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There is strong evidence of an association between severe anaphylaxis, especially hymenoptera venom induced, and mast cell (MC) disorders. It has been thought that intrinsic abnormalities in MCs, including the presence of the activating KIT D816V mutation in mastocytosis or of genetic trait, hereditary alpha-tryptasemia, may influence susceptibility to severe anaphylaxis. This article evaluates the potential mechanisms leading to severe MC activation, as well as the differential diagnosis of and range of symptoms attributable to MC mediator release. Also, we offer a global classification for disorders related to MC activation.

Systemic mastocytosis (SM) is a rare myeloid neoplasm driven in ≈95% of cases by activatingWe 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.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 D816V mutation within exon 17 has been particularly reported as one of the poor prognostic factors in pediatric acute myeloid leukemia (AML) with RUNX1-RUNX1T1. The exact frequency and the prognostic impact of KIT D816V minor clones at diagnosis were not examined. In this study, the minor clones were examined and the prognostic significance of KIT D816V mutation in pediatric patients was investigated. Consequently, 24 KIT D816V mutations (7.2%) in 335 pediatric patients were identified, and 12 of 24 were only detected via the digital droplet polymerase chain reaction method. All 12 patients were confined in core binding factor (CBF)-AML patients. The 5 year event-free survival of the patients with KIT D816V mutation was significantly inferior to those without KIT D816V mutation (44.1% [95% confidence interval (CI), 16.0%-69.4%] vs. 74.7% [95% CI, 63.0%-83.2%] P-value = 0.02, respectively). The 5 year overall survival was not different between the two groups (92.9% [95% CI, 59.0%-NA vs. 89.7% [95% CI, 69.6%-96.8%] P-value = 0.607, respectively). In this study, KIT D816V minor clones in patients with CBF-AML were confirmed and KIT D816V was considered as a risk factor for relapse in patients with RUNX1-RUNX1T1-positive AML.

[Background]: Several risk stratification models have been proposed in recent years for systemic mastocytosis but have not been directly compared. Here we designed and validated a risk stratification model for progression-free survival (PFS) and overall survival (OS) in systemic mastocytosis on the basis of all currently available prognostic factors, and compared its predictive capacity for patient outcome with that of other risk scores., [Methods]: We did a retrospective prognostic modelling study based on patients diagnosed with systemic mastocytosis between March 1, 1983, and Oct 11, 2019. In a discovery cohort of 422 patients from centres of the Spanish Network on Mastocytosis (REMA), we evaluated previously identified, independent prognostic features for prognostic effect on PFS and OS by multivariable analysis, and designed a global prognostic score for mastocytosis (GPSM) aimed at predicting PFS (GPSM-PFS) and OS (GPSM-OS) by including only those variables that showed independent prognostic value (p, [Findings]: Our GPSM-PFS and GPSM-OS models were based on unique combinations of independent prognostic factors for PFS (platelet count ≤100 × 109 cells per L, serum β2-microglobulin ≥2·5 μg/mL, and serum baseline tryptase ≥125 μg/L) and OS (haemoglobin ≤110 g/L, serum alkaline phosphatase ≥140 IU/L, and at least one mutation in SRSF2, ASXL1, RUNX1, or DNMT3A). The models showed clear discrimination between low-risk and high-risk patients in terms of worse PFS and OS prognoses in the discovery and validation cohorts, and further discrimination of intermediate-risk patients. The GPSM-PFS score was an accurate predictor of PFS in systemic mastocytosis (C-index 0·90 [95% CI 0·87–0·93], vs values ranging from 0·85 to 0·88 for pre-existing models), particularly in non-advanced systemic mastocytosis (C-index 0·85 [0·76–0·92], within the range for pre-existing models of 0·80 to 0·93). Additionally, the GPSM-OS score was able to accurately predict OS in the entire cohort (C-index 0·92 [0·89–0·94], vs 0·67 to 0·90 for pre-existing models), and showed some capacity to predict OS in advanced systemic mastocytosis (C-index 0·72 [0·66–0·78], vs 0·64 to 0·73 for pre-existing models)., [Interpretation]: All evaluated risk classifications predicted survival outcomes in systemic mastocytosis. The REMA-PFS and GPSM-PFS models for PFS, and the International Prognostic Scoring System for advanced systemic mastocytosis and GPSM-OS model for OS emerged as the most accurate models, indicating that robust prognostication might be prospectively achieved on the basis of biomarkers that are accessible in diagnostic laboratories worldwide., Carlos III Health Institute, European Regional Development Fund, Spanish Association of Mastocytosis and Related Diseases, Rare Diseases Strategy of the Spanish National Health System, Junta of Castile and León, Charles and Ann Johnson Foundation, Stanford Cancer Institute Innovation Fund, Austrian Science Fund.

Mastocytosis is a group of heterogeneous disorders resulting from the clonal proliferation of abnormal mast cells and their accumulation in the skin and/or in various extracutaneous organs. Systemic mastocytosis is the most common form of mastocytosis diagnosed in adults, characterized by mast cell infiltration of one or more extracutaneous organs (with or without skin involvement). The identification of KIT D816V mutation and the emergence of novel targeted therapies have significantly improved the diagnosis and treatment of systemic mastocytosis. However, certain aspects of clinical care, particularly the diagnosis, assessment, and management of mediator-related symptoms continue to present challenges. This manuscript discusses the recommendations outlined in the NCCN Guidelines for the diagnosis and management of patients with systemic mastocytosis.

In systemic mastocytosis (SM), qualitative and serial quantitative assessment of the KIT D816V mutation is of diagnostic and prognostic relevance. We investigated peripheral blood and bone marrow samples of 161 patients (indolent SM (ISM), n = 40, advanced SM, AdvSM, n = 121) at referral and during follow-up for the KIT D816V variant allele frequency (VAF) at the DNA-level and the KIT D816V expressed allele burden (EAB) at the RNA-level. A round robin test with four participating laboratories revealed an excellent correlation (r &gt, 0.99, R2 &gt, 0.98) between three different DNA-assays. VAF and EAB strongly correlated in ISM (r = 0.91, coefficient of determination, R2 = 0.84) but only to a lesser extent in AdvSM (r = 0.71, R2 = 0.5). However, as compared to an EAB/VAF ratio ≤2 (cohort A, 77/121 patients, 64%) receiver operating characteristic (ROC) analysis identified an EAB/VAF ratio of &gt, 2 (cohort B, 44/121 patients, 36%) as predictive for an advanced phenotype and a significantly inferior median survival (3.3 vs. 11.7 years, p = 0.005). In terms of overall survival, Cox-regression analysis was only significant for the EAB/VAF ratio &gt, 2 (p = 0.006) but not for VAF or EAB individually. This study demonstrates for the first time that the transcriptional activity of KIT D816V may play an important role in the pathophysiology of SM.

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.

Introduction: Systemic mastocytosis (SM) is characterized by the overproduction and accumulation of neoplastic mast cells (MCs) in the bone marrow, skin, and visceral organs. The KIT D816V mutation is found in approximately 90% of cases. In advanced SM (advSM), inferior survival often relates to MC-induced organ damage that may impact multiple organ systems. In addition, mediator symptoms related to MC activation can severely impact the quality of life. The oral multikinase/KIT inhibitor midostaurin was approved by the US Food and Drug Administration and the European Medicines Agency as monotherapy for advSM based on data from phase 2 clinical studies. Areas covered: This review discusses the management of common adverse events (AEs) in patients with advSM who participated in phase 2 clinical studies that led to the approval of midostaurin. Expert opinion: In the advSM population undergoing treatment with midostaurin, treatment-related AEs are often difficult to distinguish from disease-related symptoms, which can lead to premature discontinuation and improper dose reduction of midostaurin therapy in patients who might have benefitted from continued therapy. Here we present strategies to help optimize AE management and maximize the potential benefits of midostaurin in advSM.

