KIT D816V mutation burden does not correlate to clinical manifestations of indolent systemic mastocytosis

Avapritinib versus Placebo in Indolent Systemic Mastocytosis

BACKGROUND: Indolent systemic mastocytosis (ISM) is a clonal mast-cell disease driven by the KIT D816V mutation. We assessed the efficacy and safety of avapritinib versus placebo, both with best supportive care, in patients with ISM. METHODS: We randomized patients with moderate to severe ISM (total symptom score [TSS] of ≥28; scores range from 0 to 110, with higher numbers indicating more severe symptoms) two to one to avapritinib 25 mg once daily (n=141) or placebo (n=71). The primary end point was mean change in TSS based on the 14-day average of patient-reported severity of 11 symptoms. Secondary end points included reductions in serum tryptase and blood KIT D816V variant allele fraction (≥50%), reductions in TSS (≥50% and ≥30%), reduction in bone marrow mast cells (≥50%), and quality of life measures. RESULTS: From baseline to week 24, avapritinib-treated patients had a decrease of 15.6 points (95% CI, −18.6 to −12.6) in TSS compared to a decrease of 9.2 points (−13.1 to −5.2) in the placebo group; P<0.003. From baseline to Week 24, 76/141 patients (54%; 45% to 62%) in the avapritinib group compared to 0/71 patients in the placebo group achieved a ≥50% reduction in serum tryptase level; P<0.001. Edema and increases in alkaline phosphatase were more common with avapritinib than placebo; there were few treatment discontinuations because of adverse events. CONCLUSIONS: In this trial, avapritinib was superior to placebo in reducing uncontrolled symptoms and mast-cell burden in patients with ISM. The long-term safety and efficacy of this approach for patients with ISM remain the focus of the ongoing trial. (Funded by Blueprint Medicines Corporation; ClinicalTrials.gov number, NCT03731260.)

Refined Treatment Response Criteria for Indolent Systemic Mastocytosis Proposed by the ECNM-AIM Consortium

Indolent systemic mastocytosis (ISM) has a favorable prognosis and normal life expectancy. However, many patients suffer from mast cell (MC) mediator-related symptoms, which significantly affect quality of life (QoL). Cutaneous, gastrointestinal, and neurological complaints, musculoskeletal pain, and the presence of skin lesions, anaphylaxis, and osteoporosis are the main symptoms and signs in ISM and must be assessed in all patients before and during treatment. Validated mastocytosis-specific patient-reported outcome measures (PROMs) should be used for this purpose. Serum tryptase and KIT D816V allele burden are recommended as secondary outcome parameters, noting that they do not reflect the severity of signs, symptoms, and related QoL impairment, but indirectly express MC burden. Changes from baseline of 90%, 60%, and 30% indicate complete response >90%, major response 60% to 90%, partial response 30% to 60%, and no response <30% to treatment. To conclude, we recommend the use of PROMs as primary outcome parameters to define treatment response in patients with ISM in clinical trials and in everyday clinical practice.

Mastocytosis presenting with mast cell‐mediator release‐associated symptoms elicited by cyclo oxygenase inhibitors: prevalence, clinical, and laboratory features

Background

Nonsteroidal anti‐inflammatory drugs (NSAIDs) are frequently avoided in mastocytosis, because of a potential increased risk for drug hypersensitivity reactions (DHRs) due to inhibition of cyclo‐oxygenase (COX), subsequent depletion of prostaglandin E₂ and release of leukotrienes.

Objectives

Here, we aimed at determining the prevalence of mast cell (MC) mediator release symptoms triggered by NSAIDs in mastocytosis patients and the associated clinical and laboratory features of the disease.

Methods

Medical records from 418 adults to 223 pediatric mastocytosis patients were retrospectively reviewed. Patients were classified according to tolerance patterns to NSAIDs and other COX inhibitors (COXi) and compared for epidemiological, clinical and laboratory findings.

