superior Precision Medicine Strategies

Acute lymphoblastic leukemia (ALL) is the most common pediatric cancer, arising from immature lymphocytes that show uncontrolled proliferation and arrested differentiation. Genomic alterations affecting Janus kinase 2 (JAK2) correlate with some of the poorest outcomes within the Philadelphia-like subtype of ALL. Given the success of kinase inhibitors in the treatment of chronic myeloid leukemia, the discovery of activating JAK2 point mutations and JAK2 fusion genes in ALL, was a breakthrough for potential targeted therapies. However, the molecular mechanisms by which these alterations activate JAK2 and promote downstream signaling is poorly understood. Furthermore, as clinical data regarding the limitations of approved JAK inhibitors in myeloproliferative disorders matures, there is a growing awareness of the need for alternative precision medicine approaches for specific JAK2 lesions. This review focuses on the molecular mechanisms behind ALL-associated JAK2 mutations and JAK2 fusion genes, known and potential causes of JAK-inhibitor resistance, and how JAK2 alterations could be targeted using alternative and novel rationally designed therapies to guide precision medicine approaches for these high-risk subtypes of ALL.

The 5th edition of the World Health Organization Classification of Haematolymphoid Tumours: Myeloid and Histiocytic/Dendritic Neoplasms

The upcoming 5th edition of the World Health Organization (WHO) Classification of Haematolymphoid Tumours is part of an effort to hierarchically catalogue human cancers arising in various organ systems within a single relational database. This paper summarizes the new WHO classification scheme for myeloid and histiocytic/dendritic neoplasms and provides an overview of the principles and rationale underpinning changes from the prior edition. The definition and diagnosis of disease types continues to be based on multiple clinicopathologic parameters, but with refinement of diagnostic criteria and emphasis on therapeutically and/or prognostically actionable biomarkers. While a genetic basis for defining diseases is sought where possible, the classification strives to keep practical worldwide applicability in perspective. The result is an enhanced, contemporary, evidence-based classification of myeloid and histiocytic/dendritic neoplasms, rooted in molecular biology and an organizational structure that permits future scalability as new discoveries continue to inexorably inform future editions.

OUP accepted manuscript

Background

This review summarizes the case studies of PCM1-JAK2 fusion tyrosine kinase gene-related neoplasia. Recommended treatment includes JAK2 inhibitors and hematologic stem cell transplantation (HSCT), although the small number of patients has limited study of their efficacy. Herein, we present all available cases in the current searchable literature with their demographics, diagnoses, treatments, and outcomes.

Methods

PubMed, ScienceDirect, Publons, the Cochrane Library, and Google were searched with the following terms: PCM1-JAK2, ruxolitinib and myeloid/lymphoid.

Results

Sixty-six patients (mean age = 50, 77% male) had an initial diagnosis of myeloproliferative neoplasm (MPN) in 40, acute leukemia in 21 and T-cell cutaneous lymphoma in 5. Thirty-five patients (53%) had completed 5-year follow-up. The 5-year survival for the MPN, acute myelogenous leukemia (AML), acute lymphocytic leukemia, and lymphoma groups are 62.7, 14.9%, 40.0%, and 100%, respectively. Too few patients have been treated with ruxolitinib to draw conclusions regarding its effect on survival while the 5-year survival for MPN patients with or without HSCT was 80.2% (40.3%-94.8%) versus 51.5% (22.3%-74.6%), respectively. The T-cell cutaneous lymphoma patients have all survived at least 7 years.

Conclusion

This rare condition may be increasingly detected with wider use of genomics. Ruxolitinib can yield hematologic and molecular remissions. However, HSCT is, at this time, the only potentially curative treatment. Useful prognostic markers are needed to determine appropriate timing for HSCT in patients with MPN. Patients presenting with acute leukemia have a poor prognosis.

