Transient response to imatinib in a chronic eosinophilic leukemia associated with ins(9;4)(q33;q12q25) and a CDK5RAP2-PDGFRA fusion gene

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.

Eosinophilia characterized by a rare CCT6B mutation and responsive to tyrosine kinase inhibition: Case report and literature review

Hypereosinophilic syndrome is a rare disorder arising from neoplastic, or idiopathic causes. The availability of NGS panels has increasingly identified rare mutations as underlying pathogenic events and have led to reclassification of cases of idiopathic hypereosinophilic syndrome as chronic eosinophilic leukemia(CEL). In this report, we describe a case of a young man with hypereosinophilia whose disease initially did not fit the WHO criteria for CEL but harbored a rare mutation in CCT6B gene. We report our experience in successfully treating this patient with multiple tyrosine kinase inhibitors and provide literature review of this rare entity including potential treatment strategies.

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.

The Yin and Yang of Autosomal Recessive Primary Microcephaly Genes: Insights from Neurogenesis and Carcinogenesis

The stem cells of neurogenesis and carcinogenesis share many properties, including proliferative rate, an extensive replicative potential, the potential to generate different cell types of a given tissue, and an ability to independently migrate to a damaged area. This is also evidenced by the common molecular principles regulating key processes associated with cell division and apoptosis. Autosomal recessive primary microcephaly (MCPH) is a neurogenic mitotic disorder that is characterized by decreased brain size and mental retardation. Until now, a total of 25 genes have been identified that are known to be associated with MCPH. The inactivation (yin) of most MCPH genes leads to neurogenesis defects, while the upregulation (yang) of some MCPH genes is associated with different kinds of carcinogenesis. Here, we try to summarize the roles of MCPH genes in these two diseases and explore the underlying mechanisms, which will help us to explore new, attractive approaches to targeting tumor cells that are resistant to the current therapies.

Integration of a bacterial gene sequence into a chronic eosinophilic leukemia patient's genome as part of a fusion gene linker

Analysis of databases from the human genome project (HGP), the 1000 Genomes Project (1KGP), and The Cancer Genome Atlas (TCGA) revealed bacterial DNA integration into the human somatic genome, particularly in tumor tissues. Fusion genes have also been associated with tumorigenesis and 34 PDGFR fusion genes are linked to hematological malignancies. Here, we determined that a 17-bp homologous sequence in Marinobacter sp. Hb8, Rhodococcus fascians D188, Rhodococcus sp. PBTS2, Micrococcus luteus strain trpE16 and M. luteus NCTC 2665 integrates into the genome of a chronic eosinophilic leukemia patient as part of the linker for the novel CDK5RAP2-PDGFRα fusion gene. The resulting fusion protein that has CDK5RAP2’s self-activating domain and PDGFRa’s tyrosine kinase domain but lacks PDGFRa’s membrane-binding and ligand-dependent activation properties may act together with the integrated bacterial sequence to readily phosphorylate downstream targets, amplify proliferation signals and promote leukemic cancer progression.

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.

KIT D816V and JAK2 V617F mutations are seen recurrently in hypereosinophilia of unknown significance

Myeloproliferative neoplasms with eosinophilia are commonly characterized by a normal karyotype and remain poorly defined at the molecular level. We therefore investigated 426 samples from patients with hypereosinophilia of unknown significance initially referred for screening of the FIP1L1-PDGFRA (FP) fusion gene also for KIT D816V and JAK2 V617F mutations. Overall, 86 (20%) patients tested positive: FP+ in 55 (12%), KIT D816V+ in 14 (3%), and JAK2 V617F+ in 17 (4%) patients, respectively. To gain better insight into clinical characteristics, we compared these cases with 31 additional and well-characterized KIT D816V+ eosinophilia-associated systemic mastocytosis (SM-eo) patients enrolled within the "German Registry on Disorders of Eosinophils and Mast cells." Significant differences included younger age, male predominance, and higher eosinophil counts for FP+ cases while abdominal lymphadenopathy, ascites, and serum tryptase levels >100 μg/l were characteristic for those with KIT D816V. Leukocytes, hemoglobin, and splenomegaly did not differ significantly. A median of three additional mutations, most frequently TET2 and SRSF2, were identified in 12/13 KIT D816V+ SM-eo patients with available material indicating a more complex molecular pathogenesis. Median survival was not reached for FP+ cases but was only 26 and 41 months for KIT D816V+ SM and JAK2 V617F+ MPN-eo, respectively. Eosinophilia of ≥2 × 10(9) /l was identified as discriminator for inferior survival in KIT D816V+ and/or JAK2 V617F+ patients (median survival 20 months vs. not reached, P = 0.002). Thus, there is a clear prognostic and therapeutic rationale for detection of KIT D816V and JAK2 V617F in the diagnostic work up of eosinophilia.

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.

Advanced targeted, cell and gene-therapy approaches for pediatric hematological malignancies: results and future perspectives

Despite the survival of pediatric patients affected by hematological malignancies being improved in the last 20 years by chemotherapy and hematopoietic stem cell transplantation, a significant amount of patients still relapses. Treatment intensification is limited by toxic side effects and is constrained by the plateau of efficacy, while the pipeline of new chemotherapeutic drugs is running short. Therefore, novel therapeutic strategies are essential and researchers around the world are testing in clinical trials immune and gene-therapy approaches as second-line treatments. The aim of this review is to give a glance at these novel promising strategies of advanced medicine in the field of pediatric leukemias. Results from clinical protocols using new targeted “smart” drugs, immunotherapy, and gene therapy are summarized, and important considerations regarding the combination of these novel approaches with standard treatments to promote safe and long-term cure are discussed.

