Clinical features and survival of patients with indolent systemic mastocytosis defined by the updated WHO classification

[Mastocytosis-a frequently unrecognized disease]

Mastocytosis is a rare disease characterized by clonal expansion and accumulation of mast cells (MC) in various organs. Mastocytosis results from an activating mutation of the KIT surface receptor leading to an increased proliferation of MC. There are significant differences between children and adult patients with mastocytosis. Children mainly present the cutaneous form, whereas adults more often exhibit the systemic form of mastocytosis. Patients with mastocytosis may be asymptomatic or affected by a variety of symptoms. Treatment is primarily supportive and aims at symptom control. New approved targeted therapies such as midostaurin and avapritinib changed the treatment paradigm in advanced forms of the disease, and next-generation inhibitors currently in clinical trials are expected in the near future.

Systemic mastocytosis: 2023 update on diagnosis and management in adults

INTRODUCTION

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

AREAS COVERED

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

EXPERT OPINION

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

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.

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

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

Effect of Gender and Special Considerations for Women in Mastocytosis and Anaphylaxis

This article reviews the effects of gender on anaphylaxis in general and focuses on mastocytosis-specific issues. Incidence of anaphylaxis is increased in female compared with male patients during the pubertal years through the fifth decade of life, in which these disparities decrease. Estrogen is thought to increase the severity of anaphylaxis through increased endothelial nitric oxide synthase release. Despite this, all-cause fatal anaphylaxis does not appear to show a gender predilection. Systemic mastocytosis incidence is higher in women; however, mortality is increased in men owing to increased molecular and cytogenetic abnormalities.

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

OVERVIEW

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

DIAGNOSIS

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

RISK STRATIFICATION

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

MANAGEMENT

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

European Competence Network on Mastocytosis (ECNM): 20-Year Jubilee, Updates, and Future Perspectives

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.

Recent advances in diagnosis and therapy in systemic mastocytosis

Mastocytosis is a heterogeneous neoplasm characterized by accumulation of neoplastic mast cells in various organs. There are three main types: cutaneous mastocytosis (CM), systemic mastocytosis (SM), and mast cell sarcoma. CM mainly affects children and is confined to the skin, whereas SM affects adults and is characterized by extracutaneous involvement, with or without cutaneous involvement. Most cases of SM have an indolent clinical course; however, some types of SM have aggressive behavior and a poor prognosis. Recent advances in the understanding of the molecular changes in SM have changed the diagnosis and treatment of aggressive and advanced SM subtypes. The International Consensus Classification and World Health Organization refined the diagnostic criteria and classification of SM as a result of accumulation of clinical experience and advances in molecular diagnostics. Somatic mutations in the KIT gene, most frequently KIT D816V, are detected in 90% of patients with SM. Expression of CD30 and any KIT mutation were introduced as minor diagnostic criteria after the introduction of highly sensitive screening methods. SM has a wide spectrum of clinical features, and only a few drugs are effective at treating advanced SM. Currently, the mainstay of SM treatment is limited to the management of chronic symptoms related to release of mast cell mediators. Small-molecule kinase inhibitors targeting the KIT-downstream and KIT-independent pathways were recently approved for treating advanced SM. I describe recent advances in diagnosis of SM, and review the currently available and emerging therapeutic options for SM management.

Secretory and Membrane-Associated Biomarkers of Mast Cell Activation and Proliferation

Mast cells (MCs) are immune cells distributed in many organs and tissues and involved in the pathogenesis of allergic and inflammatory diseases as a major source of pro-inflammatory and vasoactive mediators. MC-related disorders are heterogeneous conditions characterized by the proliferation of MC within tissues and/or MC hyper-reactivity that leads to the uncontrolled release of mediators. MC disorders include mastocytosis, a clonal disease characterized by tissue MC proliferation, and MC activation syndromes that can be primary (clonal), secondary (related to allergic disorders), or idiopathic. Diagnosis of MC disorders is difficult because symptoms are transient, unpredictable, and unspecific, and because these conditions mimic many other diseases. Validation of markers of MC activation in vivo will be useful to allow faster diagnosis and better management of MC disorders. Tryptase, being the most specific MC product, is a widely used biomarker of proliferation and activation. Other mediators, such as histamine, cysteinyl leukotrienes, and prostaglandin D2, are unstable molecules and have limitations in their assays. Surface MC markers, detected by flow cytometry, are useful for the identification of neoplastic MC in mastocytosis but, so far, none of them has been validated as a biomarker of MC activation. Further studies are needed to identify useful biomarkers of MC activation in vivo.

