FIP1L1-PDGFRA in eosinophilic disorders: Prevalence in routine clinical practice, long-term experience with imatinib therapy, and a critical review of the literature

Chronic myelomonocytic leukemia: 2024 update on diagnosis, risk stratification and management

DISEASE OVERVIEW

Chronic myelomonocytic leukemia (CMML) is a clonal hematopoietic stem cell disorder with overlapping features of myelodysplastic syndromes and myeloproliferative neoplasms, characterized by prominent monocytosis and an inherent risk for leukemic transformation (~15%-20% over 3-5 years).

DIAGNOSIS

Newly revised diagnostic criteria include sustained (>3 months) peripheral blood (PB) monocytosis (≥0.5 × 109/L; monocytes ≥10% of leukocyte count), consistent bone marrow (BM) morphology, <20% BM or PB blasts (including promonocytes), and cytogenetic or molecular evidence of clonality. Cytogenetic abnormalities occur in ~30% of patients, while >95% harbor somatic mutations: TET2 (~60%), SRSF2 (~50%), ASXL1 (~40%), RAS pathway (~30%), and others. The presence of ASXL1 and DNMT3A mutations and absence of TET2 mutations negatively impact overall survival (ASXL1WT/TET2MT genotype being favorable).

RISK STRATIFICATION

Several risk models serve similar purposes in identifying high-risk patients that are considered for allogeneic stem cell transplant (ASCT) earlier than later. Risk factors in the Mayo Molecular Model (MMM) include presence of truncating ASXL1 mutations, absolute monocyte count >10 × 109/L, hemoglobin <10 g/dL, platelet count <100 × 109/L, and the presence of circulating immature myeloid cells; the resulting 4-tiered risk categorization includes high (≥3 risk factors), intermediate-2 (2 risk factors), intermediate-1 (1 risk factor), and low (no risk factors); the corresponding median survivals were 16, 31, 59, and 97 months. CMML is also classified as being "myeloproliferative (MP-CMML)" or "myelodysplastic (MD-CMML)," based on the presence or absence of leukocyte count of ≥13 × 109/L.

TREATMENT

ASCT is the only treatment modality that secures cure or long-term survival and is appropriate for MMM high/intermediate-2 risk disease. Drug therapy is currently not disease-modifying and includes hydroxyurea and hypomethylating agents; a recent phase-3 study (DACOTA) comparing hydroxyurea and decitabine, in high-risk MP-CMML, showed similar overall survival at 23.1 versus 18.4 months, respectively, despite response rates being higher for decitabine (56% vs. 31%).

UNIQUE DISEASE ASSOCIATIONS

These include systemic inflammatory autoimmune diseases, leukemia cutis and lysozyme-induced nephropathy; the latter requires close monitoring of renal function during leukocytosis and is a potential indication for cytoreductive therapy.

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.

Available and emerging therapies for bona fide advanced systemic mastocytosis and primary eosinophilic neoplasms

The historically poor prognosis of patients with advanced systemic mastocytosis (AdvSM) and primary eosinophilic neoplasms has shifted to increasingly favorable outcomes with the discovery of druggable targets. The multikinase/KIT inhibitor midostaurin and the highly selective KIT D816V inhibitor avapritinib can elicit marked improvements in measures of mast cell (MC) burden as well as reversion of MC-mediated organ damage (C-findings) and disease symptoms. With avapritinib, the achievement of molecular remission of KIT D816V and improved survival compared with historical therapy suggests a potential to affect disease natural history. BLU-263 and bezuclastinib are KIT D816V inhibitors currently being tested in trials of AdvSM. In the new World Health Organization and International Consensus Classifications, the category of "myeloid/lymphoid neoplasms with eosinophilia and tyrosine kinase (TK) gene fusions" is inclusive of rearrangements involving PDGFRA, PDGFRB, FGFR1, JAK2, FLT3, and ETV6::ABL1. While the successful outcomes with imatinib in FIP1L1::PDGFRA-positive cases and PDGFRB-rearranged neoplasms have become the "poster children" of these disorders, the responses of the other TK-driven neoplasms to small-molecule inhibitors are more variable. The selective FGFR inhibitor pemigatinib, approved in August 2022, is a promising therapy in aggressive FGFR1-driven diseases and highlights the role of such agents in bridging patients to allogeneic transplantation. This review summarizes the data for these approved and investigational agents and discusses open questions and future priorities regarding the management of these rare diseases.

Search, Look, and See; Late Recognised Hypereosinophilic Syndrome with Deletion (4) (q12)

The hypereosinophilic syndrome (HES) is a group of rare disorders characterized by persistently high peripheral blood eosinophiles (≥ 1.5x109/L), and related signs or symptoms of organ involvement without secondary causes. Eosinophilia with recurrent genetic abnormalities (PDGFRA/B, FGFR1) comprises a minority of these patients. In this report, we aimed to point out a case with 4q12 deletion whose diagnosis and treatment were delayed for quite a while. The patient was followed for bronchial asthma for a long time and the recognition of hypereosinophilia yielded a suspicion for HES / Chronic eosinophilic leukemia (CEL). During the initial part of his diagnostic evaluation, there was an unawareness of the cryptic deletion which was a target for tyrosine kinases. The symptoms resolved and complete cytogenetic response was achieved with 100 mg imatinib continuing for 57 months.

Chronic myelomonocytic leukemia: 2022 update on diagnosis, risk stratification, and management

DISEASE OVERVIEW

Chronic myelomonocytic leukemia (CMML) is a clonal hematopoietic stem cell disorder with overlapping features of myelodysplastic syndromes and myeloproliferative neoplasms, with an inherent risk for leukemic transformation (~15% over 3-5 years).

DIAGNOSIS

Diagnosis is based on the presence of sustained (>3 months) peripheral blood monocytosis (≥1 × 10⁹ /L; monocytes ≥10%), usually with accompanying bone marrow dysplasia. Clonal cytogenetic abnormalities occur in ~30% of patients, while >90% have somatic gene mutations. Mutations involving TET2 (~60%), SRSF2 (~50%), ASXL1 (~40%), and the oncogenic RAS pathway (~30%) are frequent, while the presence of ASXL1 and DNMT3A mutations and the absence of TET2 mutations negatively impact overall survival.

