Myeloid neoplasms with eosinophilia

The Classification of Myeloproliferative Neoplasms: Rationale, Historical Background and Future Perspectives with Focus on Unclassifiable Cases

Simple Summary

Myeloproliferative neoplasms (MPNs) are clonal hematological disorders, characterized by increased proliferation of the myeloid lineages in the bone marrow. Since their original recognition by William Damashek in 1951, MPNs have been extensively investigated at a clinical-pathological and molecular level. This prompted a progressive refinement of their classification and diagnostic criteria. Uncertainties nonetheless remain in a small (yet consistent) subset of cases, characterized by unconventional and/or overlapping clinical-pathological features. Such cases (referred to as MPN, unclassifiable [MPN-U]) encompass a broad spectrum of entities, including early phase MPNs, terminal (i.e., fibrotic) MPNs, MPNs associated with inflammatory or neoplastic disorders, and poorly characterized MPNs with clinical-pathological mismatch or atypical molecular features. In this review, we discuss the rationale behind the classification and diagnostic criteria of MPNs, focusing on the still open issues concerning MPN-U.

Abstract

Myeloproliferative neoplasms (MPNs) are a heterogeneous group of clonal hematopoietic stem cell disorders, characterized by increased proliferation of one or more myeloid lineages in the bone marrow. The classification and diagnostic criteria of MPNs have undergone relevant changes over the years, reflecting the increased awareness on these conditions and a better understanding of their biological and clinical-pathological features. The current World Health Organization (WHO) Classification acknowledges four main sub-groups of MPNs: (i) Chronic Myeloid Leukemia; (ii) classical Philadelphia-negative MPNs (Polycythemia Vera; Essential Thrombocythemia; Primary Myelofibrosis); (iii) non-classical Philadelphia-negative MPNs (Chronic Neutrophilic Leukemia; Chronic Eosinophilic Leukemia); and (iv) MPNs, unclassifiable (MPN-U). The latter are currently defined as MPNs with clinical-pathological findings not fulfilling the diagnostic criteria for any other entity. The MPN-U spectrum traditionally encompasses early phase MPNs, terminal (i.e., advanced fibrotic) MPNs, and cases associated with inflammatory or neoplastic disorders that obscure the clinical-histological picture. Several lines of evidence and clinical practice suggest the existence of additional myeloid neoplasms that may expand the spectrum of MPN-U. To gain insight into such disorders, this review addresses the history of MPN classification, the evolution of their diagnostic criteria and the complex clinical-pathological and biological features of MPN-U.

Mechanisms of resistance to FGFR1 inhibitors in FGFR1-driven leukemias and lymphomas: implications for optimized treatment

Myeloid and lymphoid neoplasms with eosinophilia and FGFR1 rearrangements (MLN-eo FGFR1) disease is derived from a pluripotent hematopoietic stem cell and has a complex presentation with a myeloproliferative disorder with or without eosinophilia and frequently presents with mixed lineage T- or B-lymphomas. The myeloproliferative disease frequently progresses to AML and lymphoid neoplasms can develop into acute lymphomas. No matter the cell type involved, or clinical presentation, chromosome translocations involving the FGFR1 kinase and various partner genes, which leads to constitutive activation of downstream oncogenic signaling cascades. These patients are not responsive to treatment regimens developed for other acute leukemias and survival is poor. Recent development of specific FGFR1 inhibitors has suggested an alternative therapeutic approach but resistance is likely to evolve over time. Mouse models of this disease syndrome have been developed and are being used for preclinical evaluation of FGFR1 inhibitors. Cell lines from these models have now been developed and have been used to investigate the mechanisms of resistance that might be expected in clinical cases. So far, a V561M mutation in the kinases domain and deletion of PTEN have been recognized as leading to resistance and both operate through the PI3K/AKT signaling axis. One of the important consequences is the suppression of PUMA, a potent enforcer of apoptosis, which operates through BCL2. Targeting BCL2 in the resistant cells leads to suppression of leukemia development in mouse models, which potentially provides an opportunity to treat patients that become resistant to FGFR1 inhibitors. In addition, elucidation of molecular mechanisms underlying FGFR1-driven leukemias and lymphomas also provides new targets for combined treatment as another option to bypass the FGFR1 inhibitor resistance and improve patient outcome.

Intermediate between Idiopathic Hypereosinophilia and Chronic Eosinophilic Leukemia: A Report of Two Hypereosinophilic Cases with Possible Novel Molecular Mutations

To distinguish a reactive eosinophilia from its malignant counterpart is challenging. Establishing clonality of the eosinophils is crucial and considered the determining factor for establishing a diagnosis. Cases of hypereosinophilia without clear reactive etiologies, no evidence of end-organ damage, normal cytogenetics, and no molecular mutations are termed as “Idiopathic Hypereosinophilia (IHE).” For cases which lie between the spectrum of chronic eosinophilic leukemia (CEL) and IHE, identification of underlying molecular abnormalities might be helpful in better understanding the disease process and prognosis. Here, we report two cases of hypereosinophilia in which five possible novel molecular mutations were identified by targeted next-generation sequencing (NGS) analysis. They were FBXW7, KM2A, TCF3, ERBB4, and MET. With multiple genetic mutations, these cases could be classified as chronic eosinophilic leukemia. Both these young patients responded well to steroid therapy. While targeted NGS is a useful tool in identifying new molecular mutation associated with hypereosinophilia, our cases raise the question of further investigating this entity and if there is a possibility of an intermediate category lying between the spectrum of CEL and IHE. Defining hypereosinophilia with clonal molecular abnormality as a malignant process may need to be revisited. Even though attempts are being made to identify mutations in IHE, it might be more significant clinically to differentiate them based on response to steroid therapy and prognosis.

Chronic Eosinophilic Leukaemia Associated with JAK2 Exon 13 Insertion/Deletion Mutations

Chronic eosinophilic leukaemia, not otherwise specified (CEL, NOS), is a diagnosis of exclusion made in cases in which there is clonal eosinophilia but an absence of genetic aberrations that define other disease subtypes. There is a need for further characterization of these cases in order to inform risk stratification and management. The importance of JAK2 mutations in myeloproliferative neoplasms (MPN) as a whole is well established, although their role specifically in eosinophilic disorders is less clear, with only a minority of cases demonstrating JAK2 abnormalities. Here, we report 2 cases with an exon 13 insertion-deletion (indel) mutation in JAK2: one with CEL-NOS and the second with an unspecified eosinophilic disorder. JAK2 indels were not detected in a screen of suspected MPN cases (n = 592) without eosinophilia that tested negative for common MPN driver mutations. Our findings thus provide further evidence for a specific association between this rare mutation and clonal eosinophilic disorders.

