Variable presence of KITD816V in clonal haematological non-mast cell lineage diseases associated with systemic mastocytosis (SM-AHNMD)

Allogeneic haematopoietic cell transplantation for advanced systemic mastocytosis: Best practice recommendations on behalf of the EBMT Practice Harmonisation and Guidelines Committee

Systemic Mastocytosis (SM) is a multifaceted clinically heterogeneous disease. Advanced SM (AdvSM) comprises three entities: aggressive SM (ASM), mast cell leukaemia (MCL) and SM with an associated hematologic neoplasm (SM-AHN), the latter accounting for 60-70% of all AdvSM cases. Detection of a disease-triggering mutation in the KIT gene (esp. KIT D816V) in >90% of the patients with ASM or SM-AHN has led to a significant improvement in therapeutic options by the implementation of two KIT-targeting kinase inhibitors: midostaurin and avapritinib. Although complete remissions have been reported, neither of these targeted agents is 'curative' in all patients and the duration of responses varies. The median overall survival, depending on the WHO subtype and scoring result, is approximately 1 to 4 years. Although the European Competence Network on Mastocytosis (ECNM) and American Initiative in Mast Cell Diseases (AIM) consensus groups recommend allogeneic haematopoietic cell transplantation (allo-HCT) in drug-resistant and other high-risk patients, there is a relative lack of information to guide clinicians on which patients with AdvSM should be considered for transplant, and how KIT inhibitors may fit into the transplant algorithm, including their use pre- and post-transplant to optimise outcomes. Following the generation of an expert panel with a specialist interest in allo-HCT and mastocytosis, these best practice recommendations were generated according to the European Society for Blood and Marrow Transplantation (EBMT) Practice Harmonisation and guidelines and ECNM methodology. We aim to provide a practical, clinically relevant and up-to-date framework to guide allo-HCT in AdvsM in 2024 and beyond.

Advanced systemic mastocytosis-Revised classification, new drugs and how we treat

Mastocytosis constitutes the neoplastic proliferation of mast cells and is broadly classified into systemic mastocytosis (SM), cutaneous mastocytosis and mast cell sarcoma. SM is further partitioned into advanced (AdvSM) and non-advanced (SM-non-Adv) subcategories. AdvSM includes aggressive SM (ASM), SM with an associated haematological neoplasm (SM-AHN) and mast cell leukaemia (MCL). In 2022, two separate expert committees representing the 5th edition of the World Health Organization (WHO5) and the International Consensus (ICC) classification systems submitted revised classification criteria for SM, highlighted by the ICC-proposed incorporation of mast cell cytomorphology in the diagnostic criteria for MCL and myeloid-lineage restriction for the AHN component in SM-AHN. Recent developments in SM also include the introduction of KIT-targeting tyrosine kinase inhibitors (KITi), including midostaurin and avapritinib, both drugs have shown potent activity in reducing mast cell and mutant KIT burden and alleviating mast cell-associated organopathy and mediator symptoms; however, their overall impact on survival or superiority over pre-KITi era treatment options (e.g. cladribine) has not been studied in a controlled setting. In the current review, we provide a summary of recent changes in disease classification and an analysis of recent clinical trials and their impact on our current treatment approach in AdvSM.

Systemic mastocytosis: 2023 update on diagnosis and management in adults

INTRODUCTION

Systemic mastocytosis (SM) is a complex and heterogeneous disease, characterized by the clonal accumulation of mast cells in one or more organs. In 2022 both the World Health Organization (WHO) and the International Consensus Classification (ICC) modified the diagnostic and classification criteria of SM. Moreover, the identification of new clinical and molecular variables has improved prognostic tools and led to increasingly individualized therapeutic strategies.

AREAS COVERED

The aim of this review is to present the updates introduced by the International Consensus Classification in diagnostic criteria of SM. In addition, we report the latest data available from the most important clinical trials in patients both with non-advanced and advanced disease, including elenestinib and bezuclastinib.

EXPERT OPINION

Diagnosis and classification of SM has evolved over years. The most recent WHO and ICC classification improved SM diagnostic work-up, providing clinicians with a clear and simplified diagnostic scheme. New approved targeted therapies such as midostaurin and avapritinib modified the treatment paradigm in patients in advanced stage, and next-generation inhibitors actually investigated in clinical trials are expected in the next future.

Management of Advanced Systemic Mastocytosis and Associated Myeloid Neoplasms

Advanced systemic mastocytosis (AdvSM) is a heterogeneous group of disorders characterized by neoplastic mast cell-related organ damage and frequently associated with a myeloid neoplasm. The 3 clinical entities that comprise AdvSM are aggressive SM (ASM), SM-associated hematologic neoplasm, and mast cell leukemia. A gain-of-function KIT D816 V mutation is the primary oncogenic driver found in about 90% of all patients with AdvSM. Midostaurin, an oral multikinase inhibitor with activity against KIT D816V, and avapritinib, an oral selective KIT D816V inhibitor are approved for AdvSM.

World Health Organization Classification and Diagnosis of Mastocytosis: Update 2023 and Future Perspectives

Experts of the European Competence Network on Mastocytosis (ECNM) and the American Initiative on Mast Cell Disorders have discussed and updated diagnostic criteria and the classification of mastocytosis, based on new insights in the field and data collected in recent years, mostly within ECNM registry projects in which studies on several thousand cases have been performed. Based on this proposal, the World Health Organization has updated its classification of mastocytosis. This article discusses the revised classification of mastocytosis in light of a rapidly moving field and the advent of new diagnostic parameters, new prognostication tools, and new therapies.

Antibody-Based and Cell Therapies for Advanced Mastocytosis: Established and Novel Concepts

Advanced systemic mastocytosis (SM) is a heterogeneous group of myeloid neoplasms characterized by an uncontrolled expansion of mast cells (MC) in one or more internal organs, SM-induced tissue damage, and poor prognosis. Advanced SM can be categorized into aggressive SM (ASM), MC leukemia (MCL), and SM with an associated hematologic neoplasm (SM-AHN). In a vast majority of all patients, neoplastic cells display a KIT mutation, mostly D816V and rarely other KIT variants. Additional mutations in other target genes, such as SRSF2, ASXL1, or RUNX1, may also be identified, especially when an AHN is present. During the past 10 years, improved treatment approaches have led to a better quality of life and survival in patients with advanced SM. However, despite the availability of novel potent inhibitors of KIT D816V, not all patients enter remission and others relapse, often with a multi-mutated and sometimes KIT D816V-negative disease exhibiting multi-drug resistance. For these patients, (poly)chemotherapy, antibody-based therapies, and allogeneic hematopoietic stem cell transplantation may be viable treatment alternatives. In this article, we discuss treatment options for patients with drug-resistant advanced SM, including novel KIT-targeting drugs, antibody-based drugs, and stem cell-eradicating therapies.

A case of high-risk AML in a patient with advanced systemic mastocytosis

Aggressive SM + AML has limited therapeutic options. Even a strong combination of decitabine-venetoclax-midostaurin has a transient effect on AML and a mitigated effect on SM. Larger series are required to identify the best therapeutic strategy.

Systemic mastocytosis in adults: 2023 update on diagnosis, risk stratification and management

OVERVIEW

Systemic mastocytosis (SM) results from clonal proliferation of mast cells (MC) in extracutaneous organs.

