Multilineage involvement of the fusion gene in patients with FIP1L1/PDGFRA-positive hypereosinophilic syndrome

Lymphomatoid papulosis associated with myeloid neoplasm with eosinophilia and FIP1L1::PDGFRA rearrangement: Successful imatinib treatment in two cases

Lymphomatoid papulosis (LyP) is a benign condition, listed among primary cutaneous CD30+ lymphoproliferative disorders. Its typical picture consists of relapsing-remitting papular lesions and it can be encountered in the course of a hematologic disease, at times representing its first manifestation. Hypereosinophilic syndromes are a heterogeneous group of disorders characterized by persistent peripheral blood hypereosinophilia that may lead to life-threatening organ damage. Among eosinophilic disorders, the subtype identified as myeloid/lymphoid neoplasm with eosinophilia and tyrosine kinase gene fusions has aroused particular interest due to its excellent response to tyrosine kinase inhibitors, including imatinib. Here, we described the case of two 33-year-old men presenting with LyP and myeloid neoplasm with eosinophilia and FIP1L1::PDGFRA rearrangement who achieved complete clinical and molecular remission of both conditions a few months after starting imatinib.

Phosflow assessment of PDGFRA phosphorylation state: A guide for tyrosine kinase inhibitor targeted therapy in hypereosinophilia patients

Clonal eosinophilia is a hematologic disorder caused by translocation in growth factor receptor (GFR) genes. Despite the identified molecular mechanisms underlying clonal hypereosinophilia, the distinction between clonal and reactive eosinophilia has remained challenging due to the diversity of partner genes for translocated GFRs. This study aimed to examine the feasibility of phosphoflow cytometry in the diagnosis of clonal hypereosinophilia through evaluating the level of platelet-derived growth factor receptor alpha (PDGFRA) phosphorylation and its correlation with PDGFRA genetic aberration. Blood samples were collected from 45 hypereosinophilia patients and 10 healthy controls. Using phosphoflow cytometry method, the phosphorylation state of PDGFRA was assessed. The specificity of phosflow results was confirmed by western blotting and eventually compared with qRT-PCR expression analysis of 3'-region of PDGFRA. To detect the genetic aberration of PDGFRA, 5'-rapid amplification of cDNA ends (5'-RACE) was performed. Phosflow analysis illustrated that 9 of 45 hypereosinophilic patients had higher level of PDGFRA phosphorylation while sequence analysis of 5'-RACE-PCR fragments confirmed that in seven cases of them, there was a PDGFRA-FIP1L1 fusion. We also verified that two of nine patients with hyperposphorylated PDGFRA hold ETV6-PDGFRA and STRN-PDGFRA rearrangements. Importantly, nine cases also had significantly higher levels of PDGFRA mRNA expression when compared with healthy controls, and cases with no PDGFRA rearrangement. These findings highlight a robust correlation between hyperphosphorylation state of PDGFRA and aberrant PDGFRA gene fusions. This implicates phosflow as an efficient and reliable technique raising an intriguing possibility that it could replace other genomic and cDNA-amplification-based diagnostic approaches with limited effectiveness.

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.

Angioimmunoblastic T-cell lymphoma and hypereosinophilic syndrome with FIP1L1/PDGFRA fusion gene effectively treated with imatinib: A case report

RATIONALE

Hypereosinophilic syndrome (HES) is a rare disorder characterized by hypereosinophilia and organ damage. Some cases of HES are caused by the FIP1L1/PDGFRA fusion gene and respond to imatinib. FIP1L1/PDGFRA-positive HES occasionally evolves into chronic eosinophilic leukemia or into another form of myeloproliferative neoplasm; however, the development of a malignant lymphoma is very rare. We present a rare case of angioimmunoblastic T-cell lymphoma (AITL) and HES with the FIP1L1/PDGFRA gene rearrangement.

PATIENT CONCERNS

A man in his 30s presented to our hospital with fever, hypereosinophilia, widespread lymphadenopathy, and splenomegaly. Laboratory tests showed hypereosinophilia, increased soluble interleukin-2 receptor, and increased vitamin B12. Positron-emission tomography with F fluorodeoxyglucose (FDG) showed positive FDG uptake in multiple enlarged lymph nodes throughout the body and the red bone marrow. A bone-marrow biopsy showed hypereosinophilia without dysplasia and an increased number of blasts. The FIP1L1/PDGFRA fusion gene was positive upon fluorescence in situ hybridization (FISH) analysis of the peripheral blood. Furthermore, biopsy of a lymph node from the neck revealed restiform hyperplasia of capillary vessels, with small lymphoma cells arranged around the capillaries. Lymphoma cells were positive for CD3, CD4, and CD10, and negative for CD20. Lymphoma cells were also positive for the FIP1L1/PDGFRA fusion gene by FISH analysis.

DIAGNOSES

From these findings, the patient was diagnosed with HES and AITL with FIP1L1/PDGFRA.

INTERVENTIONS

After the diagnosis, corticosteroid was administered but was ineffective. Imatinib was then administered.

OUTCOMES

Imatinib was very effective for treating HES and AITL, and complete remission was achieved in both.

LESSONS

This report presents the first case in which the FIP1L1/PDGFRA fusion gene was positive both in peripheral blood and lymph nodes, implying the possibility that the tumor cells acquired the FIP1L1/PDGFRA fusion gene in the early stage of hematopoietic progenitor cell developments. Imatinib was very effective in treating both HES and lymphoma, suggesting that the FIP1L1/PDGFRA fusion gene plays a key role in the pathogenesis of both HES and lymphoma.