Validation, Implementation, and Clinical Impact of the Oncomine Myeloid Targeted-Amplicon DNA and RNA Ion Semiconductor Sequencing Assay

The identification of clinically significant genes recurrently mutated in myeloid malignancies necessitates expanding diagnostic testing with higher throughput, such as targeted next-generation sequencing. We present validation of the Thermo Fisher Oncomine Myeloid Next-Generation Sequencing Panel (OMP), targeting 40 genes and 29 fusion drivers recurrently mutated in myeloid malignancies. The study includes data from a sample exchange between two Canadian hospitals demonstrating high concordance for detection of DNA and RNA aberrations. Clinical validation demonstrates high accuracy, sensitivity, and specificity of the OMP, with a lower limit of detection of 5% for single-nucleotide variants and 10% for insertions/deletions. Prospective sequencing was performed for 187 samples from 168 unique patients presenting with suspected or confirmed myeloid malignancy and other hematological conditions to assess clinical impact of identifying variants. Of detected variants, 48% facilitated or clarified diagnoses, 29% affected prognoses, and 25% had the potential to influence clinical management. Of note, OMP was essential to identifying patients with premalignant clonal states likely contributing to cytopenias. We also found that the detection of even a single variant by the OMP assay, versus 0 variants, was predictive of overall survival, independent of age, sex, or diagnosis (P = 0.03). This study demonstrates that molecular profiling of myeloid malignancies with the OMP represents a promising strategy to advance molecular diagnostics.

Association of Thrombosis With Hypereosinophilic Syndrome in Patients With Genetic Alterations

IMPORTANCE

Hypereosinophilic syndromes (HESs) are a rare group of disorders that result in overproduction of eosinophils, leading to tissue damage. Thrombotic complications in HES and associated risk factors in this patient population have not been extensively studied.

OBJECTIVE

To investigate the rates of and risk factors associated with thrombotic events in patients with HES, including markers of clonal hematopoiesis as evidenced by molecular aberrations on next-generation sequencing.

DESIGN, SETTING, AND PARTICIPANTS

This retrospective cohort study evaluated patients seen at Brigham and Women's Hospital and Harvard Medical School in Boston, Massachusetts, from January 1, 2015, to January 1, 2020. Patients who had hypereosinophilia with an absolute eosinophil count of 1500 cells/μL or greater on 2 separate occasions at least 1 month apart and who underwent genetic or molecular testing as part of their work-up were included. Patients with secondary eosinophilia were excluded.

MAIN OUTCOMES AND MEASURES

Symptomatic and asymptomatic arterial and venous thrombotic events after the diagnosis of HES and all-cause death.

RESULTS

A total of 71 patients (median age, 58 years [interquartile range (IQR), 43-67 years]; 36 women [51%]; 57 White patients [80%]) were included. Patients had a median follow-up time of 29 months (IQR, 19-49 months). Seventeen patients (24%) had 1 or more thrombotic events, including 11 venous thromboembolic events and 11 arterial thrombotic events (8 patients had ≥1 event and 3 patients had recurrent events). Patients with 1 or more thrombotic events had a higher median Eastern Cooperative Oncology Group performance status (median, 1 [IQR, 1-2] vs 0 [IQR, 0-1]; P = .002), had more frequent cardiac involvement (7 of 17 events [41%] vs 6 of 54 events [11%]; P = .01), more frequently received treatment (17 of 17 events [100%] vs 40 of 54 events [74%]; P = .02), and had more molecular aberrations on next-generation sequencing (12 of 17 [71%] vs 12 of 54 [26%]; P = .003) vs patients without thrombosis. After multivariable analysis, the presence of molecular aberration was associated with increased odds of thrombosis (adjusted odds ratio, 5.4; 95% CI, 1.1-27.7). Death occurred more frequently in patients with thrombotic events compared with those without (6 of 17 [35%] vs 2 of 54 [4%]; P = .002) and in patients with molecular aberrations compared with those without (6 of 24 [25%] vs 1 of 40 [3%]; P = .009), although only thrombotic events were significantly associated with increased odds of death after multivariable analysis.

CONCLUSIONS AND RELEVANCE

In this cohort study, thrombosis was common in patients with HES and was significantly associated with increased risk of death.

Combined Ruxolitinib and Venetoclax Treatment in a Patient with a BCR-JAK2 Rearranged Myeloid Neoplasm

Hematological malignancies with a BCR-JAK2 rearrangement have been described only sporadically in the literature over the last three decades. Although most patients suffer from a chronic myeloid neoplasm with marked eosinophilia, the clinical presentation varies significantly and can even manifest as a lymphoid malignancy. In this case report, we present a patient with a therapy-related BCR-JAK2⁺ myeloid neoplasm with extensive extramedullary disease localizing in the lymph nodes. While treatment with a JAK2 inhibitor (ruxolitinib) was not able to stop disease progression, combination treatment with inhibitors of both JAK2 and BCL2 (venetoclax) resulted in disease control for over 1.5 years. Combining these two inhibitors might be strategic in these patients, not only because BCL2 is a downstream target of JAK/STAT signaling but also because BCL2 is crucial for JAK2 inhibitor resistance. The recent inclusion of JAK2-rearranged malignancies in major classification systems and guidelines emphasizes the importance of not only getting a better understanding of the clinical phenotype of these rare disorders but also of identifying alternative treatment options for patients ineligible for allogeneic stem cell transplantation. Considering the low toxicity of combination treatment with these two small molecule inhibitors, this regimen could be further explored in future studies.

Synoptic Diagnostics of Myeloproliferative Neoplasms: Morphology and Molecular Genetics

Simple Summary

The diagnosis of myeloproliferative neoplasms requires assessment of a combination of clinical, morphological, immunophenotypic and genetic features, and this integrated, multimodal approach forms the basis for precise classification. Evaluation includes cell counts and morphology in the peripheral blood, bone marrow aspiration and trephine biopsy, and may encompass flow cytometry for specific questions. Diagnosis nowadays is completed by targeted molecular analysis for the detection of recurrent driver and, optionally, disease-modifying mutations. According to the current World Health Organization classification, all myeloproliferative disorders require assessment of molecular features to support the diagnosis or confirm a molecularly defined entity. This requires a structured molecular analysis workflow tailored for a rapid and cost-effective diagnosis. The review focuses on the morphological and molecular features of Ph-negative myeloproliferative neoplasms and their differential diagnoses, addresses open questions of classification, and emphasizes the enduring role of histopathological assessment in the molecular era.

Abstract

The diagnosis of a myeloid neoplasm relies on a combination of clinical, morphological, immunophenotypic and genetic features, and an integrated, multimodality approach is needed for precise classification. The basic diagnostics of myeloid neoplasms still rely on cell counts and morphology of peripheral blood and bone marrow aspirate, flow cytometry, cytogenetics and bone marrow trephine biopsy, but particularly in the setting of Ph− myeloproliferative neoplasms (MPN), the trephine biopsy has a crucial role. Nowadays, molecular studies are of great importance in confirming or refining a diagnosis and providing prognostic information. All myeloid neoplasms of chronic evolution included in this review, nowadays feature the presence or absence of specific genetic markers in their diagnostic criteria according to the current WHO classification, underlining the importance of molecular studies. Crucial differential diagnoses of Ph− MPN are the category of myeloid/lymphoid neoplasms with eosinophilia and gene rearrangement of PDGFRA, PDGFRB or FGFR1, or with PCM1-JAK2, and myelodysplastic/myeloproliferative neoplasms (MDS/MPN). This review focuses on morphological, immunophenotypical and molecular features of BCR-ABL1-negative MPN and their differential diagnoses. Furthermore, areas of difficulties and open questions in their classification are addressed, and the persistent role of morphology in the area of molecular medicine is discussed.