DIAGNOSIS

The major criterion is presence of multifocal MC clusters in the bone marrow and/or extracutaneous organs. Minor diagnostic criteria include elevated serum tryptase level, MC CD25/CD2/CD30 expression, and presence of activating KIT mutations.

RISK STRATIFICATION

Establishing SM subtype as per the International Consensus Classification/World Health Organization classification systems is an important first step. Patients either have indolent/smoldering SM (ISM/SSM) or advanced SM, including aggressive SM (ASM), SM with associated myeloid neoplasm (SM-AMN), and mast cell leukemia. Identification of poor-risk mutations (i.e., ASXL1, RUNX1, SRSF2, NRAS) further refines the risk stratification. Several risk models are available to help assign prognosis in SM patients.

MANAGEMENT

Treatment goals for ISM patients are primarily directed toward anaphylaxis prevention/symptom control/osteoporosis treatment. Patients with advanced SM frequently need MC cytoreductive therapy to reverse disease-related organ dysfunction. Tyrosine kinase inhibitors (TKI) (midostaurin, avapritinib) have changed the treatment landscape in SM. While deep biochemical, histological and molecular responses have been documented with avapritinib treatment, its efficacy as monotherapy against a multimutated AMN disease component in SM-AMN patients remains unclear. Cladribine continues to have a role for MC debulking, whereas interferon-α has a diminishing role in the TKI era. Treatment of SM-AMN primarily targets the AMN component, particularly if an aggressive disease such as acute leukemia is present. Allogeneic stem cell transplant has a role in such patients. Imatinib has a therapeutic role only in the rare patient with an imatinib-sensitive KIT mutation.

KIT D816V Mast Cells Derived from Induced Pluripotent Stem Cells Recapitulate Systemic Mastocytosis Transcriptional Profile

Mast cells (MCs) represent a population of hematopoietic cells with a key role in innate and adaptive immunity and are well known for their detrimental role in allergic responses. Yet, MCs occur in low abundance, which hampers their detailed molecular analysis. Here, we capitalized on the potential of induced pluripotent stem (iPS) cells to give rise to all cells in the body and established a novel and robust protocol for human iPS cell differentiation toward MCs. Relying on a panel of systemic mastocytosis (SM) patient-specific iPS cell lines carrying the KIT D816V mutation, we generated functional MCs that recapitulate SM disease features: increased number of MCs, abnormal maturation kinetics and activated phenotype, CD25 and CD30 surface expression and a transcriptional signature characterized by upregulated expression of innate and inflammatory response genes. Therefore, human iPS cell-derived MCs are a reliable, inexhaustible, and close-to-human tool for disease modeling and pharmacological screening to explore novel MC therapeutics.

Systemic mastocytosis with myeloid sarcoma and B-CLL: molecular and clonal heterogeneity in a rare case of SM-AHN with review of literature

BACKGROUND

Systemic mastocytosis (SM) is a rare myeloproliferative disease that results from a clonal proliferation of abnormal mast cells in one or more extra-cutaneous organs. Systemic mastocytosis with an associated hematological neoplasm (SM-AHN) is the second most common subgroup and is diagnosed when WHO criteria for both SM and a hematological neoplasm of non-mast cell lineage are met. The SM-AHN category as currently proposed is highly heterogeneous in terms of pathogenesis, clinical presentation, and prognosis.

CASE PRESENTATION

We present the first reported case of SM-AHN associated with two hematological malignancies of different lineages, a monocytic myeloid sarcoma and a B-cell chronic lymphatic leukemia. Cytogenetic and molecular analyses revealed a distinct clonal origin of the two associated malignancies. The SM-myeloid sarcoma clone demonstrated an abnormal karyotype, trisomy 8 and del(13)(q12.3q14.3), as well as mutations in KITD816V, DNMT3A and RUNX1. The DNMT3A mutation could be detected years before disease onset, supporting its potential role as early driver of leukemogenesis. No genetic aberrations could be identified in the CLL clone, which is assumed to present coincidentally.

CONCLUSIONS

This report highlights the importance of full diagnostic work-up in SM patients in whom an associated hematological malignancy is suspected. Moreover, the importance of genetic analysis is highlighted, as it provides additional insights in the underlying clonal pathogenesis of different phenotypes, can aid in risk stratification, and may help identify potential therapy targets.

New Insights into the Pathogenesis of Mastocytosis: Emerging Concepts in Diagnosis and Therapy

Mastocytosis is a heterogeneous group of neoplasms defined by a numerical increase and accumulation of clonal mast cells (MCs) in various organ systems. The disease may present as cutaneous mastocytosis or systemic mastocytosis (SM). On the basis of histopathological and molecular features, clinical variables, and organ involvement, SM is divided into indolent SM, smoldering SM, SM with an associated hematologic neoplasm, aggressive SM, and MC leukemia. Each variant is defined by unique diagnostic criteria and a unique spectrum of clinical presentations. A key driver of MC expansion and disease evolution is the oncogenic machinery triggered by mutant forms of KIT. The genetic background, additional somatic mutations, and comorbidities also contribute to the course and prognosis. Patients with SM may also suffer from mediator-related symptoms or even an MC activation syndrome. This article provides an update of concepts on the genetics, etiology, and pathology of mastocytosis, with emphasis on diagnostic criteria and new treatment concepts.

The international consensus classification of mastocytosis and related entities

Mastocytosis is a neoplasm characterized by a clonal proliferation of mast cells, which accumulate in one or multiple organs, associated with an extremely heterogeneous clinical presentation. The disease can be limited to the skin (cutaneous mastocytosis) that is mostly seen in childhood and usually behaves in a benign fashion. Adult patients most often present with systemic disease with or without skin lesions. This includes indolent forms such as indolent systemic mastocytosis and its subvariant bone marrow mastocytosis, and smoldering systemic mastocytosis as well as aggressive forms including aggressive systemic mastocytosis, systemic mastocytosis with an associated myeloid neoplasm (previously called systemic mastocytosis with an associated hematologic neoplasm), and mast cell leukemia. In addition, mast cell sarcoma is a rare aggressive form of mastocytosis that can present in the skin as well as at extracutaneous sites. This review article focuses on the updates in mastocytosis of the 2022 international consensus classification (ICC).

Available and emerging therapies for bona fide advanced systemic mastocytosis and primary eosinophilic neoplasms

The historically poor prognosis of patients with advanced systemic mastocytosis (AdvSM) and primary eosinophilic neoplasms has shifted to increasingly favorable outcomes with the discovery of druggable targets. The multikinase/KIT inhibitor midostaurin and the highly selective KIT D816V inhibitor avapritinib can elicit marked improvements in measures of mast cell (MC) burden as well as reversion of MC-mediated organ damage (C-findings) and disease symptoms. With avapritinib, the achievement of molecular remission of KIT D816V and improved survival compared with historical therapy suggests a potential to affect disease natural history. BLU-263 and bezuclastinib are KIT D816V inhibitors currently being tested in trials of AdvSM. In the new World Health Organization and International Consensus Classifications, the category of "myeloid/lymphoid neoplasms with eosinophilia and tyrosine kinase (TK) gene fusions" is inclusive of rearrangements involving PDGFRA, PDGFRB, FGFR1, JAK2, FLT3, and ETV6::ABL1. While the successful outcomes with imatinib in FIP1L1::PDGFRA-positive cases and PDGFRB-rearranged neoplasms have become the "poster children" of these disorders, the responses of the other TK-driven neoplasms to small-molecule inhibitors are more variable. The selective FGFR inhibitor pemigatinib, approved in August 2022, is a promising therapy in aggressive FGFR1-driven diseases and highlights the role of such agents in bridging patients to allogeneic transplantation. This review summarizes the data for these approved and investigational agents and discusses open questions and future priorities regarding the management of these rare diseases.

