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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., D.D.M., J.J.L., and M.C.C. were supported by the Division of Intramural Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health. P.V. was supported by the Austrian Science Fund (FWF) (grant nos. F4704-B20 and P32470-B).

Mast cell activation (MCA) is common and occurs in a number of pathologic conditions, including IgE-dependent and independent allergic reactions, atopic disorders, autoimmune processes, and mastocytosis. In a subset of patients, no underlying disease and no known trigger of MCA are found. When the symptoms are severe, systemic, and recurrent, and accompanied by a diagnostic increase in the serum tryptase level or other mast cell mediators, an MCA syndrome (MCAS) may be diagnosed. In these patients, the symptoms typically respond to drugs suppressing MCA, mediator production in mast cells, or mediator effects. In each case, diagnostic consensus criteria must be fulfilled to diagnose MCAS. In other patients, MCA may be local, less severe, or less acute, or may be suspected but not confirmed, so that the diagnostic criteria of MCAS are not fulfilled. In these patients, it may be difficult to prove MCA, for example, by measuring multiple mast cell mediators or basophil activation, the latter as a surrogate of IgE-dependent hypersensitivity. However, validated diagnostic criteria for implicating suspected MCA behind such conditions are lacking, even if some of these conditions have recently been assigned to an International Classification of Diseases-10-Clinical Modification code (ICD-10-CM). In this article, we discuss diagnostic features and criteria and propose a ICD-10-CM–adjusted classification for disorders associated with MCA, herein referred to as MCA disorders (MCADs), with special emphasis on the delineation between confirmed MCAS, MCAD not fulfilling MCAS criteria, and suspected MCAD that is not present. In addition, we discuss the discrimination between overt MCAD and predisposing conditions, such as atopic states, mastocytosis, and hereditary alpha tryptasemia., T.G. was supported by grants from the Konsul TH C Bergh Foundation and the Stockholm County Council Research Funds (ALF), Sweden. M.C.C., J.J.L, and D.D.M. were supported by the Division of Intramural Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health (NIH). The content is solely the responsibility of the authors and does not represent the official views of the NIH. P.V. was supported by the Austrian Science Fund (FWF; projects P32470-B and F4704-B20).

Supplemental Table S2

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 systemic mastocytosis. Cancer Res; 77(6); 1261–70. ©2017 AACR.

In 2002, the European Competence Network on Mastocytosis (ECNM) was launched as a multidisciplinary collaborative initiative to increase the awareness and to improve diagnosis and management of patients with mast cell (MC) disorders. The ECNM consists of a net of specialized centers, expert physicians, and scientists who dedicate their work to MC diseases. One essential aim of the ECNM is to timely distribute all available information about the disease to patients, doctors, and scientists. In the past 20 years, the ECNM has expanded substantially and contributed successfully to the development of new diagnostic concepts, and to the classification, prognostication, and treatments of patients with mastocytosis and MC activation disorders. The ECNM also organized annual meetings and several working conferences, thereby supporting the development of the World Health Organization classification between 2002 and 2022. In addition, the ECNM established a robust and rapidly expanding patient registry and supported the development of new prognostic scoring systems and new treatment approaches. In all projects, ECNM representatives collaborated closely with their U.S. colleagues, various patient organizations, and other scientific networks. Finally, ECNM members have started several collaborations with industrial partners, leading to the preclinical development and clinical testing of KIT-targeting drugs in systemic mastocytosis, and some of these drugs received licensing approval in recent years. All these networking activities and collaborations have strengthened the ECNM and supported our efforts to increase awareness of MC disorders and to improve diagnosis, prognostication, and therapy in patients.

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., T. I. George was supported by the ARUP Institute for Clinical and Experimental Pathology. K. Hartmann was supported by the Swiss National Science Foundation, grant number 310030_207705. D. D. Metcalfe, J. J. Lyons, and M. Carter were supported by the Division of Intramural Research, National Institutes of Allergic and Infectious Diseases, National Institutes of Health (NIH). The content is solely the responsibility of the authors and does not represent the official views of the NIH. P. Valent was supported by the Austrian Science Funds (FWF), projects F4701-B20 and F4704-B20.

Patients with core-binding factor (CBF) acute myeloid leukemia (AML), caused by either t(8;21)(q22;q22) or inv(16)(p13q22)/t(16;16)(p13;q22), have higher complete remission rates and longer survival than patients with other subtypes of AML. However, ∼40% of patients relapse, and the literature suggests that patients with inv(16) fare differently from those with t(8;21). We retrospectively analyzed 537 patients with CBF-AML, focusing on additional cytogenetic aberrations to examine their impact on clinical outcomes. Trisomies of chromosomes 8, 21, or 22 were significantly more common in patients with inv(16)/t(16;16): 16% vs 7%, 6% vs 0%, and 17% vs 0%, respectively. In contrast, del(9q) and loss of a sex chromosome were more frequent in patients with t(8;21): 15% vs 0.4% for del(9q), 37% vs 0% for loss of X in females, and 44% vs 5% for loss of Y in males. Hyperdiploidy was more frequent in patients with inv(16) (25% vs 9%, whereas hypodiploidy was more frequent in patients with t(8;21) (37% vs 3%. In multivariable analyses (adjusted for age, white blood counts at diagnosis, and KIT mutation status), trisomy 8 was associated with improved overall survival (OS) in inv(16), whereas the presence of other chromosomal abnormalities (not trisomy 8) was associated with decreased OS. In patients with t(8;21), hypodiploidy was associated with improved disease-free survival; hyperdiploidy and del(9q) were associated with improved OS. KIT mutation (either positive or not tested, compared with negative) conferred poor prognoses in univariate analysis only in patients with t(8;21).