Case report: The devil was hidden in the mastocytes - an unusually fulminant case of indolent systemic mastocytosis in a 45-year-old patient, missed for almost 20 years

Indolent systemic mastocytosis (ISM) represents the most common form of SM, typically following a slow clinical course. While anaphylactic reactions may come up in the life course of an ISM patient, these are often moderate and do not pose a threat to patient's health. Here, we present an undiagnosed case of ISM with recurrent severe anaphylactic episodes following consumption of food and emotional stress. One of these episodes led to anaphylactic shock, necessitating temporary mechanical ventilation and intensive care unit (ICU) support. Besides hypotension, a diffuse, itchy, red rash was the only notable clinical finding. Upon recovery, we found abnormally high baseline serum tryptase level as well as 10% bone marrow (BM) infiltration by multifocal, dense clusters of CD117+/mast cell tryptase+/CD25+ mast cells (MCs), consolidating the diagnosis of ISM. Prophylactic treatment with a histamine receptor antagonist was initiated, resulting in milder episodes thereafter. Diagnosis of ISM requires a high level of suspicion; its prompt recognition and treatment are important in preventing potentially life-threatening anaphylactic episodes.

Disease correlates and clinical relevance of hereditary α-tryptasemia in patients with systemic mastocytosis

BACKGROUND

Systemic mastocytosis (SM) encompasses a heterogeneous group of clonal disorders characterized by abnormal expansion of mast cells (MCs). Beyond KIT and other genes recurrently mutated in myeloid neoplasms, several genetic variants have been described as predisposing to the development of the disease and influencing its clinical phenotype. Increased copy number variants of the TPSAB1 gene were identified as a cause of nonclonal elevated tryptasemia and defined as hereditary α-tryptasemia (HαT). Moreover, HαT is enriched in patients with SM, where it can affect the incidence of mediator-related symptoms.

OBJECTIVE

In a multicenter data set of 444 patients with MC disorders, we aimed to investigate the clinical correlates of germline TPSAB1 copy number gains.

METHODS

Droplet digital PCR was performed in all cases to ascertain the presence of HαT. Clinical history along with blood values and bone marrow examination were analyzed.

RESULTS

We confirmed a higher incidence of HαT⁺ cases (n = 59, 13.3%) in patients diagnosed with mastocytosis with respect to the general population (approximately 5%). HαT⁺ patients were characterized by a lower MC-associated disease burden and higher levels of tryptase. Several disease variables were coherent with this pattern, from bone marrow MC infiltration to MC-related histopathologic traits, which also accounted for a significantly higher incidence of clonal MC activation syndrome in HαT⁺ (10.2%) compared to HαT^- (3.4%, P = .029) patients. We also confirmed that HαT⁺ carriers had a significantly higher frequency of anaphylaxis, without relevant differences for other clinical manifestations.

CONCLUSION

These findings on a large patient series support and extend previous data, and suggest that knowledge of HαT status may be useful for personalized management of patients with SM.

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

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

Comprehensive mastocytosis data analysis from a single center

Mastocytosis is a very rare disorder and is divided into three prognostically distinct variants by World Health Organization: Cutaneous mastocytosis (CM), systemic mastocytosis (SM), and mast cell sarcoma or localized mast cell (MC) tumors. The wide range of complaints may cause patients to consult various clinics, with resulting mis- or underdiagnosis. Therefore, cooperation between different subspecialties is of paramount importance. In this article, we have compiled 104 adult mastocytosis cases diagnosed and followed in our Hematology and other clinics. 86 (82.7%) of 104 patients had systemic mastocytosis. Osteoporosis, disease-related complications, and secondary malignancies are important topics in this group. We know that indolent form has great survival. But smoldering or aggressive mastocytosis has a poor prognosis. CM and indolent SM have a significantly better prognosis compared to aggressive SM (p < 0.001). We found that the presence of more than 25% of mast cells in the bone marrow, the presence of concomitant marrow dysplasia, and the presence of disease-related complications affect survival (p < 0.001). In addition to the WHO classification, the IPSM scoring system is indicative of the prognosis in this rare disease.

