Identification of a novel imatinib responsive KIF5B-PDGFRA fusion gene following screening for PDGFRA overexpression in patients with hypereosinophilia

Tyrosine phosphorylation of CARM1 promotes its enzymatic activity and alters its target specificity

An important epigenetic component of tyrosine kinase signaling is the phosphorylation of histones, and epigenetic readers, writers, and erasers. Phosphorylation of protein arginine methyltransferases (PRMTs), have been shown to enhance and impair their enzymatic activity. In this study, we show that the hyperactivation of Janus kinase 2 (JAK2) by the V617F mutation phosphorylates tyrosine residues (Y149 and Y334) in coactivator-associated arginine methyltransferase 1 (CARM1), an important target in hematologic malignancies, increasing its methyltransferase activity and altering its target specificity. While non-phosphorylatable CARM1 methylates some established substrates (e.g. BAF155 and PABP1), only phospho-CARM1 methylates the RUNX1 transcription factor, on R223 and R319. Furthermore, cells expressing non-phosphorylatable CARM1 have impaired cell-cycle progression and increased apoptosis, compared to cells expressing phosphorylatable, wild-type CARM1, with reduced expression of genes associated with G2/M cell cycle progression and anti-apoptosis. The presence of the JAK2-V617F mutant kinase renders acute myeloid leukemia (AML) cells less sensitive to CARM1 inhibition, and we show that the dual targeting of JAK2 and CARM1 is more effective than monotherapy in AML cells expressing phospho-CARM1. Thus, the phosphorylation of CARM1 by hyperactivated JAK2 regulates its methyltransferase activity, helps select its substrates, and is required for the maximal proliferation of malignant myeloid cells.

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

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

Hematological Neoplasms with Eosinophilia

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

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

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

FIP1L1-PDGFRA fusion gene in T-lymphoblastic lymphoma: A case report

BACKGROUND

T-lymphoblastic lymphoma (T-LBL) is an aggressive malignancy of T-lymphoid precursors, rarely co-occurring with myeloid/lymphoid neoplasms with eosinophilia (M/LNs-Eo), with consequent rearrangement of tyrosine kinase (TK)-related genes. The FIP1L1-PDGFRA fusion gene is the most frequent molecular abnormality seen in eosinophilia-associated myeloproliferative disorders, but is also present in acute myeloid leukemia (AML), T-lymphoblastic leukemia/lymphoma (TLL), or both simultaneously. T-LBL mainly affects children and young adults, involving lymph node, bone marrow, and thymus. It represents about 85% of all immature lymphoblastic lymphomas, whereas immature B-cell lymphomas comprise approximately 15% of all cases of LBL.

CASE

In this case report, we present an example of T cell lymphoblastic lymphoma with coexistent eosinophelia, treated successfully with a tyrosine-kinase inhibitor (TKI).

CONCLUSION

FIP1L1-PDGFRA-positive T-LBL and myeloproliferative disorders have excellent response to low-dose treatment with (TKI) imatinib. Most patients achieve rapid and complete hematologic and molecular remission within weeks.

Receptor Tyrosine Kinases and Their Signaling Pathways as Therapeutic Targets of Curcumin in Cancer

Receptor tyrosine kinases (RTKs) are transmembrane cell-surface proteins that act as signal transducers. They regulate essential cellular processes like proliferation, apoptosis, differentiation and metabolism. RTK alteration occurs in a broad spectrum of cancers, emphasising its crucial role in cancer progression and as a suitable therapeutic target. The use of small molecule RTK inhibitors however, has been crippled by the emergence of resistance, highlighting the need for a pleiotropic anti-cancer agent that can replace or be used in combination with existing pharmacological agents to enhance treatment efficacy. Curcumin is an attractive therapeutic agent mainly due to its potent anti-cancer effects, extensive range of targets and minimal toxicity. Out of the numerous documented targets of curcumin, RTKs appear to be one of the main nodes of curcumin-mediated inhibition. Many studies have found that curcumin influences RTK activation and their downstream signaling pathways resulting in increased apoptosis, decreased proliferation and decreased migration in cancer both in vitro and in vivo. This review focused on how curcumin exhibits anti-cancer effects through inhibition of RTKs and downstream signaling pathways like the MAPK, PI3K/Akt, JAK/STAT, and NF-κB pathways. Combination studies of curcumin and RTK inhibitors were also analysed with emphasis on their common molecular targets.