Results

Overall, 87% of adults and 91% of pediatric patients tolerated NSAIDs and other COXi. Among adult and pediatric patients presenting DHRs, 5% and 0% reacted to multiple NSAIDs, 4% and 0.7% were single reactors, and 3% and 8% were single reactors with known tolerance to paracetamol but unknown tolerance to other COXi, respectively. Among adults, hypersensitivity to ≥2 drugs was more frequent among females (p = 0.009), patients with prior history of anaphylaxis to triggers other than NSAIDs or other COXi and Hymenoptera venom (p = 0.009), presence of baseline flushing (p = 0.02), baseline serum tryptase ≥48 ng/ml (p = 0.005) and multilineage KIT mutation (p = 0.02). In contrast, tolerance to NSAIDs and other COXi was more frequent among males (p = 0.02), in patients with anaphylaxis caused by Hymenoptera venom (p = 0.02), among individuals who had skin lesions due to mastocytosis (p = 0.01), and in cases that had no baseline pruritus (p = 0.006). Based on these parameters, a score model was designed to stratify mastocytosis patients who have never received NSAIDs or other COXi apart from paracetamol, according to their risk of DHR.

Conclusions

Our results suggest that despite the frequency of MC mediator related symptoms elicited by NSAIDs and other COXi apart from paracetamol is increased among mastocytosis patients versus the general population, it is lower than previously estimated and associated with unique disease features. Patients that tolerated NSAIDs and other COXi following disease onset should keep using them. In turn, adults with unknown tolerance to such drugs and a positive score should be challenged with a preferential/selective COX‐2 inhibitor, while the remaining may be challenged with ibuprofen.

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

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

Assessment of Osteoporosis and Fracture Risk in Mastocytosis Within a North American Cohort

BACKGROUND

Systemic mastocytosis (SM), a clonal expansion of mast cells affecting multiple organs including the skeletal system, puts patients at risk for osteoporosis and fractures. Various aspects of skeletal disease in SM have been reported among European cohorts.

OBJECTIVE

To determine fracture prevalence and risk predictors in SM in a North American (NA) cohort and compare findings with studies of other populations.

METHODS

Fifty patients, aged 25-74 years, were grouped based on fracture type and history. Data collected included laboratory findings and radiographic markers such as serum tryptase, bone turnover markers, dual-energy x-ray absorptiometry images, and trabecular bone scores. We performed univariate and multivariate analyses of these findings.

RESULTS

Fracture history was found in 74% of patients. Significantly different median age, body mass index, dual-energy x-ray absorptiometry scores, and alkaline phosphatase levels were observed between fracture groups, consistent with French and Dutch studies. Significant findings included the difference in trabecular bone scores among fracture groups, the association between alkaline phosphatase and fracture type and occurrence, and the model for predicting fracture risk based on DXA spine T-scores, alkaline phosphatase, and age (81.3% accuracy and 77.1% sensitivity).

CONCLUSIONS

Our findings in an NA cohort are in overall agreement with those reported in European studies of skeletal disease and fracture risk for individuals with SM. We include an interactive calculator designed from a predictive model based on the NA cohort, which may be used for improved screening for fracture risk.

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.

Scoring the Risk of Having Systemic Mastocytosis in Adult Patients with Mastocytosis in the Skin

BACKGROUND

Mastocytosis in adults often presents with skin lesions. A bone marrow biopsy is necessary to confirm or exclude the presence of systemic mastocytosis (SM) in these cases. When a bone marrow biopsy is not performed, the provisional diagnosis is mastocytosis in the skin (MIS). No generally accepted scoring system has been established to estimate the risk of SM in these patients.

OBJECTIVE

To develop a risk score to predict SM in adults with MIS.

METHODS

We examined 1145 patients with MIS from the European Competence Network on Mastocytosis Registry who underwent a bone marrow biopsy. A total of 944 patients had SM and 201 patients had cutaneous mastocytosis; 63.7% were female, and 36.3% were male. Median age was 44 ± 13.3 years. The median serum tryptase level amounted to 29.3 ± 81.9 ng/mL. We established a multivariate regression model using the whole population of patients as a training and validation set (bootstrapping). A risk score was developed and validated with receiver-operating curves.

RESULTS

In the multivariate model, the tryptase level (P < .001), constitutional/cardiovascular symptoms (P = .014), and bone symptoms/osteoporosis (P < .001) were independent predictors of SM (P < .001; sensitivity, 90.7%; specificity, 69.1%). A 6-point risk score was established (risk, 10.7%-98.0%) and validated.