Expression of the interleukin-21 and phosphorylated extracellular signal regulated kinase 1/2 in Kimura disease

OBJECTIVE

To investigate the expressions of interleukin (IL)-21 and phosphorylated extracellular signal regulated kinase 1/2 (pERK1/2) in Kimura disease (KD) and to correlate the findings with clinical and prognostic variables.

METHODS

Immunohistochemical analysis of IL-21 and pERK1/2 was performed in 18 cases of KD and five gender- and age-matched control samples. Clinical data were extracted and patients followed up for a mean period of 32.1 months.

RESULTS

After a mean follow-up period of 32.1 months (range 1-102 months), recurrence was diagnosed as the end point for seven patients-that is, a 44% (7/16) cumulative recurrence rate. In comparison with gender- and age-matched controls, patients showed strong in situ expressions of IL-21 and pERK1/2, respectively (p<0.05). Patients with strong IL-21 staining intensity and overexpression of pERK1/2 had a lower recurrence rate than those with moderate staining intensity (p=0.049, p=0.019, respectively). However, differences were not statistically significant by gender, age, eosinophils, location, multiplicity, laterality, size, duration and primary outbreak. pERK1/2 was the independent prognostic factor (p=0.020), while age, gender, eosinophils, multiplicity, laterality, size, duration, primary outbreak and expression of IL-21 were not.

CONCLUSIONS

This study suggests that the IL-21/pERK1/2 pathway is activated in KD, and pERK1/2 might be considered as a potential prognostic indicator in KD.

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.

[FIP1L1-PDGFRА-positive myeloproliferative disease with eosinophilia: A rare case with multiple organ dysfunction and a response to tyrosine kinase inhibitor therapy]

The described case of FIP1L1-PDGFRА-positive myeloproliferative disease is characterized by an atypical aggressive course to develop severe specific complications as injuries to the brain, heart, lung, and intestine. Pathogenetic therapy with imatinib could stabilize a patient's state, but failed to produce a complete hematological response. Switching from imatinib to dasatinib could produce sustained clinical, hematological, and molecular remissions.

Eosinophilia in mast cell disease

Eosinophils and mast cells coexist in clonal and nonclonal disorders. The interplay between these cells is complex and not fully understood. Discussed are both allergic/nonclonal disorders in which both cell types are increased in number are likely to play a role in pathogenesis and clonal disorders in which both cell types are affected and play key roles in pathogenesis. Finally, some treatment options, keeping both disorders in mind, are discussed. Future directions in thinking about these disorders are also briefly explored.

The Differential Diagnosis of Eosinophilia in Neoplastic Hematopathology

Eosinophilia in the peripheral blood is classified as primary (clonal) hematologic neoplasms or secondary (nonclonal) disorders, associated with hematologic or nonhematologic disorders. This review focuses on the categories of hematolymphoid neoplasms recognized by the 2008 World Health Organization Classification of Tumours and Haematopoietic and Lymphoid Tissues that are characteristically associated with eosinophilia. We provide a systematic approach to the diagnosis of these neoplastic proliferations via morphologic, immunophenotypic, and molecular-based methodologies, and provide the clinical settings in which these hematolymphoid neoplasms occur. We discuss recommendations that eosinophilia working groups have published addressing some of the limitations of the current classification scheme.

Review of current classification, molecular alterations, and tyrosine kinase inhibitor therapies in myeloproliferative disorders with hypereosinophilia

Recent advances in our understanding of the molecular mechanisms underlying hypereosinophilia have led to the development of a ‘molecular’ classification of myeloproliferative disorders with eosinophilia. The revised 2008 World Health Organization classification of myeloid neoplasms included a new category called “myeloid and lymphoid neoplasms with eosinophilia and abnormalities of PDGFRA, PDGFRB or FGFR1.” Despite the molecular heterogeneity of PDGFR (platelet-derived growth factor receptor) rearrangements, tyrosine kinase inhibitors at low dose induce rapid and complete hematological remission in the majority of these patients. Other kinase inhibitors are promising. Further discoveries of new molecular alterations will direct the development of new specific inhibitors. In this review, an update of the classifications of myeloproliferative disorders associated with hypereosinophilia is discussed together with open and controversial questions. Molecular mechanisms and promising results of tyrosine kinase inhibitor treatments are reviewed.

Systemic mast cell activation disease: the role of molecular genetic alterations in pathogenesis, heritability and diagnostics

Despite increasing understanding of its pathophysiology, the aetiology of systemic mast cell activation disease (MCAD) remains largely unknown. Research has shown that somatic mutations in kinases are necessary for the establishment of a clonal mast cell population, in particular mutations in the tyrosine kinase Kit and in enzymes and receptors with crucial involvement in the regulation of mast cell activity. However, other, as yet undetermined, abnormalities are necessary for the manifestation of clinical disease. The present article reviews molecular genetic research into the identification of disease-associated genes and their mutational alterations. The authors also present novel data on familial systemic MCAD and review the associated literature. Finally, the importance of understanding the molecular basis of inherited mutations in terms of diagnostics and therapy is emphasized.