Eosinophilic Granulomatosis With Polyangiitis: Dissecting the Pathophysiology

Eosinophilic Granulomatosis with Polyangiitis (EGPA) is a rare multisystemic disease classified both amongst hypereosinophilic disorders and ANCA-associated vasculitis. Vessel inflammation and eosinophilic proliferation are the hallmarks of the disease and main effectors of organ damage. Two distinct disease phenotypes have classically been described according to ANCA-status: the ANCA-negative subset with eosinophil-driven manifestation and the ANCA-positive one with vasculitic manifestations. An analogous dichotomization has also been backed by histological findings and a distinct genetic background. EGPA is typically consider a Th2-mediated disease and blood and tissue eosinophilia represent the cornerstone of diagnosis. Besides, ANCA are known for inducing endothelial injury and vascular inflammation by activating the circulating neutrophils. Thus, the pathogenesis of EGPA seems to be mediated by two coexisting mechanisms. However, the verbatim application of this strict dualism cannot always be translated into routine clinical practice. In the present review we describe the current knowledge on the eosinophilic and ANCA-mediated aspects of EGPA pathogenesis. Finally, we review the rationale of the currently proposed EGPA dichotomy and future research perspectives.

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.

RET fusions in solid tumors

The RET proto-oncogene has been well-studied. RET is involved in many different physiological and developmental functions. When altered, RET mutations influence disease in a variety of organ systems from Hirschsprung's disease and multiple endocrine neoplasia 2 (MEN2) to papillary thyroid carcinoma (PTC) and non-small cell lung cancer (NSCLC). Changes in RET expression have been discovered in 30-70% of invasive breast cancers and 50-60% of pancreatic ductal adenocarcinomas in addition to colorectal adenocarcinoma, melanoma, small cell lung cancer, neuroblastoma, and small intestine neuroendocrine tumors. RET mutations have been associated with tumor proliferation, invasion, and migration. RET fusions or rearrangements are somatic juxtapositions of 5' sequences from other genes with 3' RET sequences encoding tyrosine kinase. RET rearrangements occur in approximately 2.5-73% of sporadic PTC and 1-3% of NSCLC patients. The most common RET fusions are CDCC6-RET and NCOA4-RET in PTC and KIF5B-RET in NSCLC. Tyrosine kinase inhibitors are drugs that target kinases such as RET in RET-driven (RET-mutation or RET-fusion-positive) disease. Multikinase inhibitors (MKI) target various kinases and other receptors. Several MKIs are FDA-approved for cancer therapy (sunitinib, sorafenib, vandetanib, cabozantinib, regorafenib, ponatinib, lenvatinib, alectinib) and non-oncologic disease (nintedanib). Selective RET inhibitor drugs LOXO-292 (selpercatinib) and BLU-667 (pralsetinib) are also undergoing phase I/II and I clinical trials, respectively, with preliminary results demonstrating partial response and low incidence of serious adverse events. RET fusions provide a viable therapeutic target for oncologic treatment, and further study is warranted into the prevalence and pathogenesis of RET fusions as well as development of current and new tyrosine kinase inhibitors.

