Pathophysiologic implications of elevated prevalence of hereditary alpha-tryptasemia in all mastocytosis subtypes.

BACKGROUND: Mastocytosis and monoclonal mast cell (MC) activation syndrome (MMAS) are heterogeneous conditions characterized by the accumulation of atypical MCs. Despite the recurrent involvement of KIT mutations, the pathophysiologic origin of mastocytosis and MMAS is unclear. Although hereditary α-tryptasemia (HαT, related to TPSAB1 gene duplication) is abnormally frequent in these diseases, it is not known whether the association is coincidental or causal. OBJECTIVE: We evaluated the prevalence of HαT in all mastocytosis subtypes and MMAS and assessed the pathophysiologic association with HαT. METHODS: Clinical data, laboratory data, KIT mutations, TPSAB1 duplication (assessed by droplet digital PCR), and HαT prevalence were retrospectively recorded for all patients with mastocytosis and MMAS registered in the French national referral center database and compared to a control cohort. To increase the power of our analysis for advanced systemic mastocytosis (advSM), we pooled our cohort with literature cases. RESULTS: We included 583 patients (27 with MMAS and 556 with mastocytosis). The prevalence of HαT in mastocytosis was 12.6%, significantly higher than in the general population (5.7%, P = .002) and lower than in MMAS (33.3%, P = .02). HαT+ patients were more likely to have anaphylactic reactions and less likely to have cutaneous lesions than HαT- patients (43.0% vs 24.4%, P = .006; 57.7% vs 75.6%, respectively, P = .006). In the pooled analysis, the prevalence of HαT was higher in advSM (11.5%) than in control cohorts (5.2%, P = .01). CONCLUSION: Here we confirm the increase incidence of anaphylaxis in HαT+ mastocytosis patients. The increased prevalence of HαT in all subtypes of systemic mastocytosis (including advSM) is suggestive of pathophysiologic involvement.

Eosinophilia in a patient with aggressive systemic mastocytosis harboring a KIT D816V mutation: A case report.

Eosinophilia may result from three main causes: secondary (reactive), primary (clonal), and/or idiopathic. The diagnosis of idiopathic eosinophilia must be made based on excluding all reactive or clonal causes. However, some causes may be very rare so as to be misdiagnosed as idiopathic. We present the case of eosinophilia caused by aggressive systemic mastocytosis, originally recognized as idiopathic. Lymphadenopathy, dysmyelopoiesis, and hepatosplenomegaly gradually appeared and deteriorated with increasing eosinophils. This case carried KIT D816V mutation. The BCR::ABL fusion gene and the mutations in JAK2 V617F, PDGFRα, and PDGFRß in bone marrow were all negative. PHF6, PPM1D, and TET2 mutations were demonstrable. The patient was prescribed to avapritinib. The condition was effectively controlled. However, the patient discontinued medication for economic reasons 5 months later. Disease progression happened and died 10 months after diagnosis. Our study indicates that gene mutation detection at diagnosis is helpful for patient accurate diagnosis and targeted therapy of such patients.

KIT Mutations and Other Genetic Defects in Mastocytosis: Implications for Disease Pathology and Targeted Therapies.

A KIT activating mutation (usually KIT D816V) is detected in neoplastic cells in greater than 90% of indolent patients with systemic mastocytosis (SM). In more advanced variants of SM, additional genetic defects can be found in several myeloid malignancy-related genes, which can be detected by applying next-generation sequencing. Currently, the techniques recommended to detect the KIT D816V mutation and quantify the mutational burden in peripheral blood, bone marrow, or other organs/tissues are allele specific-quantitative PCR or droplet digital PCR. These techniques are useful for diagnosis, prognostication, follow-up and monitoring of therapeutic efficacy of cytoreductive agents in patients with SM.

Tyrosine Kinase Inhibitors in Non-advanced Systemic Mastocytosis.