Introduction. Patients with eosinophilia (an increased number of eosinophilic granulocytes > 0.5 × 109/l in the blood) are encountered in all medical specialties and frequently need thorough workup to identify the eliciting causes and decide whether treatment is indicated. In Denmark, highly specialised centres for eosinophilic diseases or conditions have been established to provide a foundation for the management of complicated cases. Here, we present experiences from such a multidisciplinary centre. Methods. This was a retrospective study of all patients seen in our tertiary centre for eosinophilia in the 2016-2019 period. Results. Referrals mainly derived from specialised secondary care and to a lesser degree from primary care physicians. Patients were either asymptomatic or exhibited symptoms from up to three organ systems and presented a median eosinophil count of 1.7 × 109/l. Up to eight new clonality analyses or imaging studies per patient were performed after referral. One of these, T-cell receptor analysis, was performed frequently but provided limited information, whereas, e.g., flow cytometry proved more clinically applicable owing to its broader diagnostic range. In total, 51 patients were evaluated and classified as secondary (59%), myeloid neoplasm with PDGFRA rearrangement (2%), idiopathic hypereosinophilic syndrome (31%) and idiopathic hypereosinophilia (8%). Conclusion. The value of a multidisciplinary and versatile approach in a highly specialised centre has a positive impact on diagnostic processes as well as on the evaluation of treatment need.

Mast cell neoplasms are an emerging challenge in the fields of internal medicine, allergy, immunology, dermatology, laboratory medicine, and pathology. In this review, we discuss the current standards for the diagnosis and prognostication of mast cell neoplasms with special reference to clinically relevant germline and somatic gene variants. In patients with cutaneous mastocytosis or with indolent systemic mastocytosis (SM), various KIT-activating mutations act as key molecular drivers of the disease. In adults, KIT p.D816V is by far the most prevalent driver, whereas other KIT mutants are detected in nearly 40% of children. In advanced SM, including aggressive SM, SM with an associated hematological neoplasm, and mast cell leukemia, additional somatic mutations in other genes, such as SRSF2, JAK2, RUNX1, ASXL1, or RAS, may be detected. These drivers are more frequently detected in SM with an associated hematological neoplasm, particularly in male patients. Recently, hereditary alpha-tryptasemia has been identified as a genetic trait more prevalent in SM compared with healthy controls. Moreover, hereditary alpha-tryptasemia is more frequent in patients with SM with Hymenoptera venom allergy and severe mediator-related symptoms than in patients with SM without symptoms. On the basis of this knowledge, we propose a diagnostic algorithm in which genetic markers are applied together with clinical and histopathologic criteria to establish the diagnosis and prognosis in SM.

In recent years, knowledge about mechanisms underlying mast cell activation (MCA) and accumulation in various pathologic conditions increased substantially. In addition, criteria and a classification of MCA syndromes (MCASs) have been set forth. MCAS is defined by typical clinical symptoms, a substantial increase in serum tryptase level during an attack over the patient's baseline tryptase, and a response of the symptoms to drugs targeting mast cells, mediator production, and/or mediator effects. Alternative diagnostic criteria of MCAS have also been suggested, but these alternative criteria often lack specificity and validation. In this report, we critically review the contemporary literature relating to MCAS and compare the specificity, sensitivity, and strength of MCAS-related parameters within proposals to diagnose and classify MCAS and its variants. Furthermore, we highlight the need to apply specific consensus criteria in the evaluation and classification of MCAS in individual patients. This is an urgent and important medical necessity because as an increasing number of patients are being given a misdiagnosis of MCAS based on nonspecific criteria, which contributes to confusion and frustration by patients and caregivers and sometimes may delay recognition and treatment of correct medical conditions that often turn out to be unrelated to MCA. (C) 2021 The Authors. Published by Elsevier Inc. on behalf of the American Academy of Allergy, Asthma & Immunology.

Mastocytosis is a hematologic neoplasm characterized by expansion and focal accumulation of neoplastic mast cells (MC) in diverse organs, including the skin, bone marrow (BM), spleen, liver, and gastrointestinal tract. The World Health Organization classification divides the disease into prognostically distinct variants of cutaneous mastocytosis (CM) and systemic mastocytosis (SM). Although this classification remains valid, recent developments in the field and the advent of new diagnostic and prognostic parameters created a need to update and refine definitions and diagnostic criteria in MC neoplasms. In addition, MC activation syndromes (MCAS) and genetic features predisposing to SM and MCAS have been identified. To discuss these developments and refinements in the classification, we organized a Working Conference comprised of experts from Europe and the United States in August 2020. This article reports on outcomes from this conference. Of particular note, we propose adjustments in the classification of CM and SM, refinements in diagnostic criteria of SM variants, including smoldering SM and BM mastocytosis (BMM), and updated criteria for MCAS and other conditions involving MC. CD30 expression in MC now qualifies as a minor SM criterion, and BMM is now defined by SM criteria, absence of skin lesions and absence of B- and C-findings. A basal serum tryptase level exceeding 20 ng/mL remains a minor SM criterion, with recognition that hereditary alpha-tryptasemia and various myeloid neoplasms may also cause elevations in tryptase. Our updated proposal will support diagnostic evaluations and prognostication in daily practice and the conduct of clinical trials in MC disorders.