RISK-STRATIFICATION

Molecularly integrated prognostic models include the Groupe Français des Myélodysplasies, Mayo Molecular Model (MMM), and the CMML specific prognostic model. Risk factors incorporated into the MMM include presence of truncating ASXL1 mutations, absolute monocyte count >10 × 10⁹ /L, hemoglobin <10 g/dL, platelet count <100 × 10⁹ /L, and the presence of circulating immature myeloid cells. The MMM stratifies CMML patients into four groups: high (≥3 risk factors), intermediate-2 (2 risk factors), intermediate-1 (1 risk factor), and low (no risk factors), with median survivals of 16, 31, 59, and 97 months, respectively.

RISK-ADAPTED THERAPY

Hypomethylating agents such as 5-azacitidine and decitabine are commonly used, with overall response rates of ~40%-50% and complete remission rates of ~7%-17%; with no impact on mutational allele burdens. Allogeneic stem cell transplant is the only potentially curative option but is associated with significant morbidity and mortality.

World Health Organization-defined eosinophilic disorders: 2022 update on diagnosis, risk stratification, and management

DISEASE OVERVIEW

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

DIAGNOSIS

Hypereosinophilia (HE) has generally been defined as a peripheral blood eosinophil count greater than 1.5 × 10⁹ /L. After exclusion of secondary causes of eosinophilia, diagnostic evaluation of primary eosinophilias relies on morphologic review of the blood and marrow, standard cytogenetics, fluorescence in situ hybridization, next generation sequencing gene assays, 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 2016 World Health Organization endorses a semi-molecular classification scheme of disease subtypes. This includes the major category "myeloid/lymphoid neoplasms with eosinophilia and rearrangement of PDGFRA, PDGFRB, or FGFR1 or with PCM1-JAK2", and the myeloproliferative neoplasm subtype, "chronic eosinophilic leukemia, not otherwise specified" (CEL, NOS). 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 (eg, < 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. 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, was recently approved by the US Food and Drug Administration for patients with idiopathic HES. The use of the IL-5 receptor antibody benralizumab, as well as other targeted therapies such as JAK2 and FGFR1 inhibitors, is under active investigation.

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.

Epidemiology, clinical picture and long-term outcomes of FIP1L1-PDGFRA-positive myeloid neoplasm with eosinophilia: Data from 151 patients

FIP1L1-PDGFRA-positive myeloid neoplasm with eosinophilia (F/P+ MN-eo) is a rare disease: robust epidemiological data are lacking and reported issues are scarce, of low sample-size and limited follow-up. Imatinib mesylate (IM) is highly efficient but no predictive factor of relapse after discontinuation has yet been identified. One hundred and fifty-one patients with F/P+ MN-eo (143 males; mean age at diagnosis 49 years; mean annual incidence: 0.18 case per million population) were included in this retrospective nationwide study involving all French laboratories who perform the search of F/P fusion gene (study period: 2003-2019). The main organs involved included the spleen (44%), skin (32%), lungs (30%), heart (19%) and central nervous system (9%). Serum vitamin B12 and tryptase levels were elevated in 74/79 (94%) and 45/57 (79%) patients, respectively, and none of the 31 patients initially treated with corticosteroids achieved complete hematologic remission. All 148 (98%) IM-treated patients achieved complete hematologic and molecular (when tested, n = 84) responses. Forty-six patients eventually discontinued IM, among whom 20 (57%) relapsed. In multivariate analysis, time to IM initiation (continuous HR: 1,01 [0.99-1,03]; P = .05) and duration of IM treatment (continuous HR: 0,97 [0,95-0,99]; P = .004) were independent factors of relapse after discontinuation of IM. After a mean follow-up of 80 (56) months, the 1, 5- and 10-year overall survival rates in IM-treated patients were 99%, 95% and 84% respectively. In F/P+ MN-eo, prompt initiation of IM and longer treatment durations may prevent relapses after discontinuation of IM.

Myeloid/Lymphoid Neoplasms with Eosinophilia and TK Fusion Genes, Version 3.2021, NCCN Clinical Practice Guidelines in Oncology

Eosinophilic disorders and related syndromes represent a heterogeneous group of neoplastic and nonneoplastic conditions, characterized by more eosinophils in the peripheral blood, and may involve eosinophil-induced organ damage. In the WHO classification of myeloid and lymphoid neoplasms, eosinophilic disorders characterized by dysregulated tyrosine kinase (TK) fusion genes are recognized as a new category termed, myeloid/lymphoid neoplasms with eosinophilia and rearrangement of PDGFRA, PDGFRB or FGFR1 or with PCM1-JAK2. In addition to these aforementioned TK fusion genes, rearrangements involving FLT3 and ABL1 genes have also been described. These new NCCN Guidelines include recommendations for the diagnosis, staging, and treatment of any one of the myeloid/lymphoid neoplasms with eosinophilia (MLN-Eo) and a TK fusion gene included in the 2017 WHO Classification, as well as MLN-Eo and a FLT3 or ABL1 rearrangement.

Paratrabecular myelofibrosis and occult mastocytosis are strong morphological clues to suspect FIP1L1-PDGFRA translocation in hypereosinophilia

To study the clinico-haematological and histopathological characteristics of FIP1L1-PDGFRA rearranged hypereosinophilia/hypereosinophilic syndrome (F/P+ve HE/HES), a retrospective analysis of patients with F/P+ve HE diagnosed over a period of 43 months was performed. Peripheral blood smears, bone marrow aspirate (BMA) and biopsies (BMB) were reviewed in each case and; reticulin stain and immunohistochemistry for mast cell tryptase (MCT) and CD117 was performed. F/P+ve HE was diagnosed in a total of ten patients during study period. All patients were males with a median age of 36 years (23-44 years). The median duration of presenting complaints was 7 months (2 months-3 years) which included specific symptoms related to various organs (80% of cases). Anaemia, thrombocytopenia and splenomegaly were seen in 60%, 50% and 90% of the cases respectively. Mastocytosis was not obvious in BMA but identified by MCT on BMB in all cases. Myelofibrosis (grade ≥ 1) was seen in 80% of the cases and includes multifocal paratrabecular fibrosis in 50% of the biopsies. Our study shows that bone marrow mastocytosis and myelofibrosis are very useful morphological indicators to suspect F/P+ve HE and suggests the routine use of reticulin staining and MCT immunohistochemistry in all BMBs performed for the evaluation of HE/HES.