Natural Selection Equally Supports the Human Tendencies in Subordination and Domination: A Genome-Wide Study With in silico Confirmation and in vivo Validation in Mice

We proposed the following heuristic decision-making rule: "IF {an excess of a protein relating to the nervous system is an experimentally known physiological marker of low pain sensitivity, fast postinjury recovery, or aggressive, risk/novelty-seeking, anesthetic-like, or similar agonistic-intolerant behavior} AND IF {a single nucleotide polymorphism (SNP) causes overexpression of the gene encoding this protein} THEN {this SNP can be a SNP marker of the tendency in dominance} WHILE {underexpression corresponds to subordination} AND vice versa." Using this decision-making rule, we analyzed 231 human genes of neuropeptidergic, non-neuropeptidergic, and neurotrophinergic systems that encode neurotrophic and growth factors, interleukins, neurotransmitters, receptors, transporters, and enzymes. These proteins are known as key factors of human social behavior. We analyzed all the 5,052 SNPs within the 70 bp promoter region upstream of the position where the protein-coding transcript starts, which were retrieved from databases Ensembl and dbSNP using our previously created public Web service SNP_TATA_Comparator (http://beehive.bionet.nsc.ru/cgi-bin/mgs/tatascan/start.pl). This definition of the promoter region includes all TATA-binding protein (TBP)-binding sites. A total of 556 and 552 candidate SNP markers contributing to the dominance and the subordination, respectively, were uncovered. On this basis, we determined that 231 human genes under study are subject to natural selection against underexpression (significance p < 0.0005), which equally supports the human tendencies in domination and subordination such as the norm of a reaction (plasticity) of the human social hierarchy. These findings explain vertical transmission of domination and subordination traits previously observed in rodent models. Thus, the results of this study equally support both sides of the century-old unsettled scientific debate on whether both aggressiveness and the social hierarchy among humans are inherited (as suggested by Freud and Lorenz) or are due to non-genetic social education, when the children are influenced by older individuals across generations (as proposed by Berkowitz and Fromm).

Oncogenic Function of a KIF5B-MET Fusion Variant in Non-Small Cell Lung Cancer

A kinesin family member 5b (KIF5B)-MET proto-oncogene, receptor tyrosine kinase (MET) rearrangement was reported in patients with lung adenocarcinoma but its oncogenic function was not fully evaluated. We used one-step reverse transcription-polymerase chain reaction for RNA samples to screen for the KIF5B-MET fusion in 206 lung adenocarcinoma and 28 pulmonary sarcomatoid carcinoma patients. Genomic breakpoints of KIF5B-MET were determined by targeted next-generation sequencing. Soft agar colony formation assays, proliferation assays, and a xenograft mouse model were used to investigate its oncogenic activity. In addition, specific MET inhibitors were administered to evaluate their anti-tumor activities. A KIF5B-MET fusion variant in a patient with a mixed-type adenocarcinoma and sarcomatoid tumor was identified, and another case was found in a pulmonary sarcomatoid carcinoma patient. Both cases carried the same chimeric gene, a fusion between exons 1-24 of KIF5B and exons 15-21 of MET. KIF5B-MET-overexpressing cells exhibited significantly increased proliferation and colony-forming ability. Xenograft tumors harboring the fusion gene demonstrated significantly elevated tumor growth. Ectopic expression of the fusion gene stimulated the phosphorylation of KIF5B-MET as well as downstream STAT3, AKT, and ERK1/2 signaling pathways. The MET inhibitors significantly repressed cell proliferation; phosphorylation of downstream STAT3, AKT, and ERK1/2; and xenograft tumorigenicity. In conclusion, the KIF5B-MET variant was demonstrated to have an oncogenic function in cancer cells. These findings have immediate clinical implications for the targeted therapy of subgroups of non-small cell lung cancer patients.

