Mutational Landscape in Myeloproliferative Neoplasms (MPN) and Eosinophilia: Diagnostic and Treatment

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Mutational Landscape in Myeloproliferative Neoplasms (MPN) and Eosinophilia: Diagnostic and Treatment – Section 12

Mutational Landscape in Myeloproliferative Neoplasms (MPN) With Eosinophilia: Diagnosis and Treatment

Andreas Reiter1, Nicholas C.P. Cross2 1 Department of Hematology and Oncology, University Hospital Mannheim, Heidelberg University, Mannheim, Germany; 2 Wessex Regional Genetics Laboratory, Salisbury, and Faculty of Medicine, University of Southampton, UK.

Take-home messages: Clonality-associated eosinophilia is established through the ﬁnding of cytogenetic aberrations, tyrosine kinase fusion genes and point mutations. PDGFRA and PDGFRB fusion genes are exquisitely sensitive to imatinib, conferring an excellent prognosis. New tyrosine kinase inhibitors are promising for MPN in association with FGFR1 (pemigatinib) and JAK2 (ruxolitinib) fusion genes but allogeneic stem cell transplantation remains an important treatment option.

Establishment of clonality by genetic techniques in patients with the WHO subcategory of myeloid/lymphoid neoplasms with unexplained eosinophilia has important prognostic and therapeutic eosinophilia (MLN-eo) and associated TK fusion genes.4 Some implications, ranging between watch and wait and rapid∗ ∗ cytogenetically cryptic fusion genes, mainly due to inversions or allogeneic hematopoietic stem cell transplantation (HSCT). 1, 2 small deletions, for example, ZMYM2-FLT3 or DIAPH1- The most frequent molecular aberration is the cytogenetically PDGFRB,5 have been identified through RNA sequencing, which cryptic FIP1L1-PDGFRA tyrosine kinase (TK) fusion gene, which should become a routine diagnostic tool in the near future. is usually identified by RT-PCR or FISH analysis, for which cells Besides eosinophilia, recurrent non-genetic characteristics of from peripheral blood are sufficient. We consider RT-PCR as the TK fusion gene driven MLN-eo include (a) elevated serum levels of gold standard, being aware of several FISH-negative/RT-PCR- tryptase, vitamin B12, and LDH, (b) cytopenias and monocytosis, positive cases but not vice versa. In contrast, the vast majority of (c) hepatosplenomegaly and lymphadenopathy, and (d) variable related but rare TK fusion genes with rearrangement of PDGFRB levels of fibrosis and increased numbers of spindle-shaped and (most frequently ETV6-PDGFRB or CCDC88C-PDGFRB), loosely scattered, CD25+ positive neoplastic mast cells in the bone FGFR1 (eg, ZMYM2-FGFR1), JAK2 (eg, PCM1-JAK2), ABL1 marrow. Of note, eosinophilia can be absent, for example, in (eg, ETV6-ABL1)orFLT3 (eg, ETV6-FLT3) are usually identified association with involvement of FGFR1 or PDGFRB fusion through cytogenetic analysis of cells derived from a bone marrow genes, which may at least in part depend on the partner gene, for aspirate.3 Distinct reciprocal translocations, most frequently t(5;12) example, BCR. Special attention should be paid to the bone (q31-q33;p13) or t(8;13)(p11;q12), which imply involvement of marrow biopsy which should always include an aspirate for PDGFRB at 5q32 and FGFR1 at 8p11, guide the confirmation standard morphology, cytogenetics and FACS (eg, T-cells, blasts) of the fusion gene by RT-PCR/sequencing analysis, which is and a core biopsy. The proportion of missed or incorrect essential for molecular follow-up of response to therapy. Another diagnoses whilst differentiating between clonal and reactive recurrent fusion, ETV6-ABL1, is created through a more complex eosinophilia is a concern and most prominent is the oversight of rearrangement but can also be cytogenetically cryptic. Due to its systemic mastocytosis.6,7 Particularly important is the evaluation strong association with eosinophilia, it should be included in of proliferation and dysplasia of non-eosinophilic lineages, fiber staining and immunohistochemistry of megakaryocytes, mono- 8 AR has received honoraria and travel support from Novartis and Incyte plus cytes, mast cells and blasts. Unexpected molecular genetic results research support from Novartis. NCPC received honoraria for advisory boards should prompt a re-evaluation and final diagnosis should consider from Novartis and Incyte plus research support from Novartis. both morphology and genetic profile (Fig. 1). Copyright © 2020 the Author(s). Published by Wolters Kluwer Health, Inc. on The FIP1L1-PDGFRA fusion gene is exquisitely sensitive to behalf of the European Hematology Association. This is an open access article low-dose imatinib, for example, 100mg/day following diagnosis distributed under the terms of the Creative Commons Attribution-Non and 3 Â 100mg/week as maintenance dose after achievement of Commercial-No Derivatives License 4.0 (CCBY-NC-ND), where it is permissible to 9–12 download and share the work provided it is properly cited. The work cannot be complete molecular remission (CMR). Imatinib 100mg/day changed in any way or used commercially without permission from the journal. has also been successfully used in patients with PDGFRB fusion 13 HemaSphere (2020) 4:S2 genes. Rarely, patients are diagnosed in primary lymphoid or Received: 21 January 2020 / Accepted: 11 May 2020 myeloid blast phase, which is often present at extramedullary sites

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Reiter and Cross Mutational Landscape in Myeloproliferative Neoplasms (MPN) With Eosinophilia