The international consensus classification of mastocytosis and related entities

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

Antineoplastic efficacy profiles of avapritinib and nintedanib in KIT D816V+ systemic mastocytosis: a preclinical study

Systemic mastocytosis (SM) is a hematopoietic neoplasm with a complex pathology and a variable clinical course. Clinical symptoms result from organ infiltration by mast cells (MC) and the effects of pro-inflammatory mediators released during MC activation. In SM, growth and survival of MC are triggered by various oncogenic mutant-forms of the tyrosine kinase KIT. The most prevalent variant, D816V, confers resistance against various KIT-targeting drugs, including imatinib. We examined the effects of two novel promising KIT D816V-targeting drugs, avapritinib and nintedanib, on growth, survival, and activation of neoplastic MC and compared their activity profiles with that of midostaurin. Avapritinib was found to suppress growth of HMC-1.1 cells (KIT V560G) and HMC-1.2 cells (KIT V560G + KIT D816V) with comparable IC₅₀ values (0.1-0.25 µM). In addition, avapritinib was found to inhibit the proliferation of ROSA^{KIT WT} cells, (IC₅₀: 0.1-0.25 µM), ROSA^{KIT D816V} cells (IC₅₀: 1-5 µM), and ROSA^{KIT K509I} cells (IC₅₀: 0.1-0.25 µM). Nintedanib exerted even stronger growth-inhibitory effects in these cells (IC₅₀ in HMC-1.1: 0.001-0.01 µM; HMC-1.2: 0.25-0.5 µM; ROSA^{KIT WT}: 0.01-0.1 µM; ROSA^{KIT D816V}: 0.5-1 µM; ROSA^{KIT K509I}: 0.01-0.1 µM). Avapritinib and nintedanib also suppressed the growth of primary neoplastic cells in most patients with SM examined (avapritinib IC₅₀: 0.5-5 µM; nintedanib IC₅₀: 0.1-5 µM). Growth-inhibitory effects of avapritinib and nintedanib were accompanied by signs of apoptosis and decreased surface expression of the transferrin receptor CD71 in neoplastic MC. Finally, we were able to show that avapritinib counteracts IgE-dependent histamine secretion in basophils and MC in patients with SM. These effects of avapritinib may explain the rapid clinical improvement seen during treatment with this KIT inhibitor in patients with SM. In conclusion, avapritinib and nintedanib are new potent inhibitors of growth and survival of neoplastic MC expressing various KIT mutant forms, including D816V, V560G, and K509I, which favors the clinical development and application of these new drugs in advanced SM. Avapritinib is of particular interest as it also blocks mediator secretion in neoplastic MC.

Delayed Diagnosis of Indolent Systemic Mastocytosis as the Cause of Unexplained Skin Rash: A Case Report

Mastocytosis is a heterogeneous group of disorders in which mast cells exhibit clonal proliferation that infiltrates one or more organs. In cutaneous mastocytosis, the mast cells infiltrate the skin only, whereas systemic mastocytosis is diagnosed when at least one extra-cutaneous site is involved, with or without the skin being affected. Given the rarity of mastocytosis and the fact that skin rash can be a manifestation of different conditions and many clinicians are not familiar with this disorder, an accurate diagnosis may be delayed. We report a delayed diagnosis of indolent systemic mastocytosis in a 40-year-old gentleman who had been complaining of an unexplained skin rash for 6 years.

Perceptions of patient disease burden and management approaches in systemic mastocytosis: Results of the TouchStone Healthcare Provider Survey

BACKGROUND

Systemic mastocytosis (SM) is a rare clonal neoplasm driven by the KIT D816V mutation and has a broad range of debilitating symptoms. In this study, the authors evaluated SM disease perceptions and management strategies among US health care providers (HCPs).

METHODS

Hematologist/oncologist (H/O) HCPs and allergist/immunologist (A/I) HCPs who were treating four or more patients with SM completed an online, 51-item TouchStone HCP Survey, which queried provider characteristics, perceptions of disease burden, and current management. Descriptive analyses by specialty and SM subtype were performed.

RESULTS

Of 304 HCPs contacted, 111 (37%) met eligibility criteria, including 51% A/I specialists and 49% H/O specialists. On average, the HCPs had 14 years of practice experience and cared for 20 patients with SM. A/I HCPs saw more patients with nonadvanced SM (78%) compared with H/O HCPs, who saw similar proportions of patients with nonadvanced SM (54%) and advanced SM (46%). HCPs reported testing 75% of patients for the KIT D816V mutation and found an estimated prevalence of 47%. On average, HCPs estimated 8 months between symptom onset and SM diagnosis. HCPs reported that 62% of patients with indolent SM felt depressed or discouraged because of symptoms. In terms of treatment goals for SM, both types of specialists prioritized symptom improvement for nonadvanced SM and improved survival for advanced SM while also prioritizing improving patient quality of life.