Genetic Basis of Myocarditis: Myth or Reality?

The genetic basis of myocarditis remains an intriguing concept, at least as long as the definition of myocarditis constitutes the definitive presence of myocardial inflammation sufficient to cause the observed ventricular dysfunction in the setting of cardiotropic infections. Autoimmune or immune-mediated myocardial inflammation constitutes a complex area of clinical interest, wherein numerous and not yet fully understood role of hereditary auto-inflammatory diseases can result in inflammation of the pericardium and myocardium. Finally, myocardial involvement in hereditary immunodeficiency diseases, cellular and humoral, is a possible trigger for infections which may complicate the diseases themselves. Whether the role of constitutional genetics can make the patient susceptible to myocardial inflammation remains yet to be explored.

Chronic Myelomonocytic leukemia: 2020 update on diagnosis, risk stratification and management

DISEASE OVERVIEW

Chronic myelomonocytic leukemia (CMML) is a clonal hematopoietic stem cell disorder with overlapping features of myelodysplastic syndromes and myeloproliferative neoplasms, with an inherent risk for leukemic transformation (~15% over 3-5 years).

DIAGNOSIS

Diagnosis is based on the presence of sustained (>3 months) peripheral blood monocytosis (≥1 × 10⁹ /L; monocytes ≥10%), along with bone marrow dysplasia. Clonal cytogenetic abnormalities occur in ~ 30% of patients, while >90% have gene mutations. Mutations involving TET2 (~60%), SRSF2 (~50%), ASXL1 (~40%) and the oncogenic RAS pathway (~30%) are frequent; while the presence of ASXL1 and DNMT3A mutations and the absence of TET2 mutations negatively impact over-all survival.

RISK STRATIFICATION

Molecularly integrated prognostic models include; the Groupe Français des Myélodysplasies (GFM), Mayo Molecular Model (MMM) and the CMML specific prognostic model (CPSS-Mol). Risk factors incorporated into the MMM include presence of nonsense or frameshift ASXL1 mutations, absolute monocyte count>10 × 10⁹ /L, hemoglobin <10 g/dL, platelet count <100 × 10⁹ /L and the presence of circulating immature myeloid cells. The MMM stratifies CMML patients into four groups; high (≥3 risk factors), intermediate-2 (2 risk factors), intermediate-1 (1 risk factor) and low (no risk factors), with median survivals of 16, 31, 59 and 97 months, respectively.

RISK-ADAPTED THERAPY

Hypomethylating agents such as 5-azacitidine and decitabine are commonly used, with overall response rates of ~40%-50% and complete remission rates of ~7%-17%; with no impact on mutational allele burdens. Allogeneic stem cell transplant is the only potentially curative option, but is associated with significant morbidity and mortality.

Hypereosinophilic syndromes in the precision medicine era: clinical, molecular aspects and therapeutic approaches (targeted therapies)

Introduction: Hypereosinophilic syndromes are a heterogeneous group of disorders that may be associated with life-threatening organ injury as a result of tissues infiltration by eosinophils. The main goal of therapy is to mitigate eosinophil-mediated organ damage. When possible, therapy should be directed at the underlying etiology. However, even in the absence of any known cause, when organ damage is present, hypereosinophilia must be treated promptly and aggressively to reduce potential morbidity and mortality.Areas covered: Conventional therapies, including corticosteroids, hydroxyurea (hydroxycarbamide) and interferon-alpha, have shown variable efficacy and a non-negligible toxicity emphasizing the need of new therapeutic strategies based on drugs with different mechanisms of action.Expert opinion: Tyrosine kinase inhibitors have a central role among targeted therapies of hypereosinophilic syndromes. Imatinib, initially empirically used based on its activity in chronic myeloid leukemia, achieved preliminary excellent results further confirmed in large series of patients. Third-generation tyrosine kinase inhibitors such as ponatinib, while active in vitro and in vivo in animals, still deserve confirmation in properly designed clinical trials. In addition, clinical investigation on monoclonal antibodies against interleukin-5, interleukin-5Rα, IgE, and CD52 represents a promising area of research.

[Differential diagnosis of hypereosinophilia]

Eosinophilia is defined as an elevated absolute number of eosinophilic leukocytes in peripheral blood or tissue. Its absolute number also defines the grade of eosinophilia. The main causes are allergic (including drug side effects) and infectious triggers but malignant and autoimmune diseases can also result in eosinophilia. Severe eosinophilia with the number of eosinophils >5000/µl are mostly caused by myeloproliferative disorders, eosinophilic granulomatosis with polyangiitis or during tissue migration in parasitic tissue infections. Hypereosinophilic syndrome is defined as eosinophilia with >1500 eosinophils/µl and a duration of more than 6 months by exclusion of parasitic infections, allergies or other causes of tissue eosinophilia with end-organ damage. For the diagnosis of a persistent eosinophilia a detailed medical history and physical examination should be followed by early organ screening, infection diagnostics especially for helminth infections and hematological laboratory analyses including bone marrow investigations.

World Health Organization-defined eosinophilic disorders: 2019 update on diagnosis, risk stratification, and management

DISEASE OVERVIEW

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

DIAGNOSIS

Hypereosinophilia has generally been defined as a peripheral blood eosinophil count greater than 1.5 × 10⁹ /L, and may be associated with tissue damage. After 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, flow immunophenotyping, and T-cell clonality assessment 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 2016 World Health Organization endorses a semi-molecular classification scheme of disease subtypes. This includes the major category "myeloid/lymphoid neoplasms with eosinophilia and rearrangement of PDGFRA, PDGFRB, or FGFR1 or with PCM1-JAK2", and the MPN subtype, "chronic eosinophilic leukemia, not otherwise specified" (CEL, NOS). Lymphocyte-variant hypereosinophilia 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 (eg, <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. Corticosteroids are first-line therapy for patients with lymphocyte-variant hypereosinophilia and HES. Hydroxyurea and interferon-alfa have demonstrated efficacy as initial treatment and in steroid-refractory cases of HES. In addition to hydroxyurea, second line 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. The use of antibodies against interleukin-5 (IL-5) (mepolizumab), the IL-5 receptor (benralizumab), as well as other targets on eosinophils remains an active area of investigation.