LABORATORY FEATURES GENETICS ORGAN INVOLVEMENT ( F i g u r e _ 1 ) T D $ F I G ] [ • Monocytosis, blasts • FIP1L1-PDGFRA • Bone marrow, spleen • Serum: LDH, tryptase, AP, • Cytogenec analysis • Sinus, lung, GIT, kidneys IgE, vitamin B12, troponin, • Mutaons (speciﬁc, NGS) • Heart, Skin inﬂammaon markers • T-cell clonality (FACS, PCR) • “Paern and number”

TYROSINE KINASE MUTATION REACTIVE EOSINOPHILIA FUSION GENE

Lymphoma Vasculis Solid tumor HES Single organ

PDGFRA/B: imanib KIT D816V: KIT inhibitor Corcosteroids, FGFR1: pemiganib JAK2 V617F: JAK inhibitor methotrexate, azathioprine, JAK2: ruxolinib JAK2 ex13InDel: JAK inhibitor cyclophosphamide, ABL1: ima-, nilo-, dasanib STAT5B N642H: - IL5 anbodies FLT3: suninib, sorafenib

Resistance, Addional somac mutaons progression or relapse e.g. ASXL1, SRSF2, RUNX1

Allogeneic SCT

Figure 1. Diagnostic work-up and treatment options in eosinophilia-associated disorders.

in terms of T-cell, rarely B-cell lymphoma, or myeloid sarcoma.14 associated with TK fusion genes or increased numbers of blast cells Without evidence from in vitro data or clinical trials, we occur very rarely. Recent data have highlighted the presence of recommend treating patients in blast phase with imatinib 400 additional somatic mutations which are either defining specific mg/day and to only consider dose reduction to 100mg/day after subtypes of∗ myeloid neoplasms, for example, KIT D816V or JAK2 achievement of sustained CMR and the availability of frequent V617F,29, 30 or which are otherwise known to be of prognostic – sensitive molecular monitoring.13 15 Recent data have suggested relevance in myeloid neoplasms. Because significant eosinophilia is that imatinib can be interrupted/stopped∗ in FIP1L1-PDGFRA present in 20% to 30% of patients with KIT D816V positive positive patients11,16,17, 18 in a similar way as in BCR-ABL1 advanced systemic mastocytosis, KIT D816 V represents in fact the positive CML. In FIP1L1-PDGFRA positive patients, we have not second most common eosinophilia-associated molecular aberration yet observed primary resistance while the secondary resistance after FIP1L1-PDGFRA. Clinical markers indicating KIT D816V may occasionally be caused by point mutations, for example, positive advSM include cytopenia(s), monocytosis, elevated tryptase 19 T674I or D842V. Despite encouraging in vitro data, potential and alkaline phosphatase∗ in serum, signs of portal hypertension and 29, 30 second-generation inhibitors, for example, nilotinib, have not malabsorption. Other recurrent∗ mutations include STAT5B been effective and most patients reported have died within 12 N642H and JAK2 ex13InDel. 31,32 Extended molecular profiling months of emergence of imatinib-resistance.20 Potentially active of STAT5B N642H and KIT D816V positive patients has revealed new drugs are either off-label, for example, midostaurin (T674I21) that the prognosis is predominantly determined by presence and or ponatinib (T674I and D842V22,23), or only available in clinical number of additional somatic mutations, for example, SRSF2, trials, for example, pemigatinib or avapritinib (D842V). Due to ASXL1, RUNX1.Besidesthespecific use of KIT- (eg, midostaurin, the poor prognosis, rapid HSCT should be considered in eligible avapritinib) or JAK-inhibitors (eg, ruxolitinib), these patients may patients. ETV6-ABL1 positive patients can achieve complete and be candidates for treatment with hydroxyurea or interferon-alpha. durable remissions on ABL1-inhibitors with a better outcome Overall, all patients should be carefully checked upon eligibility of with nilotinib or dasatinib compared to imatinib.24 The situation HSCT because of the association of eosinophilia with additional is different for patients with FGFR1 and JAK2 fusion genes.25 somatic mutations and consequently adverse prognosis. Primary or secondary blast phase in bone marrow or at extramedullary sites is frequent and rapidly emerging. Patients References may therefore receive primary treatment with intensive chemo- ∗1. Reiter A, Gotlib J. Myeloid neoplasms with eosinophilia. Blood. therapy but only rarely achieve durable remissions because of 2017;129:704–714. primary resistance or early relapse. This may change through Concise overview on myeloid neoplasms with eosinophilia. the availability of ruxolitinib (JAK2)24,26,27 and pemigatinib ∗ 28 2. Valent P, Klion AD, Horny HP, et al. Contemporary consensus (FGFR1). Patients can achieve complete remissions, but the proposal on criteria and classification of eosinophilic disorders and fi long-term bene t is yet unknown and (early) allogeneic HSCT related syndromes. J Allergy Clin Immunol. 2012;130:607–612. should always remain an option in every eligible patient. Concise overview on diagnostic criteria and classification of eosinophilia- The diagnostic criteria of “chronic eosinophilic leukemia, not associated disorders. otherwise specified (CEL, NOS)” include a cytogenetic or molecular 3. Baer C, Muehlbacher V, Kern W, et al. Molecular genetic genetic abnormality (with exception of an eosinophilia-associated characterization of myeloid/lymphoid neoplasms associated with TK fusion gene) or blast cells ≥2% in the peripheral blood or >5% eosinophilia and rearrangement of PDGFRA, PDGFRB, FGFR1 or in the BM. However, cytogenetic abnormalities other those being PCM1-JAK2. Haematologica. 2018;103:e348–e350.

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Reiter and Cross Mutational Landscape in Myeloproliferative Neoplasms (MPN) With Eosinophilia

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