Case Report: Whole genome sequencing identifies CCDC88C as a novel JAK2 fusion partner in pediatric T-cell acute lymphoblastic leukemia

In the present report, we applied whole genome sequencing (WGS) to genetically characterize a case of pediatric T-cell acute lymphoblastic leukemia (ALL) refractory to standard therapy. WGS identified a novel JAK2 fusion, with CCDC88C as a partner. CCDC88C encodes a protein part of the Wnt signaling pathway and has previously been described in hematological malignancies as fusion partner to FLT3 and PDGFRB. The novel CCDC88C::JAK2 fusion gene results in a fusion transcript, predicted to produce a hybrid protein, which retains the kinase domain of JAK2 and is expected to respond to JAK2 inhibitors. This report illustrates the potential of WGS in the diagnostic setting of ALL.

Diagnosis and Treatment of Myeloproliferative Neoplasms With PCM1-JAK2 Rearrangement: Case Report and Literature Review

Myeloproliferative neoplasm (MPN) with PCM1-JAK2 rearrangement is a rare disease with poor prognosis and lacks uniform treatment guidelines. Several studies confirmed the efficacy of ruxolitinib in hematological malignancies with PCM1-JAK2 fusion, but the efficacy is variable. Here, we report two patients diagnosed with MPN with PCM1-JAK2 fusion who were treated with ruxolitinib-based regimen, including the first case of ruxolitinib combined with pegylated interferon (Peg-IFN), and we conduct a literature review. We found that ruxolitinib combined with Peg-IFN is an effective treatment option in the case of poor efficacy of ruxolitinib monotherapy.

Lymphoid blast transformation in an MPN with BCR-JAK2 treated with ruxolitinib: putative mechanisms of resistance

The basis for acquired resistance to JAK inhibition in patients with JAK2-driven hematologic malignancies is not well understood. We report a patient with a myeloproliferative neoplasm (MPN) with a BCR activator of RhoGEF and GTPase (BCR)-JAK2 fusion with initial hematologic response to ruxolitinib who rapidly developed B-lymphoid blast transformation. We analyzed pre-ruxolitinib and blast transformation samples using genome sequencing, DNA mate-pair sequencing (MPseq), RNA sequencing (RNA-seq), and chromosomal microarray to characterize possible mechanisms of resistance. No resistance mutations in the BCR-JAK2 fusion gene or transcript were identified, and fusion transcript expression levels remained stable. However, at the time of blast transformation, MPseq detected a new IKZF1 copy-number loss, which is predicted to result in loss of normal IKZF1 protein translation. RNA-seq revealed significant upregulation of genes negatively regulated by IKZF1, including IL7R and CRLF2. Disease progression was also characterized by adaptation to an activated B-cell receptor (BCR)-like signaling phenotype, with marked upregulation of genes such as CD79A, CD79B, IGLL1, VPREB1, BLNK, ZAP70, RAG1, and RAG2. In summary, IKZF1 deletion and a switch from cytokine dependence to activated BCR-like signaling phenotype represent putative mechanisms of ruxolitinib resistance in this case, recapitulating preclinical data on resistance to JAK inhibition in CRLF2-rearranged Philadelphia chromosome-like acute lymphoblastic leukemia.