Avapritinib for advanced systemic mastocytosis

Avapritinib, a highly selective inhibitor of KIT D816V, was approved by the Food and Drug Administration in 2021 for treatment of advanced systemic mastocytosis (AdvSM) and by the European Medicines Agency in 2022 for AdvSM after prior systemic therapy. The phase 1 EXPLORER and phase 2 PATHFINDER trials demonstrated that avapritinib can elicit complete and durable clinical responses and molecular remission of KIT D816V. Key management challenges relate to the complex mutational landscape of AdvSM, often found with an associated hematologic neoplasm.

International Consensus Classification of Myeloid Neoplasms and Acute Leukemias: integrating morphologic, clinical, and genomic data

The classification of myeloid neoplasms and acute leukemias was last updated in 2016 within a collaboration between the World Health Organization (WHO), the Society for Hematopathology, and the European Association for Haematopathology. This collaboration was primarily based on input from a clinical advisory committees (CACs) composed of pathologists, hematologists, oncologists, geneticists, and bioinformaticians from around the world. The recent advances in our understanding of the biology of hematologic malignancies, the experience with the use of the 2016 WHO classification in clinical practice, and the results of clinical trials have indicated the need for further revising and updating the classification. As a continuation of this CAC-based process, the authors, a group with expertise in the clinical, pathologic, and genetic aspects of these disorders, developed the International Consensus Classification (ICC) of myeloid neoplasms and acute leukemias. Using a multiparameter approach, the main objective of the consensus process was the definition of real disease entities, including the introduction of new entities and refined criteria for existing diagnostic categories, based on accumulated data. The ICC is aimed at facilitating diagnosis and prognostication of these neoplasms, improving treatment of affected patients, and allowing the design of innovative clinical trials.

Histopathology and Molecular Genetics in Systemic Mastocytosis: Implications for Clinical Management

The diagnosis of systemic mastocytosis (SM) is based on various clinical, dermatological, serological, and hematological findings but essentially relies on histological evidence of an abnormal increase in tissue-localized mast cells (MCs). The extra-cutaneous organ most frequently affected is the bone marrow (BM), and therefore, histological examination of trephine biopsy specimens of the iliac crest is mandatory on suspicion of SM. At microscopic examination, neoplastic MCs show aberrant morphology, usually with prominent spindling. Immunohistochemistry is a useful tool in the diagnosis of SM because mast cell (MC) infiltrates may be slight and scarce, in a mixed background of lymphohistiocytic cells, eosinophils, and plasma cells. Moreover, neoplastic MCs exhibit an aberrant phenotype. Recent evidence, largely derived from molecular genetics, has enhanced the diagnostic capability of SM, also providing the basis for adequate prognostic and therapeutic evaluation. The cases herein reported illustrate the variable clinical manifestations and disease course of SM, focusing on diagnostic and therapeutic challenges. In accordance with the World Health Organization (WHO) classification and the International Consensus Classification (ICC) systems, our findings emphasize the importance of an integrated diagnostic approach for SM, with proper application of diverse assessment methodologies in order to improve SM classification and treatment effectiveness.

Proposed European Competence Network on Mastocytosis-American Initiative in Mast Cell Diseases (ECNM-AIM) Response Criteria in Advanced Systemic Mastocytosis

Advanced systemic mastocytosis (AdvSM) is characterized by the presence of KIT D816V and other somatic mutations (eg, in SRSF2, ASXL1, and RUNX1) in 95% and 60% to 70% of patients, respectively. The biological and clinical consequences of AdvSM include multilineage involvement (eg, associated hematologic neoplasm) in 60% to 80% of patients, variable infiltration and damage (C-findings) of predominantly bone marrow and visceral organs through affected mast cell (MC) and non-MC lineages, and elevated levels of serum tryptase. Recently, the treatment landscape has substantially changed with the introduction of the multikinase/KIT inhibitor midostaurin and the selective KIT D816V inhibitor avapritinib. In this review, we discuss the evolution of AdvSM response criteria that have been developed to better capture clinical benefit (eg, improved responses and progression-free and overall survival). We propose refined response criteria from European Competence Network on Mastocytosis and American Initiative in Mast Cell Diseases investigators that use a tiered approach to segregate the effects of histopathologic (eg, bone marrow MC burden, tryptase), molecular (eg, KIT D816V variant allele frequency), clinical (eg, C-findings), and symptom response on long-term outcomes. These response criteria require evaluation in future prospective clinical trials of selective KIT inhibitors and other novel agents.

Standards of Pathology in the Diagnosis of Systemic Mastocytosis: Recommendations of the EU-US Cooperative Group

Pathology plays a central role in the diagnosis of systemic mastocytosis (SM), its delineation from other neoplasms and reactive conditions, and in monitoring of SM under therapy. The morphologic hallmark of SM is the accumulation of spindle-shaped, hypogranulated mast cells (MCs) in bone marrow (BM) and other extracutaneous tissues. Four of the 5 World Health Organization-defined diagnostic criteria (ie, compact MC aggregates [=major criterion]; atypical MC morphology; activating KIT point mutations; aberrant expression of CD25 and/or CD2 and/or CD30 in MCs [=minor criteria]) can be addressed by the pathologist. The final classification of SM variants as either BM mastocytosis, indolent SM, smoldering SM, aggressive SM (ASM), SM with an associated hematologic neoplasm (SM-AHN), or MC leukemia (MCL) has important prognostic significance and requires the integration of certain morphological, clinical, radiological, and biochemical data, referred to as B- and C-findings. Substantial diagnostic challenges may be posed to the pathologist and clinician especially in the so-called advanced SM variants, that is, ASM, MCL, and SM-AHN. In this article, updated recommendations of the EU-US Cooperative Group regarding standards of pathology in the diagnosis of SM, presented during the year 2020 Working Conference held in September in Vienna, are reported.

Comprehensive Analysis of Acquired Genetic Variants and Their Prognostic Impact in Systemic Mastocytosis

Systemic mastocytosis (SM) is a rare clonal haematopoietic stem cell disease in which activating KIT mutations (most commonly KIT D816V) are present in virtually every (>90%) adult patient at similar frequencies among non-advanced and advanced forms of SM. The KIT D816V mutation is considered the most common pathogenic driver of SM. Acquisition of this mutation early during haematopoiesis may cause multilineage involvement of haematopoiesis by KIT D816V, which has been associated with higher tumour burden and additional mutations in other genes, leading to an increased rate of transformation to advanced SM. Thus, among other mutations, alterations in around 30 genes that are also frequently mutated in other myeloid neoplasms have been reported in SM cases. From these genes, 12 (i.e., ASXL1, CBL, DNMT3A, EZH2, JAK2, KRAS, NRAS, SF3B1, RUNX1, SF3B1, SRSF2, TET2) have been recurrently reported to be mutated in SM. Because of all the above, assessment of multilineage involvement of haematopoiesis by the KIT D816V mutation, in the setting of multi-mutated haematopoiesis as revealed by a limited panel of genes (i.e., ASXL1, CBL, DNMT3A, EZH2, NRAS, RUNX1 and SRSF2) and associated with a poorer patient outcome, has become of great help to identify SM patients at higher risk of disease progression and/or poor survival who could benefit from closer follow-up and eventually also early cytoreductive treatment.