CONCLUSIONS

Using a large data set of the European Competence Network on Mastocytosis Registry, we created a risk score to predict the presence of SM in patients with MIS. Although the score will need further validation in independent cohorts, our score seems to discriminate safely between patients with SM and with pure cutaneous mastocytosis.

Fracture Risk Reduction by Bisphosphonates in Mastocytosis?

BACKGROUND

Fragility fractures (FFxs) and osteoporosis are frequent manifestations of indolent systemic mastocytosis (ISM). So far, the effect of antiosteoporotic therapy on FFxs has scarcely been investigated.

OBJECTIVE

This study evaluates the long-term effect of bisphosphonate treatment on FFxs, bone mineral density (BMD), and bone resorption in patients with ISM in daily clinical practice.

METHODS

Patients with ISM who received bisphosphonates because of osteoporosis and/or FFxs were retrospectively analyzed (n = 58). Fractures were recorded by vertebral fracture assessment, X-rays of the thoracolumbar spine, medical records, and a questionnaire. Five-year analysis (n = 30) was made by comparing observed 5-year FFx risk with MastFx-predicted FFx risk for patients with ISM not treated with antiosteoporotic drugs and analyzing 5-year change in BMD and serum collagen C telopeptide (sCTx) Z-scores.

RESULTS

During the median follow-up of 7.3 years, 14 of 58 patients suffered 40 FFxs. Five- and 10-year FFx-free survival were 81.9% (standard error [SE], 5.5%) and 67.0% (SE, 7.7%), respectively. FFx risk was significantly higher in patients with previous vertebral FFxs (P = .004), lower femoral BMD at baseline (P = .042), and history of anaphylaxis (P = .028). No 5-year FFx risk reduction could be proven, possibly due to the small sample size. The lumbar BMD Z-score significantly increased from median (interquartile range [IQR]) -2.20 (-2.80 to -1.50) to -1.50 (-2.30 to -0.60) (P < .001, n = 27). The sCTx Z-score decreased from median 0.71 (IQR, -0.59 to 2.39) to -0.95 (-1.30 to -0.16) (P = .008, n = 15).

CONCLUSION

Bisphosphonates significantly increase BMD and decrease sCTx in patients with ISM. However, FFxs still frequently occur. Especially patients with previous FFxs remain at high risk of new FFxs.

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

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

Molecular quantification of tissue disease burden is a new biomarker and independent predictor of survival in mastocytosis

A high allele burden of the KIT D816V mutation in peripheral blood or bone marrow aspirates indicates multi-lineage hematopoietic involvement and has been associated with an aggressive clinical course of systemic mastocytosis. Since mast cells are substantially underrepresented in these liquid specimens, their mutation burden likely underestimates the tumor burden of the disease. We used a novel previously validated digital polymerase chain reaction (PCR) method for KIT D816V analysis to systematically analyze the mutation burden in formalin-fixed, paraffin-embedded bone marrow tissue sections of 116 mastocytosis patients (91 with indolent and 25 with advanced systemic mastocytosis), and to evaluate for the first time the clinical value of the tissue mutation burden as a novel biomarker. The KIT D816V mutation burden in the tissue was significantly higher and correlated better with bone marrow mast cell infiltration (r=0.68 vs. 0.48) and serum tryptase levels (r=0.68 vs. 0.58) compared to that in liquid specimens. Furthermore, the KIT D816V tissue mutation burden was: (i) significantly higher in advanced than in indolent systemic mastocytosis (P=0.001); (ii) predicted survival of patients in multivariate analyses independently; and (iii) was significantly reduced after response to cytoreductive therapy. Finally, digital PCR was more sensitive in detecting KIT D816V in bone marrow sections of indolent systemic mastocytosis patients than melting curve analysis after peptide nucleic acid-mediated PCR clamping (97% vs. 89%; P<0.05). In summary, digital PCR-based measurement of KIT D816V mutation burden in the tissue represents a novel biomarker with independent prognostic significance that can also be employed for monitoring disease progression and treatment response in systemic mastocytosis.