INTRODUCTION: Exercise induced anaphylaxis (EIA) denotes a range of disorders where anaphylaxis occurs in relation to physical exercise. Typical symptoms include flushing, pruritus, urticaria, angioedema, respiratory symptoms, gastro-intestinal symptoms, hypotension, and collapse during or after exercise. The far best described entity within EIA is food-dependent exercise-induced anaphylaxis (FDEIA), where symptoms only occur in combination with food intake. Frequency and predictability of symptoms vary, and some patients experience symptoms only if exercise is accompanied by other co-factors Areas covered: In the present review, we aimed to provide an overview of EIA, diagnostic workup, causes, management and discuss areas in need of further research. Expert opinion: Though rare, EIA is an entity that all allergists and practicing physicians should recognize. The pathophysiological and immunological mechanisms of EIA are largely unknown. Management is centered upon avoidance of eliciting factors, where emergency plans are individualized, except a mandatory prescription of an adrenaline auto-injector.

Mast cell activation syndrome (MCAS) is a condition characterized by recurrent episodes of clinically relevant, systemic, severe reactions to mast cell (MC)-derived mediators released in the context of anaphylaxis or another acute MC-related event. It is important to document MC involvement in these reactions in order to establish the diagnosis MCAS. The most specific and reliable marker of systemic MC activation is an acute and substantial event-related (transient) increase in the serum tryptase level over the individual’s baseline value. However, the baseline level of tryptase varies depending on the underlying disease and the genetic background. For example, an estimated 3–5% of healthy individuals exhibit duplications or multiple copies of the TPSAB1 gene encoding for alpha-tryptase, and over 30% of all patients with myeloid neoplasms, including mastocytosis, have elevated basal tryptase levels. Therefore, it is of utmost importance to adjust the event-related diagnostic (MCAS-confirming) increase in tryptase over the individual baseline in a robust approach. To address this challenge, the 20% + 2 formula was proposed by the consensus group in 2012. Since then, this approach has been validated in clinical practice by independent groups and found to be sound. In the current article, we discuss the emerging importance and value of the 20% + 2 formula in clinical practice and its role as a criterion of severe systemic MC activation and MCAS.

Mastocytosis is a rare myeloid neoplasm characterized by uncontrolled expansion of mast cells, driven in >80% of affected individuals by acquisition of the KIT D816V mutation. To explore the hypothesis that inherited variation predisposes to mastocytosis, we performed a two-stage genome-wide association study, analyzing 1,035 individuals with KIT D816V positive disease and 17,960 healthy control individuals from five European populations. After quality control, we tested 592,007 SNPs at stage 1 and 75 SNPs at stage 2 for association by using logistic regression and performed a fixed effects meta-analysis to combine evidence across the two stages. From the meta-analysis, we identified three intergenic SNPs associated with mastocytosis that achieved genome-wide significance without heterogeneity between cohorts: rs4616402 (pmeta = 1.37 × 10−15, OR = 1.52), rs4662380 (pmeta = 2.11 × 10−12, OR = 1.46), and rs13077541 (pmeta = 2.10 × 10−9, OR = 1.33). Expression quantitative trait analyses demonstrated that rs4616402 is associated with the expression of CEBPA (peQTL = 2.3 × 10−14), a gene encoding a transcription factor known to play a critical role in myelopoiesis. The role of the other two SNPs is less clear: rs4662380 is associated with expression of the long non-coding RNA gene TEX41 (peQTL = 2.55 × 10−11), whereas rs13077541 is associated with the expression of TBL1XR1, which encodes transducin (β)-like 1 X-linked receptor 1 (peQTL = 5.70 × 10−8). In individuals with available data and non-advanced disease, rs4616402 was associated with age at presentation (p = 0.009; beta = 4.41; n = 422). Additional focused analysis identified suggestive associations between mastocytosis and genetic variation at TERT, TPSAB1/TPSB2, and IL13. These findings demonstrate that multiple germline variants predispose to KIT D816V positive mastocytosis and provide novel avenues for functional investigation., A full list of the investigators who contributed to the generation of the WTCCC data is available from the WTCCC website, funding for which was provided by The Wellcome Trust under award 07611. The KORA study was initiated and financed by the Helmholtz Zentrum München—German Research Center for Environmental Health, which is funded by the German Federal Ministry of Education and Research (BMBF) and by the State of Bavaria. Furthermore, KORA research was supported within the Munich Center of Health Sciences (MC-Health), Ludwig-Maximilians-Universität, as part of LMUinnovativ. The KORA Study Group consists of A. Peters (speaker), J. Heinrich, R. Holle, R. Leidl, C. Meisinger, K. Strauch, and their co-workers, who are responsible for the design and conduct of the KORA studies. We gratefully acknowledge the contribution of all members of field staff conducting the KORA study, and we are grateful to all study participants of KORA for their invaluable contributions to this study. The InCHIANTI study baseline (1998–2000) was supported as a “targeted project” (ICS110.1/RF97.71) by the Italian Ministry of Health and in part by the U.S. National Institute on Aging (263 MD 9164 and 263 MD 821336). The Spanish mastocytosis cohort and the Spanish National DNA Bank were supported by grants from the Instituto de Salud Carlos III and FEDER (PI16/00642 and PT17/0015/0044). The Italian cohort of mastocytosis-affected individuals was funded by the Associazione Italiana per la Ricerca sul cancro, Mynerva project, 21267. The Novo Nordisk Foundation Center for Basic Metabolic Research is an independent Research Center at the University of Copenhagen partially funded by an unrestricted donation from the Novo Nordisk Foundation. A.A.Z.D. was supported by a Lady Tata International Award; G.G., N.C.P.C., Y.H., A.J.C., and W.J.T. were supported by Blood Cancer UK (13002 and 18007).