Structural Alterations of MET Trigger Response to MET Kinase Inhibition in Lung Adenocarcinoma Patients

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Receptor Tyrosine Kinases: Translocation Partners in Hematopoietic Disorders

Receptor tyrosine kinases (RTKs) activate various signaling pathways and regulate cellular proliferation, survival, migration, and angiogenesis. Malignant neoplasms often circumvent or subjugate these pathways by promoting RTK overactivation through mutation or chromosomal translocation. RTK translocations create a fusion protein containing a dimerizing partner fused to an RTK kinase domain, resulting in constitutive kinase domain activation, altered RTK cellular localization, upregulation of downstream signaling, and novel pathway activation. While RTK translocations in hematological malignancies are relatively rare, clinical evidence suggests that patients with these genetic abnormalities benefit from RTK-targeted inhibitors. Here, we present a timely review of an exciting field by examining RTK chromosomal translocations in hematological cancers, such as Anaplastic Lymphoma Kinase (ALK), Fibroblast Growth Factor Receptor (FGFR), Platelet-Derived Growth Factor Receptor (PDGFR), REarranged during Transfection (RET), Colony Stimulating Factor 1 Receptor (CSF1R), and Neurotrophic Tyrosine Kinase Receptor Type 3 (NTRK3) fusions, and discuss current therapeutic options.

Platelet-derived growth factor receptors (PDGFRs) fusion genes involvement in hematological malignancies

PURPOSE

To investigate oncogenic platelet-derived growth factor receptor(PDGFR) fusion genes involvement in hematological malignancies, the advances in the PDGFR fusion genes diagnosis and development of PDGFR fusions inhibitors.

METHODS

Literature search was done using terms "PDGFR and Fusion" or "PDGFR and Myeloid neoplasm" or 'PDGFR and Lymphoid neoplasm' or "PDGFR Fusion Diagnosis" or "PDGFR Fusion Targets" in databases including PubMed, ASCO.org, and Medscape.

RESULTS

Out of the 36 fusions detected, ETV6(TEL)-PDGFRB and FIP1L1-PDGFRA fusions were frequently detected, 33 are as a result of chromosomal translocation, FIP1L1-PDGFRA and EBF1-PDGFRB are the result of chromosomal deletion and CDK5RAP2- PDGFRΑ is the result of chromosomal insertion. Seven of the 34 rare fusions have detectable reciprocals.

CONCLUSION

RNA aptamers are promising therapeutic target of PDGFRs and diagnostic tools of PDGFRs fusion genes. Also, PDGFRs have variable prospective therapeutic strategies including small molecules, RNA aptamers, and interference therapeutics as well as development of adaptor protein Lnk mimetic drugs.

Mutations in tyrosine kinase and tyrosine phosphatase and their relevance to the target therapy in hematologic malignancies

Protein tyrosine kinases and protein tyrosine phosphatases play pivotal roles in regulation of cellular phosphorylation and signal transduction with opposite functions. Accumulating evidences have uncovered the relevance of genetic alterations in these two family members to hematologic malignancies. This review underlines progress in understanding the pathogenesis of these genetic alterations including mutations and aberrant expression and the evolving protein tyrosine kinases and protein tyrosine phosphatases targeted therapeutic strategies in hematologic neoplasms.

Comparison of two leukocytapheresis protocols in a case of idiopathic hypereosinophilic syndrome

BACKGROUND

Hypereosinophilic syndrome (HEOS) is rare, and the efficacy of leukocytapheresis in this context is unclear. We here report the successful treatment of a patient with idiopathic HEOS with four leukocytapheresis procedures using two protocols.

CASE

A 4-year-old female presented with cardiac and respiratory dysfunction, and WBC of 225 K/μL with 96% eosinophils. Leukocytapheresis was started after initiation of methylprednisolone and hydroxyurea. She received two leukocytapheresis with polymorphonuclear cell (PMN) protocol, followed by initiation of imatinib therapy, then two leukocytapheresis with mononuclear cell (MNC) protocol. After the fourth leukocytapheresis, her WBC decreased to 69 K/μL with 82% eosinophils. She was discharged on hospital day 21 under stable condition with WBC of 22 K/μL with 86% eosinophils. WBC count and eosinophil percentage continued to decrease, and were 6.4 K/μL and 52% by 2 weeks and 3.9 K/μL and 4.9% by 3 months after discharge, respectively.