An evaluation of masitinib for treating systemic mastocytosis

Introduction: Systemic Mastocytosis (SM) is a complex family of rare diseases, against which pharmacological therapies are still very few. It is a c-kit driven disease, whose disregulation leads to uncontrolled activation and proliferation of mast cells (MCs) with consequent release of effector molecules which are responsible for its clinical manifestations. Areas covered: Masitinib is a relatively new potential drug against SM and its chemical structure strictly derives from imatinib, the first tyrosine kinase inhibitor which entered the pharmaceutical market about 15 years ago. In this review, the authors present masitinib in all its properties, from chemistry to pharmacology and toxicity to its potential clinical application in SM, focusing the discussion on the few clinical trials in which it has been involved, with a particular attention on the still open challenge to determine how to measure the response to therapy. Expert opinion: In spite of their similarity in chemistry and biological activity against submolecular targets, masitinib is much more selective towards c-kit receptors than other tyrosine kinases, such as Bcl-Abl. Furthermore, its ability to inhibit degranulation, cytokine production and MCs migration from bone marrow gives it a great chance to become an important therapeutic option for selected SM patients.

Mastocytosis: One Word for Different Diseases

Mastocytosis is a neoplastic disease originating from tissue infiltration by transformed mast cells. The diagnosis requires a high grade of suspicion due to the large variety of presenting symptoms. The World Health Organization classification recognizes localized (cutaneous) and systemic forms of the disease, with these forms showing different degrees of aggressiveness. Mastocytosis is often a multiorgan disease, and its correct management requires a multidisciplinary team of experienced consultants to provide overall patient care. Bone marrow evaluation by molecular analyses, skeleton X-ray and abdominal scan together with allergologic and dermatologic evaluation constitute the essential diagnostic work-up for adult patients with mastocytosis. As clinical situations vary, treatment options range from the use of drugs to treat the symptoms, such as anti-H1 receptors and steroids, to UV irradiation, which is overwhelmingly used in patients with cutaneous mastocytosis (CM) or indolent systemic mastocytosis, to cytoreductive treatment to control life-threatening symptoms or organ damage in the more aggressive forms of the disease. Prognosis also widely differs among patients diagnosed with mastocytosis, with the spectrum ranging from an almost normal life expectancy for those with CM and to less than 1-year median overall survival for those with mast cell leukemia.

Characterization of CD34+ hematopoietic cells in systemic mastocytosis: Potential role in disease dissemination

BACKGROUND

Recent studies show that most systemic mastocytosis (SM) patients, including indolent SM (ISM) with (ISMs+) and without skin lesions (ISMs-), carry the KIT D816V mutation in PB leukocytes. We investigated the potential association between the degree of involvement of BM hematopoiesis by the KIT D816V mutation and the distribution of different maturation-associated compartments of bone marrow (BM) and peripheral blood (PB) CD34⁺ hematopoietic precursors (HPC) in ISM and identified the specific PB cell compartments that carry this mutation.

METHODS

The distribution of different maturation-associated subsets of BM and PB CD34⁺ HPC from 64 newly diagnosed (KIT-mutated) ISM patients and 14 healthy controls was analyzed by flow cytometry. In 18 patients, distinct FACS-purified PB cell compartments were also investigated for the KIT mutation.

RESULTS

ISM patients showed higher percentages of both BM and PB MC-committed CD34⁺ HPC vs controls, particularly among ISM cases with MC-restricted KIT mutation (ISM_MC ); this was associated with progressive blockade of maturation of CD34⁺ HPC to the neutrophil lineage from ISM_MC to multilineage KIT-mutated cases (ISM_ML ). Regarding the frequency of KIT-mutated cases and cell populations in PB, variable patterns were observed, the percentage of KIT-mutated PB CD34⁺ HPC, eosinophils, neutrophils, monocytes and T cells increasing from ISMs-_MC and ISMs+_MC to ISM_ML patients.

CONCLUSION

The presence of the KIT D816V mutation in PB of ISM patients is associated with (early) involvement of circulating CD34⁺ HPC and multiple myeloid cell subpopulations, KIT-mutated PB CD34⁺ HPC potentially contributing to early dissemination of the disease.

Pediatric Expression of Mast Cell Activation Disorders

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.

Omalizumab prevents anaphylaxis and improves symptoms in systemic mastocytosis: Efficacy and safety observations

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.

Digital PCR: A Sensitive and Precise Method for KIT D816V Quantification in Mastocytosis

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.

Patterns of anaphylaxis after diagnostic workup: A follow-up study of 226 patients with suspected anaphylaxis

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.