Myeloid/lymphoid neoplasms with FLT3 rearrangement

Myeloid/lymphoid neoplasms (M/LN) with 13q12/FLT3 rearrangement have been suggested as candidates for possible inclusion in the World Health Organization classification group of M/LN with eosinophilia (M/LN-eo). We report 12 patients with confirmed FLT3 rearrangement, six with t(12;13)/ETV6-FLT3; one with ins(13;22)/BCR-FLT3; and five with an unconfirmed partner gene located on chromosome bands 2p16, 3q27, 5q15, 5q35, and 7q36. Disease presentations were heterogeneous, including lymphoblastic leukemia/lymphoma, myeloid sarcoma, chronic eosinophilic leukemia, chronic myelomonocytic leukemia, and myelodysplastic syndrome. However, some common features were observed, such as extramedullary involvement (n = 7, 58%), associated eosinophilia in blood, bone marrow, or tissue (n = 8, 67%), multilineage involvement, either as biphasic myeloid/lymphoid neoplasms (n = 2) or mixed phenotype acute leukemia (n = 2). Mutations were detected in 4/8 (50%) patients by next-generation sequencing. None (0/10) had FLT3 or KIT mutations. Eleven patients received disease-based chemotherapy or hypomethylating agents, three received FLT3 inhibitors, and five patients proceeded to hematopoietic stem cell transplant. Together with a review of 16 cases published in the literature, it is apparent that M/LNs with FLT3 rearrangement show disease features reminiscent of members in the category of M/LN-eo with PDGFRA, PDGFRB, FGFR1, and PCM1/JAK2 rearrangement, characterized by a specific gene rearrangement, frequent eosinophilia, multi-lineage involvement and therapeutic benefit from kinase inhibitors.

T-Cell Lymphoblastic Lymphoma Arising in the Setting of Myeloid/Lymphoid Neoplasms with Eosinophilia: LMO2 Immunohistochemistry as a Potentially Useful Diagnostic Marker

Simple Summary

Rarely, T-lymphoblastic lymphoma (T-LBL) may develop in the setting of myeloid/lymphoid neoplasms with eosinophilia. Given important therapeutic implications, it is crucial to identify T-LBL arising in this particular context. LIM domain only 2 (LMO2) is known to be overexpressed in almost all sporadic T-LBL and not in immature TdT-positive T-cells in the thymus and in indolent T-lymphoblastic proliferations. We retrospectively evaluated the clinical, morphological, immunohistochemical and molecular features of 11 cases of T-LBL occurring in the setting of myeloid/lymphoid neoplasms with eosinophilia and investigated the immunohistochemical expression of LMO2 in this setting of T-LBL. Interestingly, 9/11 cases were LMO2 negative, with only 2 cases showing partial expression. In our study, we would suggest that LMO2 immunostaining, as part of the diagnostic panel for T-LBL, may represent a useful marker to identify T-LBL developing in the context of myeloid/lymphoid neoplasms with eosinophilia.

Abstract

Background: Rarely, T-lymphoblastic lymphoma (T-LBL) may develop in the setting of myeloid/lymphoid neoplasms with eosinophilia (M/LNs-Eo), a group of diseases with gene fusion resulting in overexpression of an aberrant tyrosine kinase or cytokine receptor. The correct identification of this category has relevant therapeutic implications. LIM domain only 2 (LMO2) is overexpressed in most T-LBL, but not in immature TdT-positive T-cells in the thymus and in indolent T-lymphoblastic proliferations (iT-LBP). Methods and Results: We retrospectively evaluated 11 cases of T-LBL occurring in the context of M/LNs-Eo. Clinical, histological, immunohistochemical and molecular features were collected and LMO2 immunohistochemical staining was performed. The critical re-evaluation of these cases confirmed the diagnosis of T-LBL with morphological, immunohistochemical and molecular features consistent with T-LBL occurring in M/LNs-Eo. Interestingly, LMO2 immunohistochemical analysis was negative in 9/11 cases, whereas only 2 cases revealed a partial LMO2 expression with a moderate and low degree of intensity, respectively. Conclusions: LMO2 may represent a potentially useful marker to identify T-LBL developing in the context of M/LNs-Eo. In this setting, T-LBL shows LMO2 immunohistochemical profile overlapping with cortical thymocytes and iT-LBP, possibly reflecting different molecular patterns involved in the pathogenesis of T-LBL arising in the setting of M/LNs-Eo.