Systemic mastocytosis is associated with KIT D816V mutation in more than 90% of cases. Patients with non-advanced forms of mastocytosis (indolent systemic mastocytosis, bone marrow mastocytosis, and smoldering systenic mastocytosis) have a low rate of progession to advanced variants and generally have a comparable life expectancy to age-matched general population. Symptomatology in non-advanced mastocytosis is variable and is related to mast cell mediator release. While some patients require no or minimal symptomatic therapy with antimediator drugs, other may suffer from refractory symptoms impacting the quality of life despite being on multiple anti-mediator drugs. KIT tyrosine kinase inhibitors have been approved for advanced SM, and avapritinib has also been recently approved as the first such inhibitor for indolent systemic mastocytosis. Other TKIs are currently in clinical trials for patients with non-advanced SM who have persistent and severe symptoms despite optimized antimediator therapy. This article will review the current state of the science and available clinical data from trials of tyrosine kinase inhibitors in non-advanced systemic mastocytosis.

Case Report: Evolution of KIT D816V-Positive Systemic Mastocytosis to Myeloid Neoplasm With PDGFRA Rearrangement Responsive to Imatinib.

Systemic mastocytosis (SM) is a rare neoplasm resulting from extracutaneous infiltration of clonal mast cells (MC). The clinical features of SM are very heterogenous and treatment should be highly individualized. Up to 40% of all SM cases can be associated with another hematological neoplasm, most frequently myeloproliferative neoplasms. Here, we present a patient with indolent SM who subsequently developed a myeloid neoplasm with PDGFRA rearrangement with complete response to low-dose imatinib. The 63-year-old patient presented with eosinophilia and elevated serum tryptase level. Bone marrow analysis revealed aberrant MCs in aggregates co-expressing CD2/CD25 and KIT D816V mutation (0.01%), and the FIP1L1-PDGFRA fusion gene was not identified. In the absence of 'B' and 'C' findings, we diagnosed an indolent form of SM. For 2 years after the diagnosis, the absolute eosinophil count progressively increased. Bone marrow evaluation showed myeloid hyperplasia and the FIP1L1-PDGFRA fusion gene was detected. Thus, the diagnosis of myeloid neoplasm with PDGFRA rearrangement was established. The patient was treated with imatinib 100 mg daily and rapidly obtained a complete molecular remission. The clinical, biological, and therapeutic aspects of SM might be challenging, especially when another associated hematological disease is diagnosed. Little is known about the underlying molecular and immunological mechanisms that can promote one entity prevailing over the other one. Currently, the preferred concept of SM pathogenesis is a multimutated neoplasm in which KIT mutations represent a "phenotype modifier" toward SM. Our patient showed an evolution from KIT mutated indolent SM to a myeloid neoplasm with PDGFRA rearrangement; when the eosinophilic component expanded, a regression of the MC counterpart was observed. In conclusion, extensive clinical monitoring associated with molecular testing is essential to better define these rare diseases and consequently their prognosis and treatment.

New Insights into the Pathogenesis of Systemic Mastocytosis.

Mastocytosis is a type of myeloid neoplasm characterized by the clonal, neoplastic proliferation of morphologically and immunophenotypically abnormal mast cells that infiltrate one or more organ systems. Systemic mastocytosis (SM) is a more aggressive variant of mastocytosis with extracutaneous involvement, which might be associated with multi-organ dysfunction or failure and shortened survival. Over 80% of patients with SM carry the KIT D816V mutation. However, the KIT D816V mutation serves as a weak oncogene and appears to be a late event in the pathogenesis of mastocytosis. The management of SM is highly individualized and was largely palliative for patients without a targeted form of therapy in past decades. Targeted therapy with midostaurin, a multiple kinase inhibitor that inhibits KIT, has demonstrated efficacy in patients with advanced SM. This led to the recent approval of midostaurin by the United States Food and Drug Administration and European Medicines Agency. However, the overall survival of patients treated with midostaurin remains unsatisfactory. The identification of genetic and epigenetic alterations and understanding their interactions and the molecular mechanisms involved in mastocytosis is necessary to develop rationally targeted therapeutic strategies. This review briefly summarizes recent developments in the understanding of SM pathogenesis and potential treatment strategies for patients with SM.

Diagnosis of Primary Mast Cell Disorders in Anaphylaxis: Value of KIT D816V in Peripheral Blood.