Mast cells and eosinophils in mastocytosis, chronic eosinophilic leukemia, and non-clonal disorders

Mast cells and eosinophils often travel in the same biologic circles. In non-clonal states, such as allergic and inflammatory conditions, cell-to-cell contact and the pleiotropic actions of multiple cytokines and chemokines, derived from local tissues or mast cells themselves, foster the co-recruitment of these cells to the same geographic cellular niche. While eosinophils and mast cells serve critical roles as part of the host immune response and in maintenance of normal homeostasis, these cell types can undergo neoplastic transformation due to the development of clonal molecular abnormalities that arise in early hematopoietic progenitors. The dysregulated tyrosine kinases, D816V KIT and FIP1L1-PDGFRA, are the prototypic oncogenic lesions resulting in systemic mastocytosis (SM) and chronic eosinophilic leukemia, respectively. We review the pathobiology of these myeloproliferative neoplasms (MPNs) with a focus on the relationship between mast cells and eosinophils, and discuss murine models, which further elucidate how the phenotype of these diseases can be influenced by stem cell factor (SCF) and expression of the potent eosinophilopoietic cytokine, interleukin-5 (IL-5). Therapy of SM and FIP1L1-PDGFRA-positive disease and the prognostic relevance of increased peripheral blood and tissue mast cells in hematolymphoid malignancies will also be addressed.

Markers of tyrosine kinase activity in eosinophilic esophagitis: a pilot study of the FIP1L1-PDGFRα fusion gene, pERK 1/2, and pSTAT5

The pathogenesis of eosinophilic esophagitis (EoE) is incompletely understood. In certain eosinophilic diseases, activation of tyrosine kinase after fusion of the Fip1-like-1 and platelet-derived growth factor receptor-α genes (F-P fusion gene) mediates eosinophilia via downstream effectors such as extracellular-regulated kinase (ERK1/2) and signal transducers and activators of transcription (STAT5). This mechanism has not been examined in EoE. Our aim was to detect the F-P fusion gene, pERK1/2, and pSTAT5 in esophageal tissue from patients with EoE, gastroesophageal reflux disease (GERD), and normal controls. We performed a cross-sectional pilot study comparing patients with steroid-responsive and steroid-refractory EoE, to GERD patients and normal controls. EoE cases were defined by consensus guidelines. Fluorescence in situ hybridization (FISH) was performed to detect the F-P fusion gene and immunohistochemistry (IHC) was performed to detect pERK1/2 and pSTAT5 in esophageal biopsies. Twenty-nine subjects (median age 30 years [range 1-59]; 16 males; 24 Caucasians) were included: eight normal, six GERD, and 15 EoE (five steroid-refractory). On FISH, 98%, 99%, and 99% of the nuclei in the normal, GERD, and EoE groups, respectively, were normal (P= 0.42). On IHC, a median of 250, 277, and 479 nuclei/mm(2) stained for pERK 1/2 in the normal, GERD, and EoE groups, respectively (P= 0.07); the refractory EoE patients had the highest degree pERK 1/2 staining (846 nuclei/mm(2); P= 0.07). No trend was seen for pSTAT5. In conclusion, the F-P fusion gene was not detected with increased frequency in EoE. Patients with EoE had a trend toward higher levels of pERK 1/2, but not STAT5, in the esophageal epithelium, with highest levels in steroid-refractory EoE patients.

Eosinophilic myeloproliferative disorders

Despite recent attempts to define and classify patients with marked eosinophilia and features consistent with myeloproliferative disease, areas of controversy remain. These are particularly apparent in situations in which multiple lineages are involved in a clonal process and clinical manifestations are overlapping. Although the introduction of new molecular diagnostics and targeted therapies has begun to clarify the boundaries between some of these disorders, several questions remain with respect to the classification of patients with myeloproliferative hypereosinophilic syndrome (HES) of unknown etiology.

[Synchronous detection of T-cell clonality and FIP1L1-PDGFRA fusion gene in a hypereosinophilic syndrome]

We report a 49-year-old man suffering from chronic hypereosinophilia whose biological tests revealed a gene rearrangement between FIP1L1 and PDGFRA as well as a T-cell clonality. After 1 year of therapy with imatinib mesylate (100 mg daily), the patient was clinically asymptomatic, the fusion transcript was undetectable using RTQ-PCR and no lymphoproliferative disorders occurred. This unique combination raises the question of the physiopathology of such a grey zone hypereosinophilia and their management.

FIP1L1/PDGFR alpha-associated systemic mastocytosis

Since the identification of the FIP1L1/PDGFRA fusion gene as a pathogenic cause of the hypereosinophilic syndrome (HES), the importance of the molecular classification of HES leading to the diagnosis of chronic eosinophilic leukemia (CEL) has been recognized. As a result, a new category, 'myeloid and lymphoid neoplasm with eosinophilia and abnormalities in PDGFRA, PDGFRB or FGFR1', has recently been added to the new WHO criteria for myeloid neoplasms. FIP1L1/PDGFR alpha-positive disorders are characterized by clonal hypereosinophilia, multiple organ dysfunctions due to eosinophil infiltration, systemic mastocytosis (SM) and a dramatic response to treatment with imatinib mesylate. A murine HES/CEL model by the introduction of FIP1L1/PDGFR alpha and IL-5 overexpression also shows SM, representing patients with FIP1L1/PDGFR alpha-positive HES/CEL/SM. The murine model and the in vitro development system of FIP1L1/PDGFR alpha-positive mast cells revealed the interaction between FIP1L1/PDGFR alpha, IL-5 and stem cell factor in the development of HES/CEL/SM. Current findings of FIP1L1/PDGFR alpha-positive HES/CEL are reviewed focusing on aberrant mast cell development leading to SM.

T-cell abnormalities are present at high frequencies in patients with hypereosinophilic syndrome

BACKGROUND

A T-cell clone, thought to be the source of eosinophilopoietic cytokines, identified by clonal rearrangement of the T-cell receptor and by the presence of aberrant T-cell immunophenotype in peripheral blood defines lymphocytic variant of hypereosinophilic syndrome (L-HES).