Precision medicine in allergic disease-food allergy, drug allergy, and anaphylaxis-PRACTALL document of the European Academy of Allergy and Clinical Immunology and the American Academy of Allergy, Asthma and Immunology

This consensus document summarizes the current knowledge on the potential for precision medicine in food allergy, drug allergy, and anaphylaxis under the auspices of the PRACTALL collaboration platform. PRACTALL is a joint effort of the European Academy of Allergy and Clinical Immunology and the American Academy of Allergy, Asthma and Immunology, which aims to synchronize the European and American approaches to allergy care. Precision medicine is an emerging approach for disease treatment based on disease endotypes, which are phenotypic subclasses associated with specific mechanisms underlying the disease. Although significant progress has been made in defining endotypes for asthma, definitions of endotypes for food and drug allergy or for anaphylaxis lag behind. Progress has been made in discovery of biomarkers to guide a precision medicine approach to treatment of food and drug allergy, but further validation and quantification of these biomarkers are needed to allow their translation into practice in the clinical management of allergic disease.

Masitinib for treatment of severely symptomatic indolent systemic mastocytosis: a randomised, placebo-controlled, phase 3 study

BACKGROUND

Indolent systemic mastocytosis, including the subvariant of smouldering systemic mastocytosis, is a lifelong condition associated with reduced quality of life. Masitinib inhibits KIT and LYN kinases that are involved in indolent systemic mastocytosis pathogenesis. We aimed to assess safety and efficacy of masitinib versus placebo in severely symptomatic patients who were unresponsive to optimal symptomatic treatments.

METHODS

In this randomised, double-blind, placebo-controlled, phase 3 study, we enrolled adults (aged 18-75 years) with indolent or smouldering systemic mastocytosis, according to WHO classification or documented mastocytosis based on histological criteria, at 50 centres in 15 countries. We excluded patients with cutaneous or non-severe systemic mastocytosis after a protocol amendment. Patients were centrally randomised (1:1) to receive either oral masitinib (6 mg/kg per day over 24 weeks with possible extension) or matched placebo with minimisation according to severe symptoms. The primary endpoint was cumulative response (≥75% improvement from baseline within weeks 8-24) in at least one severe baseline symptom from the following: pruritus score of 9 or more, eight or more flushes per week, Hamilton Rating Scale for Depression of 19 or more, or Fatigue Impact Scale of 75 or more. We assessed treatment effect using repeated measures methodology for rare diseases via the generalised estimating equation model in a modified intention-to-treat population, including all participants assigned to treatment minus those who withdrew due to a non-treatment-related cause. We assessed safety in all patients who received at least one dose of study drug. This trial is registered with ClinicalTrials.gov, number NCT00814073.

FINDINGS

Between Feb 19, 2009, and July 15, 2015, 135 patients were randomly assigned to masitinib (n=71) or placebo (n=64). By 24 weeks, masitinib was associated with a cumulative response of 18·7% in the primary endpoint (122·6 responses of 656·5 possible responses [weighted generalised estimating equation]) compared with 7·4% for placebo (48·9 of 656·5; difference 11·3%; odds ratio 3·6; 95% CI 1·2-10·8; p=0·0076). Frequent severe adverse events (>4% difference from placebo) were diarrhoea (eight [11%] of 70 in the masitinib group vs one [2%] of 63 in the placebo group), rash (four [6%] vs none), and asthenia (four [6%] vs one [2%]). The most frequent serious adverse events were diarrhoea (three patients [4%] vs one [2%]) and urticaria (two [3%] vs none), and no life-threatening toxicities occurred. One patient in the placebo group died (unrelated to study treatment).

INTERPRETATION

These study findings indicate that masitinib is an effective and well tolerated agent for the treatment of severely symptomatic indolent or smouldering systemic mastocytosis.

FUNDING

AB Science (Paris, France).

Risk of solid cancer, cardiovascular disease, anaphylaxis, osteoporosis and fractures in patients with systemic mastocytosis: A nationwide population-based study

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.