Mastocytosis is a neoplasm characterized by an accumulation of mast cells in various organs and increased risk for severe anaphylaxis in patients with concomitant allergies. Coronavirus disease 2019 (COVID-19) is a pandemic that is associated with a relatively high rate of severe lung disease and mortality. The mortality is particularly high in those with certain comorbidities and increases with age. Recently, several companies have developed an effective vaccination against COVID-19. Although the reported frequency of severe side effects is low, there is an emerging discussion about the safety of COVID-19 vaccination in patients with severe allergies and mastocytosis. However, even in these patients, severe adverse reactions are rare. We therefore recommend the broad use of COVID-19 vaccination in patients with mastocytosis on a global basis. The only well-established exception is a known or suspected allergy against a constituent of the vaccine. Safety measures, including premedication and postvaccination observation, should be considered in all patients with mastocytosis, depending on the individual personal risk and overall situation in each case. The current article provides a summary of published data, observations, and expert opinion that form the basis of these recommendations.

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.

This document summarizes the aims of GA2 LEN/HAEi Angioedema Centers of Reference and Excellence (ACAREs) and elaborates the requirements that ACAREs must fulfill to become certified. It also provides (see Appendix S1) background information on GA2LEN and HAEi, including HAEi member organizations and regional patient advocates, on why we need an Angioedema Center of Reference and Excellence (ACARE) program and network, and on the accreditation and certification process, governance and funding, and on the interaction with other GA2LEN networks of centers of reference and excellence. The protocols, aims, requirements, and provisions related to becoming a certified CARE are based on (a) the experience of the GA2LEN UCARE network and (b) input from angioedema patients, general practitioners, and angioedema specialists.

Mastocytosis is defined as a heterogeneous group of disorders characterized by clonal expansion and aberrant activation of mast cells. Most cases are associated with gain-of-function mutations in KIT, the receptor for stem cell factor, the major cytokine involved in mast cell growth and differentiation. While a rare disease, it is increasingly diagnosed due to the refinements in diagnostic criteria and increased physician and patient awareness. Novel therapeutic approaches targeting mast cell survival and activation makes it important to correctly diagnosing the disease. This chapter serves as an introduction on the symptomatology, diagnostic criteria, classification, and treatment of mastocytosis, which are discussed in more detail in other chapters of the book. Mastocytosis is defined as a heterogeneous group of disorders characterized by clonal expansion and aberrant activation of mast cells. Most cases are associated with gain-of-function mutations in KIT, the receptor for stem cell factor, the major cytokine involved in mast cell growth and differentiation. While a rare disease, it is increasingly diagnosed due to the refinements in diagnostic criteria and increased physician and patient awareness. Novel therapeutic approaches targeting mast cell survival and activation makes it important to correctly diagnosing the disease. This chapter serves as an introduction on the symptomatology, diagnostic criteria, classification, and treatment of mastocytosis, which are discussed in more detail in other chapters of the book.