The coronavirus disease 2019 (COVID-19) (caused by severe acute respiratory syndrome coronavirus 2) pandemic has massively distorted our health care systems and caused catastrophic consequences in our affected communities. The number of victims continues to increase, and patients at risk can only be protected to a degree, because the virulent state may be asymptomatic. Risk factors concerning COVID-19 induced morbidity and mortality include advanced age, an impaired immune system, cardiovascular or pulmonary diseases, obesity, diabetes mellitus, and cancer treated with chemotherapy. Here, we discuss the risk and impact of COVID-19 in patients with mastocytosis and mast cell activation syndromes. Because no published data are yet available, expert opinions are, by necessity, based on case experience and reports from patients. Although the overall risk to acquire the severe acute respiratory syndrome coronavirus 2 may not be elevated in mast cell disease, certain conditions may increase the risk of infected patients to develop severe COVID-19. These factors include certain comorbidities, mast cell activation related events affecting the cardiovascular or bronchopulmonary system, and chemotherapy or immunosuppressive drugs. Therefore, such treatments should be carefully evaluated on a case-by-case basis during a COVID-19 infection. In contrast, other therapies, such as anti-mediator-type drugs, venom immunotherapy, or vitamin D, should be continued. Overall, patients with mast cell disorders should follow the general and local guidelines in the COVID-19 pandemic and advice from their medical provider.

is missing (Short communication).

Persistent dysregulation of IL-6 production and signaling have been implicated in the pathology of various cancers. In systemic mastocytosis, increased serum levels of IL-6 associate with disease severity and progression, although the mechanisms involved are not well understood. Since systemic mastocytosis often associates with the presence in hematopoietic cells of a somatic gain-of-function variant in KIT, D816V-KIT, we examined its potential role in IL-6 upregulation. Bone marrow mononuclear cultures from patients with greater D816V allelic burden released increased amounts of IL-6 which correlated with the percentage of mast cells in the cultures. Intracellular IL-6 staining by flow cytometry and immunofluorescence was primarily associated with mast cells and suggested a higher percentage of IL-6 positive mast cells in patients with higher D816V allelic burden. Furthermore, mast cell lines expressing D816V-KIT, but not those expressing normal KIT or other KIT variants, produced constitutively high IL-6 amounts at the message and protein levels. We further demonstrate that aberrant KIT activity and signaling are critical for the induction of IL-6 and involve STAT5 and PI3K pathways but not STAT3 or STAT4. Activation of STAT5A and STAT5B downstream of D816V-KIT was mediated by JAK2 but also by MEK/ERK1/2, which not only promoted STAT5 phosphorylation but also its long-term transcription. Our study thus supports a role for mast cells and D816V-KIT activity in IL-6 dysregulation in mastocytosis and provides insights into the intracellular mechanisms. The findings contribute to a better understanding of the physiopathology of mastocytosis and suggest the importance of therapeutic targeting of these pathways.

Mastocytosis is a group of rare hematologic neoplasms characterized by abnormal accumulation of mast cells (MCs) in one or several organs. In most adult patients, systemic mastocytosis (SM) is diagnosed; whereas in children, the disease is mostly restricted to the skin. In adults, neoplastic MCs display frequently the KIT D816V mutation, while pediatric patients are often positive for non-KIT D816V mutations. SM is divided into indolent SM (ISM), smoldering SM (SSM), SM with an associated hematologic neoplasm (SM-AHN), aggressive SM (ASM), and MC leukemia (MCL). The last three variants are collectively termed “advanced SM” and have a poorer prognosis than ISM. In advanced SM patients, additional oncogenic lesions, including RAS, TET2, SRSF2, ASXL1, CBL, and/or RUNX1 mutations, have been recently described. These lesions may accumulate, thus worsening the prognosis. Therefore, advanced SM is frequently a multi-mutated disease for which KIT-targeted drugs might probably not be sufficient for a permanent cure.

Mastocytosis is a group of rare disorders characterized by abnormal accumulation of mast cells in one or several organs. Mastocytosis can be seen at any age; but, in adults, the disease is usually systemic and chronic. Patients with indolent systemic mastocytosis (SM) are usually treated symptomatically, but cytoreductive treatments are needed in more advanced SM. In most patients with SM, an activating KIT D816V mutation is found. Thus, patients with advanced SM benefit from treatment with KIT-targeting tyrosine kinase inhibitors. However, none of these drugs are curative; new targeted drugs or combinations are still needed to improve patients' outcome.

The molecular pathogenesis of Systemic Mastocytosis (SM) is driven by mutations in the KIT gene, with 95% of patients having a mutation in exon 17, D816V, leading to constant proliferation of mast cells (Garcia-Montero et al, 2006; Jara-Acevedo et al, 2015; Vaes et al, 2017). Targeted therapeutics have revealed clinical activity in these patients, but toxicities such as cognitive effects, intracranial hemorrhage, hypertension, and edema may limit dosing and availability of these therapies. While the exact cause of these effects is difficult to determine, numerous closely related kinases, such as wild type PDGFRα, PDGFRβ, KIT, VEGFR2 (KDR), and CSF1R (FMS), are considered to be anti-targets, with previous evidence of their inhibition linked to observed clinical toxicities (Liu & Kurzrock, 2015; Giles et al., 2009; Jayson et al., 2005). Bezuclastinib (CGT9486) was designed to selectively inhibit KIT D816V versus these other closely related kinase anti-targets. Additionally, we demonstrate that bezuclastinib has minimal brain penetration, together with no observed CNS-related toxicities in nonclinical studies. Herein, we present results from cell-based kinase profiling assays, which demonstrate that bezuclastinib has a significant and unique selectivity to KIT D816V relative to the aforementioned kinases when tested head-to-head against other clinically relevant compounds in SM. Additionally, a similar selectivity profile was observed for a broader panel of kinases, ion channels, transporters, and enzymes, which will be presented here, including drug concentrations and target engagement achieved with recent in vivo studies. Importantly, we also show that bezuclastinib has minimal brain penetration, a preferred feature of an anti-Kit molecule due to CNS-related adverse events observed in these indications. In a tissue distribution study performed in rats, bezuclastinib shows a brain:plasma ratio Disclosures Guarnieri: Cogent Biosciences: Current Employment. Cable: Cogent Biosciences: Current Employment. Bouhana: Cogent Biosciences: Current Employment. Sullivan: Cogent Biosciences: Current Employment. Ball: Cogent Biosciences: Current Employment. Sachs: Cogent Biosciences: Current Employment. Winski: Cogent Biosciences: Current Employment. Robinson: Cogent Biosciences: Current Employment.