DESIGN AND METHODS

Peripheral blood samples from 42 patients who satisfied the diagnostic criteria for HES were studied for T-cell receptor clonal rearrangement by polymerase chain reaction according to BIOMED-2. The T-cell immunophenotype population was assessed in peripheral blood by flow cytometry. The FIP1L1-PDGFRA fusion gene was detected by nested polymerase chain reaction.

RESULTS

Forty-two HES patients (18 males and 24 females) with a median age at diagnosis of 56 years (range 17-84) were examined in this study. Their median white blood cell count was 12.9 x 10(9)/L (range 5.3-121), with an absolute eosinophil count of 4.5 x 10(9)/L (range 1.5-99) and a median eosinophilic bone marrow infiltration of 30% (range 11-64). Among the 42 patients, clonal T-cell receptor rearrangements were detected in 18 patients (42.8%). Patients with T-cell receptor clonality included: T-cell receptor beta in 15 patients (35%), T-cell receptor gamma in 9 (21%) and T-cell receptor delta in 9 (21%) patients, respectively. Clonality was detected in all three T-cell receptor loci in 4 cases, in two loci in 7 patients and in one T-cell receptor locus in the remaining 7 patients. The FIP1L1-PDGFRA fusion transcript was absent in all but 2 patients with T-cell receptor clonality. Three patients out of 42 revealed an aberrant T-cell immunophenotype. In some patients, an abnormal CD4:CD8 ratio was demonstrated.

CONCLUSIONS

T-cell abnormalities are present at high frequencies in patients with HES.

Philadelphia chromosome-negative chronic myeloproliferative disease

Session 2 of the 2007 Workshop of the Society for Hematopathology/European Association for Haematopathology was focused on Philadelphia chromosome-negative chronic myeloproliferative diseases (Ph- MPDs), recently termed chronic myeloproliferative neoplasms. The presented and submitted cases highlighted some important issues and also impending problems associated with the diagnosis and classification. Cases included predominantly rare entities like chronic eosinophilic leukemia and related disorders, chronic neutrophilic leukemia, and others with specific genetic abnormalities that allowed molecularly targeted therapy. In this context, the distinctive role of a positive JAK2(V617F) mutation for the diagnosis of Ph- MPD was underscored, including entities with a low allele burden and the discrimination from reactive disorders (autoimmune myelofibrosis, reactive thrombocytosis). Although novel genetic and molecular approaches have significantly improved the way we classify Ph- MPD, a combined clinicopathologic approach, including representative bone marrow specimens, still remains the yardstick for diagnosis.

The hypereosinophilic syndromes: current concepts and treatments

The hypereosinophilic syndromes (HES) encompass a spectrum of diseases that have increased blood eosinophils and tissue damage in common. The clinical manifestations are protean and may involve any organ system, but especially the skin. Our understanding of these diseases has drastically changed over the past 15 years, along with new classifications that characterize patients with marked eosinophilia. One HES variant, myeloproliferative, is actually chronic eosinophilic leukaemia with a unique genetic marker, FIP1L1-PDGFRA. Such patients are well-controlled by administration of the kinase inhibitor, imatinib, and remissions appear durable with continued imatinib therapy. FIP1L1-PDGFRA is expressed in several cell lineages, thus explaining increases in neutrophils and mast cells in HES. The lymphocytic HES variant is associated with T-cell clones producing interleukin-5 (IL-5) and can evolve into lymphoma. While myeloproliferative and lymphocytic HES are well established and permit elimination of the term, idiopathic, to these varieties, most HES patients do not fall into these categories and are classified as complex (using the 2006 Workshop Report). A recent study showed that a monoclonal antibody to IL-5, mepolizumab, reduced glucocorticoid therapy in HES patients who did not possess the FIP1L1-PDGFRA mutation while controlling eosinophilia and preventing recurrence or progression of tissue damage. These advances augur well for continued progress in the understanding and treatment of HES.

[Hematological disorders and hypereosinophilias]

Hematological disorders are the third cause of hypereosinophilia, after allergic and parasitic diseases. Hematological disorders associated with hypereosinophilias can be classified as clonal, reactive or idiopathic, and recently the improvements of cytogenetic, molecular biology and immunology have allowed to revisit numerous cases previously diagnosed as idiopathic hypereosinophilic syndrome. Reactive eosinophilias are mainly associated with lymphoma or abnormal, often clonal T lymphoid population. Clonal eosinophilia is related either to various myeloid malignancies or to a genuine myeloproliferative disorder from the eosinophile lineage, the so-called chronic eosinophilic leukaemia. Chronic eosinophilic leukaemia can be associated with recurrent genes rearrangements involving PDGFRA, PDGFRB and FGFR1 or with clonal abnormalities not yet categorized. Idiopathic hypereosinophilic syndrome remains an exclusive diagnosis in presence of moderate or severe unexplained eosinophilia with target organ damage. The purpose of the diagnostic work-up of hypereosinophilic syndrome is to evidence either an abnormal T cell population or a clonal haematopoiesis. Imatinib mesylate dramatically improves chronic eosinophilic leukaemias associated with PDGFR abnormalities, while corticosteroids are still the main treatment for the other patients. In a near future, advances could arise from identification of new genes involved in clonal eosinophilia or in alternative therapy such as the anti-IL-5 antibodies.