Purpose: The selective tyrosine kinase inhibitor avapritinib has been shown to improve skin lesions in pts with ISM (Hartmann K et al. EACCI 2020. Abstract 1832). We assessed numbers and immunophenotypic changes of MCs in bone marrow (BM) and skin biopsies from lesional tissue (LT) and non-lesional tissue (NLT) in 39 pts with ISM from Part 1 of the placebo-controlled PIONEER (NCT03731260) study. Methods: BM biopsies and aspirates were obtained at Screening; skin biopsies from LT and NLT were obtained at Screening and end of Week 12 (W12). Immunohistochemistry was performed on formalin-fixed sections using the Ventana Benchmark assay with CD117, tryptase, CD25, CD30, and CD34 antibodies. Samples were centrally reviewed by three pathologists. Statistical significance of MC numbers and immunophenotypic changes were assessed. Data cut-off was December 4, 2020. Results: Screening BM biopsies had median 10% (range, 1-60%) MCs, of which 90% (10-100%) were spindled. BM aspirates had median 1% (0-10%) MCs, of which 5% (2-6%) were immature. Median number of MCs/mm2 was 355 (53-4300) in LT and 90 (10-540) in NLT. At W12, avapritinib reduced median number of MCs/mm2 in LT (143 [33-837]) but not NLT (102 [32-207]). BM biopsies had higher median rates of CD25+ and CD30+ MCs (90% CD25+/50% CD30+) compared with skin LT (2% CD25+/10% CD30+) and NLT (1% CD25+/1% CD30+) (Table). Avapritinib produced significant reductions in the proportion of CD30+ MCs in LT at W12 versus placebo (P=0.0053) and non-significant reductions in CD30+ MCs in NLT (P=0.0988). Conclusions: CD25+ and CD30+ MCs were observed in both LT and NLT skin biopsies; however, at markedly lower levels than seen in BM. Treatment with avapritinib decreased the total number of MCs as well as the number of CD30+ and CD25+ MC in both LT and NLT with statistically significant decreases in the CD30+ MC fraction in LT. This is the first study to examine changes in MCs in LT and NLT or ISM during precision therapy of ISM. Table. Immunophenotypic changes of MCs in BM and skin biopsies at screening and W12MC PhenotypeBone MarrowSkin Lesional TissueSkin Non-Lesional TissueAvapritinibPlaceboAvapritinibPlaceboScreening (n=39)Screening (n=25)W12 (n=17)Screening (n=8)W12 (n=7)Screening (n=25)W12 (n=21)Screening (n=8)W12 (n=7)CD25+, median % (range)90 (0-100)2 (1-40)2 (1-10)3 (1-50)5 (2-5)1 (1-5)2 (1-10)2 (1-5)5 (2-5)CD30+, median % (range)50 (0-100)10 (1-100)1 (1-5)13 (1-80)5 (1-30)1 (1-20)1 (1-2)2 (1-30)1 (1-10)Abbreviations: BM, bone marrow; MC, mast cell; W12, Week 12. Citation Format: Tracy George, Sigurd Broesby-Olsen, David Wada, Scott Florell, Karin Hartman, Frank Siebenhaar, Cem Akin, Kate Newberry, Hongliang Shi, Maria Roche, Marcus Maurer, Hanneke Oude Elberink. Changes in mast cell (MC) numbers and phenotype in patients (pts) with indolent systemic mastocytosis (ISM) treated with avapritinib [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr CT168.

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.