Systemic mastocytosis (SM) is characterized by excessive accumulation of mast cells in bone marrow and other extracutaneous tissues encompassing a spectrum of variants ranging from non-advanced to advanced disease (Shomali et al, 2018). Advanced systemic mastocytosis (AdvSM) is an aggressive and life-threatening form of SM with an overall survival from The molecular pathogenesis of SM is driven by mutations in the KIT gene leading to ligand-independent proliferation of mast cells, with 95% of patients carrying the D816V mutation in exon 17 (Garcia-Montero et al, 2006; Jara-Acevedo et al, 2015; Vaes et al, 2017). Bezuclastinib, an oral, highly selective tyrosine kinase inhibitor with potent activity against KIT D816V has shown preliminary clinical activity and a tolerable safety profile in a Ph 1/2 study of patients with advanced solid tumors including gastrointestinal stromal tumor (GIST). In that study, a reduction in KIT exon 17 mutational burden was observed in subjects treated with bezuclastinib. This reduction was temporally associated with a reduction in tumor burden supporting bezuclastinib as an active therapy in KIT-driven diseases (Wagner et al, 2018). Other agents targeting the KIT D816V mutations have shown activity in the treatment of AdvSM; however, toxicities such as cognitive impairment, intracranial hemorrhage, and edema may limit dosing and appropriateness of these therapies. Besides targeting KIT D816V, bezuclastinib was designed to avoid other closely related kinases with known liabilities, such as PDGFRα, PDGFRβ, wild-type KIT, VEGFR2 (KDR), and CSF1R (FMS). Additionally, minimal brain penetration has been observed with bezuclastinib, and no CNS toxicities have been identified in preclinical studies. This is a multi-center, Phase 2, open-label, 2-part clinical study to evaluate the safety, efficacy, pharmacokinetics (PK), and pharmacodynamics (PD) of bezuclastinib in subjects with AdvSM. This study will enroll subjects who meet WHO diagnostic criteria for AdvSM, have measurable SM-related organ damage according to modified IWG-MRT-ECNM consensus eligibility and response criteria, and have a baseline serum tryptase of ≥20 ng/mL. The diagnosis of AdvSM and evidence of measurable disease will be confirmed by an Eligibility Committee prior to enrollment. This study will enroll approximately 140 patients. Part 1 will consist of a dose optimization period to determine the optimal dose of bezuclastinib for subjects with AdvSM. Subjects will be randomized into one of four dose cohorts (50, 100, or 200 mg twice daily, or 400 mg once daily) in a 1:1:1:1 manner. A planned interim analysis to assess safety, efficacy, and biomarker endpoints will occur when approximately half the planned number of Part 1 patients have been evaluated through at least 2 cycles of treatment. After all subjects in Part 1 complete at least two cycles, the optimal dose will be selected. Part 2 will enroll subjects at the selected dose level to determine efficacy of bezuclastinib and to further characterize safety, PK, and PD. The primary assessment of efficacy is overall response rate, defined as the percentage of subjects classified as confirmed responders (CR, CR with incomplete hematologic recovery [CRh], partial response [PR], and clinical improvement [CI]) according to modified IWG-MRT-ECNM response criteria as assessed by a Central Response Review Committee (CRRC). Data from this study will support continued development of bezuclastinib in SM including Non-Advanced SM. This study opened in June 2021. Disclosures Gotlib: BMS: Research Funding; Kartos: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; PharmaEssentia: Honoraria, Membership on an entity's Board of Directors or advisory committees; Cogent Biosciences: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Chair for the Eligibility and Central Response Review Committee, Research Funding; Allakos: Consultancy; Abbvie: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Deciphera: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Incyte: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Blueprint Medicines: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. George: Celgene: Consultancy; Blueprint Medicines: Consultancy; Bristol Meyers Squibb: Consultancy; Incyte Corporation: Consultancy. Deininger: Sangamo: Consultancy, Membership on an entity's Board of Directors or advisory committees; Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Part of a Study Management Committee, Research Funding; Novartis: Consultancy, Research Funding; Incyte: Consultancy, Honoraria, Research Funding; SPARC, DisperSol, Leukemia & Lymphoma Society: Research Funding; Fusion Pharma, Medscape, DisperSol: Consultancy; Blueprint Medicines Corporation: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Part of a Study Management Committee, Research Funding. Tashi: PharmaEssentia: Membership on an entity's Board of Directors or advisory committees, Other: Advisory Board. Pullarkat: Amgen, Dova, and Novartis: Consultancy, Honoraria; AbbVie, Amgen, Genentech, Jazz Pharmaceuticals, Novartis, Pfizer, and Servier: Membership on an entity's Board of Directors or advisory committees. Bose: Celgene Corporation: Honoraria, Research Funding; Astellas: Research Funding; NS Pharma: Research Funding; Novartis: Honoraria; Promedior: Research Funding; BMS: Honoraria, Research Funding; CTI BioPharma: Honoraria, Research Funding; Sierra Oncology: Honoraria; Incyte Corporation: Honoraria, Research Funding; Blueprint Medicines: Honoraria, Research Funding; Pfizer: Research Funding; Kartos Therapeutics: Honoraria, Research Funding; Constellation Pharmaceuticals: Research Funding. Payumo: Cogent Biosciences, Inc: Current Employment. Pilla: Cogent Biosciences: Current Employment. Jolin: Cogent Biosciences: Current Employment. DeAngelo: Abbvie: Research Funding; Takeda: Consultancy; Servier: Consultancy; Pfizer: Consultancy; Novartis: Consultancy, Research Funding; Jazz: Consultancy; Incyte: Consultancy; Forty-Seven: Consultancy; Autolus: Consultancy; Amgen: Consultancy; Agios: Consultancy; Blueprint: Research Funding; Glycomimetrics: Research Funding. OffLabel Disclosure: Study is for investigational agent

BACKGROUND: Patients with systemic mastocytosis (SM) may suffer from mast cell (MC) mediator-related symptoms insufficiently controlled by conventional therapy. Omalizumab is an established treatment in other MC-driven diseases, but experiences in SM are limited.OBJECTIVE: To assess the efficacy and safety of omalizumab in SM.METHODS: In our patient cohort, we evaluated all SM patients treated with omalizumab. A physician global assessment of type and severity of symptoms was performed at baseline, at 3 and 6 months and at latest follow-up. Quality of life was assessed by visual analogue scale. S-tryptase and KIT D816V allele burden were monitored.RESULTS: A total of 14 adult SM patients (10 ISM, 2 BMM, 1 SSM, and 1 ASM-AHN) received omalizumab with a median duration of 17 months (range: 1-73 months). One patient was excluded due to concomitant cytoreductive therapy. In the remaining 13 patients, we observed a significant reduction in symptoms, with complete symptom control in five (38.5%), major response in three (23.1%), and a partial response in three (23.1%) patients, whereas two patients (15.4%) withdrew due to subjective side-effects at first dose. The treatment was most effective for recurrent anaphylaxis and skin symptoms, less for gastrointestinal, musculoskeletal, and neuropsychiatric symptoms. Patient-reported quality of life showed significant improvement. No significant changes in s-tryptase/KIT D816V allele burden were observed. No severe adverse events were recorded.CONCLUSIONS: Omalizumab appears to be a promising treatment option in SM, effectively preventing anaphylaxis and improving chronic MC mediator-related symptoms, insufficiently controlled by conventional therapy. Controlled studies are needed to substantiate findings.

