A Novel IL3-ETV6 Fusion in Chronic Eosinophilic Leukemia Not Otherwise Specified With t(5; 12) (q31; p13): A Case Report and Literature Review

How I diagnose and treat myeloid/lymphoid neoplasms with tyrosine kinase gene fusions

ABSTRACT

The fifth edition of the World Health Organization (WHO) classification and the International Consensus Classification (ICC) both include a category "myeloid/lymphoid neoplasms (MLN) with eosinophilia (eo) and tyrosine kinase (TK) gene fusions" (WHO, MLN-TK; ICC, M/LN-eo-TK). This rare group comprises phenotypically and prognostically heterogeneous disorders, which present a significant diagnostic challenge. The rapid and reliable identification of patients with MLN-TK may be delayed due to genetic complexity and significant phenotypic differences, including the chronic phase and primary/secondary blast phase (BP) of myeloid, lymphoid, or mixed phenotype in the bone marrow (BP-BM) and/or at extramedullary sites (extramedullary disease [EMD]). As a result, the entire armamentarium of conventional molecular genetic and cytogenetic techniques complemented by modern sequencing technologies, such as RNA sequencing or whole-genome sequencing, are often required to identify an underlying TK fusion. TK inhibitors (TKIs) with variable efficacy are available for all fusion genes, but a long-term favorable clinical course under TKI monotherapy is currently only observed in MLN-PDGFRA/PDGFRB fusion genes on imatinib. Because primary/secondary BP-BM/EMD occurs more frequently in MLN-FGFR1/JAK2/FLT3/ETV6::ABL1, a sequential combination of selective TKIs with or without prior intensive chemotherapy, rarely local radiotherapy, and/or subsequent allogeneic hematopoietic cell transplantation should be considered.

Novel ETV6::RAPGEF6 fusion gene in chronic eosinophilic leukemia: compiling evidence on the role of IL3 overexpression in tumorigenesis

Chronic eosinophilic leukemia (CEL) is a rare myeloproliferative neoplasm. Diagnosis of CEL is often challenging, notably because of the lack of recurrent and specific molecular event. We report here a case of CEL occurring in a 49-year-old man who presented a persistent hypereosinophilia (HE) associated with anemia and thrombopenia. Karyotyping showed a translocation t(5;12)(q31;p13). Targeted RNA Sequencing identified a novel ETV6::RAPGEF6 fusion gene, confirmed by RT-PCR. Despite several lines of treatment, the patient died after 16 months of duration with transformation to acute myeloid leukemia (AML).Contrary to myeloid/lymphoid neoplasms with eosinophilia and tyrosine kinase gene fusions (MLN-TK), where fusion genes are both class defining and involve tyrosine kinase genes as the 3' partner, fusion genes are exceedingly rare in non-MLN-TK myeloid malignancies with HE. The most reported fusion gene is ETV6::ACSL6, in rare cases. Previously, overexpression of IL3 (interleukin 3) has been described in myeloid neoplasms with ETV6::ACSL6 (previously named ACS2). In our case of CEL with the ETV6::RAPGEF6 fusion, we also demonstrated overexpression of IL3, which could potentially result from the proximity of the IL3 gene to RAPGEF6, similar to what is observed with ACSL6 and IL3. The use of RNA sequencing in routine diagnosis of CEL could provide evidence for clonal event such as gene fusion, improving diagnosis as well as prognosis and therapeutic approaches.

A case of adult ETV6-ASCL6 fusion gene positive chronic myeloproliferative tumor and literature review

ETV6-ASCL6 fusion gene plays an important role in hematopoiesis and hematological malignancies, but it is rare in hematological diseases. This paper describes a case of etv6-ascl6 fusion gene positive patient who was successively diagnosed as myelofibrosis, eosinophilic leukemia, basophilic leukemia and secondary acute myeloid leukemia. The clinical manifestations and disease evolution have its unique characteristics.

World Health Organization and International Consensus Classification of eosinophilic disorders: 2024 update on diagnosis, risk stratification, and management

DISEASE OVERVIEW

The eosinophilias encompass a broad range of non-hematologic (secondary or reactive) and hematologic (primary or clonal) disorders with the potential for end-organ damage.

DIAGNOSIS

Hypereosinophilia (HE) has generally been defined as a peripheral blood eosinophil count greater than 1.5 × 109/L, and may be associated with tissue damage. After the exclusion of secondary causes of eosinophilia, diagnostic evaluation of primary eosinophilias relies on a combination of various tests. They include morphologic review of the blood and marrow, standard cytogenetics, fluorescence in situ hybridization, molecular testing and flow immunophenotyping to detect histopathologic or clonal evidence for an acute or chronic hematolymphoid neoplasm.

RISK STRATIFICATION

Disease prognosis relies on identifying the subtype of eosinophilia. After evaluation of secondary causes of eosinophilia, the 2022 World Health Organization and International Consensus Classification endorse a semi-molecular classification scheme of disease subtypes. This includes the major category "myeloid/lymphoid neoplasms with eosinophilia and tyrosine kinase gene fusions" (MLN-eo-TK), and the MPN subtype, "chronic eosinophilic leukemia" (CEL). Lymphocyte-variant HE is an aberrant T-cell clone-driven reactive eosinophila, and idiopathic hypereosinophilic syndrome (HES) is a diagnosis of exclusion.

RISK-ADAPTED THERAPY

The goal of therapy is to mitigate eosinophil-mediated organ damage. For patients with milder forms of eosinophilia (e.g., <1.5 × 109/L) without symptoms or signs of organ involvement, a watch and wait approach with close follow-up may be undertaken. Identification of rearranged PDGFRA or PDGFRB is critical because of the exquisite responsiveness of these diseases to imatinib. Pemigatinib was recently approved for patients with relapsed or refractory FGFR1-rearranged neoplasms. Corticosteroids are first-line therapy for patients with lymphocyte-variant HE and HES. Hydroxyurea and interferon-α have demonstrated efficacy as initial treatment and in steroid-refractory cases of HES. Mepolizumab, an interleukin-5 (IL-5) antagonist monoclonal antibody, is approved by the U.S Food and Drug Administration for patients with idiopathic HES. Cytotoxic chemotherapy agents, and hematopoietic stem cell transplantation have been used for aggressive forms of HES and CEL, with outcomes reported for limited numbers of patients. Targeted therapies such as the IL-5 receptor antibody benralizumab, IL-5 monoclonal antibody depemokimab, and various tyrosine kinase inhibitors for MLN-eo-TK, are under active investigation.