T-Cell Lymphoblastic Lymphoma Arising in the Setting of Myeloid/Lymphoid Neoplasms with Eosinophilia: LMO2 Immunohistochemistry as a Potentially Useful Diagnostic Marker

Simple Summary

Rarely, T-lymphoblastic lymphoma (T-LBL) may develop in the setting of myeloid/lymphoid neoplasms with eosinophilia. Given important therapeutic implications, it is crucial to identify T-LBL arising in this particular context. LIM domain only 2 (LMO2) is known to be overexpressed in almost all sporadic T-LBL and not in immature TdT-positive T-cells in the thymus and in indolent T-lymphoblastic proliferations. We retrospectively evaluated the clinical, morphological, immunohistochemical and molecular features of 11 cases of T-LBL occurring in the setting of myeloid/lymphoid neoplasms with eosinophilia and investigated the immunohistochemical expression of LMO2 in this setting of T-LBL. Interestingly, 9/11 cases were LMO2 negative, with only 2 cases showing partial expression. In our study, we would suggest that LMO2 immunostaining, as part of the diagnostic panel for T-LBL, may represent a useful marker to identify T-LBL developing in the context of myeloid/lymphoid neoplasms with eosinophilia.

Abstract

Background: Rarely, T-lymphoblastic lymphoma (T-LBL) may develop in the setting of myeloid/lymphoid neoplasms with eosinophilia (M/LNs-Eo), a group of diseases with gene fusion resulting in overexpression of an aberrant tyrosine kinase or cytokine receptor. The correct identification of this category has relevant therapeutic implications. LIM domain only 2 (LMO2) is overexpressed in most T-LBL, but not in immature TdT-positive T-cells in the thymus and in indolent T-lymphoblastic proliferations (iT-LBP). Methods and Results: We retrospectively evaluated 11 cases of T-LBL occurring in the context of M/LNs-Eo. Clinical, histological, immunohistochemical and molecular features were collected and LMO2 immunohistochemical staining was performed. The critical re-evaluation of these cases confirmed the diagnosis of T-LBL with morphological, immunohistochemical and molecular features consistent with T-LBL occurring in M/LNs-Eo. Interestingly, LMO2 immunohistochemical analysis was negative in 9/11 cases, whereas only 2 cases revealed a partial LMO2 expression with a moderate and low degree of intensity, respectively. Conclusions: LMO2 may represent a potentially useful marker to identify T-LBL developing in the context of M/LNs-Eo. In this setting, T-LBL shows LMO2 immunohistochemical profile overlapping with cortical thymocytes and iT-LBP, possibly reflecting different molecular patterns involved in the pathogenesis of T-LBL arising in the setting of M/LNs-Eo.

Identification of Early Diagnostic and Prognostic Biomarkers via WGCNA in Stomach Adenocarcinoma

Stomach adenocarcinoma (STAD) is a leading cause of cancer deaths, and the outcome of the patients remains dismal for the lack of effective biomarkers of early detection. Recent studies have elucidated the landscape of genomic alterations of gastric cancer and reveal some biomarkers of advanced-stage gastric cancer, however, information about early-stage biomarkers is limited. Here, we adopt Weighted Gene Co-expression Network Analysis (WGCNA) to screen potential biomarkers for early-stage STAD using RNA-Seq and clinical data from TCGA database. We find six gene clusters (or modules) are significantly correlated with the stage-I STADs. Among these, five hub genes, i.e., MS4A1, THBS2, VCAN, PDGFRB, and KCNA3 are identified and significantly de-regulated in the stage-I STADs compared with the normal stomach gland tissues, which suggests they can serve as potential early diagnostic biomarkers. Moreover, we show that high expression of VCAN and PDGFRB is associated with poor prognosis of STAD. VCAN encodes a large chondroitin sulfate proteoglycan that is the main component of the extracellular matrix, and PDGFRB encodes a cell surface tyrosine kinase receptor for members of the platelet-derived growth factor (PDGF) family. Consistently, Gene Ontology (GO) analysis of differentially expressed genes in the STADs indicates terms associated with extracellular matrix and receptor ligand activity are significantly enriched. Protein-protein network interaction analysis (PPI) and Gene Set Enrichment Analysis (GSEA) further support the core role of VCAN and PDGFRB in the tumorigenesis. Collectively, our study identifies the potential biomarkers for early detection and prognosis of STAD.

Eosinophils and eosinophil-associated disorders: immunological, clinical, and molecular complexity

Eosinophils and their mediators play a crucial role in various reactive states such as bacterial and viral infections, chronic inflammatory disorders, and certain hematologic malignancies. Depending on the underlying pathology, molecular defect(s), and the cytokine- and mediator-cascades involved, peripheral blood and tissue hypereosinophilia (HE) may develop and may lead to organ dysfunction or even organ damage which usually leads to the diagnosis of a HE syndrome (HES). In some of these patients, the etiology and impact of HE remain unclear. These patients are diagnosed with idiopathic HE. In other patients, HES is diagnosed but the etiology remains unknown — these patients are classified as idiopathic HES. For patients with HES, early therapeutic application of agents reducing eosinophil counts is usually effective in avoiding irreversible organ damage. Therefore, it is important to systematically explore various diagnostic markers and to correctly identify the disease elicitors and etiology. Depending on the presence and type of underlying disease, HES are classified into primary (clonal) HES, reactive HES, and idiopathic HES. In most of these patients, effective therapies can be administered. The current article provides an overview of the pathogenesis of eosinophil-associated disorders, with special emphasis on the molecular, immunological, and clinical complexity of HE and HES. In addition, diagnostic criteria and the classification of eosinophil disorders are reviewed in light of new developments in the field.

Targeted FGFR inhibition results in a durable remission in an FGFR1-driven myeloid neoplasm with eosinophilia

A novel PCM1-FGFR1 gene rearrangement was identified in a patient with a myeloid neoplasm with eosinophilia. Futibatinib, an oral selective small molecule inhibitor of FGFR1-4, resulted in a durable complete hematologic and cytogenetic remission.

A cryptic imatinib-sensitive G3BP1-PDGFRB rearrangement in a myeloid neoplasm with eosinophilia

Targeted RNA sequencing detected a cryptic G3BP1-PDGFRB rearrangement in a myeloid neoplasm with eosinophilia and normal FISH studies. Consistent with the patient’s response to imatinib, we demonstrate this rearrangement is oncogenic and sensitive to TKI in cell culture.