Systemic mastocytosis (SM) is characterized by activating mutations in KIT, usually KIT D816V in >90% of patients. According to the WHO classification, detection of KIT D816V is a minor diagnostic criterion. Moreover, a reduction of the RNA-based KIT D816V expressed allele burden (EAB) of ≥25% at month 6 is a favorable marker for improved survival in midostaurin-treated advanced SM (AdvSM) patients. However, only limited data exist upon the comparison between RNA-based and DNA-based quantitative KIT D816V mutation analyses. We therefore collected peripheral blood samples from 161 SM patients (indolent SM [ISM], n=40; AdvSM, n=121) at time of referral. We applied a real time reverse-transcriptase polymerase chain reaction (qRT-PCR) assay for assessment of the KIT D816V EAB and a chip-based digital PCR (dPCR) for the quantification of the DNA-based KIT D816V variant allele frequency (VAF, QuantStudio 3D dPCR System, ThermoFisher Scientific, Massachusetts, USA). The limit of detection (LOD) was assessed through serial dilution experiments with DNA from healthy individuals and DNA from a SM patient with a KIT D816V VAF of approximately 50%. All samples were analyzed in two independent dPCR runs. In an inital round-robin test for an inter-laboratory (n=4) comparison on 30 DNA samples (ISM, n=7; AdvSM, n=19), we found a very good correlation between 3 different chip-based digital PCR systems (dPCR; droplet-based dPCR, ddPCR, BioRad Laboratories, California, USA; quantitative real-time PCR, qPCR, California, USA; dPCR vs. ddPCR r=0.99, R2=0.99; dPCR vs. qPCR r=0.99, R2=0.98). In ISM patients, the comparison between EAB and VAF revealed a strong linear relationship with a correlation (r) of 0.91 and a coefficient of determination (R2) of 0.84, which was significantly inferior (r=0.71; R2=0.5) in AdvSM patients. In 45/121 (37%) and 76/121 (63%) of AdvSM patients, the EAB/VAF ratio was ≤2 (cohort A) or >2 (cohort B). To confirm the significant disparity between EAB and VAF in individual patients, serial analyses of at least 3 samples in 12 patients revealed a stable EAB/VAF ratio during follow-up. The comparison between cohort A and cohort B revealed significant differences in terms of a higher median hemoglobin level (p=0.006), a lower percentage of patients with hemoglobin 2 present with an aggressive phenotype and adverse prognosis as compared to patients with EAB/VAF ratio ≤2. We therefore recommend to routinely determine KIT D816V EAB and VAF in AdvSM patients. Disclosures Fabarius: Novartis: Research Funding. Reiter:Blueprint: Consultancy, Honoraria, Other: Travel reimbursement; Deciphera: Consultancy, Honoraria, Other: Travel reimbursement; Novartis: Consultancy, Honoraria, Other: Travel reimbursement, Research Funding.

Mast cell activation (MCA) accompanies diverse physiologic and pathologic processes and is one of the more frequently encountered conditions in medicine. MCA-related symptoms are usually mild and often transient. In such cases, histamine receptor blockers and other mediator-targeting drugs can usually control MCA. In severe cases, an MCA syndrome (MCAS) may be diagnosed. However, overt MCAS is an unusual condition, and many patients referred because of suspected MCAS are diagnosed with other diseases (autoimmune, neoplastic, or infectious) unrelated to MCA or suffer from MCA-related (eg, allergic) disorders and/or comorbidities without fulfilling criteria of an overt MCAS. These considerations are important as more and more patients are informed that they may have MCA or even MCAS without completing a thorough medical evaluation. In fact, in several instances, symptoms are misinterpreted as MCA/MCAS, and other clinically relevant conditions are not thoroughly pursued. The number of such referrals is increasing. To avoid such unnecessary referrals and to prevent misdiagnoses, we here propose a diagnostic algorithm through which a clinically relevant (systemic) MCA can be suspected and MCAS can subsequently be documented or excluded. In addition, the algorithm proposed should help guide the investigating care providers to consider the 2 principal diagnoses that may underlie MCAS, namely, severe allergy and systemic mastocytosis accompanied by severe MCA. Although validation is required, we anticipate that this algorithm will facilitate the management of patients with suspected MCAS., This study was supported in part by the Austrian Science Fund (FWF), projects F4701-B20 and F4704-B20, and the Division of Intramural Research, National Institute of Allergy and Infectious Diseases.

Recent studies have demonstrated that the KIT D816V mutation is reliably detected in blood in adults with mastocytosis when using appropriate techniques [1–3]. Mutation analysis of blood has theref...

[Background]: The WHO classification separates mastocytosis into distinct variants, but prognostication remains a clinical challenge. The aim of this study was to improve prognostication for patients with mastocytosis., [Methods]: We analysed data of the registry of the European Competence Network on Mastocytosis including 1639 patients (age 17–90 years) diagnosed with mastocytosis according to WHO criteria between Jan 12, 1978, and March 16, 2017. Univariate and multivariate analyses with Cox regression were applied to identify prognostic variables predicting survival outcomes and to establish a prognostic score. We validated this International Prognostic Scoring System in Mastocytosis (IPSM) with data of 462 patients (age 17–79 years) from the Spanish network Red Española de Mastocitosis diagnosed between Jan 22, 1998, and Nov 2, 2017., [Findings]: The prognostic value of the WHO classification was confirmed in our study (p, [Interpretation]: The IPSM scores for patients with non-advanced and advanced mastocytosis can be used to predict survival outcomes and guide treatment decisions. However, the predictive value of the IPSM needs to be confirmed in forthcoming trials., This work was supported by the Austrian Science Fund (SFB grants F4701-B20 and F4704-B20, to PV), Deutsche Forschungsgemeinschaft (RA 2838, to AI), Koeln Fortune Program, Faculty of Medicine, University of Cologne (216/2016, to AI), Charles and Ann Johnson Foundation (to JG), and Instituto de Salud Carlos III and fondos FEDER (PI16/00642 and CB16/12/00400, to AO). VS is a senior clinical researcher of the Research Foundation Flanders/Fonds Wetenschappelijk Onderzoek (1804518N). CB is supported by the Clinical Research Fund of the University Hospitals Leuven.

BACKGROUND: Little is known about the epidemiology of advanced systemic mastocytosis (advSM).OBJECTIVES: To investigate epidemiologic features and diagnostic pitfalls of advSM in Germany.METHODS: Therefore, 140 patients from a single German reference center of the European Competence Network on Mastocytosis between 2003 and 2018 were analyzed.RESULTS: The patients' median age was 68 years (range, 26-86 years), and male versus female ratio was 2:1. An elevated serum tryptase, a KIT D816 mutation, and additional somatic mutations, for example, in SRSF2, ASXL1, or RUNX1, were identified in 95%, 91%, and 74% of patients, respectively. Median overall survival was 3.5 years (range, 0.03-14.3 years; male vs female 2.6 vs 4.2 years; P = .02). Two categories of misdiagnoses were identified in 51 of 140 (36%) patients: First, systemic mastocytosis (SM) was overlooked in 28 of 140 (20%) patients primarily diagnosed with various subtypes of myeloid neoplasms. Second, 23 of 140 (16%) patients were diagnosed with supposed progression from indolent SM to advSM; however, combination of an elevated KIT D816V variant allele frequency in peripheral blood (n = 22), monocytosis (n [ 9), eosinophilia (n = 6), and/or mutations in SRSF2, ASXL1, or RUNX1 (n = 10) suggest that distinct signs of potential advSM were overlooked in virtually all patients. Based on locally diagnosed patients in an area of 2.5 million inhabitants, but obviously without considering more, yet unrecognized cases, the incidence and prevalence of advSM is at least 0.8 and 5.2, respectively, per 1 million inhabitants.CONCLUSIONS: Adequate analyses of tryptase levels, bone marrow morphology, and genetics in patients with myeloid neoplasms or SM would help to prevent the significant underdiagnosis of advSM. (C) 2020 American Academy of Allergy, Asthma & Immunology