Chronic myelomonocytic leukemia: 2018 update on diagnosis, risk stratification and management

DISEASE OVERVIEW

Chronic myelomonocytic leukemia (CMML) is a clonal hematopoietic stem cell disorder with overlapping features of myelodysplastic syndromes and myeloproliferative neoplasms, with an inherent risk for leukemic transformation (∼15%-20% over 3-5 years).

DIAGNOSIS

Diagnosis is based on the presence of sustained (>3 months) peripheral blood monocytosis (≥1 × 10⁹ /L; monocytes ≥10%), along with bone marrow dysplasia. Clonal cytogenetic abnormalities occur in ∼ 30% of patients, while >90% have gene mutations. Mutations involving TET2 (∼60%), SRSF2 (∼50%), ASXL1 (∼40%) and the oncogenic RAS pathway (∼30%) are frequent; while the presence of ASXL1 and DNMT3A mutations and the absence of TET2 mutations negatively impact over-all survival.

RISK STRATIFICATION

Molecularly integrated prognostic models include; the Groupe Français des Myélodysplasies (GFM), Mayo Molecular Model (MMM), and the CMML specific prognostic model (CPSS-Mol). Risk factors incorporated into the MMM include presence of nonsense or frameshift ASXL1 mutations, absolute monocyte count > 10 × 10⁹ /L, hemoglobin <10 gm/dL, platelet count <100 × 10⁹ /L and the presence of circulating immature myeloid cells. The MMM stratifies CMML patients into 4 groups; high (≥3 risk factors), intermediate-2 (2 risk factors), intermediate-1 (1 risk factor), and low (no risk factors), with median survivals of 16, 31, 59, and 97 months, respectively.

RISK-ADAPTED THERAPY

Hypomethylating agents such as 5-azacitidine and decitabine are commonly used, with overall response rates of ∼30%-40% and complete remission rates of ∼7%-17%; with no impact on mutational allele burdens. Allogeneic stem cell transplant is the only potentially curative option, but is associated with significant morbidity and mortality.

World Health Organization-defined eosinophilic disorders: 2017 update on diagnosis, risk stratification, and management

DISEASE OVERVIEW

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

DIAGNOSIS

Hypereosinophilia has generally been defined as a peripheral blood eosinophil count greater than 1500/mm³ and may be associated with tissue damage. After exclusion of secondary causes of eosinophilia, diagnostic evaluation of primary eosinophilias relies on a combination of morphologic review of the blood and marrow, standard cytogenetics, fluorescent in situ-hybridization, flow immunocytometry, and T-cell clonality assessment to detect histopathologic or clonal evidence for an acute or chronic myeloid or lymphoproliferative disorder.

RISK STRATIFICATION

Disease prognosis relies on identifying the subtype of eosinophilia. After evaluation of secondary causes of eosinophilia, the 2016 World Health Organization endorses a semi-molecular classification scheme of disease subtypes which includes the major category "myeloid/lymphoid neoplasms with eosinophilia and rearrangement of PDGFRA, PDGFRB, or FGFR1 or with PCM1-JAK2," and the "MPN subtype, chronic eosinophilic leukemia, not otherwise specified" (CEL, NOS). Lymphocyte-variant hypereosinophilia 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., < 1500/mm³ ) 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. Corticosteroids are first-line therapy for patients with lymphocyte-variant hypereosinophilia and HES. Hydroxyurea and interferon-alpha have demonstrated efficacy as initial treatment and steroid-refractory cases of HES. In addition to hydroxyurea, second line cytotoxic chemotherapy agents and hematopoietic cell transplant have been used for aggressive forms of HES and CEL with outcomes reported for limited numbers of patients. The use of antibodies against interleukin-5 (IL-5) (mepolizumab), the IL-5 receptor (benralizumab), and CD52 (alemtuzumab), as well as other targets on eosinophils remains an active area of investigation.

Tyrosine Kinase Inhibitors in the Treatment of Eosinophilic Neoplasms and Systemic Mastocytosis

The World Health Organization's semimolecular classification of eosinophilias emphasizes neoplasms driven by fusion tyrosine kinases. More than 80% of patients with systemic mastocytosis carry the KIT D816V mutation, the primary driver of disease pathogenesis. Genetic annotation of these diseases is critical and affords opportunities for targeted therapy. This article discusses our understanding of the mutated tyrosine kinome of eosinophilic neoplasms and systemic mast cell disease, and the successes and limitations of available therapies. Use of tyrosine kinase inhibitors as a bridge to hematopoietic stem cell transplantation, and development of more selective and potent tyrosine kinase inhibitors is also highlighted.

The Eosinophil in Health and Disease: from Bench to Bedside and Back

Historically, eosinophils have been considered as end-stage cells involved in host protection against parasitic infection and in the mechanisms of hypersensitivity. However, later studies have shown that this multifunctional cell is also capable of producing immunoregulatory cytokines and soluble mediators and is involved in tissue homeostasis and modulation of innate and adaptive immune responses. In this review, we summarize the biology of eosinophils, including the function and molecular mechanisms of their granule proteins, cell surface markers, mediators, and pathways, and present comprehensive reviews of research updates on the genetics and epigenetics of eosinophils. We describe recent advances in the development of epigenetics of eosinophil-related diseases, especially in asthma. Likewise, recent studies have provided us with a more complete appreciation of how eosinophils contribute to the pathogenesis of various diseases, including hypereosinophilic syndrome (HES). Over the past decades, the definition and criteria of HES have been evolving with the progress of our understanding of the disease and some aspects of this disease still remain controversial. We also review recent updates on the genetic and molecular mechanisms of HES, which have spurred dramatic developments in the clinical strategies of diagnosis and treatment for this heterogeneous group of diseases. The conclusion from this review is that the biology of eosinophils provides significant insights as to their roles in health and disease and, furthermore, demonstrates that a better understanding of eosinophil will accelerate the development of new therapeutic strategies for patients.