FINDINGS

WBC and absolute eosinophil (aEO) counts decreased by an average of 29.0 and 30.4% per leukocytapheresis, respectively. Normalized to estimated blood volume, procedures with PMN and MNC protocols changed, on average, WBC by -10.7 and -12.1%, aEO by -10.4 and -13.4%, platelet by -8.1 and -19.2%, and fluid balance by -129 and -47 mL, respectively.

CONCLUSION

Leukocytapheresis was effective in decreasing WBC and aEO counts in HEOS, with PMN and MNC protocols achieving similar reductions. However, PMN protocol resulted in greater negative fluid balance and MNC protocol resulted in greater platelet loss. J. Clin. Apheresis 31:481-489, 2016. © 2015 Wiley Periodicals, Inc.

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.

How I treat hypereosinophilic syndromes

Hypereosinophilic syndromes (HESs) are a group of rare disorders characterized by peripheral blood eosinophilia of 1.5 × 10(9)/L or higher and evidence of end organ manifestations attributable to the eosinophilia and not otherwise explained in the clinical setting. HESs are pleomorphic in clinical presentation and can be idiopathic or associated with a variety of underlying conditions, including allergic, rheumatologic, infectious, and neoplastic disorders. Moreover, the etiology of the eosinophilia in HESs can be primary (myeloid), secondary (lymphocyte-driven), or unknown. Although corticosteroids remain the first-line therapy for most forms of HESs, the availability of an increasing number of novel therapeutic agents, including tyrosine kinase inhibitors and monoclonal antibodies, has necessarily altered the approach to treatment of HESs. This review presents an updated treatment-based approach to the classification of patients with presumed HES and discusses the roles of conventional and novel agents in the management of these patients.

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.

Eosinophilic myeloid neoplasms

PURPOSE OF REVIEW

In 2012, idiopathic hypereosinophilic syndrome (HES) is still the prevalent diagnosis in patients with persistent eosinophilia, in which a primary or secondary cause of eosinophilia has not been identified. HES is considered a provisional diagnosis until a primary or secondary cause of hypereosinophilia is established. The discovery of imatinib-sensitive fusion proteins in a subset of patients with hypereosinophilia has changed the way we approach the diagnosis and treatment of eosinophilic myeloid neoplasms [eosinophilic myeloproliferative neoplasms (MPNs)]. Despite the recent diagnostic developments, diagnosis of hypereosinophilic MPN is only made in 10-20% of patients with persistent primary hypereosinophilia.

RECENT FINDINGS

In 2008 the World Health Organization (WHO) established a semi-molecular classification of hypereosinophilic MPNs. The discovery of PDGFRA, PDGFRB, FGFR1, JAK-2, and FLT3 fusion proteins in patients with eosinophilic MPNs provide opportunities for targeted therapy. Patients with hypereosinophilic MPNs associated with PDGFRA and PDGFRB fusion genes are responsive to imatinib.

SUMMARY

Ongoing research continues to expand our understanding of the pathophysiology of persistent primary hypereosinophilia and clarify the boundaries between some of these disorders. A key challenge is to identify new targets for therapy and limit the number of patients who are classified as having HES.

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.

Clinical management of the hypereosinophilic syndromes

Hypereosinophilic syndromes (HESs) are rare disorders characterized by marked hypereosinophilia that is directly responsible for organ damage or dysfunction. Different pathogenic mechanisms have been discovered in patient subgroups leading to the characterization of myeloproliferative and lymphocytic disease variants. In the updated terminology, idiopathic HES is now restricted to patients with HES of undetermined etiology. The practical clinical approach of patients with the different HES variants is reviewed herein, focusing on specific diagnostic tools and therapeutic options. Corticosteroids, hydroxyurea and IFN-α remain the classical agents for treatment of most patients with HESs. The specific role of therapeutic compounds that have become available more recently, namely, tyrosine kinase inhibitors and IL-5 antagonists, is discussed.