CONCLUSIONS

Both A/I and H/O specialists highlighted unmet needs for patients with SM. The HCPs surveyed reported a lower rate of KIT D816V mutations and a perceived shorter time between symptom onset and SM diagnosis compared with published estimates.

LAY SUMMARY

Specialists treating systemic mastocytosis (SM) completed a 51-item questionnaire about their clinical practices and perceptions of disease impact. The study included 111 hematology, oncology, allergy, and immunology physicians. Physicians reported that most patients had nonadvanced disease, yet SM symptoms significantly disrupted their patients' lives. Physicians estimated that SM is diagnosed within months of symptom onset, in contrast with published reports of years' long delays reported by patients with SM. This study identified unmet needs that can inform educational and patient management priorities in this rare disease.

How persons with systemic mastocytosis describe the time between symptom onset and receiving diagnosis

AIM

The aim of the study was to explore how persons with systemic mastocytosis (SM) described the time between the onset of symptoms and signs and getting the diagnosis.

BACKGROUND

SM is a rare disease caused by the accumulation of clonal mast cells with abnormal function. The symptoms and signs of the disease are varied, often diffuse and affect individuals differently. Due to this complexity, a multi-disciplinary diagnostic approach is required, in which general practitioners play an important part in identifying and referring patients relevant for such investigations.

METHODS

Sixteen persons with SM were interviewed about their experiences of the time before the diagnosis was received. Systematic text condensation was used in the analysis process.

FINDINGS

The time between symptom and signs onset and diagnosis was perceived as difficult. SM often had a complex and unpredictable effect on a person's daily life, long before diagnosis. In the analysis, three themes were found. Having symptoms and signs with an unknown cause included the participants' descriptions of numerous symptoms and signs, often years before diagnosis. These could be severe and result in worries for both participants and their next-of-kin. Dealing with the symptoms and signs encompassed the different ways in which the participants coped with the symptoms and signs, and sought relief. Being a patient without a diagnosis underlined the lack of information and knowledge within healthcare, often resulting in a delayed or incorrect diagnosis. The study highlighted the importance of a person-centred approach and the need to increase knowledge of the disease within primary care, to shorten this stressful and vulnerable time.

Clinical Outcomes of Adults with Systemic Mastocytosis: A 15-Year Multidisciplinary Experience

Systemic mastocytosis (SM) is a rare, clonal, clinically heterogeneous disorder of the mast cells (MCs), and mainly affects adults. The present study aims to describe the clinical and laboratory features as well as the outcomes of SM. A 15-year retrospective study was conducted on 195 consecutive SM patients (aged ≥ 18 years) diagnosed in 2006−2020 at the Multidisciplinary Mastocytosis Center at Karolinska University Hospital. Patients with indolent SM (ISM) represented the most common SM variant (88.2%). Furthermore, the frequencies of aggressive SM and SM with associated non-mast-cell hematological neoplasm were 4.1% and 7.7%, respectively. The prevalence of SM in the adult population of the Stockholm region was estimated to be 10.6/100,000 inhabitants, and the mean incidence of SM cases in the Stockholm region was 0.77/100,000 people per year. In this series, tryptase levels were below 20 ng/mL in 51 patients (26%). Osteoporosis was present in 21.9% of all cases. Interestingly, there was no progression from ISM to advanced SM variants in our study. Furthermore, overall survival was significantly better in ISM patients compared to advanced SM patients (p < 0.0001). Our data suggest that the early recognition and correct diagnosis of SM has prognostic significance.

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.

Tyrosine kinase inhibitors for the treatment of indolent systemic mastocytosis: are we there yet?