FIP1L1-PDGFRalpha imposes eosinophil lineage commitment on hematopoietic stem/progenitor cells

Although leukemogenic tyrosine kinases (LTKs) activate a common set of downstream molecules, the phenotypes of leukemia caused by LTKs are rather distinct. Here we report the molecular mechanism underlying the development of hypereosinophilic syndrome/chronic eosinophilic leukemia by FIP1L1-PDGFRalpha. When introduced into c-Kit(high)Sca-1(+)Lineage(-) cells, FIP1L1-PDGFRalpha conferred cytokine-independent growth on these cells and enhanced their self-renewal, whereas it did not immortalize common myeloid progenitors in in vitro replating assays and transplantation assays. Importantly, FIP1L1-PDGFRalpha but not TEL-PDGFRbeta enhanced the development of Gr-1(+)IL-5Ralpha(+) eosinophil progenitors from c-Kit(high)Sca-1(+)Lineage(-) cells. FIP1L1-PDGFRalpha also promoted eosinophil development from common myeloid progenitors. Furthermore, when expressed in megakaryocyte/erythrocyte progenitors and common lymphoid progenitors, FIP1L1-PDGFRalpha not only inhibited differentiation toward erythroid cells, megakaryocytes, and B-lymphocytes but aberrantly developed eosinophil progenitors from megakaryocyte/erythrocyte progenitors and common lymphoid progenitors. As for the mechanism of FIP1L1-PDGFRalpha-induced eosinophil development, FIP1L1-PDGFRalpha was found to more intensely activate MEK1/2 and p38(MAPK) than TEL-PDGFRbeta. In addition, a MEK1/2 inhibitor and a p38(MAPK) inhibitor suppressed FIP1L1-PDGFRalpha-promoted eosinophil development. Also, reverse transcription-PCR analysis revealed that FIP1L1-PDGFRalpha augmented the expression of C/EBPalpha, GATA-1, and GATA-2, whereas it hardly affected PU.1 expression. In addition, short hairpin RNAs against C/EBPalpha and GATA-2 and GATA-3KRR, which can act as a dominant-negative form over all GATA members, inhibited FIP1L1-PDGFRalpha-induced eosinophil development. Furthermore, FIP1L1-PDGFRalpha and its downstream Ras inhibited PU.1 activity in luciferase assays. Together, these results indicate that FIP1L1-PDGFRalpha enhances eosinophil development by modifying the expression and activity of lineage-specific transcription factors through Ras/MEK and p38(MAPK) cascades.

Molecular drug targets in myeloproliferative neoplasms: mutant ABL1, JAK2, MPL, KIT, PDGFRA, PDGFRB and FGFR1

Therapeutically validated oncoproteins in myeloproliferative neoplasms (MPN) include BCR-ABL1 and rearranged PDGFR proteins. The latter are products of intra- (e.g. FIP1L1-PDGFRA) or inter-chromosomal (e.g.ETV6-PDGFRB) gene fusions. BCR-ABL1 is associated with chronic myelogenous leukaemia (CML) and mutant PDGFR with an MPN phenotype characterized by eosinophilia and in addition, in case of FIP1L1-PDGFRA, bone marrow mastocytosis. These genotype-phenotype associations have been effectively exploited in the development of highly accurate diagnostic assays and molecular targeted therapy. It is hoped that the same will happen in other MPN with specific genetic alterations: polycythemia vera (JAK2V617F and other JAK2 mutations), essential thrombocythemia (JAK2V617F and MPL515 mutations), primary myelofibrosis (JAK2V617F and MPL515 mutations), systemic mastocytosis (KITD816V and other KIT mutations) and stem cell leukaemia/lymphoma (ZNF198-FGFR1 and other FGFR1 fusion genes). The current review discusses the above-listed mutant molecules in the context of their value as drug targets.

FIP1L1/PDGFRalpha synergizes with SCF to induce systemic mastocytosis in a murine model of chronic eosinophilic leukemia/hypereosinophilic syndrome

Expression of the fusion gene FIP1-like 1/platelet-derived growth factor receptor alpha (FIP1L1/PDGFRalpha, F/P) and dysregulated c-kit tyrosine kinase activity are associated with systemic mastocytosis (SM) and chronic eosinophilic leukemia (CEL)/hypereosinophilic syndrome (HES). We analyzed SM development and pathogenesis in a murine CEL model induced by F/P in hematopoietic stem cells and progenitors (HSCs/Ps) and T-cell overexpression of IL-5 (F/P-positive CEL mice). These mice had more mast cell (MC) infiltration in the bone marrow (BM), spleen, skin, and small intestine than control mice that received a transplant of IL-5 transgenic HSCs/Ps. Moreover, intestinal MC infiltration induced by F/P expression was severely diminished, but not abolished, in mice injected with neutralizing anti-c-kit antibody, suggesting that endogenous stem cell factor (SCF)/c-kit interaction synergizes with F/P expression to induce SM. F/P-expressing BM HSCs/Ps showed proliferation and MC differentiation in vitro in the absence of cytokines. SCF stimulated greater migration of F/P-expressing MCs than mock vector-transduced MCs. F/P-expressing bone marrow-derived mast cells (BMMCs) survived longer than mock vector control BMMCs in cytokine-deprived conditions. The increased proliferation and survival correlated with increased SCF-induced Akt activation. In summary, F/P synergistically promotes MC development, activation, and survival in vivo and in vitro in response to SCF.