Biological Modulators in Eosinophilic Diseases

Eosinophils can regulate local and systemic inflammation, and their presence in higher numbers appears to play an important role in the pathology of various atopic and inflammatory diseases. Eosinophil maturation, recruitment, and survival depend on several cytokine regulators, including interleukin (IL)-5, IL-4, and IL-13 as well as growth factors such as GM-CSF. Over the last decade, the approach to treating eosinophilic diseases has changed greatly. A number of biologic modulators have been developed to target eosinophilic inflammatory pathways, and their usage has resulted in variable clinical improvement in the treatment of eosinophilic-associated conditions. Novel targeted therapies that are safe and effective for treating these disorders are being investigated. This review summarizes the clinical use of biologic agents that have been studied in clinical trials or approved for treating eosinophilic diseases.

Chronic myelomonocytic leukemia: 2016 update on diagnosis, risk stratification, and management

Chronic myelomonocytic leukemia (CMML) is a clonal hematopoietic stem cell disorder characterized by overlapping features of myelodysplastic syndromes and myeloproliferative neoplasms. Diagnosis is based on the presence of persistent (>3 months) peripheral blood monocytosis (>1 × 10(9) /L), along with bone marrow dysplasia. Clonal cytogenetic abnormalities occur in ∼20-30% of patients, while >90% have gene mutations. Mutations involving TET2 (∼60%), SRSF2 (∼50%), ASXL1 (∼40%), and RAS (∼30%) are frequent; with only ASXL1 mutations negatively impacting overall survival. Two molecularly integrated, CMML-specific prognostic models include; the Groupe Français des Myélodysplasies (GFM) and the Molecular Mayo Model (MMM). The GFM model segregates patients into 3 groups based on: age >65 years, WBC >15 × 10(9) /L, anemia, platelets <100 × 10(9) /L, and ASXL1 mutation status, with respective median survivals of 56 (low), 27.4 (intermediate), and 9.2 (high) months. The MMM is based on ASXL1 mutational status, absolute monocyte count >10 × 10(9) /L, hemoglobin <10 g/dL, platelets <100 × 109/L and circulating immature myeloid cells. This model stratifies patients into four groups; high (≥3 risk factors), intermediate-2 (2 risk factors), intermediate-1 (1 risk factor) and low (no risk factors), with median survivals of 16, 31, 59, and 97 months, respectively. Hypomethylating agents such as 5-azacitidine and decitabine are commonly used, with overall response rates of ∼30-40% and complete remission rates of ∼7-17%. Allogeneic stem cell transplant is the only potentially curative option, but is associated with significant morbidity and mortality. Individualized therapy, including epigenetic modifiers and small molecule inhibitors, are exciting prospects. Am. J. Hematol. 91:632-642, 2016. © 2016 Wiley Periodicals, Inc.

Eosinophilia in Hematologic Disorders

Eosinophilia in the peripheral blood can be the manifestation various medical conditions, including benign or malignant disorders. There are 3 main types of eosinophilia-associated myeloid neoplasms (MN-eos): myeloid and lymphoid neoplasms, chronic eosinophilic leukemia not otherwise specified, and idiopathic hypereosinophilic syndrome (HES). Imatinib mesylate has revolutionized the treatment of molecularly defined MN-eos, and novel agents have been successfully used to treat HES. The discovery of new, recurrent molecular alterations in patients with MN-eos may improve their diagnosis and therapy. This review focuses on the hematologist's approach to a patient with eosinophilia and treatment options for those with eosinophilic myeloid neoplasms.

Cytogenetic and molecular abnormalities in chronic myelomonocytic leukemia

Chronic myelomonocytic leukemia (CMML) is a clonal stem cell disorder associated with peripheral blood monocytosis and an inherent tendency to transform to acute myeloid leukemia. CMML has overlapping features of myelodysplastic syndromes and myeloproliferative neoplasms. Clonal cytogenetic changes are seen in ~30%, whereas gene mutations are seen in >90% of patients. Common cytogenetic abnormalities include; trisomy 8, -Y, -7/del(7q), trisomy 21 and del(20q), with the Mayo-French risk stratification effectively risk stratifying patients based on cytogenetic abnormalities. Gene mutations frequently involve epigenetic regulators (TET2 ~60%), modulators of chromatin (ASXL1 ~40%), spliceosome components (SRSF2 ~50%), transcription factors (RUNX1 ~15%) and signal pathways (RAS ~30%, CBL ~15%). Of these, thus far, only nonsense and frameshift ASXL1 mutations have been shown to negatively impact overall survival. This has resulted in the development of contemporary, molecularly integrated (inclusive of ASXL1 mutations) CMML prognostic models, including Molecular Mayo Model and the Groupe Français des Myélodysplasies model. Better understanding of the prevalent genetic and epigenetic dysregulation has resulted in emerging targeted treatment options for some patients. The development of an integrated (cytogenetic and molecular) prognostic model along with CMML-specific response assessment criteria are much needed future goals.

Chronic Myelomonocytic Leukemia: Focus on Clinical Practice

Chronic myelomonocytic leukemia (CMML) is a clonal stem cell disorder with features that overlap those of myelodysplastic syndromes (MDSs) and myeloproliferative neoplasms (MPNs). Chronic myelomonocytic leukemia often results in peripheral blood monocytosis and has an inherent tendency to transform to acute myeloid leukemia. Clonal cytogenetic changes are seen in approximately 30% of patients, and molecular abnormalities are seen in more than 90%. Gene mutations involving TET2 (∼60%), SRSF2 (∼50%), ASXL1 (∼40%), and RAS (∼30%) are frequent, with nonsense and frameshift ASXL1 mutations being the only mutations identified thus far to have an independent negative prognostic effect on overall survival. Contemporary molecularly integrated prognostic models (inclusive of ASXL1 mutations) include the Molecular Mayo Model and the Groupe Français des Myélodysplasies model. Given the lack of formal treatment and response criteria, management of CMML is often extrapolated from MDS and MPN, with allogeneic stem cell transplant being the only curative option. Hydroxyurea and other cytoreductive agents have been used to control MPN-like features, while epigenetic modifiers such as hypomethylating agents have been used for MDS-like features. Given the relatively poor response to these agents and the inherent risks associated with hematopoietic stem cell transplant, newer drugs exploiting molecular and epigenetic abnormalities in CMML are being developed. The creation of CMML-specific response criteria is a much needed step in order to improve clinical outcomes.