Mastocytosis and Anaphylaxis

This article updates current knowledge on epidemiology, risk factors, triggers, and management of anaphylaxis in patients with mastocytosis. Hyperactive mast cells and higher number of effector mast cells are speculated to facilitate anaphylaxis in this condition. In children, increased risk is limited to those with extensive skin involvement and high tryptase. In adults, manifestations of anaphylaxis are severe with high frequency of cardiovascular symptoms. Hymenoptera stings are the most common triggers for these reactions; however, idiopathic anaphylaxis and reactions to food or drugs occur. Patients with mastocytosis should be informed about risk of anaphylaxis and prescribing emergency self-medication and installing emergency preparedness before general anesthesia is considered.

Endocrine manifestations of systemic mastocytosis in bone

Systemic Mastocytosis (SM) is characterized by accumulation of clonal, neoplastic proliferations of abnormal mast cells (MC) in one or more organ system other than skin. Presence of these multifocal clusters of abnormal mast cells is an essential feature of SM. Frequently associated with D816V (KIT) mutation, the presence of this mutation and elevated serum tryptase are minor criteria for diagnosis. SM manifestations depend on the degree of mast cell proliferation, activation and degranulation. SM has a variable prognosis and presentation, from indolent to "smoldering" to life-threatening disease. Bone manifestations of SM include: osteopenia with or without lytic lesions, osteoporosis with or without atraumatic fracture, osteosclerosis with increased bone density, and isolated lytic lesions. Male sex, older age, higher bone resorption markers, lower DKK1 level, lower BMD, absence of urticaria pigmentosa, and alcohol intake are all associated with increased risk of fracture. Treatment of SM is generally palliative. Most therapy is symptom-directed; and, infrequently, chemotherapy for refractory symptoms is indicated. Anti-histamines may alleviate direct bone effects of histamine. Bisphosphonates, including alendronate, clodronate, pamidronate and zoledronic acid are recommended as a first line treatment of SM and osteoporosis. Interferon α may act synergistically with bisphosphonates. As elevation of RANKL and OPG is reported in SM, denosumab could be an effective therapy for bone manifestations of SM.

Pharmacological treatment options for mast cell activation disease

Mast cell activation disease (MCAD) is a term referring to a heterogeneous group of disorders characterized by aberrant release of variable subsets of mast cell (MC) mediators together with accumulation of either morphologically altered and immunohistochemically identifiable mutated MCs due to MC proliferation (systemic mastocytosis [SM] and MC leukemia [MCL]) or morphologically ordinary MCs due to decreased apoptosis (MC activation syndrome [MCAS] and well-differentiated SM). Clinical signs and symptoms in MCAD vary depending on disease subtype and result from excessive mediator release by MCs and, in aggressive forms, from organ failure related to MC infiltration. In most cases, treatment of MCAD is directed primarily at controlling the symptoms associated with MC mediator release. In advanced forms, such as aggressive SM and MCL, agents targeting MC proliferation such as kinase inhibitors may be provided. Targeted therapies aimed at blocking mutant protein variants and/or downstream signaling pathways are currently being developed. Other targets, such as specific surface antigens expressed on neoplastic MCs, might be considered for the development of future therapies. Since clinicians are often underprepared to evaluate, diagnose, and effectively treat this clinically heterogeneous disease, we seek to familiarize clinicians with MCAD and review current and future treatment approaches.

Detection of the KIT D816V mutation in peripheral blood of systemic mastocytosis: diagnostic implications

Recent studies have found the KIT D816V mutation in peripheral blood of virtually all adult systemic mastocytosis patients once highly sensitive PCR techniques were used; thus, detection of the KIT D816V mutation in peripheral blood has been proposed to be included in the diagnostic work-up of systemic mastocytosis algorithms. However, the precise frequency of the mutation, the biological significance of peripheral blood-mutated cells and their potential association with involvement of bone marrow hematopoietic cells other than mast cells still remain to be investigated. Here, we determined the frequency of peripheral blood involvement by the KIT D816V mutation, as assessed by two highly sensitive PCR methods, and investigated its relationship with multilineage involvement of bone marrow hematopoiesis. Overall, our results confirmed the presence of the KIT D816V mutation in peripheral blood of most systemic mastocytosis cases (161/190; 85%)--with an increasing frequency from indolent systemic mastocytosis without skin lesions (29/44; 66%) to indolent systemic mastocytosis with skin involvement (124/135; 92%), and more aggressive disease subtypes (11/11; 100%)--as assessed by the allele-specific oligonucleotide-qPCR method, which was more sensitive (P<.0001) than the peptide nucleic acid-mediated PCR approach (84/190; 44%). Although the presence of the KIT mutation in peripheral blood, as assessed by the allele-specific oligonucleotide-qPCR technique, did not accurately predict for multilineage bone marrow involvement of hematopoiesis, the allele-specific oligonucleotide-qPCR allele burden and the peptide nucleic acid-mediated-PCR approach did. These results suggest that both methods provide clinically useful and complementary information through the identification and/or quantification of the KIT D816V mutation in peripheral blood of patients suspected of systemic mastocytosis.