JAK2 Rearrangements Are a Recurrent Alteration in CD30+ Systemic T-Cell Lymphomas With Anaplastic Morphology

Peripheral T-cell lymphoma (PTCL) comprises a heterogenous group of rare mature T-cell neoplasms. While some PTCL subtypes are well-characterized by histology, immunophenotype, and recurrent molecular alterations, others remain incompletely defined. In particular, the distinction between CD30+ PTCL, not otherwise specified and anaplastic lymphoma kinase (ALK)-negative anaplastic large cell lymphoma can be subject to disagreement. We describe a series of 6 JAK2 rearrangements occurring in a cohort of 97 CD30+ ALK- PTCL (6%), assembled after identifying an index case of a novel PABPC1-JAK2 fusion in a case of ALK- anaplastic large cell lymphoma with unusual classic Hodgkin lymphoma (CHL)-like features. Fusions were identified using a comprehensive next-generation sequencing based assay performed between 2013 and 2020. Five of 6 cases (83%) showed JAK2 rearrangements with 4 novel partners: TFG, PABPC1, ILF3, and MAP7, and 1 case demonstrated a previously described PCM1-JAK2 fusion. By morphology, all cases showed anaplastic large cells and multinucleated Reed-Sternberg-like cells within a polymorphous inflammatory background with frequent eosinophilia reminiscent of CHL. By immunohistochemistry, atypical large cells expressed CD30 with coexpression of at least 1 T-cell marker, aberrant loss of at least 1 T-cell marker and, in 4 of 5 cases stained (80%), unusual CD15 coexpression. These findings suggest that a subset of CD30+ ALK- systemic PTCL with anaplastic morphology carry JAK2 rearrangements, some of which appear to show CHL-like morphologic features. The presence of JAK2 rearrangements in cases of CD30+ PTCL augments current classification and may provide a therapeutic target via JAK2 inhibition.

Myeloid/Lymphoid Neoplasms Associated With Eosinophilia and Rearrangements of PDGFRA, PDGFRB, or FGFR1 or With PCM1-JAK2

OBJECTIVES

To summarize cases submitted to the 2019 Society for Hematopathology/European Association for Haematopathology Workshop under the category of myeloid/lymphoid neoplasms with eosinophilia and PDGFRA, PDGFRB, or FGFR1 or with PCM1-JAK2 rearrangements, focusing on recent updates and relevant practice findings.

METHODS

The cases were summarized according to their respective gene rearrangement to illustrate the spectrum of clinical, laboratory, and histopathology manifestations and to explore the appropriate molecular genetic tests.

RESULTS

Disease presentations were heterogeneous, including myeloproliferative neoplasms (MPNs), myelodysplastic syndromes (MDSs), MDS/MPN, acute myeloid leukemia, acute B- or T-lymphoblastic lymphoma/acute lymphoblastic lymphoma (ALL/LBL), or mixed-lineage neoplasms. Frequent extramedullary involvement occurred. Eosinophilia was common but not invariably present. With the advancement of RNA sequencing, cryptic rearrangements were recognized in genes other than PDGFRA. Additional somatic mutations were more frequent in the FGFR1-rearranged cases. Cases with B-ALL presentations differed from Philadelphia-like B-ALL by the presence of an underlying MPN. Cases with FLT3 and ABL1 rearrangements could be potential candidates for future inclusion in this category.

CONCLUSIONS

Accurate diagnosis and classification of this category of myeloid/lymphoid neoplasms has important therapeutic implications. With the large number of submitted cases, we expand our understanding of these rare neoplasms and improve our ability to diagnose these genetically defined disorders.

Molecular Pathogenesis and Treatment Perspectives for Hypereosinophilia and Hypereosinophilic Syndromes

Hypereosinophilia (HE) is a heterogeneous condition with a persistent elevated eosinophil count of >350/mm³, which is reported in various (inflammatory, allergic, infectious, or neoplastic) diseases with distinct pathophysiological pathways. HE may be associated with tissue or organ damage and, in this case, the disorder is classified as hypereosinophilic syndrome (HES). Different studies have allowed for the discovery of two major pathogenetic variants known as myeloid or lymphocytic HES. With the advent of molecular genetic analyses, such as T-cell receptor gene rearrangement assays and Next Generation Sequencing, it is possible to better characterize these syndromes and establish which patients will benefit from pharmacological targeted therapy. In this review, we highlight the molecular alterations that are involved in the pathogenesis of eosinophil disorders and revise possible therapeutic approaches, either implemented in clinical practice or currently under investigation in clinical trials.