World Health Organization-defined eosinophilic disorders: 2015 update on diagnosis, risk stratification, and management

DISEASE OVERVIEW

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

DIAGNOSIS

Hypereosinophilia has generally been defined as a peripheral blood eosinophil count greater than 1,500/mm(3) and may be associated with tissue damage. After exclusion of secondary causes of eosinophilia, diagnostic evaluation of primary eosinophilias relies on a combination of morphologic review of the blood and marrow, standard cytogenetics, fluorescent in situ-hybridization, flow immunocytometry, and T-cell clonality assessment to detect histopathologic or clonal evidence for an acute or chronic myeloid or lymphoproliferative disorder.

RISK STRATIFICATION

Disease prognosis relies on identifying the subtype of eosinophilia. After evaluation of secondary causes of eosinophilia, the 2008 World Health Organization establishes a semi-molecular classification scheme of disease subtypes including 'myeloid and lymphoid neoplasms with eosinophilia and abnormalities of PDGFRA, PDGFRB, or FGFR1', chronic eosinophilic leukemia, not otherwise specified, (CEL, NOS), lymphocyte-variant hypereosinophilia, and idiopathic hypereosinophilic syndrome (HES), which is a diagnosis of exclusion.

RISK-ADAPTED THERAPY

The goal of the therapy is to mitigate eosinophil-mediated organ damage. For patients with milder forms of eosinophilia (e.g. < 1,500/mm(3) ) 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. Corticosteroids are first-line therapy for patients with lymphocyte-variant hypereosinophilia and HES. Hydroxyurea and interferon-alpha have demonstrated efficacy as initial treatment and steroid-refractory cases of HES. In addition to hydroxyurea, second line cytotoxic chemotherapy agents and hematopoietic cell transplant have been used for aggressive forms of HES and CEL with outcomes reported for limited numbers of patients. Although clinical trials have been performed with anti IL-5 (mepolizumab) and anti-CD52 (alemtuzumab) antibodies, their therapeutic role in primary eosinophilic diseases and HES has yet to be established.

Hematolymphoid neoplasms associated with rearrangements of PDGFRA, PDGFRB, and FGFR1

OBJECTIVES

This session of the 2013 Society for Hematopathology/European Association for Haematopathology Workshop was dedicated to tumors currently included in the World Health Organization (WHO) classification category of myeloid and lymphoid neoplasms with eosinophilia and abnormalities of PDGFRA, PDGFRB, and FGFR1.

METHODS

We use the cases submitted to this session to review the clinicopathologic and genetic spectrum of these neoplasms, methods for their diagnosis, and issues related to the WHO classification terminology. Since many patients with these neoplasms have eosinophilia, we also briefly mention other causes of clonal eosinophilia.

RESULTS

These neoplasms are the result of gene fusions involving any one of these three tyrosine kinase genes. A variety of gene fusion partners have been found consistently for each category of neoplasms. Diagnoses of these neoplasms are often highly challenging and require a high index of suspicion and a multidisciplinary approach.

CONCLUSIONS

Early recognition of these neoplasms is important because patients with neoplasms associated with PDGFRA or PDGFRB fusions often respond to tyrosine kinase inhibitor therapy, whereas patients with neoplasms associated with FGFR1 fusions usually do not respond.

Diagnostic challenges during pretreatment long-term follow-up in a patient with FIP1L1-PDGFRA-positive eosinophilia

Obtaining a precise characterization of eosinophilia is crucial, as successful treatment relies on the underlying etiology of the disease. Platelet-derived growth factor receptor alpha-related disorders were first specified in 2008 as a distinct group of clonal eosinophilic disorders with exceptional responsiveness to imatinib. We herein present the case of a man with myeloid neoplasm and eosinophilia in whom a definitive diagnosis could not be adequately made based on histopathological features who was ultimately diagnosed only after extensive molecular analyses and successfully treated with imatinib. In addition, we discuss the diagnostic and therapeutic approaches to treating patients presenting with eosinophilia.

Imatinib: a breakthrough of targeted therapy in cancer

Deregulated protein tyrosine kinase activity is central to the pathogenesis of human cancers. Targeted therapy in the form of selective tyrosine kinase inhibitors (TKIs) has transformed the approach to management of various cancers and represents a therapeutic breakthrough. Imatinib was one of the first cancer therapies to show the potential for such targeted action. Imatinib, an oral targeted therapy, inhibits tyrosine kinases specifically BCR-ABL, c-KIT, and PDGFRA. Apart from its remarkable success in CML and GIST, Imatinib benefits various other tumors caused by Imatinib-specific abnormalities of PDGFR and c-KIT. Imatinib has also been proven to be effective in steroid-refractory chronic graft-versus-host disease because of its anti-PDGFR action. This paper is a comprehensive review of the role of Imatinib in oncology.

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

The FIP1L1-PDGFRA rearrangement results in constitutive activation of the tyrosine kinase PDGFRA. Neoplasms harboring this rearrangement are responsive to imatinib mesylate at doses much lower than those recommended for the treatment of chronic myelogenous leukemia. Only a single report has described the identification of FIP1L1-PDGFRA in chronic myelomonocytic leukemia (CMML). Herein, we present a case report of a patient in whom the FIP1L1-PDGFRA was discovered as he evolved from CMML to acute myeloid leukemia (AML). The presence of a dominant neoplastic clone with FIP1L1-PDGFRA rearrangement was suspected on the basis of sudden onset of peripheral and bone marrow eosinophilia and confirmed by fluorescence in situ hybridization and molecular diagnostic tests. Whereas the patient was initially refractory to chemotherapy before the rearrangement was detected, subsequent therapy with imatinib led to complete remission.