Context: Detection of the KIT D816V mutation in the bone marrow (BM) is one of the minor criteria for the diagnosis of systemic mastocytosis (SM). Because in most SM patients, the number of neoplastic mast cells (MCs) in the BM is low, the use of molecular techniques, such as ASO-qPCR, with elevated sensitivity is recommended. Droplet digital PCR (ddPCR) is a promising alternative to ASO-qPCR for D816V testing. Objective: We evaluated a commercial ddPCR assay for the detection of KIT D816V in SM. ddPCR was performed on a BioRad QX200 instrument using the ddPCR™ Mutation Assay: KIT p.D816V, Human (Bio-Rad). Patients: PB samples from 13 healthy donors (HDs) were used as negative controls; the D816V-positive HMC-1.2 cell line was used as positive control. Thirty-five BM samples from patients with suspected SM, either with neoplastic mast cell infiltration Results: In HMC 1.2 cells, ddPCR measured an allele burden (AB) of 50%, consistent with the heterozygous status. No D816V-positive events were detected in the HDs. Comparison between ddPCR and ASO-qPCR revealed high concordance in mutation detection and quantitation, even at low AB levels. ddPCR identified D816V in 70/151 patients prospectively evaluated for diagnosis of SM. According to WHO criteria, 49 were later diagnosed with ISM, 13 with aggressive SM, 4 with smouldering SM, 2 with SM with an associated clonal hematopoietic non-MC disease, and 2 with MC leukemia. The median AB in all positive SM patients was 0.34%. Patients with advanced SM showed a higher D816V AB (median, 15.23%) compared with patients with ISM and smouldering SM (median, 0.27%). All patients positive for D816V in BM also tested positive in the PB. Conclusion: ddPCR proved accurate and precise and was able to detect D816V in PB when the BM was positive. We propose ddPCR as a valid alternative to ASO-qPCR for straightforward and sensitive detection of D816V in SM.

Author(s): Ustun, Celalettin; Morgan, Elizabeth; Moodie, Erica EM; Pullarkat, Sheeja; Yeung, Cecilia; Broesby-Olsen, Sigurd; Ohgami, Robert; Kim, Young; Sperr, Wolfgang; Vestergaard, Hanne; Chen, Dong; Kluin, Philip M; Dolan, Michelle; Mrozek, Krzysztof; Czuchlewski, David; Horny, Hans-Peter; George, Tracy I; Kristensen, Thomas Kielsgaard; Ku, Nam K; Yi, Cecilia Arana; Moller, Michael Boe; Marcucci, Guido; Baughn, Linda; Schiefer, Ana-Iris; Hilberink, JR; Pullarkat, Vinod; Shanley, Ryan; Kohlschmidt, Jessica; Coulombe, Janie; Salhotra, Amandeep; Soma, Lori; Cho, Christina; Linden, Michael A; Akin, Cem; Gotlib, Jason; Hoermann, Gregor; Hornick, Jason; Nakamura, Ryo; Deeg, Joachim; Bloomfield, Clara D; Weisdorf, Daniel; Litzow, Mark R; Valent, Peter; Huls, Gerwin; Perales, Miguel-Angel; Borthakur, Gautam | Abstract: BackgroundAlthough the prognosis of core-binding factor (CBF) acute myeloid leukemia (AML) is better than other subtypes of AML, 30% of patients still relapse and may require allogeneic hematopoietic cell transplantation (alloHCT). However, there is no validated widely accepted scoring system to predict patient subsets with higher risk of relapse.MethodsEleven centers in the US and Europe evaluated 247 patients with t(8;21)(q22;q22).ResultsComplete remission (CR) rate was high (92.7%), yet relapse occurred in 27.1% of patients. A total of 24.7% of patients received alloHCT. The median disease-free (DFS) and overall (OS) survival were 20.8 and 31.2 months, respectively. Age, KIT D816V mutated (11.3%) or nontested (36.4%) compared with KIT D816V wild type (52.5%), high white blood cell counts (WBC), and pseudodiploidy compared with hyper- or hypodiploidy were included in a scoring system (named I-CBFit). DFS rate at 2 years was 76% for patients with a low-risk I-CBFit score compared with 36% for those with a high-risk I-CBFit score (P l 0.0001). Low- vs high-risk OS at 2 years was 89% vs 51% (P l 0.0001).ConclusionsI-CBFit composed of readily available risk factors can be useful to tailor the therapy of patients, especially for whom alloHCT is not need in CR1 (ie, patients with a low-risk I-CBFit score).

Background: Systemic mastocytosis (SM) is a hematological disease characterized by organ infiltration by neoplastic mast cells. Almost all SM patients have a mutation in the gene encoding the tyrosine kinase receptor KIT causing a D816V substitution and autoactivation of the receptor. Mast cells and CD34+ hematopoietic progenitors can carry the mutation, however, in which progenitor cell subset the mutation arises is unknown. We aimed to investigate the distribution of the D816V mutation in single mast cells and single hematopoietic stem and progenitor cells. Methods: Fluorescence-activated single-cell index sorting and D816V mutation assessment were applied to analyze mast cells and more than 10,000 CD34+ bone marrow progenitors across 10 hematopoietic progenitor subsets. In vitro assays verified cell-forming potential. Findings: We found that in SM 60-99% of the mast cells harbored the D816V mutation. Despite increased frequencies of mast cells in SM patients compared with control subjects, the hematopoietic progenitor subset frequencies were comparable. Nevertheless, the mutation could be detected throughout the hematopoietic landscape of SM patients, from hematopoietic stem cells to more lineage-primed progenitors. In addition, we demonstrate that FcεRI+ bone marrow progenitors exhibit mast cell-forming potential, and we describe aberrant CD45RA expression on SM mast cells for the first time. Interpretation: The KIT D816V mutation arises in early hematopoietic stem and progenitor cells and the mutation frequency is approaching 100% in mature mast cells, which express the aberrant marker CD45RA.

BACKGROUND The analytically sensitive detection of KIT D816V in blood and bone marrow is important for diagnosing systemic mastocytosis (SM). Additionally, precise quantification of the KIT D816V variant allele fraction (VAF) is relevant clinically because it helps to predict multilineage involvement and prognosis in cases of advanced SM. Digital PCR (dPCR) is a promising new method for sensitive detection and accurate quantification of somatic mutations. METHODS We performed a validation study of dPCR for KIT D816V on 302 peripheral blood and bone marrow samples from 156 patients with mastocytosis for comparison with melting curve analysis after peptide nucleic acid-mediated PCR clamping (clamp-PCR) and allele-specific quantitative real-time PCR (qPCR). RESULTS dPCR showed a limit of detection of 0.01% VAF with a mean CV of 8.5% and identified the mutation in 90% of patients compared with 70% for clamp-PCR (P < 0.001). Moreover, dPCR for KIT D816V was highly concordant with qPCR without systematic deviation of results, and confirmed the clinical value of KIT D816V VAF measurements. Thus, patients with advanced SM showed a significantly higher KIT D816V VAF (median, 2.43%) compared with patients with indolent SM (median, 0.14%; P < 0.001). Moreover, dPCR confirmed the prognostic significance of a high KIT D816V VAF regarding survival (P < 0.001). CONCLUSIONS dPCR for KIT D816V provides a high degree of precision and sensitivity combined with the potential for interlaboratory standardization, which is crucial for the implementation of KIT D816V allele burden measurement. Thus, dPCR is suitable as a new method for KIT D816V testing in patients with mastocytosis.