Integrated genomic analysis using chromosomal microarray, fluorescence in situ hybridization and mate pair analyses: Characterization of a cryptic t(9;22)(p24.1;q11.2)/BCR-JAK2 in myeloid/lymphoid neoplasm with eosinophilia

The 2016 World Health Organization entity 'Myeloid/lymphoid neoplasms with eosinophilia and rearrangement of PDGFRA, PDGFRB or FGFR1, or with PCM1-JAK2' encompasses a group of rare neoplasms that result from the formation of a fusion gene that leads to expression of an aberrant tyrosine kinase. This entity also contains variant JAK2 fusion partners, and detection of this defining event can be facilitated by various cytogenetic and molecular methods. Cryptic rearrangements of 9p24/JAK2 can be particularly challenging to identify. We describe the use of chromosomal microarray analysis (CMA), fluorescence in situ hybridization (FISH) with a probe for JAK2, and genomic mate pair analysis to describe a complex karyotype with a t(9;22) that produced a functional BCR-JAK2 fusion, leading to the appropriate diagnosis for the patient. This case highlights the importance of using an integrated genomic approach to fully define complex aberrations to assign proper diagnoses.

Contemporary Classification and Diagnostic Evaluation of Hypereosinophilia

OBJECTIVES

To provide an in-depth review of the classification and diagnostic evaluation of hypereosinophilia (HE), with a focus on eosinophilic neoplasms.

METHODS

A review of published literature was performed, and exemplary HE cases were identified.

RESULTS

Causes of HE are diverse and can be grouped under three categories: primary (neoplastic), secondary (reactive), and idiopathic. Advances in cytogenetics and molecular diagnostics have led to elucidation of the genetic basis for many neoplastic hypereosinophilic disorders. One common molecular feature is formation of a fusion gene, resulting in the expression of an aberrantly activated tyrosine kinase (TK). The World Health Organization endorsed a biologically oriented classification scheme and created a new major disease category, namely, "myeloid/lymphoid neoplasms with eosinophilia and rearrangement of PDGFRA, PDGFRB or FGFR1, or with PCM1-JAK2." Rearrangement of other TK genes and activating somatic mutation(s) in TK genes have also been reported in eosinophilic neoplasms. Diagnostic evaluation of HE involves a combination of clinical, histopathologic, and immunophenotypic analyses, as well as molecular genetic testing, including next-generation sequencing-based mutation panels. The management of primary HE is largely guided by the underlying molecular genetic abnormalities.

CONCLUSIONS

A good knowledge of recent advances in HE is necessary to ensure prompt and accurate diagnosis, as well as to help optimize patient care.

Chronic myeloid leukemia presenting in lymphoblastic crisis, a differential diagnosis with Philadelphia-positive B-lymphoblastic leukemia

Rare patients with chronic myeloid leukemia (CML) can present initially in lymphoblastic crisis (LBC) mimicking Ph + B-lymphoblastic leukemia (B-ALL). We retrospectively reviewed 275 adults who diagnosed initially as Ph + B-ALL and identified 28 patients with at least one of three features supporting the diagnosis of CML-LBC: 1) a large discrepancy between the blast count and Ph + clone; 2) Ph + clone persistent when B-ALL in remission; 3) BCR/ABL1 fusion detected in segmented cells. BCR-ABL1 fusions were p210 in 25 patients and p190 in 3 patients. In comparison to patients with Ph + B-ALL, patients with CML-LBC were older; had higher leukocyte and absolute neutrophil counts; higher immature myeloid cells in peripheral blood; lower blast counts; and inferior outcomes. In addition, we prospectively analyzed 26 patients with Ph + B-lymphoblastic leukemia and identified 8 patients with features more consistent with CML-LBC. These findings highlight the importance of distinguishing CML-LBC from de novo Ph + B-ALL.