TET2 regulates immune tolerance in chronically activated mast cells

Mutation of the TET2 DNA-hydroxymethylase has been associated with a number of immune pathologies. The disparity in phenotype and clinical presentation among these pathologies leads to questions regarding the role of TET2 mutation in promoting disease evolution in different immune cell types. Here we show that, in primary mast cells, Tet2 expression is induced in response to chronic and acute activation signals. In TET2-deficient mast cells, chronic activation via the oncogenic KITD816V allele associated with mastocytosis, selects for a specific epigenetic signature characterized by hypermethylated DNA regions (HMR) at immune response genes. H3K27ac and transcription factor binding is consistent with priming or more open chromatin at both HMR and non-HMR in proximity to immune genes in these cells, and this signature coincides with increased pathological inflammation signals. HMR are also associated with a subset of immune genes that are direct targets of TET2 and repressed in TET2-deficient cells. Repression of these genes results in immune tolerance to acute stimulation that can be rescued with vitamin C treatment or reiterated with a Tet inhibitor. Overall, our data support a model where TET2 plays a direct role in preventing immune tolerance in chronically activated mast cells, supporting TET2 as a viable target to reprogram the innate immune response for innovative therapies.

Standards of Genetic Testing in the Diagnosis and Prognostication of Systemic Mastocytosis in 2022: Recommendations of the EU-US Cooperative Group

Mastocytosis comprises rare heterogeneous diseases characterized by an increased accumulation of abnormal mast cells in various organs/tissues. The pathogenesis of mastocytosis is strongly linked to the presence of KIT-activating mutations. In systemic mastocytosis (SM), the most frequent mutation encountered is KIT p.D816V, whose presence constitutes one of the minor diagnostic criteria. Different techniques are used to search and quantify the KIT p.D816V mutant; however, allele-specific quantitative PCR and droplet digital PCR are today the most sensitive. The analysis of the KIT p.D816V allele burden has undeniable interest for diagnostic, prognostic, and therapeutic monitoring. The analysis of non-mast cell hematological compartments in SM is similarly important because KIT p.D816V multilineage involvement is associated with a worse prognosis. In addition, in advanced forms of SM, mutations in genes other than KIT are frequently identified and affect negatively disease outcome and response to therapy. Thus, combined quantitative and sensitive analysis of KIT mutations and next-generation sequencing of other recurrently involved myeloid genes make it possible to better characterize the extent of the affected cellular compartments and additional molecular aberrations, providing a more detailed overview of the complex mutational landscape of SM, in relation with the clinical heterogeneity of the disease. In this article, we report the latest recommendations of the EU-US Cooperative Group presented in September 2020 in Vienna during an international working conference, on the techniques we consider standard to detect and quantify the KIT p.D816V mutant in SM and additional myeloid mutations found in SM subtypes.

Superior Efficacy of Midostaurin Over Cladribine in Advanced Systemic Mastocytosis: A Registry-Based Analysis

PURPOSE

On the basis of data from the German Registry on Disorders of Eosinophils and Mast Cells, we compared the efficacy of midostaurin and cladribine in patients with advanced systemic mastocytosis (AdvSM).

PATIENTS AND METHODS

Patients with AdvSM (n = 139) were treated with midostaurin only (n = 63, 45%), cladribine only (n = 23, 17%), or sequentially (midostaurin-cladribine, n = 30, 57%; cladribine-midostaurin, n = 23, 43%). Prognosis was assessed through the Mutation-Adjusted Risk Score (MARS). Besides the comparison of efficacy between midostaurin and cladribine on response (eg, organ dysfunction, bone marrow mast cell [MC] infiltration, and tryptase), overall survival (OS), and leukemia-free survival, we focused on the impact of treatment on involved non-MC lineages, for example, monocytes or eosinophils, and the KIT D816V expressed allele burden.

RESULTS

Midostaurin only was superior to cladribine only with effects from responses on MC and non-MC lineages conferring on a significantly improved OS (median 4.2 v 1.9 years, P = .033) and leukemia-free survival (2.7 v 1.3 years, P = .044) on the basis of a propensity score-weighted analysis of parameters included in MARS. Midostaurin compensated the inferior efficacy of cladribine in first- and second-line treatment. On midostaurin in any line, response of eosinophilia did not improve its baseline adverse prognostic impact, whereas response of monocytosis proved to be a positive on-treatment parameter. Multivariable analysis allowed to establish three risk categories (low/intermediate/high) through the combination of MARS and the reduction of the KIT D816V expressed allele burden of ≥ 25% at month 6 (median OS not reached v 3.0 years v 1.0 year; P < .001).

CONCLUSION

In this registry-based analysis, midostaurin revealed superior efficacy over cladribine in patients with AdvSM. In midostaurin-treated patients, the combination of baseline MARS and molecular response provided a compelling three-tier risk categorization (MARSv2.0) for OS.

Successful Imatinib Treatment for Systemic Mastocytosis Associated With Myelodysplastic/Myeloproliferative Neoplasm: Report of a Case and Literature Review

Systemic mastocytosis (SM) is a heterogeneous disease characterized by the expansion of mast cells in one or more tissues, frequently characterized by the presence of KITD816V mutation. The updated World Health Organization (WHO) classification of myeloid neoplasms recognizes SM with an associated hematological neoplasm (SM-AHN) as a new subtype among the others, which is depicted by the coexistence of SM with another hematological clonal disease. Prognosis is very different among SM patients, while its treatment, although highly personalized, is still challenging. Here we report a case of KITD816V-unmutated SM associated with MDS/MPN successfully treated with imatinib.

Combined Inhibition of Polo-Like Kinase-1 and Wee1 as a New Therapeutic Strategy to Induce Apoptotic Cell Death in Neoplastic Mast Cells

Systemic mastocytosis (SM) is due to the pathologic accumulation of neoplastic mast cells in one or more extracutaneous organ(s). Although midostaurin, a multikinase inhibitor active against both wild-type and D816V-mutated KIT, improves organ damage and symptoms, a proportion of patients relapse or have resistant disease. It is well known that Aurora kinase A (AKA) over-expression promotes tumorigenesis, but its role in the pathogenesis of systemic mastocytosis (SM) has not yet been investigated. Evidence from the literature suggests that AKA may confer cancer cell chemo-resistance, inhibit p53, and enhance Polo-like kinase 1 (Plk1), CDK1, and cyclin B1 to promote cell cycle progression. In this study, we aimed to investigate the pathogenetic role of AKA and Plk1 in the advanced forms of SM. We demonstrate here, for the first time, that SM cell lines display hyper-phosphorylated AKA and Plk1. Danusertib (Aurora kinase inhibitor) and volasertib (Plk1 inhibitor) inhibited growth and induced apoptotic cell death in HMC-1.1 and -1.2 cells. Their growth-inhibitory effects were associated with cell cycle arrest and the activation of apoptosis. Cell cycle arrest was associated with increased levels of phospho-Wee1. Wee1 inhibition by MK1775 after 24 h treatment with danusertib or volasertib, when cells were arrested in G2 phase and Wee1, was overexpressed and hyper-activated, resulting in a significantly higher rate of apoptosis than that obtained from concomitant treatment with danusertib or volasertib + MK1775 for 48 h. In conclusion, Plk1 and AKA, alone or together with Wee1, are attractive therapeutic targets in neoplastic MCs. Repurposing Plk1 or AKA ± Wee1 inhibitors in advanced clinical development for other indications is a therapeutic strategy worthy of being explored, in order to improve the outcome of patients with advanced SM.