ETV6 fusion genes in hematological malignancies: a review

Translocations involving band 12p13 are one of the most commonly observed chromosomal abnormalities in human leukemia and myelodysplastic syndrome. Their frequently result in rearrangements of the ETV6 gene. At present, 48 chromosomal bands have been identified to be involved in ETV6 translocations, insertions or inversions and 30 ETV6 partner genes have been molecularly characterized. The ETV6 protein contains two major domains, the HLH (helix-loop-helix) domain, encoded by exons 3 and 4, and the ETS domain, encoded by exons 6 through 8, with in between the internal domain encoded by exon 5. ETV6 is a strong transcriptional repressor, acting through its HLH and internal domains. Five potential mechanisms of ETV6-mediated leukemogenesis have been identified: constitutive activation of the kinase activity of the partner protein, modification of the original functions of a transcription factor, loss of function of the fusion gene, affecting ETV6 and the partner gene, activation of a proto-oncogene in the vicinity of a chromosomal translocation and dominant negative effect of the fusion protein over transcriptional repression mediated by wild-type ETV6. It is likely that ETV6 is frequently involved in leukemogenesis because of the large number of partners with which it can rearrange and the several pathogenic mechanisms by which it can lead to cell transformation.

Kinesins and cancer

Kinesins are a family of molecular motors that travel unidirectionally along microtubule tracks to fulfil their many roles in intracellular transport or cell division. Over the past few years kinesins that are involved in mitosis have emerged as potential targets for cancer drug development. Several compounds that inhibit two mitotic kinesins (EG5 (also known as KIF11) and centromere-associated protein E (CENPE)) have entered Phase I and II clinical trials either as monotherapies or in combination with other drugs. Additional mitotic kinesins are currently being validated as drug targets, raising the possibility that the range of kinesin-based drug targets may expand in the future.

Eosinophilic myeloid disorders

The discovery of therapeutically relevant mutations involving platelet-derived growth factor receptors alpha and beta (PDGFRA and PDGFRB) changed the way we evaluate and treat patients with clonal eosinophilia. Despite our improved understanding of the pathobiology of clonal eosinophilia, more than 50% of patients are diagnosed with idiopathic disease, 10% to 20% with a clonal myeloid disorder, and the remainder with a lymphocytic variant. The World Health Organization classification of tumors recognized the importance of a semi-molecular classification of eosinophilic myeloid disorders and divided them into two major subgroups: (1) myeloid and lymphoid neoplasms with eosinophilia and abnormalities of PDGFRA, PDGFRB, or fibroblast growth factor receptor 1 (FGFR1); and (2) chronic eosinophilic leukemia, not otherwise specified. A key challenge remains the identification of tyrosine kinase responsive molecular lesions in patients in whom the pathogenesis of clonal eosinophilia remains unclear.

A transforming KIF5B and RET gene fusion in lung adenocarcinoma revealed from whole-genome and transcriptome sequencing

The identification of the molecular events that drive cancer transformation is essential to the development of targeted agents that improve the clinical outcome of lung cancer. Many studies have reported genomic driver mutations in non-small-cell lung cancers (NSCLCs) over the past decade; however, the molecular pathogenesis of >40% of NSCLCs is still unknown. To identify new molecular targets in NSCLCs, we performed the combined analysis of massively parallel whole-genome and transcriptome sequencing for cancer and paired normal tissue of a 33-yr-old lung adenocarcinoma patient, who is a never-smoker and has no familial cancer history. The cancer showed no known driver mutation in EGFR or KRAS and no EML4-ALK fusion. Here we report a novel fusion gene between KIF5B and the RET proto-oncogene caused by a pericentric inversion of 10p11.22-q11.21. This fusion gene overexpresses chimeric RET receptor tyrosine kinase, which could spontaneously induce cellular transformation. We identified the KIF5B-RET fusion in two more cases out of 20 primary lung adenocarcinomas in the replication study. Our data demonstrate that a subset of NSCLCs could be caused by a fusion of KIF5B and RET, and suggest the chimeric oncogene as a promising molecular target for the personalized diagnosis and treatment of lung cancer.