Activating KIT mutations are part of the pathogenesis of systemic mastocytosis (SM). Nilotinib is a tyrosine kinase inhibitor that potently inhibits activated forms of KIT. This phase 2, open-label, single-arm study (CAMN107A2101; www.clinicaltrials.gov NCT00109707) evaluated nilotinib in patients with SM. Patients with SM [aggressive SM (ASM), indolent SM, or other] received nilotinib 400 mg twice daily. C-findings were collected retrospectively to assess response using criteria proposed after trial initiation. Response was evaluated using improvements in laboratory findings (for all patients) and ASM response criteria (for the ASM subgroup). In 61 patients enrolled, the median nilotinib exposure was 232 days (range 3–1274 days) with a median follow-up of 34.7 months. In patients with ASM (n = 37), the overall response rate was 21.6 %. In the eight responders, all of whom had a KIT D816V mutation at any time, mast cell infiltration and tryptase level decreased by 70 % and 29.8 %, respectively; absolute neutrophil count increased by 94.7 %. Laboratory parameters also improved in the non-ASM subgroups. Overall survival at 24 months was 81.2 % (95 % CI 70.6–91.8 %) with median survival not yet reached. New or worsening grade 3/4 hematologic adverse events (AEs) included thrombocytopenia (10.3 %), anemia (10.0 %), and neutropenia (6.9 %). The most common grade 3/4 nonhematologic drug-related AEs were diarrhea (6.6 %) and headache (4.9 %). Eleven patients (9 with ASM, 2 with MCL) died, 10 due to progressive disease; 7 deaths occurred ≥28 days after treatment discontinuation. Nilotinib 400 mg twice daily was effective in some patients with SM, including patients with mutated KIT D816V.

In this issue of Blood , Jawhar and colleagues describe the results of quantitative KIT D816V allele burden testing and next-generation sequencing of a panel of myeloid genes to characterize molecular correlates of response and progression on midostaurin therapy in patients with advanced systemic mastocytosis. 1

Mastocytosis is a term used to denote a heterogeneous group of conditions defined by the expansion and accumulation of clonal (neoplastic) tissue mast cells in various organs. The classification of the World Health Organization (WHO) divides the disease into cutaneous mastocytosis, systemic mastocytosis, and localized mast cell tumors. On the basis of histomorphologic criteria, clinical parameters, and organ involvement, systemic mastocytosis is further divided into indolent systemic mastocytosis and advanced systemic mastocytosis variants, including aggressive systemic mastocytosis and mast cell leukemia. The clinical impact and prognostic value of this classification has been confirmed in numerous studies, and its basic concept remains valid. However, refinements have recently been proposed by the consensus group, the WHO, and the European Competence Network on Mastocytosis. In addition, new treatment options are available for patients with advanced systemic mastocytosis, including allogeneic hematopoietic stem cell transplantation and multikinase inhibitors directed against KIT D816V and other key signaling molecules. Our current article provides an overview of recent advances in the field of mastocytosis, with emphasis on classification, prognostication, and emerging new treatment options in advanced SM., This study was supported by the Austrian Science Funds, SFB grant F47-04 (to P.V.), by the German Research Council, grant HA 2393/6-1 (to K.H.) and by the NIAID Division of Intramural Research (to D.M.).

Mastocytosis is an emerging differential diagnosis in patients with more or less specific mediator-related symptoms. In some of these patients, typical skin lesions are found and the diagnosis of mastocytosis can be established. In other cases, however, skin lesions are absent, which represents a diagnostic challenge. In the light of this unmet need, we developed a diagnostic algorithm for patients with suspected mastocytosis. In adult patients with typical lesions of mastocytosis in the skin, a bone marrow (BM) biopsy should be considered, regardless of the basal serum tryptase concentration. In adults without skin lesions who suffer from mediator-related or other typical symptoms, the basal tryptase level is an important parameter. In those with a slightly increased tryptase level, additional investigations, including a sensitive KIT mutation analysis of blood leucocytes or measurement of urinary histamine metabolites, may be helpful. In adult patients in whom (i) KIT D816V is detected and/or (ii) the basal serum tryptase level is clearly increased (>25-30 ng/ ml) and/or (iii) other clinical or laboratory features suggest the presence of 'occult' mastocytosis or another haematologic neoplasm, a BM investigation is recommended. In the absence of KIT D816V and other signs or symptoms of mastocytosis or another haematopoietic disease, no BM investigation is required, but the clinical course and tryptase levels are monitored in the follow-up. In paediatric patients, a BM investigation is usually not required, even if the tryptase level is increased. Although validation is required, it can be expected that the algorithm proposed herein will facilitate the management of patients with suspected mastocytosis and help avoid unnecessary referrals and investigations., This work was supported in part by the Austrian Science Funds (FWF) Project SFB F4611 and SFB F4704-B20 and the Division of Intramural Research, NIAID.

KIT D816V is present in a majority of patients with systemic mastocytosis (SM). We determined the KIT D816V allele burden by quantitative real-time PCR in bone marrow and peripheral blood of 105 patients with mastocytosis. KIT D816V was detected in 92/105 patients (88%). Significant differences in the median allele burden were observed between disease subgroups: cutaneous mastocytosis (0.042%), indolent SM (0.285%), smoldering SM (5.991%), aggressive SM (9.346%), and SM with associated hematologic non-mast cell lineage disease (3.761%) (P < 0.001). The KIT D816V burden also correlated with serum tryptase (R = 0.5, P < 0.005) but not with mast cell infiltration in bone marrow or mediator symptoms. Moreover, the allele burden was of prognostic significance regarding survival (P < 0.01). Patients responding to cytoreductive therapy showed a significant decrease in KIT D816V (P < 0.05). To conclude, the KIT D816V burden correlates with the variant of mastocytosis, predicts survival, and is a valuable follow-up parameter in SM.

The recent progress in sensitive KIT D816V mutation analysis suggests that mutation analysis of peripheral blood (PB) represents a promising diagnostic test in mastocytosis. However, there is a need for systematic assessment of the analytical sensitivity and specificity of the approach in order to establish its value in clinical use. We therefore evaluated sensitive KIT D816V mutation analysis of PB as a diagnostic test in an entire case-series of adults with mastocytosis. We demonstrate for the first time that by using a sufficiently sensitive KIT D816V mutation analysis, it is possible to detect the mutation in PB in nearly all adult mastocytosis patients. The mutation was detected in PB in 78 of 83 systemic mastocytosis (94%) and 3 of 4 cutaneous mastocytosis patients (75%). The test was 100% specific as determined by analysis of clinically relevant control patients who all tested negative. Mutation analysis of PB was significantly more sensitive than serum tryptase >20 ng/mL. Of 27 patients with low tryptase, 26 tested mutation positive (96%). The test is furthermore readily available and we consider the results to serve as a foundation of experimental evidence to support the inclusion of the test in diagnostic algorithms and clinical practice in mastocytosis.

Background: Mastocytosis is either cutaneous (with skin-limited proliferation of mast cells) or systemic (with mast cells in extracutaneous sites). The onset of solitary mastocytoma in an adult is rare. Purpose: A woman with the new onset of solitary mastocytoma is described. The clinical features of patients with adult-onset solitary mastocytoma are summarized. Recommendations for the evaluation and treatment of individuals with adult-onset solitary mastocytoma are proposed. Methods: PubMed was searched with the key words: adult, CD2, CD25, cell, cutaneous, disease, KIT, KIT D816V, mast, mastocytoma, mutation, pigmentosa, solitary, tryptase, and urticarial. The papers generated by the search, and their references, were reviewed. Results: A 38-year-old Taiwanese woman presented with an asymptomatic brown patch, which morphologically mimicked a dysplastic nevus, on her right abdomen; biopsy demonstrated a solitary mastocytoma. Comprehensive evaluation (including serologic and bone marrow examination) excluded systemic mastocytosis and her residual mastocytoma is being monitored. Adult-onset solitary mastocytoma has been described in 16 patients. Lesions were either on the head and neck (5/14), torso (5/14) or extremities (4/14). Urtication following lesion rubbing was noted in 79% (11/14) of patients. Excision of the mastocytoma [75% (9/12)] was the most common treatment. Other management approaches included corticosteroids (topical or intralesional), antihistamines (systemic) or observation. Systemic symptoms were noted in 5 patients: flushing (3 women) and pruritus (3 women); gastrointestinal symptoms and headaches, flushing and/or anaphylaxis were each noted in one woman. None of the patients with adult-onset solitary mastocytoma had systemic mastocytosis; however, only 3 women were evaluated for systemic mastocytosis. Conclusions: Systemic mastocytosis is common in adults with new onset cutaneous mastocytosis. Therefore, a conservative work up for new onset solitary mastocytosis in adults is proposed to include complete blood cell counts, serum chemistries (including liver function tests), and serum tryptase level and bone marrow biopsy to evaluate for mast cell clusters, morphology and immunophenotype and KIT gene mutation in codon 816. Similar serologic testing should be considered annually for adult-onset solitary mastocytosis patients without systemic disease.