Mast Cell Sarcoma of the Retroperitoneum With Concurrent Systemic Mastocytosis and an Undisclosed Associated Hematologic Neoplasm: A Case Report

Mastocytosis is a rare disorder affecting both children and adults by gathering of functionally defective mast cells in the body’s tissues. The World Health Organization (WHO) classified mastocytosis into cutaneous mastocytosis, systemic mastocytosis (SM), and mast cell sarcoma (MCS). We hereby present a case of retroperitoneal MCS with concurrent systemic mastocytosis and an undisclosed associated hematological neoplasm (SM-undisclosed AHN). The diagnosis of MCS and SM was made after the second biopsy over retroperitoneal mass, lymph node, and ovary for rapidly progressive disease with the presentation of unexplained recurrent flushing, palpitation, and shock, in addition to abdominal pain. A clonal myeloid neoplasm was also suspected by the karyotype and hemogram data. Unfortunately, the patient succumbed to the disease quickly. Apart from this unique case, the previously reported cases of SM with MCS in the literature were also reviewed.

Establishing diagnostic criteria for mastocytosis in skin biopsies

AIMS

The diagnosis of mastocytosis in skin biopsies can be challenging - particularly in cases with very few mast cells. More diagnostic criteria are needed.

METHODS AND RESULTS

We analyzed 103 skin biopsies from patients with mastocytosis and compared them with biopsies from inflammatory skin lesions and normal skin. Using CD117 immunostaining, we determined the mast cell distribution pattern, the percentage of mast cells in the inflammatory infiltrate, and the mast cell count per mm². We found that a sheet-like or subepidermal distribution of mast cells was specific for mastocytosis. The most significant feature was the percentage of mast cells and not the mast cell count. We found that a mast cell percentage above 40% was fully specific in both adults and children but lacked sensitivity, especially in adults. In children, all cases with a percentage below 40% harbored a number of mast cells above 90 per mm², allowing a straightforward diagnosis. In adults, the diagnosis was more challenging and cases with less than 40% of mast cells could be diagnosed on account of a number of mast cells above 40 per mm², with 88.5% sensitivity and 95.2% specificity. Additional signs might be useful in difficult cases. However, CD25 immunostaining was not useful.

CONCLUSIONS

We confirmed that the criteria currently applied in the bone marrow were not appropriate for the skin. Accordingly, we developed an algorithm for the diagnosis of mastocytosis in skin biopsies with a high level of interrater reproducibility (mean kappa 0.8).

Avapritinib for Systemic Mastocytosis

INTRODUCTION

Systemic mastocytosis (SM) is a rare myeloid neoplasm driven in ≈95% of cases by activating KIT mutations, usually D816V. SM can be indolent (ISM), smoldering (SSM) and advanced (AdvSM), the latter characterized by organ damage resulting from infiltrating neoplastic mast cells. The vast majority of cases are indolent, with near-normal life expectancy, although symptoms can be severe. AdvSM, comprising aggressive SM, SM with an associated hematologic neoplasm and mast cell leukemia, however, carries a poor prognosis. Avapritinib is a highly potent and selective inhibitor of mutant KIT.

AREAS COVERED

We provide an overview of SM, including the current therapeutic landscape, and discuss avapritinib in detail: its chemistry and discovery, pharmacodynamic and pharmacokinetic data, current approval status and safety and efficacy profiles in both advanced and non-advanced SM.

EXPERT OPINION

With a response rate of 75% amongst evaluable patients with AdvSM and marked reductions observed in measures of mast cell and disease burden, avapritinib stands out as a highly effective targeted therapy for this mutant KIT-driven disease. Cognitive impairment may occur, and intracranial hemorrhage has been reported, particularly in association with severe thrombocytopenia. Early results in patients with ISM/SSM are encouraging. Avapritinib is now approved in the US for AdvSM.

Mast cell differentiation of leukemic blasts in diverse myeloid neoplasms: A potential pre-myelomastocytic leukemia condition

INTRODUCTION

Myeloid neoplasm with blasts showing mast cell (MC)-differentiation and MC-component less than 10% of all nucleated cells but not fulfilling the criteria for systemic mastocytosis with associated hematological neoplasm (SM-AHN) or myelomastocytic leukemia (MML) has not been described in the literature. Herein, we report a study of diverse myeloid malignancies with blasts showing MC-differentiation but not meeting the criteria for SM-AHN or MML. We also evaluated the utility of flow-cytometric immunophenotyping (FCI) in the characterization of immature-MCs (iMCs).

METHODS

We identified nine patients of myeloid neoplasms and studied their morphological, FCI, immunohistochemistry, cytogenetic and molecular characteristics. We also compared the immunophenotypic features of MCs from patient samples with control samples.

RESULTS

The study included patients with newly-diagnosed acute myeloid leukemia (n = 4), chronic myelomonocytic leukemia (n = 1), and chronic myeloid leukemia on follow-up (n = 4) showing MC differentiation in leukemic-blasts. These patients had mildly increased MCs (range, 0.5%-3%) in bone-marrow morphology, including immature-forms and did not meet the criteria for either SM-AHN or MML. On FCI, iMCs were positive for bright-CD117, heterogeneous-CD34, dim-to-negative-HLADR, and moderate-CD203c expression. Expression-levels of CD123 and CD38 were higher (p < 0.001) but CD33 and CD45 were lower in iMCs compared to mature-MC from control samples (p = 0.019 and p = 0.0037).

CONCLUSION

We reported a rare finding of MC differentiation of leukemic blasts in diverse myeloid neoplasms and proposed it as a potential pre-myelomastocytic leukemia condition. We described the distinct immunophenotypic signature of immature-MCs using commonly used markers and highlighted the utility of FCI for the diagnosis of this entity.

Systemic mastocytosis in adults: 2021 Update on diagnosis, risk stratification and management

OVERVIEW

Systemic mastocytosis (SM) results from a clonal proliferation of abnormal mast cells (MC) in extra-cutaneous organs.

DIAGNOSIS

The major criterion is presence of multifocal clusters of spindled MC in the bone marrow. Minor diagnostic criteria include elevated serum tryptase level, abnormal MC CD25 expression, and presence of KITD816V mutation.

RISK STRATIFICATION

Establishing SM subtype as per the World Health Organization classification system is an important first step. Broadly, patients either have indolent/smoldering SM (ISM/SSM) or advanced SM, the latter includes aggressive SM (ASM), SM with associated hematological neoplasm (SM-AHN), and mast cell leukemia (MCL). Identification of poor-risk mutations (ie, ASXL1, RUNX1, SRSF2, NRAS) further refines the risk stratification. Recently, clinical and hybrid clinical-molecular risk models have been developed to more accurately assign prognosis in SM patients.

MANAGEMENT

Treatment goals for ISM patients are primarily directed towards anaphylaxis prevention/symptom control/osteoporosis treatment. Patients with advanced SM frequently need MC cytoreductive therapy to ameliorate disease-related organ dysfunction. High response rates have been seen with small-molecule inhibitors that target mutant-KIT, including midostaurin (Food and Drug Administration approved) or avapritinib (investigational). Other options for MC cytoreduction include cladribine or interferon-α, although head-to-head comparisons are lacking. Treatment of SM-AHN primarily targets the AHN component, particularly if an aggressive disease such as acute myeloid leukemia is present. Allogeneic stem cell transplant can be considered in such patients, or in those with relapsed/refractory advanced SM. Imatinib has a limited therapeutic role in SM; effective cytoreduction is limited to those with imatinib-sensitive KIT mutations.