Diagnosis and treatment of mixed phenotype (T-myeloid/lymphoid) acute leukemia with novel ETV6-FGFR2 rearrangement

Myeloid/lymphoid neoplasms with eosinophilia are driven by aberrant tyrosine kinases in pluripotent cells and display variable phenotypes. FGFR-driven hematolymphoid neoplasms are targetable by TKI inhibitors such as ponatinib; studies of specific FGFR inhibitors are ongoing.

Clinical utility of next generation sequencing to detect IGH/IL3 rearrangements [t(5;14)(q31.1;q32.1)] in B-lymphoblastic leukemia/lymphoma

The t(5;14)(q31.1;q32.1) associated with B-lymphoblastic leukemia/lymphoma (B-ALL/LBL) is a rare, recurrent genetic abnormality recognized as a distinct entity by the 2017 World Health Organization (WHO) classification. In these cases, the IGH enhancer region (14q32.1) is juxtaposed to the vicinity of the IL3 gene (5q31.1), resulting in increased production of interleukin-3 (IL3) and subsequently a characteristic reactive eosinophilia. B-ALL with t(5;14)(q31.1;q32.1) may have a low lymphoblast count that can complicate detection of t(5;14)(q31.1;q32.1) by conventional chromosome studies. We have identified four patients with IGH/IL3 rearrangements despite normal conventional chromosome studies in each case [one patient had a non-clonal t(5;14)(q31;q32) finding]. Fluorescence in situ hybridization utilizing a laboratory-developed IGH break-apart probe set identified IGH rearrangements in three of four cases, and a next generation sequencing (NGS) based assay, mate-pair sequencing (MPseq), was required to characterize the IGH/IL3 rearrangements in each case. Three patients demonstrated a balanced t(5;14)(q31.1;q32.1) while one patient had a cryptic insertion of the IL3 gene into the IGH region. These results demonstrate that NGS-based assays, such as MPseq, confer an advantage in the detection of IGH/IL3 rearrangements that are otherwise challenging to characterize by traditional cytogenetic methodologies.

Partial Response to Sorafenib in a Child With a Myeloid/Lymphoid Neoplasm, Eosinophilia, and a ZMYM2-FLT3 Fusion

Dysregulated tyrosine kinases in myeloid/lymphoid neoplasms with eosinophilia are rare, but do occur in children. To increase awareness of this diagnosis, we present a child who was diagnosed after a 3-year disease history. The patient was initially treated according to a T-cell lymphoblastic lymphoma protocol, but genetic analyses at recurrence revealed microdeletions resulting in an in-frame fusion of ZMYM2 and FLT3. Treatment with sorafenib, an FLT3 tyrosine kinase inhibitor, rapidly resulted in significant reduction of lymphadenopathy and normalization of white blood cell and eosinophil counts. At 17 months of treatment, he remains in complete hematologic, but not molecular remission.

Precision medicine in myeloid malignancies

Myeloid malignancies have always been at the forefront of an improved understanding of the molecular pathogenesis of cancer. In accordance, over the last years, basic research focusing on the aberrations underlying malignant transformation of myeloid cells has provided the basis for precision medicine approaches and subsequently has led to the development of powerful therapeutic strategies. In this review article, we will recapitulate what has happened since in the 1980s the use of all-trans retinoic acid (ATRA), as a first targeted cancer therapy, has changed one of the deadliest leukemia subtypes, acute promyelocytic leukemia (APL), into one that can be cured without classical chemotherapy today. Similarly, imatinib, the first molecularly designed cancer therapy, has revolutionized the management of chronic myeloid leukemia (CML). Thus, targeted treatment approaches have become the paradigm for myeloid malignancy, but many questions still remain unanswered, especially how identical mutations can be associated with different phenotypes. This might be linked to the impact of the cell of origin, gene-gene interactions, or the tumor microenvironment including the immune system. Continuous research in the field of myeloid neoplasia has started to unravel the molecular pathways that are not only crucial for initial treatment response, but also resistance of leukemia cells under therapy. Ongoing studies focusing on leukemia cell vulnerabilities do already point to novel (targetable) "Achilles heels" that can further improve myeloid cancer therapy.

Lab tests for MPN

Molecular laboratory investigations for myeloproliferative neoplasm (MPN) can ideally be divided into two distincts groups, those for the detection of the BCR-ABL rearrangement (suspect of chronic myeloid leukemia) and those for the variants determination of the driver genes of the negative Philadelphia forms (MPN Ph neg). The BCR-ABL detection is based on RT-Polymerase Chain Reaction techniques and more recently on droplet digital PCR (ddPCR). For this type of analysis, combined with chromosome banding analysis (CBA) and Fluorescent in situ hybridization (FISH), it is essential to quantify BCR-ABL mutated copies by standard curve method. The investigation on driver genes for MPN Ph neg forms includes activity for erythroid forms such as Polycythemia Vera (test JAK2V617F and JAK2 exon 12), for non-erythroid forms such as essential thrombocythemia and myelofibrosis (test JAK2V617F, CALR exon 9, MPL exon 10), for "atypical" ones such as mastocytosis (cKIT D816V test) and for hypereosinophilic syndrome (FIP1L1-PDGFRalpha test). It's crucial to assign prognosis value through calculating allelic burden of JAK2 V617F variant and determining CALR esone 9 variants (type1/1like, type2/2like and atypical ones). A fundamental innovation for investigating triple negative cases for JAK2, CALR, MPL and for providing prognostic score is the use of Next Generation Sequencing panels containing high molecular risk genes as ASXL1, EZH2, TET2, IDH1/IDH2, SRSF2. This technique allows to detect additional or subclonal mutations which are usually acquired in varying sized sub-clones of hematopoietic progenitors. These additional variants have a prognostic significance and should be indagated to exclude false negative cases.

Myeloid tumors accompanying systemic mastocytosis, basophilia, and abnormal platelet-derived growth factor receptor β: A case report

INTRODUCTION

Myeloid neoplasms with platelet-derived growth factor receptor β (PDGFRB) rearrangement usually present with eosinophilia in the peripheral blood and bone marrow. Here we report a case of systemic mastocytosis related myeloid neoplasms with basophilia and PRKG2-PDGFRB fusion gene.

PATIENTS CONCERNS

A 53-year-old male patient felt fatigue with thrombocythemia and normal hemoglobin over 2 years. Considering the possibility of primary thrombocytosis, the patient was treated with hydroxyurea and interferon. Then the therapy was stopped due to adverse events and worsen condition.