BACKGROUND: Anaphylaxis is frequent in patients suffering from primary mast cell disorders (PMCDs). In patients without mastocytosis in the skin (MIS) and a baseline serum tryptase (bST) less than 30 ng/mL, the diagnosis of PMCD is challenging. In these patients, detection of the KIT D816V mutation in peripheral blood (PB) has been suggested as screening tool for a PMCD. OBJECTIVE: In this study, we investigated whether KIT D816V in PB can contribute to the decision to perform a bone marrow (BM) biopsy in patients with anaphylaxis without MIS and a bST less than 30 ng/mL. METHODS: We selected 74 patients with severe anaphylaxis without MIS and a bST less than 30 ng/mL. All underwent a BM biopsy. KIT D816V mutation was quantified in both PB and BM using digital droplet polymerase chain reaction (ddPCR). RESULTS: Diagnosis of a PMCD was established in 40 patients (54%). Median bST for patients with and without PMCD was, respectively, 9.5 ng/mL (range 4.2-27 ng/mL) and 4.9 ng/mL (range 2.2-20.3 ng/mL) (P <.001). KIT D816V in PB was detected in 16 out of 40 (40%) patients with PMCD. KIT D816V in BM was detected in 22 out of 40 (55%) patients with PMCD. CONCLUSIONS: In patients without MIS and a bST less than < 30 ng/mL who experience anaphylaxis, determination of KIT D816V mutation in PB is of limited help in deciding when to proceed to a BM biopsy. Therefore, KIT D816V in PB mutation analysis should be interpreted together with scoring tools to make a better assessment in identifying patients who should undergo BM biopsy.

Real-World Efficacy of Midostaurin in Aggressive Systemic Mastocytosis.

In April 2017 midostaurin was approved by the US Food and Drug Administration for the treatment of patients with aggressive systemic mastocytosis (ASM). So far, very limited real world data on its efficacy is available. Thirteen patients aged from 48 to 79 years, who received midostaurin in the early access program, were included in the study. Midostaurin was used both in first (n = 5) and subsequent lines of treatment (n = 8). The median duration of exposure was 9 months. Most patients (77%, n = 10) had a clinical improvement already as soon as the second month of therapy. Objective response was noted in 4 (50%) of eight evaluated patients. Among responders, we observed a decrease in serum tryptase level (median 74.14%) and bone marrow infiltration by mast cells (median 50%) in the sixth month of treatment. In one case, in the 10th month of treatment, allogenic stem cell transplantation was performed, achieving complete remission. Five patients died, three due to progression of disease, one in the course of secondary acute myeloid leukemia and one due to reasons not related to mastocytosis. Treatment is ongoing in seven patients. We found that midostaurin therapy is beneficial to patients with ASM.

Practical management of adverse events in patients with advanced systemic mastocytosis receiving midostaurin.

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.

New Approach to Paediatric Mastocytosis: Implications of KIT D816V Mutation Detection in Peripheral Blood.

is missing (Short communication).

A Rare Case of Systemic Mastocytosis With Associated Clonal Hematological Non-Mast Cell Lineage Disease That Transformed to Acute Leukemia With IDH2 Mutation.

An elderly 72-year-old man presented with anemia, thrombocytopenia, monocytosis, splenomegaly and lymphadenopathy. Bone marrow biopsy was consistent with mast cell neoplasm with positive CD117, CD25, CD34 myeloblasts and polymerase chain reaction (PCR) revealed mutation of D816V. He developed bilateral femoral neck fractures and biopsy confirmed that he has systemic mastocytosis (SM). He received cladribine and midostaurin with stable disease for 21 months. His SM with associated clonal hematological non-mast cell lineage disease (SM-AHNMD) transformed to acute myelogenous leukemia with isocitrate dehydrogenase 2 (IDH2) mutation. A trial of enasidenib was given for 5 months but without any response. Patient decided to go with home hospice and died afterwards.

Prospective evaluation of the diagnostic value of sensitive KIT D816V mutation analysis of blood in adults with suspected systemic mastocytosis.