Successful imatinib treatment of cardiac involvement of FIP1L1-PDGFRA-positive chronic eosinophilic leukemia followed by severe hepatotoxicity

Imatinib is highly effective for the treatment of chronic eosinophilic leukemia (CEL) caused by the FIP1L1-PDGFRA fusion gene. However, its effectiveness for cardiac involvement of CEL has remained unclear. We describe a 46-year-old man with CEL treated with imatinib. Reverse transcriptase-polymerase chain reaction and sequencing analyses revealed a FIP1L1-PDGFRA fusion transcript with FIP1L1 intron 10 fused to PDGFRA exon 12, and fluorescent in situ hybridization analysis confirmed the interstitial deletion in chromosome 4q12. On admission, the patient had left heart failure accompanied by a large thrombus in the left ventricle. After pretreatment with furosemide and prednisolone, we started imatinib treatment at 100 mg/day. Eosinophilia disappeared within 1 week, and the left ventricular thrombus was resolved within 5 months. At 6 months after starting imatinib, the patient showed grade 4 liver dysfunction. A liver biopsy revealed hepatocyte necrosis with lymphocyte infiltration. Fortunately, the FIP1L1-PDGFRA fusion transcript had become undetectable, and imatinib treatment was stopped. The liver dysfunction resolved within a month. Although the CEL relapsed 6 months later, imatinib could be successfully resumed in combination with 25 mg/day of prednisolone. Thus, imatinib may be very effective for treating the early cardiac involvement of FIP1L1-PDGFRA-positive CEL, but it needs to be used cautiously.

Chronic eosinophilic leukemias and the myeloproliferative variant of the hypereosinophilic syndrome

Among patients with hypereosinophilia, a myeloproliferative variant is recognized. In many of these patients a diagnosis of eosinophilic leukemia can be made. The molecular mechanism is often a fusion gene, incorporating part of PDGFRA or PDGFRB, encoding anaberrant tyrosine kinase. Prompt diagnosis of such cases is important since specific tyrosine kinase inhibitor therapy is indicated.

Synchronous FIP1L1-PDGFRA-positive chronic eosinophilic leukemia and T-cell lymphoblastic lymphoma: a bilineal clonal malignancy

Several reports of successful empirical treatment of idiopathic hypereosinophilic syndrome with imatinib led to the recent identification of the FIP1L1-PDGFRA fusion gene rearrangement, which characterizes a distinctive group of chronic eosinophilic leukemias. This fusion gene can be detected in eosinophils, neutrophils, mast cells, T cells, B cells and monocytes in FIP1L1-PDGFRA-positive hypereosinophilic patients suggesting a multilineage involvement. Furthermore, the same FIP1L1-PDGFRA rearrangement was identified in patients with hypereosinophilia and atypical mast cell proliferations, raising the question of a disease with two concomitant lines of differentiation. In addition, a recent report noted two cases with the association of FIP1L1-PDGFRA-positive chronic eosinophilic leukemia and T-cell lymphoblastic lymphoma (T-LBL). We report here the only third case of synchronous chronic eosinophilic leukemia and T-LBL, both associated with a FIP1L1-PDGFRA fusion transcript, confirming the occurrence of such disease and suggesting a clonal proliferation with two lines of differentiation probably arising from a primitive multipotent medullary stem cell.

Classification and diagnosis of myeloproliferative neoplasms: the 2008 World Health Organization criteria and point-of-care diagnostic algorithms

The 2001 World Health Organization (WHO) treatise on the classification of hematopoietic tumors lists chronic myeloproliferative diseases (CMPDs) as a subdivision of myeloid neoplasms that includes the four classic myeloproliferative disorders (MPDs)-chronic myelogenous leukemia, polycythemia vera (PV), essential thrombocythemia (ET) and primary myelofibrosis (PMF)-as well as chronic neutrophilic leukemia (CNL), chronic eosinophilic leukemia/hypereosinophilic syndrome (CEL/HES) and 'CMPD, unclassifiable'. In the upcoming 4th edition of the WHO document, due out in 2008, the term 'CMPDs' is replaced by 'myeloproliferative neoplasms (MPNs)', and the MPN category now includes mast cell disease (MCD), in addition to the other subcategories mentioned above. At the same time, however, myeloid neoplasms with molecularly characterized clonal eosinophilia, previously classified under CEL/HES, are now removed from the MPN section and assembled into a new category of their own. The WHO diagnostic criteria for both the classic BCR-ABL-negative MPDs (that is PV, ET and PMF) and CEL/HES have also been revised, in the 2008 edition, by incorporating new information on their molecular pathogenesis. The current review highlights these changes and also provides diagnostic algorithms that are tailored to routine clinical practice.

Hypereosinophilic syndromes

Hypereosinophilic syndromes (HES) constitute a rare and heterogeneous group of disorders, defined as persistent and marked blood eosinophilia (> 1.5 × 10⁹/L for more than six consecutive months) associated with evidence of eosinophil-induced organ damage, where other causes of hypereosinophilia such as allergic, parasitic, and malignant disorders have been excluded. Prevalence is unknown. HES occur most frequently in young to middle-aged patients, but may concern any age group. Male predominance (4–9:1 ratio) has been reported in historic series but this is likely to reflect the quasi-exclusive male distribution of a sporadic hematopoietic stem cell mutation found in a recently characterized disease variant. Target-organ damage mediated by eosinophils is highly variable among patients, with involvement of skin, heart, lungs, and central and peripheral nervous systems in more than 50% of cases. Other frequently observed complications include hepato- and/or splenomegaly, eosinophilic gastroenteritis, and coagulation disorders. Recent advances in underlying pathogenesis have established that hypereosinophilia may be due either to primitive involvement of myeloid cells, essentially due to occurrence of an interstitial chromosomal deletion on 4q12 leading to creation of the FIP1L1-PDGFRA fusion gene (F/P⁺ variant), or to increased interleukin (IL)-5 production by a clonally expanded T cell population (lymphocytic variant), most frequently characterized by a CD3^-CD4⁺ phenotype. Diagnosis of HES relies on observation of persistent and marked hypereosinophilia responsible for target-organ damage, and exclusion of underlying causes of hypereosinophilia, including allergic and parasitic disorders, solid and hematological malignancies, Churg-Strauss disease, and HTLV infection. Once these criteria are fulfilled, further testing for eventual pathogenic classification is warranted using appropriate cytogenetic and functional approaches. Therapeutic management should be adjusted to disease severity and eventual detection of pathogenic variants. For F/P⁺ patients, imatinib has undisputedly become first line therapy. For others, corticosteroids are generally administered initially, followed by agents such as hydroxycarbamide, interferon-alpha, and imatinib, for corticosteroid-resistant cases, as well as for corticosteroid-sparing purposes. Recent data suggest that mepolizumab, an anti-IL-5 antibody, is an effective corticosteroid-sparing agent for F/P-negative patients. Prognosis has improved significantly since definition of HES, and currently depends on development of irreversible heart failure, as well as eventual malignant transformation of myeloid or lymphoid cells.