World Health Organization-defined eosinophilic disorders: 2014 update on diagnosis, risk stratification, and management

DISEASE OVERVIEW

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

DIAGNOSIS

Hypereosinophilia (HE) has generally been defined as a peripheral blood eosinophil count greater than 1,500/mm(3) and may be associated with tissue damage. After exclusion of secondary causes of eosinophilia, diagnostic evaluation of primary eosinophilias relies on a combination of morphologic review of the blood and marrow, standard cytogenetics, fluorescent in situ hybridization, flow immunocytometry, and T-cell clonality assessment to detect histopathologic or clonal evidence for an acute or chronic myeloid or lymphoproliferative disorder.

RISK STRATIFICATION

Disease prognosis relies on identifying the subtype of eosinophilia. After evaluation of secondary causes of eosinophilia, the 2008 World Health Organization establishes a semimolecular classification scheme of disease subtypes including "myeloid and lymphoid neoplasms with eosinophilia and abnormalities of PDGFRA, PDGFRB, or FGFR1', chronic eosinophilic leukemia, not otherwise specified" (CEL, NOS), lymphocyte-variant HE, and idiopathic hypereosinophilic syndrome (HES), which 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., <1,500/mm(3)) 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. Corticosteroids are first-line therapy for patients with lymphocyte-variant HE and HES. Hydroxyurea and interferon-alpha have demonstrated efficacy as initial treatment and steroid-refractory cases of HES. In addition to hydroxyurea, second-line cytotoxic chemotherapy agents and hematopoietic cell transplant have been used for aggressive forms of HES and CEL with outcomes reported for limited number of patients. Although clinical trials have been performed with anti-IL-5 (mepolizumab) and anti-CD52 (alemtuzumab) antibodies, their therapeutic role in primary eosinophilic diseases and HES has yet to be established.

Novel t(5;19) Translocation in a Patient with PDGFRB Associated Chronic Leukemia: Implications for Treatment Strategy

Myeloproliferative disorders are variable disorders, based on the genetic abnormality present and the cell line progenitors that are affected. In this case, we discuss a novel gene translocation in the subset of PDGFRB mutations, first seen with prominent hyperbasophilia. This case demonstrates the possibility for lower therapeutic doses of imatinib mesylate than previously reported, in order to control leukocyte counts and reverse the genetic mutation.

Hypereosinophilic syndrome - lymphocytic variant transforming into peripheral T-cell lymphoma with severe oral manifestations

Hypereosinophilic syndrome (HES) is a rare disease defined by organ damage directly attributable to hypereosinophilia of any type. Here, we report for the first time the case of a patient with a lymphocytic type of HES (HES-L) who had liver, skin, spleen, lung, bone marrow, digestive track, and mouth involvement. Associated T-cells displayed an aberrant CD30+ phenotype and were monoclonal. Thymus activated and regulated chemokine serum level was positive. Despite steroids (Cortancyl 20 mg [Sanofi Aventis, France], imatinib mesylate [Glivec 400 mg; Novartis Europharm], interferon alpha 2A [Roferon-A 3 MUI/0.5 ml; Roche]) and other lines of therapy including imatinib mesylate treatment, an oral necrotic lesion developed, and finally progressed into a peripheral CD30+ T-cell lymphoma. CHOP chemotherapy (cyclophosphamide, hydroxydoxorubicin, oncovin, prednisone), interferon-α, and mepolizumab were ineffective. Although progression into peripheral T-cell lymphoma is documented as a rare complication of HES-L, severe oral extension of HES-L is described for the first time.

Myeloid neoplasms associated with eosinophilia and rearrangement of PDGFRA, PDGFRB, and FGFR1: a review

Myeloid and lymphoid neoplasms with eosinophilia and abnormalities of platelet-derived growth factor receptor alpha (PDGFRA), platelet-derived growth factor receptor beta (PDGFRB), and fibroblast growth factor receptor-1 (FGFR1) are a group of hematologic neoplasms resulting from the formation of abnormal fusion genes that encode constitutively activated tyrosine kinases. These entities are now separated into their own major category in the 2008 World Health Organization classification of hematolymphoid tumors. Although eosinophilia is characteristic of these diseases, the clinical presentation of the three entities is variable. Conventional cytogenetics (karyotyping) will detect the majority of abnormalities involving PDGFRB and FGFR1, but florescence in situ hybridization (FISH)/molecular studies are required to detect factor interacting with PAP (FIP1L1)-PDGFRA as the characteristic 4q12 interstitial deletion is cryptic. Imatinib mesylate (imatinib) is the first-line therapy for patients with abnormalities of PDGFRA/B, whereas patients with FGFR1 fusions are resistant to this therapy and carry a poor prognosis. The discovery of novel gene rearrangements associated with eosinophilia will further guide our understanding of the molecular pathobiology of these diseases and aid in the development of small-molecule inhibitors that inhibit deregulated hematopoiesis.

World Health Organization-defined eosinophilic disorders: 2012 update on diagnosis, risk stratification, and management

DISEASE OVERVIEW

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

DIAGNOSIS

Hypereosinophilia has generally been defined as a peripheral blood eosinophil count greater than 1,500/mm(3) and may be associated with tissue damage. After exclusion of secondary causes of eosinophilia, diagnostic evaluation of primary eosinophilias relies on a combination of morphologic review of the blood and marrow, standard cytogenetics, fluorescent in situ-hybridization, flow immunocytometry, and T-cell clonality assessment to detect histopathologic or clonal evidence for an acute or chronic myeloid or lymphoproliferative disorder.