Introduction: Systemic mastocytosis (SM) is a rare clonal mast cell (MC) neoplasm characterized by MC accumulation and is primarily driven by the KIT D816V mutation. The D816V mutation is located in the activation loop of the KIT receptor tyrosine kinase resulting in constitutive activation of the receptor, causing aberrant MC proliferation and hyperactivation. MC mediator release can lead to severe clinical manifestations including skin, gastrointestinal, neurocognitive, skeletal, and systemic symptoms. Indolent SM is the most common subtype of SM; abnormal activation of mast cells leads to debilitating symptoms, poor quality of life, and has life-threatening consequences such as anaphylaxis. Although symptomatic treatments are used to control symptom severity (eg, cromolyn sodium, antihistamines, leukotriene inhibitors, omalizumab), there are no approved disease-modifying therapies to reduce MC burden and activation. Avapritinib is a potent, selective tyrosine kinase inhibitor that targets the KIT D816V mutant. Avapritinib has shown good tolerability in toxicology and safety pharmacology studies when assessed at active doses. PIONEER (NCT03731260) is an international, multicenter, randomized, double-blind, placebo-controlled, phase 2 study investigating the safety and efficacy of avapritinib in patients with indolent SM and symptoms inadequately controlled by best supportive care (BSC). PIONEER Part 1 assessed the safety and pharmacokinetics of avapritinib and identified the recommended phase 2 dose of 25 mg once daily in 4-weekly cycles. PIONEER Part 2 will assess the safety and efficacy of 25 mg avapritinib once daily versus placebo with BSC in patients with indolent SM whose symptoms are not adequately controlled by BSC. Study design and methods: PIONEER Part 2 will enroll approximately 204 patients with indolent SM who will be randomized 2:1 to avapritinib plus BSC (25 mg once daily; n=136) or matched placebo plus BSC (n=68), stratified by baseline serum tryptase level (97% power to detect superiority of avapritinib compared with placebo using a 2-sample Fisher Exact test, with a 1-sided type I error rate of 0.025, for the primary endpoint at Week 24. PIONEER Part 2 will enroll patients at sites in the USA, Canada, and Europe. Patients who complete PIONEER Part 1 or Part 2 will be eligible to enter an open-label extension to evaluate long-term safety and efficacy of avapritinib 25 mg once daily. Disclosures Akin: Novartis: Consultancy; Blueprint Medicines Corporation: Consultancy, Research Funding. Elberink:Novartis: Research Funding; Blueprint Medicines Corporation: Membership on an entity's Board of Directors or advisory committees. Gotlib:Deciphera: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: co-chair of the Study Steering Committee and Research Funding; Blueprint Medicines Corporation: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Chair of the Response Adjudication Committee and Research Funding, Research Funding. Sabato:Blueprint Medicines Corporation: Other: My institution received research funding. Hartmann:Allergopharma: Consultancy, Honoraria, Other: reimbursement of travel expenses , Research Funding; Blueprint Medicines Corporation: Consultancy, Honoraria, Other: reimbursement of travel expenses , Research Funding; Deciphera: Consultancy, Honoraria, Other: reimbursement of travel expenses , Research Funding; Menarini: Honoraria, Other: reimbursement of travel expenses , Research Funding; Novartis: Consultancy, Honoraria, Other: reimbursement of travel expenses , Research Funding; Takeda: Consultancy, Honoraria, Other: reimbursement of travel expenses , Research Funding; Euroimmun: Honoraria, Other: reimbursement of travel expenses , Research Funding; Thermofisher: Other: reimbursement of travel expenses , Research Funding; ALK-ABello: Consultancy, Honoraria, Other: reimbursement of travel expenses , Research Funding. Broesby-Olsen:Thermo Fisher: Honoraria; Novartis: Honoraria; Blueprint Medicines Corporation: Honoraria, Other: study steering committee member. Castells:Annals of Allergy, Asthma & Immunology: Other: Editorial Board; Blueprint Medicines Corporation: Consultancy, Other: Clinical trials: Principle Investigator; UpToDate: Other: Author fee. Heaney:Partner Therapeutics: Consultancy; AbbVie: Consultancy; Sierra Oncology: Research Funding; Novartis: Consultancy, Research Funding; Incyte: Research Funding; Deciphera: Research Funding; CTI Biopharma: Consultancy, Research Funding; BMS: Research Funding; Blueprint Medicines Corporation: Research Funding. George:Celgene: Consultancy; Deciphera: Other: consultancy, but has received no financial compensation for the past 12 months; Blueprint Medicines Corporation: Consultancy, Other: I have received no funding for this research. ARUP Laboratories, owned by the University of Utah, has received funding; Allakos: Consultancy. Siebenhaar:Hyphens: Other: received honoraria (advisory board, speaker) and/or institutional grant/research support ; Pediapharm: Other: received honoraria (advisory board, speaker) and/or institutional grant/research support ; Aralez: Other: received honoraria (advisory board, speaker) and/or institutional grant/research support ; SunPharma: Other; Moxie: Other: received honoraria (advisory board, speaker) and/or institutional grant/research support ; Allakos: Other: received honoraria (advisory board, speaker) and/or institutional grant/research support ; Novartis: Other: received honoraria (advisory board, speaker) and/or institutional grant/research support ; Sanofi: Other: received honoraria (advisory board, speaker) and/or institutional grant/research support ; Glenmark: Other: received honoraria (advisory board, speaker) and/or institutional grant/research support ; Uriach: Other; Biocryst: Other: received honoraria (advisory board, speaker) and/or institutional grant/research support ; Blueprint Medicines Corporation: Honoraria, Research Funding. Radia:Blueprint Medicines Corporation: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees, Other: Education events. Triggiani:Deciphera: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Blueprint Medicines Corporation: Membership on an entity's Board of Directors or advisory committees. DeAngelo:Abbvie: Research Funding; Jazz: Consultancy; Incyte Corporation: Consultancy; Forty-Seven: Consultancy; Pfizer: Consultancy; Shire: Consultancy; Amgen: Consultancy; Takeda: Consultancy; Glycomimetics: Research Funding; Novartis: Consultancy, Research Funding; Autolos: Consultancy; Agios: Consultancy; Blueprint Medicines Corporation: Consultancy, Research Funding. Reiter:Gilead: Other: travel support ; Incyte: Consultancy, Other: travel support ; AOP: Consultancy, Other: travel support ; Celgene,: Consultancy, Other: travel support ; Abbvie: Consultancy, Other: travel support ; Deciphera: Consultancy, Other: travel support ; Blueprint: Consultancy, Other: travel support ; Novartis: Consultancy, Honoraria, Other: travel support , Research Funding. Hew:Blueprint Medicines Corporation: Current Employment, Current equity holder in publicly-traded company. Lin:Blueprint Medicines Corporation: Current Employment, Current equity holder in publicly-traded company. Roche:Blueprint Medicines Corporation: Current Employment, Current equity holder in publicly-traded company; Epizyme: Other: outside the submitted work. Maurer:Novartis: Honoraria, Other; Regeneron: Honoraria, Other; UCB: Honoraria, Other; ThirdHarmonicBio: Honoraria, Other; Sanofi: Honoraria, Other; Roche: Honoraria, Other; FAES: Honoraria, Other: institutional grant/research support; Dr. Pfleger: Honoraria, Other: institutional grant/research support; Blueprint Medicines Corporation: Honoraria, Other: institutional grant/research support; Bayer: Honoraria, Other: institutional grant/research support; AstraZeneca: Honoraria, Other: institutional grant/research support; Amgen: Honoraria, Other: institutional grant/research support; Allakos: Honoraria, Other: institutional grant/research support; Moxie: Honoraria, Other; Merckle Recordati: Honoraria, Other; Uriach: Honoraria, Other; CellDex: Honoraria, Other; GIInnovation: Honoraria, Other; Lilly: Honoraria, Other; Kyowa Kirin: Honoraria, Other; Innate Pharma: Honoraria, Other: institutional grant/research support; GSK: Honoraria, Other: institutional grant/research support; Genentech: Honoraria, Other: institutional grant/research support.

This study evaluates adherence to adrenaline autoinjector prescriptions in a cohort of well-characterized anaphylaxis patients. The overall retrieval rate was 76% with the highest rate in patients with severe anaphylaxis. Special attention is needed in patients with unknown elicitors and in young adults, comprising the largest proportion of non-adherent patients. Trial registration No intervention performed. Retrospective data used with permission from the Danish Data Protection Agency and Regional Committees on Health Research Ethics

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...