Indolent systemic mastocytosis (ISM) is the most prevalent form of systemic mastocytosis. Many patients with ISM suffer from mast cell (MC) mediator-related symptoms In a small number of patients, hematologic progression is seen in the follow up. In some patients with ISM, symptoms arising from MC-derived mediators including gastrointestinal symptoms, anaphylaxis, neuropsychiatric symptoms are kept under control with conventional mediator-targeting drugs or MC-stabilizing agents. However, in a substantial number of patients, the symptoms are refractory to such conventional therapy. For these patients, novel drugs and targeted approaches are considered. One reasonable approach may be to apply tyrosine kinase inhibitors directed against KIT and other key kinase targets expressed in neoplastic MC in ISM. Since MC in over 90% of all patients with typical ISM display the KIT D816V mutant receptor, clinically effective KIT-targeting drugs have to be active against this mutant form of KIT. The two such most effective and well-studied agents currently available are midostaurin and avapritinib. Other KIT-targeting drugs, such as imatinib or masitinib, are less effective or even non-effective against KIT D816V and are thus only recommended for use in patients with other KIT mutant forms (non codon 816 mutations) or with wild type KIT. In the present article, we review the current state in the treatment of ISM with tyrosine kinase inhibitors, with special emphasis on treatment responses and potential adverse effects. In fact, all of these agents also have unique and common adverse effects, and their use to treat ISM patients should be balanced against their toxicity and short and long term safety.

Personalized Management Strategies in Mast Cell Disorders: ECNM-AIM User's Guide for Daily Clinical Practice

Mastocytosis is a myeloid neoplasm defined by expansion and focal accumulation of clonal mast cells (MCs) in one or more organs. The disease exhibits a complex pathology and may be complicated by MC activation, bone abnormalities, neurological problems, gastrointestinal symptoms, and/or hematologic progression. The World Health Organization divides mastocytosis into cutaneous forms, systemic mastocytosis (SM) and MC sarcoma. In most patients with SM, somatic mutations in KIT are detected. Patients with indolent SM have a normal to near-normal life expectancy, whereas patients with advanced SM, including aggressive SM and MC leukemia, have a poor prognosis. In those with advanced SM, multiple somatic mutations and an associated hematologic neoplasm may be detected. Mediator-related symptoms can occur in any type of mastocytosis. Symptoms may be mild, severe, or even life-threatening. In patients with severe acute symptoms, an MC activation syndrome may be diagnosed. In these patients, relevant comorbidities include IgE-dependent and IgE-independent allergies. Management of patients with SM is an emerging challenge in daily practice and requires in-depth knowledge and a multidisciplinary and personalized approach with selection of appropriate procedures and interventions. In this article, we review the current knowledge on SM and MC activation syndrome, with emphasis on multidisciplinary aspects in diagnosis and patient-specific management. In addition, we provide a user's guide for application of markers, algorithms, prognostic scores, and treatments for use in daily practice.

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

PURPOSE

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

PATIENTS AND METHODS

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

RESULTS

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

CONCLUSION

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

Refined diagnostic criteria for bone marrow mastocytosis: a proposal of the European competence network on mastocytosis

In the current classification of the World Health Organization (WHO), bone marrow mastocytosis (BMM) is a provisional variant of indolent systemic mastocytosis (ISM) defined by bone marrow involvement and absence of skin lesions. However, no additional diagnostic criteria for BMM have been proposed. Within the registry dataset of the European Competence Network on Mastocytosis, we compared characteristics and outcomes of 390 patients with BMM and 1175 patients with typical ISM. BMM patients were significantly older, predominantly male, had lower tryptase and lower burden of neoplastic mast cells, and displayed a higher frequency of allergic reactions, mainly triggered by Hymenoptera, than patients with typical ISM. The estimated 10-year progression-free survival of BMM and typical ISM was 95.9% and 92.6%, respectively. In BMM patients defined by WHO-based criteria, the presence of one B-Finding and tryptase level ≥125 ng/mL were identified as risk factors for progression in multivariate analyses. BMM patients without any of these risk factors were found to have better progression-free survival (p < 0.05) and better overall survival (p < 0.05) than other ISM patients. These data support the proposal to define BMM as a separate SM variant characterized by SM criteria, absence of skin lesions, absence of B-Findings, and tryptase levels <125 ng/mL.

Altered leukocyte subsets and immune proteome indicate pro-inflammatory mechanisms in mastocytosis

BACKGROUND

Indolent systemic mastocytosis (ISM) is characterized by pathological accumulation of mast cells. The mechanism behind its phenotypic heterogeneity is not well understood. Interaction of mast cells with other immune cells might cause systemic inflammation and thereby associated symptoms.

OBJECTIVE

To investigate peripheral leukocyte compartments and serum immune proteome in ISM.