Response Criteria in Advanced Systemic Mastocytosis: Evolution in the Era of KIT Inhibitors

Systemic mastocytosis (SM) is a rare clonal hematologic neoplasm, driven, in almost all cases, by the activating KIT D816V mutation that leads to the growth and accumulation of neoplastic mast cells. While patients with advanced forms of SM have a poor prognosis, the introduction of KIT inhibitors (e.g., midostaurin, and avapritinib) has changed their outlook. Because of the heterogenous nature of advanced SM (advSM), successive iterations of response criteria have tried to capture different dimensions of the disease, including measures of mast cell burden (percentage of bone marrow mast cells and serum tryptase level), and mast cell-related organ damage (referred to as C findings). Historically, response criteria have been anchored to reversion of one or more organ damage finding(s) as a minimal criterion for response. This is a central principle of the Valent criteria, Mayo criteria, and International Working Group-Myeloproliferative Neoplasms Research and Treatment and European Competence Network on Mastocytosis (IWG-MRT-ECNM) consensus criteria. Irrespective of the response criteria, an ever-present challenge is how to apply response criteria in patients with SM and an associated hematologic neoplasm, where the presence of both diseases complicates assignment of organ damage and adjudication of response. In the context of trials with the selective KIT D816V inhibitor avapritinib, pure pathologic response (PPR) criteria, which rely solely on measures of mast cell burden and exclude consideration of organ damage findings, are being explored as more robust surrogate of overall survival. In addition, the finding that avapritinib can elicit complete molecular responses of KIT D816V allele burden, establishes a new benchmark for advSM and motivates the inclusion of definitions for molecular response in future criteria. Herein, we also outline how the concept of PPR can inform a proposal for new response criteria which use a tiered evaluation of pathologic, molecular, and clinical responses.

Genomic Landscape and Risk Stratification in Chronic Myelomonocytic Leukemia

PURPOSE

The advent of next-generation sequencing has allowed for the annotation of a vast array of recurrent somatic mutations across human malignancies, ushering in a new era of precision oncology. Chronic myelomonocytic leukemia is recognized as a myelodysplastic/myeloproliferative neoplasm and displays heterogenous clinical and genetic features. Herein, we review what is currently understood regarding the genomic landscape of this disease and discuss how somatic mutations have impacted current risk stratification methods.

RECENT FINDINGS

Genomic studies in chronic myelomonocytic leukemia have identified a characteristic spectrum of cytogenetic and molecular abnormalities. Chromosomal abnormalities are detected in ~30% of patients and somatic gene mutations in up to 90% of patients, most commonly in TET2, SRSF2, and ASXL1. While cytogenetic abnormalities have long been known to impact the prognosis of myeloid neoplasms, recent studies have identified that somatic mutations impact prognosis independent of cytogenetic and clinical variables. This is best exemplified by mutations in ASXL1, which have been uniformly associated with inferior survival. These findings have led to the development of three molecularly inspired prognostic models, in an attempt to more accurately prognosticate in the disease. Our understanding of the genomic landscape of chronic myelomonocytic leukemia continues to evolve, with somatic mutations demonstrating an expanding role in diagnosis, risk stratification, and therapeutic decision-making. Given these findings, molecular profiling by next-generation sequencing should be considered standard of care in all patients.

Mastocytosis

OBJECTIVES

The 2019 Workshop of the Society for Hematopathology/European Association for Haematopathology received and reviewed cases covering the spectrum of mastocytosis and related diseases, including morphologic mimics, focusing on recent updates and relevant findings for pathologists.

METHODS

The workshop panel reviewed 99 cases of cutaneous and systemic mastocytosis (SM) and SM and associated hematologic neoplasms (SM-AHN).

RESULTS

Despite a common theme of KIT mutation (particularly D816V), mastocytosis is a heterogeneous neoplasm with a wide variety of presentations. This spectrum, including rare subtypes and extramedullary organ involvement, is discussed and illustrated by representative cases.

CONCLUSIONS

In the age of targeted treatment aimed at KIT, the accurate diagnosis and classification of mastocytosis has major implications for therapy and further interventions. Understanding the clinical, pathologic, and genetic findings of mastocytosis is crucial for selecting the proper tests to perform and subsequent arrival at a correct diagnosis in this rare disease.

Mast cells as a unique hematopoietic lineage and cell system: From Paul Ehrlich's visions to precision medicine concepts

The origin and functions of mast cells (MCs) have been debated since their description by Paul Ehrlich in 1879. MCs have long been considered 'reactive bystanders' and 'amplifiers' in inflammatory processes, allergic reactions, and host responses to infectious diseases. However, knowledge about the origin, phenotypes and functions of MCs has increased substantially over the past 50 years. MCs are now known to be derived from multipotent hematopoietic progenitors, which, through a process of differentiation and maturation, form a unique hematopoietic lineage residing in multiple organs. In particular, MCs are distinguishable from basophils and other hematopoietic cells by their unique phenotype, origin(s), and spectrum of functions, both in innate and adaptive immune responses and in other settings. The concept of a unique MC lineage is further supported by the development of a distinct group of neoplasms, collectively referred to as mastocytosis, in which MC precursors expand as clonal cells. The clinical consequences of the expansion and/or activation of MCs are best established in mastocytosis and in allergic inflammation. However, MCs have also been implicated as important participants in a number of additional pathologic conditions and physiological processes. In this article, we review concepts regarding MC development, factors controlling MC expansion and activation, and some of the fundamental roles MCs may play in both health and disease. We also discuss new concepts for suppressing MC expansion and/or activation using molecularly-targeted drugs.

Systemic mastocytosis associated with Hodgkin's lymphoma in a 4-year-old child

Systemic mastocytosis with associated clonal hematologic non-mast cell lineage disease (SM-AHN) represents a specific subtype of mastocytosis and is extremely rare in children. We describe a 4-year-old child with systemic mastocytosis associated with Hodgkin's lymphoma. The child had cutaneous mastocytosis and lymphadenopathy without other clinical features of SM, which was diagnosed only by bone marrow examination.

Recent Advances in the Molecular Biology of Systemic Mastocytosis: Implications for Diagnosis, Prognosis, and Therapy

In recent years, molecular characterization and management of patients with systemic mastocytosis (SM) have greatly benefited from the application of advanced technologies. Highly sensitive and accurate assays for KIT D816V mutation detection and quantification have allowed the switch to non-invasive peripheral blood testing for patient screening; allele burden has prognostic implications and may be used to monitor therapeutic efficacy. Progress in genetic profiling of KIT, together with the use of next-generation sequencing panels for the characterization of associated gene mutations, have allowed the stratification of patients into three subgroups differing in terms of pathogenesis and prognosis: i) patients with mast cell-restricted KIT D816V; ii) patients with multilineage KIT D816V-involvement; iii) patients with "multi-mutated disease". Thanks to these findings, new prognostic scoring systems combining clinical and molecular data have been developed. Finally, non-genetic SETD2 histone methyltransferase loss of function has recently been identified in advanced SM. Assessment of SETD2 protein levels and activity might provide prognostic information and has opened new research avenues exploring alternative targeted therapeutic strategies. This review discusses how progress in recent years has rapidly complemented previous knowledge improving the molecular characterization of SM, and how this has the potential to impact on patient diagnosis and management.