In childhood, the most common type of eczema/dermatitis is atopic dermatitis, which occurs in up to 25% of children world-wide. However, the diagnosis may sometimes be challenging and atopic dermatitis may resemble other types of dermatitis as well as other skin diseases such as psoriasis, infections, infestations and malignancies as well as metabolic, genetic and autoimmune disorders. This review will focus on how to recognize the most common types of dermatitis in children and adolescents and how to separate them from the most common differential diagnoses clinically and histologically.

BACKGROUND: While much is known on childhood atopic diseases, knowledge about persistence of atopic diseases from childhood to adulthood is limited. We therefore aimed to study the clinical course of atopic diseases and type I sensitization prospectively in an unselected cohort of adolescents followed into adulthood.METHODS: A cohort of unselected 8th-grade school children (mean age 14 years) established in 1995 and followed up in 2010 were evaluated with questionnaire, clinical examination, skin prick tests and measurements of specific IgE.RESULTS: The lifetime prevalence of atopic diseases was high and increased significantly from adolescence (31%) to adulthood (57%); particularly allergic rhinitis increased with an incidence rate of 17.5/1000 person-years. Childhood predictors for adult allergic rhinitis were atopic dermatitis, asthma and asymptomatic sensitization to pollen and house dust mite. Among those with asymptomatic sensitization in adolescence, 53%-78% developed allergic rhinitis in adulthood. Furthermore, type I sensitization increased significantly from adolescence to adulthood mostly due to increased sensitization to pollen. Type I sensitization was found mainly in those with allergic rhinitis. A high number of adults had oral allergy symptoms due to the high number of birch pollen allergic individuals.CONCLUSION: Persistence of atopic diseases in adulthood is common, and a high proportion of the adult population is sensitized giving a high prevalence of allergic rhinitis. Many with asymptomatic sensitization in adolescence will develop allergic rhinitis in adult life. The focus should be on prevention of atopic diseases and sensitization already in childhood.

In patients with systemic mastocytosis (SM), several aspects of morbidity remain poorly understood. We assessed the risk of solid cancers, cardiovascular disease, anaphylaxis, osteoporosis, and fractures in SM patients. Using Danish medical registries, we conducted a nationwide population-based cohort study including 687 adult (≥15 years) SM patients diagnosed during 1997-2012. A comparison cohort of 68,700 subjects from the general Danish population who were alive and without SM at the given SM subject's diagnosis were age- and gender-matched. Outcomes were a new diagnosis of solid cancer, venous thromboembolism (VTE), myocardial infarction (MI), stroke, anaphylaxis, osteoporosis, or fracture. For solid cancers the hazard ratio (HR) was 2.4 (95% confidence interval [CI] 1.9-2.8) with a 10-year absolute risk (AR) in the SM-cohort of 12.6% (95% CI 9.4-16.3). Specifically, we found a HR of 7.5 (95% CI 4.4-13.0) for melanoma and a HR of 2.5 (95% CI 1.7-3.5) for non-melanoma skin cancers (NMSCs). For VTE we found a HR of 1.9 (95% CI 1.2-3.0), with a 10-year AR of 3.9% (95% CI 2.3-6.1); for MI a nonsignificant increased HR of 1.4 (95% CI 0.9-2.3), with a 10-year AR of 1.8% (95% CI 0.9-3.2); and for stroke a HR of 1.6 (95% CI 1.1-2.3) with a 10-year AR of 4.6% (95% CI 2.8-6.9). The HR for anaphylaxis was 7.2 (95% CI 5.3-9.9), and the 10-year AR was 3.1% (95% CI 1.9-4.9). For osteoporosis the HR was 3.6 (95% CI 2.7-4.6) with a 10-year AR of 7.2% (95% CI 5.2-9.8). For fractures the HR was 1.2 (95% CI 0.9-1.6) and the 10-year AR was 5.9% (95% CI 3.9-8.4). SM patients are at increased risk of solid cancers - especially melanoma and NMSC-and cardiovascular disease. The risk of anaphylaxis and osteoporosis is clearly increased in SM, though absolute risk was low in this population-based study. The fracture-risk was only slightly increased. Am. J. Hematol. 91:1069-1075, 2016. © 2016 Wiley Periodicals, Inc.

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).

Mast cell activation disorders is a term proposed to cover diseases and conditions related to activation of mast cells and effects of mast cell mediators. In its broadest sense, the term encompasses a wide range of diseases from allergic asthma to rhinoconjunctivitis, urticaria, food allergy, anaphylaxis, mastocytosis, and other conditions where MC activation is contributing to the pathogenesis. This article focuses on clinical presentations, challenges, and controversies in pediatric mastocytosis and gives an overview of current knowledge and areas in need of further research.