Relapse following discontinuation of imatinib mesylate therapy for FIP1L1/PDGFRA-positive chronic eosinophilic leukemia: implications for optimal dosing

Although imatinib is clearly the treatment of choice for FIP1L1/PDGFRA-positive chronic eosinophilic leukemia (CEL), little is known about optimal dosing, duration of treatment, and the possibility of cure in this disorder. To address these questions, 5 patients with FIP1L1/PDGFRA-positive CEL with documented clinical, hematologic, and molecular remission on imatinib (400 mg daily) and without evidence of cardiac involvement were enrolled in a dose de-escalation trial. The imatinib dose was tapered slowly with close follow-up for evidence of clinical, hematologic, and molecular relapse. Two patients with endomyocardial fibrosis were maintained on imatinib 300 to 400 mg daily and served as controls. All 5 patients who underwent dose de-escalation, but neither of the control patients, experienced molecular relapse (P < .05). None developed recurrent symptoms, and eosinophil counts, serum B12, and tryptase levels remained suppressed. Reinitiation of therapy at the prior effective dose led to molecular remission in all 5 patients, although 2 patients subsequently required increased dosing to maintain remission. These data are consistent with suppression rather than elimination of the clonal population in FIP1L1/PDGFRA-positive CEL and suggest that molecular monitoring may be the most useful method in determining optimal dosing without the risk of disease exacerbation. This trial was registered at http://www.clinicaltrials.gov as no. NCT00044304.

Systemic mastocytosis: a concise clinical and laboratory review

CONTEXT

Systemic mastocytosis is characterized by abnormal growth and accumulation of neoplastic mast cells in various organs. The clinical presentation is varied and may include skin rash, symptoms related to release of mast cell mediators, and/or organopathy from involvement of bone, liver, spleen, bowel, or bone marrow.

OBJECTIVE

To concisely review pathogenesis, disease classification, clinical features, diagnosis, and treatment of mast cell disorders.

DATA SOURCES

Pertinent literature emerging during the last 20 years in the field of mast cell disorders.

CONCLUSIONS

The cornerstone of diagnosis is careful bone marrow histologic examination with appropriate immunohistochemical studies. Ancillary tests such as mast cell immunophenotyping, cytogenetic/molecular studies, and serum tryptase levels assist in confirming the diagnosis. Patients with cutaneous disease or with low systemic mast cell burden are generally managed symptomatically. In the patients requiring mast cell cytoreductive therapy, treatment decisions are increasingly being guided by results of molecular studies. Most patients carry the kit D816V mutation and are predicted to be resistant to imatinib mesylate (Gleevec) therapy. In contrast, patients carrying the FIP1L1-PDGFRA mutation achieve complete responses with low-dose imatinib therapy. Other therapeutic options include use of interferon-alpha, chemotherapy (2-chlorodeoxyadenosine), or novel small molecule tyrosine kinase inhibitors currently in clinical trials.

KIT D816V-associated systemic mastocytosis with eosinophilia and FIP1L1/PDGFRA-associated chronic eosinophilic leukemia are distinct entities

BACKGROUND

The broad and overlapping clinical manifestations of D816V KIT-associated systemic mastocytosis with eosinophilia and FIP1L1/PDGFRA-associated chronic eosinophilic leukemia (CEL), coupled with the increase in activated eosinophils and mast cells seen in both disorders, have led to confusion in the nomenclature. It is of paramount importance, however, to distinguish between these 2 groups of patients because of differences in clinical sequelae, prognoses, and selection of treatment.

OBJECTIVE

We thus sought to identify clinical and laboratory features that could be used to distinguish these 2 diagnoses.

METHODS

We compared 12 patients with D816V-positive systemic mastocytosis with eosinophilia with 17 patients with FIP1L1/PDGFRA-positive CEL. Distinguishing features were used to create a risk factor scoring system.

RESULTS

This system correctly classified 16 of 17 FIP1L1/PDGFRA-positive patients with CEL and all 12 patients with systemic mastocytosis with eosinophilia. Thirty-four FIP1L1/PDGFRA-positive patients described in the literature were also classified using this system, and although a complete set of data was not available for any of the historical patients, 21 were correctly classified.

CONCLUSION

These results reinforce the hypothesis that the FIP1L1/PDGFRA gene fusion and D816V-KIT mutation cause distinct clinical syndromes.

CLINICAL IMPLICATIONS

This novel diagnostic approach should prove helpful in clinical practice in the evaluation of patients with increased mast cells and peripheral eosinophilia.