Detection of the KITD816V mutation in myelodysplastic and/or myeloproliferative neoplasms and acute myeloid leukemia with myelodysplasia-related changes predicts concurrent systemic mastocytosis

Greater than 90% of cases of systemic mastocytosis (SM) harbor pathogenic KIT mutations, particularly KIT^D816V. Prognostically-significant pathogenic KIT mutations also occur in 30-40% of core binding factor-associated acute myeloid leukemia (CBF-AML), but are uncommonly associated with concurrent SM. By comparison, the occurrence of SM in other myeloid neoplasms bearing pathogenic KIT mutations, particularly those with a chronic course, is poorly understood. Review of clinical next-generation sequencing (NGS) performed at our institutions in patients with known or suspected hematologic malignancies over an 8-year period revealed 64 patients with both a pathogenic KIT mutation detected at one or more timepoints and available bone marrow biopsy materials. Patients with KIT^D816V-mutated myelodysplastic syndromes (MDS), myeloproliferative neoplasms (MPN), or overlap MDS/MPN (n = 22) accounted for approximately one-third of our cohort (34%). Comprehensive morphologic and immunophenotypic characterization revealed that nearly all cases (n = 20, 91%) exhibited concurrent SM. In contrast, of the 18 patients (28%) with AML and KIT^D816V, only eight (44%) showed evidence of SM at any point in their disease course (p = 0.0021); of these eight, the AML component was characterized as AML with myelodysplasia-related changes (AML-MRC) in all but one instance (n = 7, 87%). Twelve patients (19%) had pathogenic KIT mutations other than p.D816V, all in the setting of AML (CFB-AML, n = 7; AML, not otherwise specified, n = 2; AML-MRC, n = 1; acute promyelocytic leukemia, n = 1); only two of these patients (17%), both with CBF-AML, exhibited concurrent SM. The remaining 12 patients (19%) had SM without evidence of an associated hematological neoplasm (AHN). For nearly one-third of the 30 SM-AHN patients in our cohort (n = 9, 30%), the SM component of their disease was not initially clinicopathologically recognized. We propose that identification of the KIT^D816V mutation in patients diagnosed with MDS, MPN, MDS/MPN, or AML-MRC should trigger reflex testing for SM.

New developments in diagnosis, prognostication, and treatment of advanced systemic mastocytosis

Systemic mastocytosis (SM) has greatly benefited from the broad application of precision medicine techniques to hematolymphoid neoplasms. Sensitive detection of the recurrent KIT D816V mutation and use of next-generation sequencing (NGS) panels to profile the genetic landscape of SM variants have been critical adjuncts to the diagnosis and subclassification of SM, and development of clinical-molecular prognostic scoring systems. Multilineage KIT involvement and multimutated clones are characteristic of advanced SM (advSM), especially SM with an associated hematologic neoplasm (AHN). A major challenge is how to integrate conventional markers of mast cell disease burden (percentage of bone marrow mast cell infiltration and serum tryptase levels) with molecular data (serial monitoring of both KIT D816V variant allele frequency and NGS panels) to lend more diagnostic and prognostic clarity to the heterogeneous clinical presentations and natural histories of advSM. The approval of the multikinase/KIT inhibitor midostaurin has validated the paradigm of KIT inhibition in advSM, and the efficacy and safety of second-generation agents, such as the switch-control inhibitor ripretinib (DCC-2618) and the D816V-selective inhibitor avapritinib (BLU-285) are being further defined in ongoing clinical trials. Looking forward, perhaps the most fruitful marriage of the advances in molecular genetics and treatment will be the design of adaptive basket trials that combine histopathology and genetic profiling to individualize treatment approaches for patients with diverse AHNs and relapsed/refractory SM.

Bone lesions in systemic mastocytosis: Bone histomorphometry and histopathological mechanisms

Osteoporosis is considered the most frequent skeletal manifestation of systemic mastocytosis (SM). We performed a retrospective analysis of sixty patients (37 males and 23 females) who underwent a bone biopsy in the assessment of SM or in the assessment of unexplained bone fragility. Thirty-three had simultaneously a bone marrow biopsy with a Jamshidi's needle; this sample was used for immunohistochemical analysis (tryptase, c-KIT. CD20, VCAM-1). Bone biopsy was realized in 42 cases in the assessment of SM to provide histologic proof of the disease and in 18 cases in the assessment of unexplained bone fragility and surprisingly revealed a SM. An increased bone turnover was observed in patients with SM with elevated eroded surfaces, osteoclast number and bone formation rate. In addition to nodules of mast cells (MC), a high number of MC was directly apposed on the trabeculae, affixed on the osteoblasts or the lining cells. The VCAM-1 adhesion protein recognizing α4β7 and α4β1 integrins may be a candidate to explain this particular adherence. One third of the bone marrow biopsies did not exhibit MC nodules or MC infiltration and led to a false negative diagnosis for SM. SM can be discovered in the assessment of fracture or osteoporosis. Transiliac bone biopsy allows for the diagnosis of the disease more accurately than bone marrow biopsy; it also provides a histomorphometric analysis of bone remodeling.

The Spectrum of Aggressive Mastocytosis: A Workshop Report and Literature Review

Most cases of mastocytosis are indolent, usually cutaneous mastocytosis or indolent systemic mastocytosis (SM). Aggressive mast cell (MC) diseases are very rare and often fatal. They can develop de novo or due to progression of indolent forms and can present in different ways; either as MC sarcoma or as advanced SM which includes aggressive SM, MC leukemia, and SM with an associated hematological neoplasm. This review will describe these different aggressive forms of mastocytosis, illustrated by cases submitted to the workshop of the 18th Meeting of the European Association for Haematopathology, Basel 2016, organized by the European Bone Marrow Working Group. In addition, the diagnostic criteria for identifying myelomastocytic leukemia, an aggressive myeloid neoplasm with partial MC differentiation that falls short of the criteria for SM, and disease progression in patients with established mastocytosis are discussed.

Mastocytosis onset in a patient with treated hairy cell leukemia: Just a coincidence?

Mastocytosis is a mast cell disease caused by functionally defective infiltrating mast cells and CD34+ mast cell precursors. The heterogeneous group of mast cell disorders is categorized into five variants in the updated 2017 World Health Organization (WHO) classification among those systemic mastocytosis with an associated neoplasm (SM-AHN). Except for myeloid neoplasia, lymphoproliferative disorders associated to SM-AHN are more scarce. Here, we report the second case ever described of associated mastocytosis and hairy-cell disease. A 38-year-old female patient without any specific medical history was diagnosed a hairy cell leukemia and BRAF^V600E mutation was found in hairy cells. Since purine-analogs were avoided to prevent prolonged myelosuppression, she was treated with vemurafenib and rituximab. Despite early discontinuation due to vemurafenib-induced agranulocytosis, a partial response was observed. Strikingly, bone marrow biopsy performed one month after vemurafenib discontinuation revealed a nodular infiltration by 30% tumoral mastocytes. Along with elevated tryptase level, KIT^D816V mutation on mastocytes and clinical exam, the patient was diagnosed with systemic mastocytosis with an associated hematological neoplasm (SM-AHN). No BRAF^V600E mutation was found on mastocytes. The physiopathology of this association is not known and might be only a coincidence or a common genetic driver mutation enhancing mast and hairy cells.