DIAGNOSIS

Acute myelogenous leukemia (AML) diagnosis was confirmed by bone marrow morphology and flow cytometry. PDGFRB rearrangement was detected by fluorescence in situ hybridization (FISH) test, with chromosome karyotype 46,XY,t(4:5)(q21:q33). PRKG2-PDGFRB fusion was observed by next generation sequencing (NGS) and verified by RT-PCR followed by Sanger sequencing. The results of bone marrow aspiration, bone marrow biopsy, and immunophenotyping showed systemic mastocytosis-related myeloid tumor with basophilia.

INTERVENTIONS

Imatinib 400 mg/d was given on the day of admission. Azacitidine 75 mg/m2 was given for induction therapy for 10 days, and followed by one course of DHAG consolidating therapy. Imatinib was taken orally continuously.

OUTCOMES

On the 8th day of treatment, the patient's diet and fatigue improved. The hematological and bone marrow morphological remission was achieved on the 25th day. Cytogenetic complete remission was achieved 3 months later and continued to present (December 20, 2020). PRKG2-PDGFRB fusion gene turned negative 7 months later from diagnosis.

LESSONS

Patients with increased basophilic granulocyte and/or mast cells in peripheral blood and/or bone marrow should be screened for PDGFRB abnormality and myeloid or lymphatic tumor. Patients bearing PDGFRB abnormality have a good response to imatinib.

Myeloid Neoplasm with PDGFRA Rearrangement Manifesting as a Retromolar Pad Mass

Myeloid neoplasms with PDGFRA rearrangement are rare, and most commonly present with features of chronic eosinophilic leukemia; however, they rarely manifest as acute myeloid or lymphoblastic leukemia. Patients typically present with symptoms of hypereosinophilia including cardiovascular and pulmonary symptoms. An increase in mast cells is also a common feature of this disease, and there may be elevated serum tryptase with significant clinical overlap with systemic mastocytosis. Here, we present an unusual case of a myeloid neoplasm with PDGFRA rearrangement manifesting as a retromolar pad mass in a patient with a prior diagnosis of systemic mastocytosis. This case highlights the possibility of soft tissue involvement by myeloid neoplasms with PDGFRA rearrangement in the oral cavity. The identification of this entity is of significant clinical importance because many patients can be effectively treated with tyrosine kinase inhibitors.

Eosinophilia/Hypereosinophilia in the Setting of Reactive and Idiopathic Causes, Well-Defined Myeloid or Lymphoid Leukemias, or Germline Disorders

OBJECTIVES

To report the findings of the 2019 Society for Hematopathology/European Association for Haematopathology Workshop within the categories of reactive eosinophilia, hypereosinophilic syndrome (HES), germline disorders with eosinophilia (GDE), and myeloid and lymphoid neoplasms associated with eosinophilia (excluding entities covered by other studies in this series).

METHODS

The workshop panel reviewed 109 cases, assigned consensus diagnosis, and created diagnosis-specific sessions.

RESULTS

The most frequent diagnosis was reactive eosinophilia (35), followed by acute leukemia (24). Myeloproliferative neoplasms (MPNs) received 17 submissions, including chronic eosinophilic leukemia, not otherwise specified (CEL, NOS). Myelodysplastic syndrome (MDS), MDS/MPN, and therapy-related myeloid neoplasms received 11, while GDE and HES received 12 and 11 submissions, respectively.

CONCLUSIONS

Hypereosinophilia and HES are defined by specific clinical and laboratory criteria. Eosinophilia is commonly reactive. An acute leukemic onset with eosinophilia may suggest core-binding factor acute myeloid leukemia, blast phase of chronic myeloid leukemia, BCR-ABL1-positive leukemia, or t(5;14) B-lymphoblastic leukemia. Eosinophilia is rare in MDS but common in MDS/MPN. CEL, NOS is a clinically aggressive MPN with eosinophilia as the dominant feature. Bone marrow morphology and cytogenetic and/or molecular clonality may distinguish CEL from HES. Molecular testing helps to better subclassify myeloid neoplasms with eosinophilia and to identify patients for targeted treatments.

Myeloid/Lymphoid Neoplasms Associated With Eosinophilia and Rearrangements of PDGFRA, PDGFRB, or FGFR1 or With PCM1-JAK2

OBJECTIVES

To summarize cases submitted to the 2019 Society for Hematopathology/European Association for Haematopathology Workshop under the category of myeloid/lymphoid neoplasms with eosinophilia and PDGFRA, PDGFRB, or FGFR1 or with PCM1-JAK2 rearrangements, focusing on recent updates and relevant practice findings.

METHODS

The cases were summarized according to their respective gene rearrangement to illustrate the spectrum of clinical, laboratory, and histopathology manifestations and to explore the appropriate molecular genetic tests.

RESULTS

Disease presentations were heterogeneous, including myeloproliferative neoplasms (MPNs), myelodysplastic syndromes (MDSs), MDS/MPN, acute myeloid leukemia, acute B- or T-lymphoblastic lymphoma/acute lymphoblastic lymphoma (ALL/LBL), or mixed-lineage neoplasms. Frequent extramedullary involvement occurred. Eosinophilia was common but not invariably present. With the advancement of RNA sequencing, cryptic rearrangements were recognized in genes other than PDGFRA. Additional somatic mutations were more frequent in the FGFR1-rearranged cases. Cases with B-ALL presentations differed from Philadelphia-like B-ALL by the presence of an underlying MPN. Cases with FLT3 and ABL1 rearrangements could be potential candidates for future inclusion in this category.

CONCLUSIONS

Accurate diagnosis and classification of this category of myeloid/lymphoid neoplasms has important therapeutic implications. With the large number of submitted cases, we expand our understanding of these rare neoplasms and improve our ability to diagnose these genetically defined disorders.

The Efficacy of Imatinib Mesylate in the Treatment of a Rare Lytic Bone Lesion Caused by Hypereosinophilic Syndrome/Chronic Eosinophilic Leukemia: A Case Report

CASE

We report a patient with hypereosinophilia-associated massive osteolytic lesion of the sacrum who was admitted to our hospital. Genetic analysis revealed that atypical eosinophilic cells were positive for FIP1-like-1-platelet-derived growth factor receptor-alpha (FIP1L1-PDGFRA) fusion gene. Treatment was initiated with oral administration of imatinib mesylate. The patient responded rapidly to this medication with a marked reduction in eosinophilia both from the peripheral blood and FIP1L1-PDGFRA fusion gene in the bone marrow within 2 weeks, followed by gradual osteosclerotic repair of the sacrum.

CONCLUSIONS

This case study found that the drug imatinib proved very effective in the treatment of this rare condition.

A Case of Chronic Eosinophilic Leukemia in a Patient With Recurrent Cough, Dyspnea, and Eosinophilia

We report the case of a 40-year-old man with no significant past medical history who had been hospitalized multiple times over the course of one year with recurring cough, dyspnea, pruritic rash, and variable degrees of eosinophilia. He was variably diagnosed with asthma and pneumonia. After his last hospitalization with severe symptoms, the patient was referred for pulmonary evaluation where hypereosinophilia (HE) led to a hematologic workup. Fluorescence in situ hybridization revealed the FIP1L1-PDGFRA gene fusion and bone marrow analysis confirmed a diagnosis of chronic eosinophilic leukemia. The patient was treated with daily imatinib and prednisone and he was symptom-free at a four-week follow-up examination.