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.

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.

Centrosomal targeting of tyrosine kinase activity does not enhance oncogenicity in chronic myeloproliferative disorders

Constitutive tyrosine kinase activation by reciprocal chromosomal translocation is a common pathogenetic mechanism in chronic myeloproliferative disorders. Since centrosomal proteins have been recurrently identified as translocation partners of tyrosine kinases FGFR1, JAK2, PDGFRα and PDGFRβ in these diseases, a role for the centrosome in oncogenic transformation has been hypothesized. In this study, we addressed the functional role of centrosomally targeted tyrosine kinase activity. First, centrosomal localization was not routinely found for all chimeric fusion proteins tested. Second, targeting of tyrosine kinases to the centrosome by creating artificial chimeric fusion kinases with the centrosomal targeting domain of AKAP450 failed to enhance the oncogenic transforming potential in both Ba/F3 and U2OS cells, although phospho-tyrosine-mediated signal transduction pathways were initiated at the centrosome. We conclude that the centrosomal localization of constitutively activated tyrosine kinases does not contribute to disease pathogenesis in chronic myeloproliferative disorders.

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.

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.

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.

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.

[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.

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.

Therapeutic options for patients with clonal and idiopathic hypereosinophia

BACKGROUND

The hypereosinophilic syndrome (HES) comprises a heterogeneous group of disorders characterized by chronic, unexplained hypereosinophilia with organ involvement. The discovery of novel molecular targets has changed the therapeutic paradigm in HES.

OBJECTIVE

This article reviews the current medical management of patients with clonal and idiopathic hypereosinophilia with a particular emphasis on emerging new targeted therapies.

METHODS

The information contained in this review was obtained from public sources such as journals and scientific meeting abstracts. The opinions expressed in this review are solely those of the authors.

RESULTS/CONCLUSION

The development of imatinib-resistant mutations in the FIP1L1-PDGFR-alpha kinase domain has spurred the development of an array of new tyrosine kinase inhibitors. Moreover, the elucidation of the role of interleukin-5 in the pathogenesis of the lymphocytic variant of HES and the fact that CD52 is expressed on the surface of eosinophils and T cells have led to the clinical use of monoclonal antibodies such as mepolizumab, reslizumumab, and alemtuzumab for the treatment of different forms of hypereosinophilia.

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.

Aberrant cytokine signaling in leukemia

Abnormalities of cytokine and growth factor signaling pathways are characteristic of all forms of leukemia: lymphoid and myeloid, acute and chronic. In normal hematopoietic cells, cytokines provide the stimulus for proliferation, survival, self-renewal, differentiation and functional activation. In leukemic cells, these pathways are usurped to subserve critical parts of the malignant program. In this review, our current knowledge of leukemic cell cytokine signaling will be summarized, and some speculations on the significance and implications of these insights will be advanced. A better understanding of aberrant cytokine signaling in leukemia should provide additional targets for the rational therapy of these diseases.

Two novel imatinib-responsive PDGFRA fusion genes in chronic eosinophilic leukaemia

We identified two patients with a t(2;4)(p24;q12) and a t(4;12)(q2?3;p1?2), respectively, in association with BCR-ABL and FIP1L1-PDGFRA negative chronic eosinophilic leukaemia. Molecular analysis revealed a novel STRN-PDGFRA fusion for the t(2;4) and ETV6-PDGFRA for the t(4;12). The fusions were confirmed by specific amplification of the genomic breakpoints, reverse transcription polymerase chain reaction and fluorescence in situ hybridisation. Both patients were treated with imatinib and, following a rapid haematological response, achieved cytogenetic remission and a major molecular response. In conclusion, PDGFRA fuses to diverse partner genes in myeloid disorders. Identification of these fusions is important as they are particularly sensitive to imatinib.

PDGF Receptors as Targets in Tumor Treatment

Signaling through platelet-derived growth factor (PDGF) receptors contributes to multiple tumor-associated processes. The recent introduction of clinically useful PDGF inhibitors have the last years validated PDGF receptors in malignant and stromal cells as relevant cancer drug targets. Mutational activation of PDGF receptor signaling in malignant cells has been described in some rare tumor types such as dermatofibrosarcoma protuberans, a subset of GISTs, and some hematologic malignancies. Furthermore, expression of PDGF receptors on pericytes is a common characteristic of solid tumors. The clinical efficacy of novel multikinase inhibitors, such as sunitinib and sorafenib, most likely involves targeting of PDGF receptor-dependent pericytes. Preclinical studies suggest that targeting of stromal PDGF receptors might also constitute a novel strategy to enhance tumor drug uptake. Finally, recent studies have implied both pro- and antimetastatic effects of PDGF receptors on malignant and stromal cells. The studies on the roles of PDGF receptors in cancer signaling are thus presently in a dynamic phase where collaborations between oncologists, pathologists, and tumor biologists are predicted to be highly productive.