BACKGROUND: Sensitive KIT D816V mutation analysis of blood has been proposed to guide bone marrow (BM) investigation in suspected systemic mastocytosis (SM). The aim of this prospective study was for the first time to compare the D816V status of the "screening blood sample" used to guide BM biopsy in suspected SM to the outcome of the subsequent BM investigation. METHODS: Fifty-eight adult patients with suspected SM were included. The outcome of sensitive KIT D816V analysis of blood was compared to the result of the BM investigation. RESULTS: Screening blood samples from 44 of 58 patients tested D816V-positive. In 43 of these, SM was subsequently diagnosed in the BM investigation. One patient with a D816V-positive screening sample was diagnosed with monoclonal MC activation syndrome. Screening blood samples from 14 patients tested D816V-negative. SM was subsequently diagnosed in five of these, whereas nine patients did not fulfill any diagnostic SM criteria (excluding tryptase criterion). Of the 48 SM patients, 90% tested D816V-positive. Thirteen SM patients presented with Hymenoptera venom-induced anaphylaxis, no skin lesions, and baseline serum tryptase ≤20 ng/mL. Of these, 92% tested D816V-positive in the screening blood sample. CONCLUSION: This prospective study demonstrates that a D816V-positive result in a screening blood sample identifies SM among patients with hymenoptera venom-induced anaphylaxis in whom the diagnosis would most probably have been missed, with potential severe implications. The observed false-negative screening results also underline that BM investigation is mandatory in all adult patients with clear signs of, or highly suspected SM, regardless of the KIT mutation status.

Highly sensitive assays are mandatory for the differential diagnosis of patients presenting with symptoms of mast cell activation: diagnostic work-up of 38 patients.

Mastocytosis is a heterogeneous disease caused by excessive mast cell (MC) proliferation. Diagnosis of systemic mastocytosis (SM) is based on the presence of major and minor criteria defined by the World Health Organization. Symptoms of MC activation can also occur in patients without SM or without allergic or inflammatory disease. These MC activation syndromes (MCAS) can be divided into primary (monoclonal) MCAS (MMAS) vs. secondary and idiopathic MCAS. In this single center study, the diagnostic work-up of 38 patients with a clinical suspicion of SM and/or with elevated basic tryptase levels is presented. Clinical symptoms, biochemical parameters, results of bone marrow investigation, flow cytometric immunophenotyping, and molecular analysis were retrospectively reviewed. Twenty-three patients were found to have a monoclonal MC disorder of which 19 were diagnosed with SM and 4 with MMAS. In 13/19 SM patients, multifocal MC infiltrates in the bone marrow were found (major criterion), while in 6 the diagnosis was based on the presence of ≥3 minor criteria. Flow cytometric analysis of bone marrow showed CD25 expression of MCs in all patients with SM and MMAS (range: 0.002-0.3% of cells). In bone marrow, the KIT D816V mutation was detected in all SM patients but in only 2 patients with MMAS (range: 0.007-9% mutated cells). Basic tryptase elevation was demonstrated in 16/19 patients with SM but also in 9/19 patients without SM. Our study reveals the heterogeneity of primary MC disorders and the importance of sensitive assays in patients suspected of having SM.

Targeted ultradeep next-generation sequencing as a method for KIT D816V mutation analysis in mastocytosis.

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 <0.2% tested negative using NGS. We thereby demonstrate that caution should be taken when using the potentially very sensitive NGS technique for KIT D816V mutation analysis in mastocytosis, as many patients with SM have D816V mutation levels below the detection limit of NGS. A dedicated and highly sensitive KIT D816V mutation analysis therefore remains important in mastocytosis diagnostics.

Clinical and Molecular Diagnostic Evaluation of Systemic Mastocytosis in the South-Eastern Hungarian Population Between 2001-2013--A Single Centre Experience.