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.

Genetic complexity of chronic myelomonocytic leukemia

In recent years CMML has received increased attention as the most commonly observed MDS/MPN overlap syndrome. Renewed interest has occurred in part due to widespread adoption of next-generation sequencing panels that help render the diagnosis in the absence of morphologic dysplasia. Although most CMML patients exhibit somatic mutations in epigenetic modifiers, spliceosome components, transcription factors and signal transduction genes, it is increasingly clear that a small subset harbors an inherited predisposition to CMML and other myeloid neoplasms. More intriguing is the fact that the mutational spectrum observed in CMML is found in other types of myeloid leukemias, begging the question of how similar genetic backgrounds can lead to such divergent clinical phenotypes. In this review we present a contemporary snapshot of the genetic complexity inherent to CMML, explore the relationship between genotype-phenotype and present a stepwise model of CMML pathogenesis and progression.

Chronic myelomonocytic leukemia - a review

INTRODUCTION

Chronic myelomonocytic leukemia (CMML) is a clonal myeloid neoplasm, denoted by overlapping myelodysplastic and myeloproliferative features, with poor overall survival and high transformation rate to acute myeloid leukemia.

AREAS COVERED

This review, following a thorough Medline search of pertinent published literature, discusses the diagnostic criteria, the pathogenesis, and the complex genetic landscape of the disease. Prognostication, response criteria, therapeutic management of patients, efficacy of established and novel treatment modalities are thoroughly reviewed.

EXPERT OPINION

Cytogenetic abnormalities and mutations in genes involved in epigenetic and transcriptional regulation, and cell-signaling are abundant in CMML and implicated in its complex pathogenesis. As presence of these mutations carry a prognostic impact, they are increasingly incorporated in risk-stratification schemes. Novel response criteria have been proposed, considering the unique features of the disease. Although allogeneic hematopoietic stem cell transplantation remains the only treatment with curative intent, it is reserved for a minority of patients; therefore, there is an unmet need for optimizing treatment modalities, such as hypomethylating agents, and introducing novel agents, which could substantially improve survival and quality of life of CMML patients. Clinical trials dedicated specifically to CMML are needed to explore the efficacy and safety of novel treatment modalities.

Aberrant expression of NKL homeobox genes HMX2 and HMX3 interferes with cell differentiation in acute myeloid leukemia

The NKL-code describes normal expression patterns of NKL homeobox genes in hematopoiesis. Aberrant expression of NKL homeobox gene subclass members have been reported in several hematopoietic malignancies including acute myeloid leukemia (AML). Here, we analyzed the oncogenic role of the HMX-group of NKL homeobox genes in AML. Public expression profiling data–available for HMX1 and HMX2—indicate aberrant activity of HMX2 in circa 2% AML patients overall, rising to 31% in those with KMT2A/MLL rearrangements whereas HMX1 expression remains inconspicuous. AML cell lines EOL-1, MV4-11 and MOLM-13 expressed both, HMX2 and neighboring HMX3 genes, and harbored KMT2A aberrations, suggesting their potential functional association. Surprisingly, knockdown experiments in these cell lines demonstrated that KMT2A inhibited HMX2/3 which, in turn, did not regulate KMT2A expression. Furthermore, karyotyping and genomic profiling analysis excluded rearrangements of the HMX2/3 locus in these cell lines. However, comparative expression profiling and subsequent functional analyses revealed that IRF8, IL7- and WNT-signalling activated HMX2/3 expression while TNFa/NFkB- signalling proved inhibitory. Whole genome sequencing of EOL-1 identified two mutations in the regulatory upstream regions of HMX2/3 resulting in generation of a consensus ETS-site and transformation of a former NFkB-site into an SP1-site. Reporter-gene assays demonstrated that both mutations contributed to HMX2/3 activation, modifying ETS1/ELK1- and TNFalpha-mediated gene regulation. Moreover, DMSO-induced eosinophilic differentiation of EOL-1 cells coincided with HMX2/3 downregulation while knockdown of HMX2 induced cell differentiation, collectively supporting a fundamental role for these genes in myeloid differentiation arrest. Finally, target genes of HMX2/3 were identified in EOL-1 and included suppression of differentiation gene EPX, and activation of fusion gene FIP1L1-PDGFRA and receptor-encoding gene HTR7, both of which enhanced oncogenic ERK-signalling. Taken together, our study documents a leukemic role for deregulated NKL homeobox genes HMX2 and HMX3 in AML, revealing molecular mechanisms of myeloid differentiation arrest.

Severe Dizziness and Hypereosinophilia: Coincidence or Complication? A Case Report

Hypereosinophilia is a common issue in medicine. One rare cause is myeloproliferative neoplasm with PDGFRA rearrangement. In these patients, the gold standard for therapy is low-dose imatinib. We present the case of a patient with a new diagnosis of myeloproliferative neoplasm following an unconventional diagnostic pattern, which developed clinically relevant unexplained dizziness a week after starting treatment. Our case presented with lower back pain and multiple bone lesions at MRI investigation. Bone marrow and cytogenetic analysis led to the diagnosis of myeloproliferative neoplasm with PDGFRA rearrangement. We started a treatment with a tyrosine kinase inhibitor (imatinib), and the patient noticed an onset of severe, persistent and intense dizziness, which was more intense with closed eyes. Diagnostic tests were not conclusive, and dizziness persisted at 48 months of follow-up. In conclusion, clinically relevant dizziness was never described in patients with myeloproliferative neoplasm. Even if the exact physiopathological mechanism is not clear, clinicians should know that hypereosinophilia could lead to central nervous system damage.

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

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

Update on CML-Like Disorders

Chronic myeloid leukemia (CML) is defined for many years as BCR-ABL1 positive disease, but older publications refer to a poor prognosis, clinically heterogeneous entity termed 'BCR-ABL1 negative CML' constituting about 5% of CML cases. Apart from very rare CML cases with cytogenetically cryptic, atypical variant BCR-ABL1 fusions that had been inadvertently missed during the diagnostic work up, most of these cases would now be classified as a subtype of myelodysplastic/myeloproliferative neoplasm (MDS/MPN), such as atypical CML (aCML), chronic myelomonocytic leukemia (CMML), or chronic neutrophilic leukemia (CNL). A minority would be classified as systemic mastocytosis with associated hematological neoplasm (SM-AHN), myeloid/lymphoid neoplasms associated with eosinophilia and rearrangement of PDGFRA, PDGFRB, FGFR1 or with PCM1-JAK2 (MLN-eo), or chronic eosinophilic leukemia not otherwise specified (CEL-NOS).¹.