// Jilliana Monnier 1,* , Sophie Georgin-Lavialle 1,2,* , Danielle Canioni 2,3 , Ludovic Lhermitte 2,3 , Michael Soussan 4 , Michel Arock 5,6 , Julie Bruneau 2,3 , Patrice Dubreuil 2,7 , Christine Bodemer 2,8 , Marie-Olivia Chandesris 2 , Olivier Lortholary 2 , Olivier Hermine 2,9 and Gandhi Damaj 2,10,11 1 Service de Medecine Interne, Hopital Tenon, Universite Paris VI, Assistance Publique-Hopitaux de Paris (AP-HP), Paris, France 2 Centre de Reference des Mastocytoses, Faculte de Medecine et AP-HP Necker-Enfants Malades, Paris, France 3 Laboratoire d’Anatomie-Pathologie, Universite Paris Descartes, Paris Sorbonne Cite, Faculte de Medecine et AP-HP Necker-Enfants Malades, Paris, France 4 Departement de Medecine Nucleaire, Hopital Avicenne, AP-HP et Universite Paris 13, Bobigny, France 5 Laboratoire d’Hematologie, Groupe Hospitalier Pitie-Salpetriere, AP-HP, Paris, France 6 LBPA CNRS UMR8113, Ecole Normale Superieure de Cachan, Cachan, France 7 Inserm, U1068, CRCM, [Signaling, Hematopoiesis and Mechanism of Oncogenesis], Institut Paoli-Calmettes, Marseille, Aix-Marseille Univ, CNRS UMR7258, Marseille, France 8 Service de Dermatologie de l’Hopital Necker Enfants-Malades, AP-HP, Paris, France 9 Service d’hematologie Adulte, Universite Paris Descartes et Institut Imagine, Hopital Necker-Enfants Malades, Paris, France 10 Institut d’Hematologie de Basse Normandie, Centre Hospitalier Universitaire, Caen, France 11 Microenvironnement Cellulaire et Pathologies, Normandie Univ, Unicaen, MILPAT, Caen, France * These authors have contributed equally to this work Correspondence to: Gandhi Damaj, email: // Keywords : mast cell, mastocytosis, mast cell sarcoma, KIT mutations, targeted therapies Received : March 06, 2016 Accepted : August 24, 2016 Published : Spetember 01, 2016 Abstract Mast cell sarcoma (MCS) is a rare form of mastocytosis characterized by the presence of solid tumor(s) comprising malignant mast cells that harbor destructive infiltration capability and metastatic potential. Here, we present an extensive literature review and report on 23 cases of MCS, including 3 new cases from the French National Reference Center for Mastocytosis. From our analysis, it appears that MCS can occur at any age. It can manifest de novo or, to a lesser extent, may evolve from a previously established mastocytosis. Bone tumor is a frequent manifestation, and symptoms of mast cell activation are rare. Histological diagnosis can be difficult because MCS is frequently composed of highly atypical neoplastic mast cells and can thus mimic other tumors. Unexpectedly, the canonical KIT D816V mutation is found in only 21% of MCS; therefore, complete KIT gene sequencing is required. The prognosis of patients with MCS is poor, with a median survival time of less than 18 months, and progression to mast cell leukemia is not unusual. Because conventional chemotherapies usually fail, the role of targeted therapies and bone marrow transplantation warrants further investigation in such aggressive neoplasms.

Introduction: The KIT D816V oncogene is a key driver in 90-95% of patients with systemic mastocytosis (SM), a group of mast cell (MC) neoplasms including indolent SM (ISM), smoldering SM (SSM) and AdvSM. Debilitating symptoms related to MC proliferation and degranulation characterize ISM and SSM and are also prominent in AdvSM, which is further complicated by SM-related organ damage and decreased survival. Currently, there are no approved agents that selectively target KIT D816V, and there are limited tools to assess symptom improvement in SM. Avapritinib, a highly potent and selective inhibitor of the KIT D816V mutant, showed substantial clinical activity in AdvSM (83% overall response rate (ORR) per modified IWG-MRT-ECNM criteria) in the Phase 1 EXPLORER study [Deininger, et al, EHA, 2018]. We present results using a novel PRO questionnaire, the AdvSM-SAF, developed in accordance with FDA guidance, to assess changes in symptoms in the Part 2 dose expansion phase of EXPLORER. Methods: Patients (pts) received avapritinib at the recommended Phase 2 dose (300 mg once daily [QD]) in continuous 28-day (d) cycles. Pts completed the AdvSM-SAF and 2 additional PROs used in other cancers, the Patient Global Impression of Symptom Severity (PGIS) and the European Organization for Research and Treatment of Cancer Quality of Life (QLQ). PROs and KIT D816V mutant allele fraction (MAF) in blood were assessed serially as follows: AdvSM-SAF daily, from 7 d before first avapritinib dose, ie, baseline (BL: Cycle [C]1 Day [D]1) and through C12, using an electronic diary; PGIS and QLQ at BL (C1D1) and on D1 of each cycle through C12; and KIT D816V mutant allele fraction (MAF) at BL and on D1 of C3, 7, 11, and then every 6 cycles. The AdvSM-SAF assesses severity of 8 symptoms (pruritus, flushing, spots, nausea, vomiting, diarrhea, abdominal pain, fatigue) on a 0-10 scale, and 2 items assess frequency of diarrhea and vomiting. Results are analyzed as a Total Symptom Score (TSS), combining all 8 severity items (maximum symptom score=80), and as a GI domain (combining 4 symptoms: nausea, vomiting, diarrhea, abdominal pain; maximum score 40) and Skin domain (combining 3 symptoms: pruritus, flushing, spots; maximum score 30). Analyses were based on 7 d average scores. AdvSM-SAF data were summarized at BL (C1D-7 to C1D-1), and over the 7-d interval prior to C3D1 and C7D1, and correlated with QLQ, PGIS and KIT D816V MAF. Results: As of 22 June 2018, 25 pts were treated in Part 2 of the study; 24 are ongoing, and enrollment and follow-up continues. The median duration of avapritinib treatment was 5.7 mo (range, 1.7+ to 10.3+ mo). AdvSM-SAF scores for 24 pts with data are shown the Table. Mean BL TSS, GI and Skin scores were 22.6, 9.1, and 7.1. The most severe BL symptom was fatigue (mean score of 6.4). Among 21 pts with scores at C3D1 and 12 pts with scores at C7D1, mean reductions from BL TSS, GI and Skin scores were 6.4, 3.9, and 1.5 points, and 11.1, 5.7, and 4.4 points, respectively, indicating further improvement with continued treatment. Symptom reductions were seen for all 8 items at C3D1. Further symptom improvement was observed for 6 of 8 items from C3D1 to C7D1. Reductions in AdvSM-SAF TSS, GI and Skin scores significantly correlated with improvement in QLQ Emotional (EF) and Cognitive functioning (CF) scales (p values for Pearson Correlation Coefficients Conclusions: Avapritinib treatment resulted in meaningful symptom improvement as measured by the AdvSM-SAF in overall symptoms (TSS), GI and skin domains, and all individual symptoms, and improvement continued with longer duration of treatment. Reduction in AdvSM-SAF scores correlated with improvements in other PRO instruments, PGIS and QLQ, supporting the AdvSM-SAF as a useful new tool to assess symptoms in pts with AdvSM. Reduction in AdvSM-SAF scores also correlated with decreases in KIT D816V MAF, indicating that reductions in disease burden may correlate with reduced disease symptoms and improved quality of life. These data warrant further development of avapritinib in AdvSM, as well as in ISM and SSM where symptom burden and poor quality of life are the predominant disease manifestations. Disclosures Gotlib: Deciphera: Consultancy, Honoraria, Research Funding; Blueprint Medicines: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Honoraria, Research Funding; Promedior: Research Funding; Celgene: Consultancy, Honoraria, Research Funding; Kartos: Consultancy; Incyte: Consultancy, Honoraria, Research Funding; Gilead: Consultancy, Research Funding. Radia:Novartis: Speakers Bureau; Blueprint: Consultancy. DeAngelo:Glycomimetics: Research Funding; Shire: Honoraria; Pfizer Inc: Consultancy, Honoraria; Incyte: Consultancy, Honoraria; Amgen: Consultancy; Novartis Pharmaceuticals Corporation: Consultancy, Honoraria; Takeda: Honoraria; ARIAD: Consultancy, Research Funding; BMS: Consultancy; Blueprint Medicines: Honoraria, Research Funding. Bose:CTI BioPharma: Research Funding; Celgene Corporation: Honoraria, Research Funding; Pfizer, Inc.: Research Funding; Blueprint Medicines Corporation: Research Funding; Incyte Corporation: Honoraria, Research Funding; Astellas Pharmaceuticals: Research Funding; Constellation Pharmaceuticals: Research Funding. Conlan:Blueprint Medicines: Employment. Oren:Blueprint Medicines: Employment. Shi:Blueprint Medicines: Employment. Deininger:Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees; Blueprint: Consultancy.