Targeted FGFR inhibition results in a durable remission in an FGFR1-driven myeloid neoplasm with eosinophilia

A novel PCM1 -FGFR1 gene rearrangement was identified in a patient with a myeloid neoplasm with eosinophilia. Futibatinib, an oral selective small molecule inhibitor of FGFR1-4, resulted in a durable complete hematologic and cytogenetic remission.

Response to tyrosine kinase inhibitors in myeloid neoplasms associated with PCM1-JAK2, BCR-JAK2 and ETV6-ABL1 fusion genes

We report on 18 patients with myeloid neoplasms and associated tyrosine kinase (TK) fusion genes on treatment with the TK inhibitors (TKI) ruxolitinib (PCM1-JAK2, n = 8; BCR-JAK2, n = 1) and imatinib, nilotinib or dasatinib (ETV6-ABL1, n = 9). On ruxolitinib (median 24 months, range 2-36 months), a complete hematologic response (CHR) and complete cytogenetic response (CCR) was achieved by five of nine and two of nine patients, respectively. However, ruxolitinib was stopped in eight of nine patients because of primary resistance (n = 3), progression (n = 3) or planned allogeneic stem cell transplantation (allo SCT, n = 2). At a median of 36 months (range 4-78 months) from diagnosis, five of nine patients are alive: four of six patients after allo SCT and one patient who remains on ruxolitinib. In ETV6-ABL1 positive patients, a durable CHR was achieved by four of nine patients (imatinib with one of five, nilotinib with two of three, dasatinib with one of one). Because of inadequate efficacy (lack of hematological and/or cytogenetic/molecular response), six of nine patients (imatinib, n = 5; nilotinib, n = 1) were switched to nilotinib or dasatinib. At a median of 23 months (range 3-60 months) from diagnosis, five of nine patients are in CCR or complete molecular response (nilotinib, n = 2; dasatinib, n = 2; allo SCT, n = 1) while two of nine patients have died. We conclude that (a) responses on ruxolitinib may only be transient in the majority of JAK2 fusion gene positive patients with allo SCT being an important early treatment option, and (b) nilotinib or dasatinib may be more effective than imatinib to induce durable complete remissions in ETV6-ABL1 positive patients.

iAMP21 in acute myeloid leukemia is associated with complex karyotype, TP53 mutation and dismal outcome

Acute myeloid leukemia (AML) with intrachromosomal amplification of chromosome 21 (iAMP21) is rare and has not been well characterized. We report 13 patients, 7 men and 6 women, with a median age of 65 years. Eleven patients presented with AML with myelodysplasia-related changes, and two patients had therapy-related AML. Cytopenias were detected in all patients (11 pancytopenia and two bi-lineage cytopenia). Myelodysplastic changes were observed in all 11 patients with adequate cells to evaluate. Myelofibrosis was present in ten patients. All patients had a complex karyotype, including abnormalities of chromosomes 5, 7, 17, and hsr(21)(q22), and ten patients showed TP53 deletion and/or mutation. Eleven patients received AML-based chemotherapy, one of whom also received hematopoietic stem cell transplant. By the end of the last follow-up, eight patients died with median survival of 3.2 months, four patients were alive with persistent AML, and one was in complete remission. The median overall survival was 6 months for all patients. We conclude that AML with iAMP21 is often associated with cytopenias, myelodysplasia, a complex karyotype, TP53 mutation/deletion, and a poor prognosis despite current therapies.