Whole-genome sequencing and gene network modules predict gemcitabine/carboplatin-induced myelosuppression in non-small cell lung cancer patients

Gemcitabine/carboplatin chemotherapy commonly induces myelosuppression, including neutropenia, leukopenia, and thrombocytopenia. Predicting patients at risk of these adverse drug reactions (ADRs) and adjusting treatments accordingly is a long-term goal of personalized medicine. This study used whole-genome sequencing (WGS) of blood samples from 96 gemcitabine/carboplatin-treated non-small cell lung cancer (NSCLC) patients and gene network modules for predicting myelosuppression. Association of genetic variants in PLINK found 4594, 5019, and 5066 autosomal SNVs/INDELs with p ≤ 1 × 10⁻³ for neutropenia, leukopenia, and thrombocytopenia, respectively. Based on the SNVs/INDELs we identified the toxicity module, consisting of 215 unique overlapping genes inferred from MCODE-generated gene network modules of 350, 345, and 313 genes, respectively. These module genes showed enrichment for differentially expressed genes in rat bone marrow, human bone marrow, and human cell lines exposed to carboplatin and gemcitabine (p < 0.05). Then using 80% of the patients as training data, random LASSO reduced the number of SNVs/INDELs in the toxicity module into a feasible prediction model consisting of 62 SNVs/INDELs that accurately predict both the training and the test (remaining 20%) data with high (CTCAE 3–4) and low (CTCAE 0–1) maximal myelosuppressive toxicity completely, with the receiver-operating characteristic (ROC) area under the curve (AUC) of 100%. The present study shows how WGS, gene network modules, and random LASSO can be used to develop a feasible and tested model for predicting myelosuppressive toxicity. Although the proposed model predicts myelosuppression in this study, further evaluation in other studies is required to determine its reproducibility, usability, and clinical effect.

Integrated genomic analysis using chromosomal microarray, fluorescence in situ hybridization and mate pair analyses: Characterization of a cryptic t(9;22)(p24.1;q11.2)/BCR-JAK2 in myeloid/lymphoid neoplasm with eosinophilia

The 2016 World Health Organization entity 'Myeloid/lymphoid neoplasms with eosinophilia and rearrangement of PDGFRA, PDGFRB or FGFR1, or with PCM1-JAK2' encompasses a group of rare neoplasms that result from the formation of a fusion gene that leads to expression of an aberrant tyrosine kinase. This entity also contains variant JAK2 fusion partners, and detection of this defining event can be facilitated by various cytogenetic and molecular methods. Cryptic rearrangements of 9p24/JAK2 can be particularly challenging to identify. We describe the use of chromosomal microarray analysis (CMA), fluorescence in situ hybridization (FISH) with a probe for JAK2, and genomic mate pair analysis to describe a complex karyotype with a t(9;22) that produced a functional BCR-JAK2 fusion, leading to the appropriate diagnosis for the patient. This case highlights the importance of using an integrated genomic approach to fully define complex aberrations to assign proper diagnoses.

S100A8 and S100A9 Promote Apoptosis of Chronic Eosinophilic Leukemia Cells

S100A8 and S100A9 function as essential factors in inflammation and also exert antitumor or tumorigenic activity depending on the type of cancer. Chronic eosinophilic leukemia (CEL) is a rare hematological malignancy having elevated levels of eosinophils and characterized by the presence of the FIP1L1-PDGFRA fusion gene. In this study, we examined the pro-apoptotic mechanisms of S100A8 and S100A9 in FIP1L1-PDGFRα+ eosinophilic cells and hypereosinophilic patient cells. S100A8 and S100A9 induce apoptosis of the FIP1L1-PDGFRα+ EoL-1 cells via TLR4. The surface TLR4 expression increased after exposure to S100A8 and S100A9 although total TLR4 expression decreased. S100A8 and S100A9 suppressed the FIP1L1-PDGFRα-mediated signaling pathway by downregulating FIP1L1-PDGFRα mRNA and protein expression and triggered cell apoptosis by regulating caspase 9/3 pathway and Bcl family proteins. S100A8 and S100A9 also induced apoptosis of imatinib-resistant EoL-1 cells (EoL-1-IR). S100A8 and S100A9 blocked tumor progression of xenografted EoL-1 and EoL-1-IR cells in NOD-SCID mice and evoked apoptosis of eosinophils derived from hypereosinophilic syndrome as well as chronic eosinophilic leukemia. These findings may contribute to a progressive understanding of S100A8 and S100A9 in the pathogenic and therapeutic mechanism of hematological malignancy.

Contemporary Classification and Diagnostic Evaluation of Hypereosinophilia

OBJECTIVES

To provide an in-depth review of the classification and diagnostic evaluation of hypereosinophilia (HE), with a focus on eosinophilic neoplasms.

METHODS

A review of published literature was performed, and exemplary HE cases were identified.

RESULTS

Causes of HE are diverse and can be grouped under three categories: primary (neoplastic), secondary (reactive), and idiopathic. Advances in cytogenetics and molecular diagnostics have led to elucidation of the genetic basis for many neoplastic hypereosinophilic disorders. One common molecular feature is formation of a fusion gene, resulting in the expression of an aberrantly activated tyrosine kinase (TK). The World Health Organization endorsed a biologically oriented classification scheme and created a new major disease category, namely, "myeloid/lymphoid neoplasms with eosinophilia and rearrangement of PDGFRA, PDGFRB or FGFR1, or with PCM1-JAK2." Rearrangement of other TK genes and activating somatic mutation(s) in TK genes have also been reported in eosinophilic neoplasms. Diagnostic evaluation of HE involves a combination of clinical, histopathologic, and immunophenotypic analyses, as well as molecular genetic testing, including next-generation sequencing-based mutation panels. The management of primary HE is largely guided by the underlying molecular genetic abnormalities.

CONCLUSIONS

A good knowledge of recent advances in HE is necessary to ensure prompt and accurate diagnosis, as well as to help optimize patient care.

Advantages and Limitations of SNP Array in the Molecular Characterization of Pediatric T-Cell Acute Lymphoblastic Leukemia

T-cell acute lymphoblastic leukemia (T-ALL) is a highly heterogeneous disease, and numerous genetic aberrations in the leukemic genome are responsible for the biological and clinical differences among particular ALL subtypes. However, there is limited knowledge regarding the association of whole-genome copy number abnormalities (CNAs) in childhood T-ALL with the course of leukemia and its outcome. The aim of this study was to identify the pattern of whole-genome CNAs in 86 newly diagnosed childhood T-ALL cases using a high-density single-nucleotide polymorphism array. We analyzed the presence of whole-genome CNAs with respect to immunophenotype, clinical features, and treatment outcomes. A total of 769 CNAs, including trisomies, duplications, deletions, and segmental loss of heterozygosity, were detected in 86 analyzed samples. Gain or loss of chromosomal regions exceeding 10 Mb occurred in 46 cases (53%), including six cases (7%) with complex chromosomal alterations. We observed that microdeletions in selected genes (e.g., FIP1L1 and PDGFRB) were related to the clinical features. Interestingly, 13% of samples have a duplication of the two loci (MYB and AIH1—6q23.3), which never occurred alone. Single-nucleotide polymorphism array significantly improved the molecular characterization of pediatric T-ALL. Further studies with larger cohorts of patients may contribute to the selection of prognostic CNAs in this group of patients.