Paediatric mastocytosis was previously considered to be a benign and spontaneously regressing disease. However, this evolution is impossible to predict. To clarify the characteristics and course of paediatric mastocytosis, we performed a literature review of 1747 cases published between 1950 and April 2014. Lesions occurred before the age of 2 years in 90% of cases, and presented as urticaria pigmentosa (75% of cases), mastocytoma (20%) or diffuse cutaneous mastocytosis (5%). The male-to-female ratio was 1·4. KIT D816V mutation was detected in 34% of 215 tested patients. Clinical regression (complete or partial) occurred in 67% of cases and stabilization in 27%. However, the outcome was fatal in 2·9% of patients.

Mast cell leukemia (MCL), the leukemic manifestation of systemic mastocytosis (SM), is characterized by leukemic expansion of immature mast cells (MCs) in the bone marrow (BM) and other internal organs; and a poor prognosis. In a subset of patients, circulating MCs are detectable. A major differential diagnosis to MCL is myelomastocytic leukemia (MML). Although criteria for both MCL and MML have been published, several questions remain concerning terminologies and subvariants. To discuss open issues, the EU/US-consensus group and the European Competence Network on Mastocytosis (ECNM) launched a series of meetings and workshops in 2011-2013. Resulting discussions and outcomes are provided in this article. The group recommends that MML be recognized as a distinct condition defined by mastocytic differentiation in advanced myeloid neoplasms without evidence of SM. The group also proposes that MCL be divided into acute MCL and chronic MCL, based on the presence or absence of C-Findings. In addition, a primary (de novo) formofMCL should be separated from secondary MCL that typically develops in the presence of a known antecedent MC neoplasm, usually aggressive SM (ASM) or MC sarcoma. For MCL, an imminent prephase is also proposed. This prephase represents ASM with rapid progression and 5%-19% MCs in BM smears, which is generally accepted to be of prognostic significance. We recommend that this condition be termed ASM in transformation to MCL (ASM-t). The refined classification of MCL fits within and extends the currentWHO classification; and should improve prognostication and patient selection in practice as well as in clinical trials., Supported by: Fonds zur Förderung der Wissenschaftlichen Forschung in Österreich, grants #SFB-F46-10 and #SFB-F47-04, a research grant of The Mastocytosis Society (TMS) and in part by the NIAID Division of Intramural Research.

Systemic mastocytosis (SM) arises as a consequence of aberrant activation of KIT signaling, most commonly by acquisition of the KIT D816V mutation (>80-90% of patients). A recently reported phase-II-study exploring the efficacy and safety of midostaurin, a multi-targeted KIT inhibitor, in patients with advanced SM (advSM) has demonstrated major and partial responses in 60% of patients (Gotlib et al., NEJM 374, 2016). However, recent data have highlighted that the molecular pathogenesis of SM is complex. In particular, additional mutations in SRSF2, ASXL1 and/or RUNX1 (S/A/Rpos), seen in 60-70% of patients with advSM, have a significant adverse impact on disease phenotype and prognosis (Jawhar et al., Leukemia 30, 2016). In the current study, we evaluated the impact of molecular markers on response, resistance, progression and overall survival (OS) in midostaurin-treated advSM patients: 1) the S/A/R mutation profile at diagnosis, 2) the reduction of the KIT D816V allele burden (EAB) and 3) the dynamics of the clonal architecture. Between 2009 and 2015, 38 patients (68% male; median age 67 years; range, 48-76) with advSM [SM with an associated hematological neoplasm (SM-AHN), n=22; aggressive SM (ASM), n=3; mast cell leukemia (MCL), n=4; MCL-AHN, n=9] received midostaurin at our institution and were monitored for the KIT D816V EAB by quantitative RT-PCR (RT-qPCR). In addition, serial Next Generation Sequencing (NGS) analyses were performed in 16/25 multi-mutated patients. Median time from diagnosis of advSM to start of midostaurin was 12 months (range, 1-60). Twenty-one of 38 (55%) patients died; median OS was 29 months (range, 0-88) from start of midostaurin and 40 months (range, 5-115) from diagnosis. Three patients (8%) stopped midostaurin early (median 2 months; range, 1-4) because of intolerance. In the remaining 35 (92%) patients, median treatment duration was 13 months (range, 1-88). Progression/death occurred in 6/35 (17%) patients within the first 6 months and 5 (83%) patients were S/A/Rpos. Overall response rate (ORR) according to IWG-MRI-ECNM consensus criteria and OS were significantly different between S/A/Rpos (n=23) vs. S/A/Rneg (n=12) patients [ORR: 35% vs. 75%, P=0.01; OS: P=0.01, HR 4.5 (1.3-16.2), Figure 1A]. The maximal median reduction of KIT D816V EAB in 28 patients treated for >6 months was -29% (range, -100 to 71). Depending on the KIT D816V EAB at month 6, patients were classified as responders (≥25%, n=17) or non-responders ( Disclosures Valent: Celegene: Honoraria, Research Funding; Novartis: Honoraria, Research Funding; Amgen: Honoraria. Meggendorfer:MLL Munich Leukemia Laboratory: Employment.

It is presently accepted that the KIT D816V mutation is detectable in tissues with neoplastic mast cells in most patients with indolent systemic mastocytosis. In this study, neoplastic mast cells were detected in bone marrow, but not in peripheral blood, by flow cytometry in all 25 included cases of indolent systemic mastocytosis. However, the KIT D816V mutation was detected using mutation-specific qPCR in both bone marrow and peripheral blood in all 25 cases, demonstrating for the first time that the KIT D816V mutation is consistently present in non-mast cells in indolent systemic mastocytosis and that these cells are circulating in peripheral blood.