New translocation in acute myeloid leukemia M4 eos

The most common childhood malignancy is acute leukemia. Approximately 15- 20% of it, is Acute myeloid leukemia (AML). The general symptoms of this malignancy include fatigue, weakness, fever, paleness and bleeding disorders. There are two methods of classifying for AML: The French-American-British (FAB) and the World Health Organization (WHO) classification.The M4 eos subtype, also called myelomonocytic leukemia, is one subtype of AML with eosinophilia. The most common cytogenetic variations in this leukemia include inv (16) (p13q22) or the variant t (16; 16) (p13; q22). In this report, we present the first AML-M4 eos case with a new translocation that has not yet been reported.

The diagnostic challenges and clinical course of a myeloid/lymphoid neoplasm with eosinophilia and ZBTB20-JAK2 gene fusion presenting as B-lymphoblastic leukemia

We report the diagnostic challenges and the clinical course of a patient with an extraordinary presentation of B-lymphoblastic leukemia (B-ALL) with eosinophilia. We identified a novel ZBTB20-JAK2 gene fusion as a chimeric RNA transcript using the Archer platform. This gene fusion from the same patient was recently identified by Peterson et al. (2019) at the genomic level using a different sequencing technology platform. The configuration of this gene fusion predicts the production of a kinase-activating JAK2 fusion protein, which would normally lead to a diagnosis of Philadelphia chromosome–like B-ALL (Ph-like B-ALL). However, the unusual presentation of eosinophilia led us to demonstrate the presence of this gene fusion in nonlymphoid hematopoietic cells by fluorescence in situ hybridization (FISH) studies with morphologic correlation. Therefore, we believe this disease, in fact, represents blast crisis arising from an underlying myeloid neoplasm with JAK2 rearrangements. This case illustrates the difficulty in differentiating Ph-like B-ALL and myeloid/lymphoid neoplasm with eosinophilia and gene rearrangements (MLN-EGR) in blast crisis. As currently defined, the diagnosis of MLN-EGR relies on the hematologic presentations and the identification of marker gene fusions (including PCM1-JAK2, ETV6-JAK2, and BCR-JAK2). However, these same gene fusions, when limited to B-lymphoblasts, also define Ph-like B-ALL. Yet, our case does not conform to either condition. Therefore, the assessment for lineage restriction of gene rearrangements to reflect the pathophysiologic difference between B-ALL and MLN-EGR in blast crisis is likely a more robust diagnostic approach and allows the inclusion of MLN-EGR with novel gene fusions.

Identification of RNPC3 as a novel JAK2 fusion partner gene in B-acute lymphoblastic leukemia refractory to combination therapy including ruxolitinib

BACKGROUND

Hematopoietic neoplasms with chromosomal translocations involving JAK2 are rare, and most of them show myeloproliferative neoplasm-associated features, followed by B-acute lymphoblastic leukemia (B-ALL). De novo B-ALL cases with JAK2 rearrangements are suggested to be appropriately considered as BCR-ABL1-like B-ALL, but its partners varied.

METHODS

Fluorescence in situ hybridization (FISH), RNA sequencing (RNA-Seq), whole-genome sequencing, and reverse transcription polymerase chain reaction (RT-PCR) were performed to identify the pathogenic fusion gene in a 29-year-old woman with relapsed B-ALL and rare t(1;9)(p13;p22) translocation.

RESULTS

We identified RNPC3 as a new JAK2 fusion partner in the patient. She was treated with a combination of chemotherapy and targeted drug ruxolitinib and chimeric antigen receptor T-cell therapy, but failed to achieve complete remission. She had no chance to undergo allogeneic hematopoietic stem cell transplantation and died of disease progression 7 months after the initial diagnosis. Her clinical course demonstrated that this novel RNPC3-JAK2 fusion might portend an unfavorable prognosis.

CONCLUSION

This finding adds to the expanding compendium of JAK2 fusions found in B-ALL and suggests the potential need for a diagnostic FISH analysis as well as RNA-Seq in the appropriate clinical setting.