Molecular/Cytogenetic Education for Hematopathology Fellows

OBJECTIVES

At a discussion on molecular/cytogenetic education for hematopathology fellows at the 2018 Society for Hematopathology Program Directors Meeting, consensus was that fellows should understand basic principles and indications for and limitations of molecular/cytogenetic testing used in routine practice. Fellows should also be adept at integrating results of such testing for rendering a final diagnosis. To aid these consensus goals, representatives from the Society for Hematopathology and the Association for Molecular Pathology formed a working group to devise a molecular/cytogenetic curriculum for hematopathology fellow education.

CURRICULUM SUMMARY

The curriculum includes a primer on cytogenetics and molecular techniques. The bulk of the curriculum reviews the molecular pathology of individual malignant hematologic disorders, with applicable molecular/cytogenetic testing for each and following the 2017 World Health Organization classification of hematologic neoplasms. Benign hematologic disorders and bone marrow failure syndromes are also discussed briefly. Extensive tables are used to summarize genetics of individual disorders and appropriate methodologies.

CONCLUSIONS

This curriculum provides an overview of the current understanding of the molecular biology of hematologic disorders and appropriate ancillary testing for their evaluation. The curriculum may be used by program directors for training hematopathology fellows or by practicing hematopathologists.

Response to tyrosine kinase inhibitors in myeloid neoplasms associated with PCM1-JAK2, BCR-JAK2 and ETV6-ABL1 fusion genes

We report on 18 patients with myeloid neoplasms and associated tyrosine kinase (TK) fusion genes on treatment with the TK inhibitors (TKI) ruxolitinib (PCM1-JAK2, n = 8; BCR-JAK2, n = 1) and imatinib, nilotinib or dasatinib (ETV6-ABL1, n = 9). On ruxolitinib (median 24 months, range 2-36 months), a complete hematologic response (CHR) and complete cytogenetic response (CCR) was achieved by five of nine and two of nine patients, respectively. However, ruxolitinib was stopped in eight of nine patients because of primary resistance (n = 3), progression (n = 3) or planned allogeneic stem cell transplantation (allo SCT, n = 2). At a median of 36 months (range 4-78 months) from diagnosis, five of nine patients are alive: four of six patients after allo SCT and one patient who remains on ruxolitinib. In ETV6-ABL1 positive patients, a durable CHR was achieved by four of nine patients (imatinib with one of five, nilotinib with two of three, dasatinib with one of one). Because of inadequate efficacy (lack of hematological and/or cytogenetic/molecular response), six of nine patients (imatinib, n = 5; nilotinib, n = 1) were switched to nilotinib or dasatinib. At a median of 23 months (range 3-60 months) from diagnosis, five of nine patients are in CCR or complete molecular response (nilotinib, n = 2; dasatinib, n = 2; allo SCT, n = 1) while two of nine patients have died. We conclude that (a) responses on ruxolitinib may only be transient in the majority of JAK2 fusion gene positive patients with allo SCT being an important early treatment option, and (b) nilotinib or dasatinib may be more effective than imatinib to induce durable complete remissions in ETV6-ABL1 positive patients.

Systematic use of fluorescence in-situ hybridisation and clinicopathological features in the screening of PDGFRB rearrangements of patients with myeloid/lymphoid neoplasms

AIMS

Rearrangement of the platelet-derived growth factor receptor B (PDGFRB) gene defines a unique group of myeloid/lymphoid neoplasms with frequent eosinophilia and high sensitivity to tyrosine kinase inhibitors. This genetic abnormality is also rarely reported in Philadelphia-like B-cell acute lymphoblastic leukaemia/lymphoma (B-ALL). PDGFRB rearrangement was initially thought to only occur in cases with 5q31-33 rearrangement as determined with conventional cytogenetics; however, there are reported cases with cryptic rearrangements. We aim to develop a broader strategy for screening of PDGFRB rearrangements of patients with myeloid/lymphoid neoplasms.

METHODS AND RESULTS

We performed fluorescence in-situ hybridisation (FISH) for PDGFRB rearrangement in 197 patients, including 70 with B-ALL, 10 with myeloid neoplasms with 5q31-33 rearrangements, and 117 with eosinophilia (≥0.5 × 10⁹ /l in peripheral blood or ≥5% in bone marrow), and identified PDGFRB rearrangement in four of 197 (2.0%) cases. In an attempt to identify clinicopathological and genetic features that may have a stronger association with PDGFRB rearrangement, we analysed 13 patients with confirmed PDGFRB rearrangements, including 10 with myeloid neoplasms and three with B-ALL. Among the 10 patients with myeloid neoplasms, eosinophilia was present in eight, monocytosis in two, 5q31-33 rearrangement in seven, and abnormal bone marrow morphology in all. All patients with myeloid neoplasms showed an excellent response to imatinib, including a patient in blast crisis. The three B-ALL patients presented de novo, showed no eosinophilia, had a complex karyotype including 5q31-33 rearrangement, and had clinically aggressive courses with ultimate patient demise.

CONCLUSIONS

These findings suggest that a higher yield for the identification of PDGFRB rearrangement may result from an index of suspicion in patients with eosinophilia, monocytosis, bone marrow features of a myeloid neoplasm, and 5q31-33 rearrangement, and patients with Philadelphia-like B-ALL.

Myeloid neoplasm with a novel cryptic PDGFRB rearrangement detected by next-generation sequencing

Rearrangements of PDGFRB are defining cytogenetic abnormalities seen in "Myeloid/lymphoid neoplasms with eosinophilia and rearrangement of PDGFRB" and are generally evident by common cytogenetic methods. Here we present an unique case in which karyotyping and fluorescence in situ hybridization (FISH) analysis were negative, and the PDGFRB rearrangement was detected by next-generation sequencing (NGS) analysis. The patient presented with approximately one-year history of leukocytosis including neutrophilia, eosinophilia, basophilia and granulocytic left shift. Bone marrow biopsy revealed a hypercellular marrow with panmyelosis, eosinophilia and mast cell hyperplasia. Blasts were not increased. Ancillary studies revealed a normal karyotype and absence of BCR-ABL1 fusion gene. NGS identified AFAP1L1-PDGFRB fusion, which was confirmed by polymerase chain reaction amplification followed by direct Sanger sequencing. The patient was treated with imatinib and showed normalization of peripheral blood leukocytosis, which lasted for at least six months. This case highlights that cytogenetics/FISH study alone may be insufficient to detect all PDGFRB rearrangement, which is critical for the patient's management. We suggest that molecular analysis capable of detecting fusion genes should be performed in all similar cases.