Systemic mastocytosis (SM) is a rare chronic myeloproliferative neoplasm with only limited epidemiologic data published so far. We aimed to analyze the clinical and molecular diagnostic features, and the prognosis and cumulative incidence of SM cases in a cohort of south-eastern Hungarian patients of 13 year follow up. In the period 2001-2013, 35 consecutive SM cases were diagnosed in our regional centre. Immunophenotype, KIT D816V mutation frequency and clinical characteristics, and the prognosis impact of clinical subtypes were tested and compared with published data. Indolent SM (ISM) was diagnosed in 14 patients, SM with an associated clonal hematologic non-mast cell lineage disease (SM-AHNMD) in 15 patients and aggressive SM (ASM) in 6 patients. The KIT D816V mutation was found in 11/14 (78%) of the ISM cases, in 12/15 (80%) of the SM-AHNMD cases and in 5/6 (83%) of the ASM cases. The life expectancy of ISM patients was better, whereas the SM-AHNMD and ASM groups exhibited a reduced median survival. The cumulative incidence for 13 year of the SM was 0.27/10,000. We detected lower 13 year cumulative SM incidence than of published epidemiologic data due to in our analyses involved only those patients who had bone marrow biopsy and histopathologically confirmed SM. This clinical overview clearly showed that the clinical characteristics differ between ISM (UP, anaphylaxis and osteoporosis) and SM-AHNMD/ASM (cytopenia, eosinophilia and splenomegaly).

The presence of mast cell clonality in patients with unexplained anaphylaxis.

BACKGROUND: The mechanisms by which mast cells in patients with unexplained anaphylaxis (UEA) are triggered remain elusive. Onset of episodes is unpredictable and often recurrent. The substantial overlap between the clinical manifestations of UEA and clonal mast cell disorders (CMD) suggests an association between these rare disorders. The two forms of CMD characterized to date are systemic mastocytosis (SM) and monoclonal mast cell activation syndrome (MMAS). OBJECTIVE: To examine the hypothesis that the pathogenesis of UEA reflects the presence of aberrant subpopulations of mast cells. METHODS: Thirty (14 men, 16 women) patients (≥ 18 years) suffering from UEA and with no signs of cutaneous mastocytosis were recruited. Patients underwent an initial complete allergy work-up to confirm the diagnosis of UEA. Level of baseline serum tryptase (sBT) and total IgE were determined. In addition, a bone marrow examination was performed on all 30 patients to investigate possible underlying CMD. RESULTS: Fourteen (47%) of our cases (nine men, five women) were diagnosed with CMD: 10 with SM and four with MMAS. Four of the 10 patients with SM had mast cell aggregates in their bone marrow. All patients with SM exhibited a sBT level > 11.4 ng/mL, whereas this level was elevated in only two of those with MMAS and four with UAE but not diagnosed with CMD. Total IgE levels were lower in the group of patients with CMD (P < 0.03). CONCLUSION AND CLINICAL RELEVANCE: The pathogenic mechanism underlying UEA could be explained by the presence of immunophenotypically aberrant mast cells with clonal markers in 47% of our subjects, indicating that clonal mast cell disorders are present in a substantial subset of these patients. Thus, the presence of CMD should be considered in patients with UEA if they have an elevated level of sBT (≥ 11.4 ng/mL) and cardiovascular symptoms such as syncope.

Serum tryptase correlates with the KIT D816V mutation burden in adults with indolent systemic mastocytosis.

Systemic mastocytosis (SM) is characterized by the growth of neoplastic mast cells (MCs). Most adults with indolent SM carry the KIT D816V mutation. We recently introduced the D816V+ allele fraction as a disease marker in SM using a sensitive and quantitative KIT D816V mutation analysis that consistently allows mutation detection in peripheral blood (PB) and bone marrow (BM). The D816V+ allele fraction represents a quantitative measure which allows KIT D816V-positivity to be analyzed as a continuous variable instead of a categorical variable (negative/positive) as previously described. Serum tryptase represents an established disease marker in SM, and it remains to be tested whether tryptase and the D816V+ allele fraction are associated or represent independent disease markers. In this study, correlation analysis between serum tryptase, the D816V+ allele fraction in PB and BM, and the MC fraction was performed in 57 indolent systemic mastocytosis (ISM) patients. We detected significant correlations between the D816V+ allele fraction, the mature neoplastic MC fraction, and serum tryptase which represent three different biological measures of disease burden. Mutation analysis was performed in two or more PB samples in 39 patients, and the results demonstrated high stability with no overall tendency to increasing D816V+ allele fractions over time. Considerable variation was nevertheless observed in the correlation analyses. Serum tryptase reflects the mature MC load, whereas the D816V+ allele fraction includes cells other than mature MCs to a variable extent. We conclude that tryptase and the D816V+ allele fraction represent different, although correlated, measures of disease status in SM.