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.

The KIT D816V allele burden predicts survival in patients with mastocytosis and correlates with the WHO type of the disease

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.

Sensitive KIT D816V mutation analysis of blood as a diagnostic test in mastocytosis

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.

Treatment strategies in mastocytosis

Treatment recommendations for mastocytosis are based mostly on expert opinion rather than evidence obtained from controlled clinical trials. In this article, treatment options for mastocytosis are presented, with a focus on the control of mediator-related symptoms in patients with indolent disease.

A concise, practical guide to diagnostic assessment for mast cell activation disease

As recognition of mast cell (MC) involvement in a range of chronic inflammatory disorders has increased, diagnosticians’ suspicions of MC activation disease (MCAD) in their chronically mysteriously inflamed patients have similarly increased. It is now understood that the various forms of systemic mastocytosis - diseases of inappropriate activation and proliferation of MCs seemingly driven by a small set of rare, usually constitutively activating mutations in assorted MC regulatory elements - comprise merely the tip of the MCAD iceberg, whereas the far larger and far more clinically heterogeneous (and thus more difficult to recognize) bulk of the iceberg consists of assorted forms of MC activation syndrome (MCAS) which manifest little to no abnormal MC proliferation and may originate from a far more heterogeneous set of MC mutations. It is reasonable to suspect MCAD when symptoms and signs of MC activation are present and no other diagnosis better accounting for the full range of findings is present. Initial laboratory assessment should include not only routine blood counts and serum chemistries but also a serum total tryptase level, which helps direct further evaluation for mastocytosis vs MCAS. Appropriate tissue examinations are needed to diagnose mastocytosis, while elevated levels of relatively specific mast cell mediators are sought to support diagnosis of MCAS. Whether assessing for mastocytosis or MCAS, testing is fraught with potential pitfalls which can easily yield false negatives leading to erroneous rejection of diagnostic consideration of MCAD in spite of a clinical history highly consistent with MCAD. Efforts at accurate diagnosis of MCAD are worthwhile, as many patients then respond well to appropriately directed therapeutic efforts.

A concise, practical guide to diagnostic assessment for mast cell activation disease

As recognition of mast cell (MC) involvement in a range of chronic inflammatory disorders has increased, diagnosticians’ suspicions of MC activation disease (MCAD) in their chronically mysteriously inflamed patients have similarly increased. It is now understood that the various forms of systemic mastocytosis - diseases of inappropriate activation and proliferation of MCs seemingly driven by a small set of rare, usually constitutively activating mutations in assorted MC regulatory elements - comprise merely the tip of the MCAD iceberg, whereas the far larger and far more clinically heterogeneous (and thus more difficult to recognize) bulk of the iceberg consists of assorted forms of MC activation syndrome (MCAS) which manifest little to no abnormal MC proliferation and may originate from a far more heterogeneous set of MC mutations. It is reasonable to suspect MCAD when symptoms and signs of MC activation are present and no other diagnosis better accounting for the full range of findings is present. Initial laboratory assessment should include not only routine blood counts and serum chemistries but also a serum total tryptase level, which helps direct further evaluation for mastocytosis vs MCAS. Appropriate tissue examinations are needed to diagnose mastocytosis, while elevated levels of relatively specific mast cell mediators are sought to support diagnosis of MCAS. Whether assessing for mastocytosis or MCAS, testing is fraught with potential pitfalls which can easily yield false negatives leading to erroneous rejection of diagnostic consideration of MCAD in spite of a clinical history highly consistent with MCAD. Efforts at accurate diagnosis of MCAD are worthwhile, as many patients then respond well to appropriately directed therapeutic efforts.