RISK STRATIFICATION

Disease prognosis relies on identifying the subtype of eosinophilia. After evaluation of secondary causes of eosinophilia, the 2008 World Health Organization establishes a semimolecular classification scheme of disease subtypes including "myeloid and lymphoid neoplasms with eosinophilia and abnormalities of PDGFRA, PDGFRB, or FGFR1," chronic eosinophilic leukemia, not otherwise specified' (CEL, NOS), lymphocyte-variant hypereosinophilia, and idiopathic hypereosinophilic syndrome (HES), which 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., <1,500/mm(3) ) 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. Corticosteroids are first-line therapy for patients with lymphocyte-variant hypereosinophilia and HES. Hydroxyurea and interferon-alpha have demonstrated efficacy as initial treatment and steroid-refractory cases of HES. In addition to hydroxyurea, second line cytotoxic chemotherapy agents and hematopoietic cell transplant have been used for aggressive forms of HES and CEL with outcomes reported for limited numbers of patients. Although clinical trials have been performed with anti IL-5 (mepolizumab) and anti-CD52 (alemtuzumab) antibodies, their therapeutic role in primary eosinophilic diseases and HES has yet to be established.

Response to imatinib mesylate in patients with hypereosinophilic syndrome

Idiopathic hypereosinophilic syndrome (HES) is a rare disorder characterized by unexplained, persistent hypereosinophilia associated with multiple organ dysfunctions. The cause of HES is unknown and shows clinical heterogeneity. FIP1L1-PDGFRA fusion is a clonal marker for the diagnosis and treatment of HES. We prospectively studied 78 patients with chronic eosinophilia. In all cases, the most salient clinical and biological characteristics as well as the response to the therapy were analyzed. In addition, we performed conventional cytogenetics and fluorescent in situ hybridization (FISH) with three BACs covering the FIP1-like-1 (FIP1L1)/platelet-derived growth factor receptor-α gene (PDGFRA) fusion. Nineteen of 78 patients (24 %) presented criteria of HES. The majority of patients were male (18) with median age of 49 years (range 19-84 years). FIP1L1-PDGFRA fusion was found in eight patients. Patients with FIP1L1-PDGFRA fusion presented with more bone marrow eosinophils and peripheral blood eosinophilia as well as anemia, leukocytosis and thrombocytopenia. Using of low-dose imatinib mesylate (100 mg/day) a hematological and molecular remission in all patients displaying the FIP1L1-PDGFRA fusion gene was observed. Therefore, imatinib may be effective for use in the treatment of chronic eosinophilic leukemia, and patients should be treated before tissue damage.

Identification of JAK2 as a mediator of FIP1L1-PDGFRA-induced eosinophil growth and function in CEL

The Fip1-like1 (FIP1L1)-platelet-derived growth factor receptor alpha fusion gene (F/P) arising in the pluripotent hematopoietic stem cell (HSC),causes 14% to 60% of patients with hypereosinophilia syndrome (HES). These patients, classified as having F/P (+) chronic eosinophilic leukemia (CEL), present with clonal eosinophilia and display a more aggressive disease phenotype than patients with F/P (–) HES patients. The mechanisms underlying predominant eosinophil lineage targeting and the cytotoxicity of eosinophils in this leukemia remain unclear. Given that the Janus tyrosine kinase (JAK)/signal transducers and activators of transcription (Stat) signaling pathway is key to cytokine receptor-mediated eosinophil development and activated Stat3 and Stat5 regulate the expression of genes involved in F/P malignant transformation, we investigated whether and how JAK proteins were involved in the pathogenesis of F/P-induced CEL. F/P activation of JAK2, Stat3 and Stat5, were confirmed in all the 11 F/P (+) CEL patients examined. In vitro inhibition of JAK2 in EOL-1, primary F/P(+) CEL cells (PC) and T674I F/P Imatinib resistant cells(IR) by either JAK2-specific short interfering RNA (siRNA) or the tryphostin derivative AG490(AG490), significantly reduced cellular proliferation and induced cellular apoptosis. The F/P can enhance the IL-5-induced JAK2 activation, and further results indicated that JAK2 inhibition blocked IL-5-induced cellular migration and activation of the EOL-1 and PC cells in vitro. F/P-stimulation of the JAK2 suppressed cells led to a significantly reduction in Stat3 activation, but relatively normal induction of Stat5 activation. Interestingly, JAK2 inhibition also reduced PI3K, Akt and NF-κB activity in a dose-dependent manner, and suppressed expression levels of c-Myc and Survivin. These results strongly suggest that JAK2 is activated by F/P and is required for F/P stimulation of cellular proliferation and infiltration, possibly through induction of c-Myc and Survivin expression via activation of multiple signaling pathways, including NF-κB, Stat3, and PI3K/Akt.

World Health Organization-defined eosinophilic disorders: 2011 update on diagnosis, risk stratification, and management

DISEASE OVERVIEW

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

DIAGNOSIS

Hypereosinophilia has generally been defined as a peripheral blood eosinophil count greater than 1,500/mm(3) and may be associated with tissue damage. After exclusion of secondary causes of eosinophilia, diagnostic evaluation of primary eosinophilias relies on a combination of morphologic review of the blood and marrow, standard cytogenetics, fluorescent in situ-hybridization, flow immunocytometry, and T-cell clonality assessment to detect histopathologic or clonal evidence for an acute or chronic myeloid or lymphoproliferative disorder.

RISK STRATIFICATION

Disease prognosis relies on identifying the subtype of eosinophilia. After evaluation of secondary causes of eosinophilia, the 2008 World Health Organization establishes a semi-molecular classification scheme of disease subtypes including myeloid and lymphoid neoplasms with eosinophilia and abnormalities of PDGFRA, PDGFRB, or FGFR1, chronic eosinophilic leukemia, not otherwise specified (CEL, NOS), lymphocyte-variant hypereosinophilia, and idiopathic hypereosinophilic syndrome (HES), which 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. < 1,500/mm(3) ) 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. Corticosteroids are first-line therapy for patients with lymphocyte-variant hypereosinophilia and HES. Hydroxyurea and interferon-alpha have demonstrated efficacy as initial treatment and steroid-refractory cases of HES. In addition to hydroxyurea, second line cytotoxic chemotherapy agents and hematopoietic cell transplant have been used for aggressive forms of HES and CEL with outcomes reported for limited numbers of patients. Although clinical trials have been performed with anti IL-5 (mepolizumab) and anti-CD52 (alemtuzumab) antibodies, their therapeutic niche in primary eosinophilic diseases and HES have yet to be established.