The two faces of myeloproliferative neoplasms: Molecular events underlying lymphoid transformation

Multipotent haematopoietic stem cells pass through stages of differentiation with the progressive loss of developmental options leading to the production of terminally differentiated mature blood cells. This process is regulated by soluble cytokines binding to a ligand specific cell surface receptor on a precursor cell. Key to signal transduction are tyrosine kinase proteins which can be divided into two sub families, the receptor protein tyrosine kinases which are transmembrane receptors and retain an intact catalytic kinase domain and the cytoplasmic tyrosine kinases which bind to cytokine receptors. Abnormalities of tyrosine kinase proteins are well recognised in myeloid malignancies, mutation in the cytoplasmic tyrosine kinase JAK2 (V617F) is key in the pathogenesis of myeloproliferative neoplasms, and translocations involving ABL key in the development of chronic myeloid leukaemia. However tyrosine kinase mutations are increasingly recognised to play a role in the pathogenesis of a wider range of haematological cancers. This review focuses on the role of deregulated tyrosine kinase genes either as part of novel fusion proteins involving FGFR1, PDGFRα, PDGFRβ, JAK2 and ABL, or as a consequence of point mutation in JAK1 or JAK2 in the development of precursor T and B lymphoid malignancies or mixed myeloid/lymphoid disorders. We also set out some of the postulated mechanisms which underlie the association of tyrosine kinase mutations with the development of lymphoid malignancy.

Molecular diagnosis and targeted therapy of a pediatric chronic eosinophilic leukemia patient carrying TPM3-PDGFRB fusion

We report a rare pediatric chronic eosinophilic leukemia (CEL) case of an 8-year-old male whose leukemic cells carried t(1; 5)(q21; q33) chromosomal abnormality. Sequencing analysis confirmed a TPM3-PDGFRB fusion, and the breakpoint was the same as adult patient. Targeted therapy with imatinib induced a rapid hematologic response and reduction of TPM3-PDGFRB transcripts as monitored by reverse transcription real-time PCR (RT-qPCR). We then established an RT-qPCR assay applicable to detection of all possible PDGFRB fusions and also validated this assay in the patient. These data should provide a valuable reference for management of pediatric CEL.

BCR-ABL-negative chronic myeloid leukemia

Constitutive activation of protein tyrosine kinases plays a central role in the pathogenesis of myeloproliferative disorders, including BCR-ABL-negative chronic myeloid leukemia. Current research is focused on elucidating the full spectrum of causative mutations in this rare, heterogeneous disease. Activated tyrosine kinases are excellent targets for signal transduction therapy, and an accurate diagnosis including morphology, karyotyping, and molecular genetics will become increasingly important to direct individualized treatment. In addition, new molecular findings need to be incorporated into disease classification systems.

Quantification of PDGFRA alternative transcripts improves the screening for X-PDGFRA fusions by reverse transcriptase-polymerase chain reaction

Hematological malignancies with eosinophilia are often associated with fusions in PDGFRA, PDGFRB, or FGFR1 genes. RT-PCR has proved to be useful for finding new PDGFRA gene fusions, but some studies have shown overexpression of the TK domain which cannot be explained by the existence of such aberrations. This fact could be related to the expression of alternative PDGFRA transcripts. We show that quantification of the expression of three different PDGFRA fragments discriminates between PDGFRA alternative transcripts and fusion genes, and we have tested this novel methodological approach in a group of eosinophilia cases. Our data show that alternative PDGFRA transcripts should be taken into account when screening for PDGFRA aberrations, such as gene fusions, by RT-PCR. Expression from an internal PDGFRA promoter seems to be a frequent event, in both normal and leukemic samples, and is probably related to physiological conditions, but it could have a role in other tumors. Even so, we show that our RQ-PCR methodology can discriminate expression of alternative transcripts from the presence of X-PDGFRA fusion genes.