Molecular mechanisms underlying FIP1L1-PDGFRA-mediated myeloproliferation

An interstitial deletion on chromosome 4q12 resulting in the formation of the FIP1L1-PDGFRA fusion protein is involved in the pathogenesis of imatinib-sensitive chronic eosinophilic leukemia. The molecular mechanisms underlying the development of disease are largely undefined. Human CD34(+) hematopoietic progenitor cells were used to investigate the role of FIP1L1-PDGFRA in modulating lineage development. FIP1L1-PDGFRA induced both proliferation and differentiation of eosinophils, neutrophils, and erythrocytes in the absence of cytokines, which could be inhibited by imatinib. Whereas expression of FIP1L1-PDGFRA in hematopoietic stem cells and common myeloid progenitors induced the formation of multiple myeloid lineages, expression in granulocyte-macrophage progenitors induced only the development of eosinophils, neutrophils, and myeloblasts. Deletion of amino acids 30 to 233 in the FIP1L1 gene [FIP1L1(1-29)-PDGFRA] gave rise to an intermediate phenotype, exhibiting a dramatic reduction in the number of erythrocytes. FIP1L1-PDGFRA and FIP1L1(1-29)-PDGFRA both induced the activation of p38 and extracellular signal-regulated kinase 1/2 (ERK1/2) in myeloid progenitors, whereas signal transducers and activators of transcription 5 (STAT5) and protein kinase B/c-akt were only activated by FIP1L1-PDGFRA. Dominant-negative STAT5 partially inhibited FIP1L1-PDGFRA-induced colony formation, whereas combined inhibition of phosphatidylinositol-3-kinase and ERK1/2 significantly reversed FIP1L1-PDGFRA-induced colony formation. Taken together, these results suggest that expression of FIP1L1-PDFGRA in human hematopoietic progenitors induce a myeloproliferative phenotype via activation of multiple signaling molecules including phosphatidylinositol-3-kinase, ERK1/2, and STAT5.

Recurrent finding of the FIP1L1-PDGFRA fusion gene in eosinophilia-associated acute myeloid leukemia and lymphoblastic T-cell lymphoma

The FIP1L1-PDGFRA fusion gene has been described in patients with eosinophilia-associated myeloproliferative disorders (Eos-MPD). Here, we report on seven FIP1L1-PDGFRA-positive patients who presented with acute myeloid leukemia (AML, n=5) or lymphoblastic T-cell non-Hodgkin-lymphoma (n=2) in conjunction with AML or Eos-MPD. All patients were male, the median age was 58 years (range, 40-66). AML patients were negative for common mutations of FLT3, NRAS, NPM1, KIT, MLL and JAK2; one patient revealed a splice mutation of RUNX1 exon 7. Patients were treated with imatinib (100 mg, n=5; 400 mg, n=2) either as monotherapy (n=2), as maintenance treatment after intensive chemotherapy (n=3) or in overt relapse 43 and 72 months, respectively, after primary diagnosis and treatment of FIP1L1-PDGFRA-positive disease (n=2). All patients are alive, disease-free and in complete hematologic and complete molecular remission after a median time of 20 months (range, 9-36) on imatinib. The median time to achievement of complete molecular remission was 6 months (range, 1-14). We conclude that all eosinophilia-associated hematological malignancies should be screened for the presence of the FIP1L1-PDGFRA fusion gene as they are excellent candidates for treatment with tyrosine kinase inhibitors even if they present with an aggressive phenotype such as AML.

Platelet-derived growth factor receptor-alpha-associated hypereosinophilic syndrome and lymphomatoid papulosis

Fip1-like 1/platelet-derived growth factor receptor-alpha (FIP1L1/PDGFRA)-positive hypereosinophilic syndrome is a rare disorder with a poor prognosis if untreated and for which treatment with imatinib mesilate is highly effective. A 33-year-old man presented with recurrent papular skin lesions and marked peripheral eosinophilia. Skin biopsy revealed proliferation of CD30(+) T cells consistent with lymphomatoid papulosis (LyP), whereas molecular analysis of peripheral blood mononuclear cells demonstrated the presence of the FIP1L1/PDGFRA fusion gene. As the presence of this gene has important prognostic and therapeutic implications, this report underscores the importance of molecular testing in the evaluation of patients with LyP and peripheral eosinophilia.

Diagnosis and treatment of hypereosinophilic syndromes

PURPOSE OF REVIEW

The aim of this article is to provide an update of causes of hypereosinophilia, including advances in knowledge of eosinophilic leukemia, and to outline an approach to investigation. We also aim to discuss in more detail the diagnosis and management of various hypereosinophilic syndromes including the clonal eosinophilias and those driven by abnormal cytokine-secreting T cells.

RECENT FINDINGS

Our understanding of the causative genetic abnormalities in eosinophilic leukemia is increasing, as is the repertoire of techniques available to detect them. New treatments on the horizon include further tyrosine kinase inhibitors for use in eosinophilic leukemia, which should provide an alternative to imatinib for those patients who develop resistance. These may also prove useful for other hypereosinophilic syndromes without PDGFRA or PDGFRB rearrangements. Other new therapies including anti-IL5 monoclonal antibodies are proving beneficial for some patients, especially those with abnormal T-cell populations.

SUMMARY

As our understanding of the various hypereosinophilic syndromes increases, and we are able to characterize many of the causative genetic lesions in the clonal eosinophilias, we are increasingly able to select appropriate therapy for an individual patient. New therapies based on this knowledge should serve to further improve the prognosis for many patients with hypereosinophilia.