Prognostic impact of eosinophils in mastocytosis: analysis of 2350 patients collected in the ECNM Registry

Systemic mastocytosis (SM) is frequently associated with eosinophilia. To examine its prevalence and clinical impact in all WHO classification-based subcategories, we analyzed eosinophil counts in 2350 mastocytosis patients using the dataset of the European Competence Network on Mastocytosis. Ninety percent of patients had normal eosinophil counts, 6.8% mild eosinophilia (0.5-1.5 × 10⁹/l), and 3.1% hypereosinophilia (HE; >1.5 × 10⁹/l). Eosinophilia/HE were mainly present in patients with advanced SM (17%/19%), and only rarely recorded in patients with indolent and smoldering SM (5%/1%), and some patients with cutaneous mastocytosis. The eosinophil count correlated with organomegaly, dysmyelopoiesis, and the WHO classification, but not with mediator-related symptoms or allergy. Eosinophilia at diagnosis had a strong prognostic impact (p < 0.0001) on overall survival (OS) and progression-free survival (PFS), with a 10-year OS of 19% for patients with HE, 70% for those with mild eosinophilia, and 88% for patients with normal eosinophil counts. In 89% of patients with follow-up data (n = 1430, censored at start of cytoreductive therapy), eosinophils remained stable. In those with changing eosinophil counts (increase/decrease or mixed pattern), OS and PFS were inferior compared with patients with stable eosinophil counts. In conclusion, eosinophilia and HE are more prevalent in advanced SM and are predictors of a worse outcome.

Impact of somatic and germline mutations on the outcome of systemic mastocytosis

Systemic mastocytosis (SM) is a highly heterogeneous disease with indolent and aggressive forms, with the mechanisms leading to malignant transformation still remaining to be elucidated. Here, we investigated the presence and frequency of genetic variants in 34 SM patients with multilineal KIT D816V mutations. Initial screening was performed by targeted sequencing of 410 genes in DNA extracted from purified bone marrow cells and hair from 12 patients with nonadvanced SM and 8 patients with advanced SM, followed by whole-genome sequencing (WGS) in 4 cases. Somatic mutations were further investigated in another 14 patients with advanced SM. Despite the fact that no common mutation other than KIT D816V was found in WGS analyses, targeted next-generation sequencing identified 67 nonsynonymous genetic variants involving 39 genes. Half of the mutations were somatic (mostly multilineal), whereas the other half were germline variants. The presence of ≥1 multilineal somatic mutation involving genes other than KIT D816V, ≥3 germline variants, and ≥1 multilineal mutation in the SRSF2, ASXL1, RUNX1, and/or EZH2 genes (S/A/R/E genes), in addition to skin lesions, splenomegaly, thrombocytopenia, low hemoglobin levels, and increased alkaline phosphatase and β2-microglobulin serum levels, were associated with a poorer patient outcome. However, the presence of ≥1 multilineal mutation, particularly involving S/A/R/E genes, was the only independent predictor for progression-free survival and overall survival in our cohort.

Systemic mastocytosis associated with myelodysplastic/myeloproliferative neoplasms with ring sideroblasts and thrombocytosis: Report of three cases

The association of systemic mastocytosis with another hematologic neoplasia of myeloid or lymphoid origin is recognized as an advanced subvariant of mastocytosis. Here, we report the association of indolent or smoldering systemic mastocytosis with three cases of myelodysplastic/myeloproliferative neoplasms with ring sideroblasts and thrombocytosis, a recently recognized disease characterized by SF3B1 mutations. The hierarchical pattern of KIT, SF3B1, JAK2, and additional mutations was studied in whole and fractionated subpopulations of peripheral blood cells and whole bone marrow. In two cases, we could demonstrate a multilineage D816V KIT mutation, involving all myeloid lineages in one patient and also the lymphoid series in the other. Two patients displaying both SF3B1 and V617F JAK2 mutations had a very poor prognosis. Another patient bearing SF3B1, but not V617F JAK2 mutation, had a favorable response to erythropoietin treatment and long survival.

MARS: Mutation-Adjusted Risk Score for Advanced Systemic Mastocytosis

PURPOSE

To develop a risk score for patients with advanced systemic mastocytosis (AdvSM) that integrates clinical and mutation characteristics.

PATIENTS AND METHODS

The study included 383 patients with AdvSM from the German Registry on Disorders of Eosinophils and Mast Cells (training set; n = 231) and several centers for mastocytosis in the United States and Europe, all within the European Competence Network on Mastocytosis (validation set; n = 152). A Cox multivariable model was used to select variables that were predictive of overall survival (OS).

RESULTS

In multivariable analysis, the following risk factors were identified as being associated with OS: age greater than 60 years, anemia (hemoglobin < 10 g/dL), thrombocytopenia (platelets < 100 × 10⁹/L), presence of one high molecular risk gene mutation (ie, in SRSF2, ASXL1, and/or RUNX1), and presence of two or more high molecular risk gene mutations. By assigning hazard ratio–weighted points to these variables, the following three risk categories were defined: low risk (median OS, not reached), intermediate risk (median OS, 3.9 years; 95% CI, 2.1 to 5.7 years), and high risk (median OS, 1.9 years; 95% CI, 1.3 to 2.6 years; P < .001). The mutation-adjusted risk score (MARS) was independent of the WHO classification and was confirmed in the independent validation set. During a median follow-up time of 2.2 years (range, 0 to 23 years), 63 (16%) of 383 patients experienced a leukemic transformation to secondary mast cell leukemia (32%) or secondary acute myeloid leukemia (68%). The MARS was also predictive for leukemia-free survival (P < .001).

CONCLUSION

The MARS is a validated, five-parameter, WHO-independent prognostic score that defines three risk groups among patients with AdvSM and may improve up-front treatment stratification for these rare hematologic neoplasms.

KIT D816 mutated/CBF-negative acute myeloid leukemia: a poor-risk subtype associated with systemic mastocytosis

KIT D816 mutations (KIT D816mut) are strongly associated with systemic mastocytosis (SM) but are also detectable in acute myeloid leukemia (AML), where they represent an adverse prognostic factor in combination with core binding factor (CBF) fusion genes. Here, we evaluated the clinical and molecular features of KIT D816mut/CBF-negative (CBFneg) AML, a previously uncharacterized combination. All KIT D816mut/CBFneg cases (n = 40) had histologically proven SM with associated AML (SM-AML). Molecular analyses revealed at least one additional somatic mutation (median, n = 3) beside KIT D816 (e.g., SRSF2, 38%; ASXL1, 31%; RUNX1, 34%) in 32/32 (100%) patients. Secondary AML evolved in 29/40 (73%) patients from SM ± associated myeloid neoplasm. Longitudinal molecular and cytogenetic analyses revealed the acquisition of new mutations and/or karyotype evolution in 15/16 (94%) patients at the time of SM-AML. Median overall survival (OS) was 5.4 months. A screen of two independent AML databases (AMLdatabases) revealed remarkable similarities between KIT D816mut/CBFneg SM-AML and KIT D816mut/CBFneg AMLdatabases (n = 69) with regard to KIT D816mut variant allele frequency, mutation profile, aberrant karyotype, and OS suggesting underlying SM in a significant proportion of AMLdatabases patients. Bone marrow histology and reclassification as SM-AML has important clinical implications regarding prognosis and potential inclusion of KIT inhibitors in treatment concepts.