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.

Screening for diverse PDGFRA or PDGFRB fusion genes is facilitated by generic quantitative reverse transcriptase polymerase chain reaction analysis

BACKGROUND

Rapid identification of diverse fusion genes with involvement of PDGFRA or PDGFRB in eosinophilia-associated myeloproliferative neoplasms is essential for adequate clinical management but is complicated by the multitude and heterogeneity of partner genes and breakpoints.

DESIGN AND METHODS

We established a generic quantitative reverse transcriptase polymerase chain reaction to detect overexpression of the 3'-regions of PDGFRA or PDGFRB as a possible indicator of an underlying fusion.

RESULTS

At diagnosis, all patients with known fusion genes involving PDGFRA (n=5; 51 patients) or PDGFRB (n=5; 7 patients) showed significantly increased normalized expression levels compared to 191 patients with fusion gene-negative eosinophilia or healthy individuals (PDGFRA/ABL: 0.73 versus 0.0066 versus 0.0064, P<0.0001; PDGFRB/ABL: 196 versus 3.8 versus 5.85, P<0.0001). The sensitivity and specificity of the activation screening test were, respectively, 100% and 88.4% for PDGFRA and 100% and 94% for PDGFRB. Furthermore, significant overexpression of PDGFRB was found in a patient with an eosinophilia-associated myeloproliferative neoplasm with uninformative cytogenetics and an excellent response to imatinib. Subsequently, a new SART3-PDGFRB fusion gene was identified by 5'-rapid amplification of cDNA ends polymerase chain reaction (5'-RACE-PCR).

CONCLUSIONS

Quantitative reverse transcriptase polymerase chain reaction analysis is a simple and useful adjunct to standard diagnostic assays to detect clinically significant overexpression of PDGFRA and PDGFRB in eosinophilia-associated myeloproliferative neoplasms or related disorders.

KIF5B-ALK, a novel fusion oncokinase identified by an immunohistochemistry-based diagnostic system for ALK-positive lung cancer

PURPOSE

EML4-ALK is a transforming fusion tyrosine kinase, several isoforms of which have been identified in lung cancer. Immunohistochemical detection of EML4-ALK has proved difficult, however, likely as a result of low transcriptional activity conferred by the promoter-enhancer region of EML4. The sensitivity of EML4-ALK detection by immunohistochemistry should be increased adequately.

EXPERIMENTAL DESIGN

We developed an intercalated antibody-enhanced polymer (iAEP) method that incorporates an intercalating antibody between the primary antibody to ALK and the dextran polymer-based detection reagents.

RESULTS

Our iAEP method discriminated between tumors positive or negative for EML4-ALK in a test set of specimens. Four tumors were also found to be positive for ALK in an archive of lung adenocarcinoma (n = 130) and another 4 among fresh cases analyzed in a diagnostic laboratory. These 8 tumors were found to include 1 with EML4-ALK variant 1, 1 with variant 2, 3 with variant 3, and 2 with previously unidentified variants (designated variants 6 and 7). Inverse reverse transcription-PCR analysis revealed that the remaining tumor harbored a novel fusion in which intron 24 of KIF5B was ligated to intron 19 of ALK. Multiplex reverse transcription-PCR analysis of additional archival tumor specimens identified another case of lung adenocarcinoma positive for KIF5B-ALK.

CONCLUSIONS

The iAEP method should prove suitable for immunohistochemical screening of tumors positive for ALK or ALK fusion proteins among pathologic archives. Coupling of PCR-based detection to the iAEP method should further facilitate the rapid identification of novel ALK fusion genes such as KIF5B-ALK.

[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.