Genetic and phenotypic characterization of indolent T-cell lymphoproliferative disorders of the gastrointestinal tract

Indolent T-cell lymphoproliferative disorders of the gastrointestinal tract are rare clonal T-cell diseases that more commonly occur in the intestines and have a protracted clinical course. Different immunophenotypic subsets have been described, but the molecular pathogenesis and cell of origin of these lymphocytic proliferations is poorly understood. Hence, we performed targeted next-generation sequencing and comprehensive immunophenotypic analysis of ten indolent T-cell lymphoproliferative disorders of the gastrointestinal tract, which comprised CD4⁺ (n=4), CD8⁺ (n=4), CD4⁺/CD8⁺ (n=1) and CD4^-/CD8^- (n=1) cases. Genetic alterations, including recurrent mutations and novel rearrangements, were identified in 8/10 (80%) of these lymphoproliferative disorders. The CD4⁺, CD4⁺/CD8⁺, and CD4^-/CD8^- cases harbored frequent alterations of JAK-STAT pathway genes (5/6, 82%); STAT3 mutations (n=3), SOCS1 deletion (n=1) and STAT3-JAK2 rearrangement (n=1), and 4/6 (67%) had concomitant mutations in epigenetic modifier genes (TET2, DNMT3A, KMT2D). Conversely, 2/4 (50%) of the CD8⁺ cases exhibited structural alterations involving the 3' untranslated region of the IL2 gene. Longitudinal genetic analysis revealed stable mutational profiles in 4/5 (80%) cases and acquisition of mutations in one case was a harbinger of disease transformation. The CD4⁺ and CD4⁺/CD8⁺ lymphoproliferative disorders displayed heterogeneous Th1 (T-bet⁺), Th2 (GATA3⁺) or hybrid Th1/Th2 (T-bet⁺/GATA3⁺) profiles, while the majority of CD8⁺ disorders and the CD4^-/CD8^- disease showed a type-2 polarized (GATA3⁺) effector T-cell (Tc2) phenotype. Additionally, CD103 expression was noted in 2/4 CD8⁺ cases. Our findings provide insights into the pathogenetic bases of indolent T-cell lymphoproliferative disorders of the gastrointestinal tract and confirm the heterogeneous nature of these diseases. Detection of shared and distinct genetic alterations of the JAK-STAT pathway in certain immunophenotypic subsets warrants further mechanistic studies to determine whether therapeutic targeting of this signaling cascade is efficacious for a proportion of patients with these recalcitrant diseases.

Is hyperdiploidy a favorable cytogenetics in adults with B-lymphoblastic leukemia?

Hyperdiploidy (chromosomal number 51-65) is a common cytogenetic abnormality in pediatric patients with B-lymphoblastic leukemia (B-ALL) and belongs to the favorable cytogenetic subgroup. Hyperdiploidy in adult B-ALL is much less common and its clinical significance has not been well studied. Among the 1205 patients with B-ALL (1018 adults and 187 children) from our institution, 78 had a hyperdiploid karyotype, including 45 (4.4%) adults and 33 (17.6%) children (P < 0.0001). Among the patients with hyperdiploid B-ALL, the adult group had a significantly inferior survival (similar to the patients with a normal karyotype) compared with the pediatric group (median survival: 42 months vs undefined, P = 0.0029). Hyperdiploidy in adults B-ALL tended to more frequently harbor structural abnormalities (two or more) than children (53% vs 33%). Two or more structural abnormalities in a hyperdiploidy correlated with an adverse survival in adult patients (33 months vs undefined, P = 0.0008), similar to the survival of patients with a complex karyotype. We conclude that hyperdiploidy in adults with B-ALL is less favorable and more commonly contains structural abnormalities comparing to pediatric patients. We suggest that hyperdiploidy with two or more structural abnormalities are best considered as a complex karyotype in adults with B-ALL.