Aim: To investigate and gain knowledge about patients’ perspectives on everyday life with mastocytosis and how they experience, understand and manage symptoms and challenges. Background: Indolent systemic mastocytosis (ISM) is a disease characterised by the accumulation and activation of mast cells. Symptoms are diverse and range from mild to severely debilitating or even fatal. It is considered rare but is underdiagnosed due to lack of awareness. Quantitative studies have shown that ISM can negatively impact quality of life. No qualitative studies have described everyday life with the disease. Design: A qualitative interview study taking a phenomenological approach. Methods: Seven qualitative, semi-structured interviews with adult patients with ISM. The analysis was inspired by Giorgi's phenomenological method. COREQ reporting guidelines were used. Results: Three themes and five subthemes emerged from the analysis. (a) The everyday life with a rare disease, unknown to most people. Being perceived as a hypochondriac in the encounter with the health system. The diagnosis makes a difference. Expert knowledge is important. (b) Living with and handling the invisible and visible symptoms. The visible body. (c) Fearing an attack. Feeling safe and vulnerable at the same time. Conclusion: Patients with ISM are severely affected in their everyday lives, especially in terms of their relationship with family and social network. Symptoms restrict and complicate activities and participation in social contexts, and the fear of an anaphylactic attack is always present. The disease affects patients’ self-perception and sexuality. The rarity of the disease and general low awareness seems to be of great importance in the encounter with the healthcare system, both before and after diagnosis, and there is a need for expert knowledge, support and care. Relevance for clinical practice: The focus of counselling should not only be on the disease itself, but also on living life with the disease.

Background Most published studies on anaphylaxis are retrospective or register based. Data on subsequent diagnostic workup are sparse. We aimed to characterize patients seen with suspected anaphylaxis at the emergency care setting (ECS), after subsequent diagnostic workup at our Allergy Center (AC). Methods Prospective study including patients from the ECS, Odense University Hospital, during May 2013-April 2014. Possible anaphylaxis cases were daily identified based on a broad search profile including history and symptoms in patient records, diagnostic codes and pharmacological treatments. At the AC, all patients were evaluated according to international guidelines. Results Among 226 patients with suspected anaphylaxis, the diagnosis was confirmed in 124 (54.9%) after diagnostic workup; 118 of the 124 fulfilled WAO/EAACI criteria of anaphylaxis at the ECS, while six were found among 46 patients with clinical suspicion but not fulfilling the WAO/EAACI criteria at the ECS. The estimated incidence rate of anaphylaxis was 26 cases per 100 000 person-years and the one-year period prevalence was 0.04%. The most common elicitor was drugs (41.1%) followed by venom (27.4%) and food (20.6%). In 13 patients (10.5%), no elicitor could be identified. Mastocytosis was diagnosed in 7.7% of adult patients and was significantly associated with severe anaphylaxis. Atopic diseases were significantly associated only with food-induced anaphylaxis. Cofactors were present in 58.1% and were significantly associated with severe anaphylaxis. Conclusion A broad search profile in the ECS and subsequent diagnostic workup is important for identification and classification of patients with anaphylaxis. Evaluation of comorbidities and cofactors is important.

Next-generation sequencing (NGS) is becoming increasingly used for diagnostic mutation analysis in myeloid neoplasms and may also represent a feasible technique in mastocytosis. However, detection of the KIT D816V mutation requires a highly sensitive method in most patients due to the typically low mutation levels. In this study, we established an NGS-based KIT mutation analysis and analyzed the sensitivity of D816V detection using the Ion Torrent platform. Eighty-two individual NGS analyses were included in the study. All samples were also analyzed using highly sensitive KIT D816V mutation-specific qPCR. Measurements of the background level in D816V-negative samples supported a cutoff for positivity of 0.2% in three different NGS panels. Clinical samples from patients with SM that tested positive using qPCR with a D816V allele burden >0.2% also tested positive using NGS. Samples that tested positive using qPCR with an allele burden

PMCID: PMC4522520.-- et al., Although acquired mutations in KIT are commonly detected in various categories of mastocytosis, the methodologies applied to detect and quantify the mutant type and allele burden in various cells and tissues are poorly defined. We here propose a consensus on methodologies used to detect KIT mutations in patients with mastocytosis at diagnosis and during follow-up with sufficient precision and sensitivity in daily practice. In addition, we provide recommendations for sampling and storage of diagnostic material as well as a robust diagnostic algorithm. Using highly sensitive assays, KIT D816V can be detected in peripheral blood leukocytes from most patients with systemic mastocytosis (SM) that is a major step forward in screening and SM diagnosis. In addition, the KIT D816V allele burden can be followed quantitatively during the natural course or during therapy. Our recommendations should greatly facilitate diagnostic and follow-up investigations in SM in daily practice as well as in clinical trials. In addition, the new tools and algorithms proposed should lead to a more effective screen, early diagnosis of SM and help to avoid unnecessary referrals., M. Arock is supported by Fondation de France; P. Dubreuil is supported by La Ligue Nationale Contre le Cancer (équipe labellisée) and INCa; A. Garcia-Montero and A. Orfao are Supported by grants from the Instituto de Salud Carlos III, Ministry of Economy and Competitivity, Madrid, Spain (grant numbers RD12/0036/0048 and PI11/02399, FEDER) and from Fundacion Ramon Areces, Madrid, Spain (grant number CIVP16A1806); D.D. Metcalfe is supported in part by the Division of Intramural Research, NIAID; P. Valent is supported by Austrian Science Funds (FWF) Project SFB F4611 and SFB F4704-B20.

Keywords: systemic mastocytosis; KIT D816V mutation; blood; genomic DNA; messenger RNA

Key Clinical Message A change in clinical behavior of a disease should prompt search for differential diagnoses. Here, the appearance of ulcerated skin nodules in a preexisting cutaneous mastocytosis revealed a concurrent lymphomatoid papulosis – a CD30+ lymphoproliferative skin disease with histological features of a malignant lymphoma, but with a benign self‐healing course.