METHODS

Peripheral blood leukocyte phenotyping using flowcytometry in a cohort of 18 adults with ISM and 12 healthy controls. Targeted proteomics was performed to measure 169 proteins associated with inflammation on serum of another 20 ISM patients and 20 healthy controls.

RESULTS

Proportions of plasmacytoid dendritic cells (pDC) and monocytes were significantly decreased while T-helper 2 cells were increased in peripheral blood of ISM patients. Furthermore, a shift from naïve to memory T-cells was observed. Hierarchical clustering of the serum proteome revealed two distinct subgroups within ISM patients. In subgroup A (n=8), 62 proteins were significantly overexpressed, whereas subgroup B (n=12) was comparable to healthy controls. Patients in subgroup A displayed upregulated signaling pathways downstream of Toll-like receptor 4, TNF-α and interferon-γFatigue was more often present in subgroup A compared to B (75% vs. 33% respectively, p 0.06).

CONCLUSIONS

Altered distribution of leukocyte subsets and a pro-inflammatory proteome were observed in subsequent two cohorts of ISM patients. We hypothesize that neoplastic mast cells recruit and activate pDC, monocytes and T-cells leading to a vicious cycle of inflammation.

CLINICAL IMPLICATION

Characterization of inflammatory mechanisms in ISM might uncover additional targets for treatment, in particular for constitutional symptoms such as fatigue.

Systemic Mastocytosis: Multidisciplinary Approach

Systemic mastocytosis (SM) is a heterogeneous group of diseases that affect almost exclusively adults and are defined by the proliferation and accumulation of clonal mast cells (MC) in various tissues. Disease subtypes range from indolent to rare aggressive forms. Although SM is classified as a rare disease, it is believed to be likely underdiagnosed. Major signs and symptoms mainly depend on MC activation and less frequent organ infiltration, typical of more aggressive variants. Diagnosis may be challenging, and symptoms can be aspecific and involve several organs. Therefore, it is advisable to refer patients to specialized centers, having sufficient knowledge of the disease, sensitive diagnostic procedures, offering a personalized and multidisciplinary diagnostic approach, including at least hematological, allergological, dermatological, and rheumatological evaluations. A precise and timely diagnosis is required for: a) adequate counseling of patients and their physicians; b) beginning of symptomatic treatment (anti-mediator therapy); c) prevention of severe manifestations of the disease (i.e., recurrent anaphylaxis, osteoporosis, and bone fractures); d) cytoreductive treatment of advanced SM variants. This review summarizes the disease's main manifestations and describes the ideal diagnostic approach for adult patients with suspected SM, giving physicians the main notions for correct patient diagnosis and management. This review also highlights the importance of a multidisciplinary approach in this very complex disease.

Avapritinib for Systemic Mastocytosis

INTRODUCTION

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

AREAS COVERED

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

EXPERT OPINION

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

Systemic Mastocytosis: Molecular Landscape and Implications for Treatment

Over the past decade, we have witnessed significant advances in the molecular characterization of systemic mastocytosis (SM). This has provided important information for a better understanding of the pathogenesis of the disease but has also practically impacted the way we diagnose and manage it. Advances in molecular testing have run in parallel with advances in therapeutic targeting of constitutive active KIT, the major driver of the disease. Therefore, assessing the molecular landscape in each SM patient is essential for diagnosis, prognosis, treatment, and therapeutic efficacy monitoring. This is facilitated by the routine availability of novel technologies like digital PCR and NGS. This review aims to summarize the pathogenesis of the disease, discuss the value of molecular diagnostic testing and how it should be performed, and provide an overview of present and future therapeutic concepts based on fine molecular characterization of SM patients.

Health-Related Quality of Life and Influencing Factors in Adults with Nonadvanced Mastocytosis-A Cross-Sectional Study and Qualitative Approach

BACKGROUND

Mastocytosis comprises a heterogeneous group of disorders characterized by an accumulation of mast cells in 1 or more organs. Symptoms range from mild complaints to severe and life-threatening events. Impact on quality of life seems to vary widely, but influencing factors are poorly understood so far.

OBJECTIVE

To examine impairments, psychological burden, health-related quality of life (HRQOL), and possible influencing factors in patients with mastocytosis.

METHODS

In semistructured telephone interviews, patients provided information on impairments in everyday life and psychological burden caused by mastocytosis. HRQOL was measured using the Mastocytosis Quality of Life (MC-QoL) questionnaire. Clinical data were collected from patient files.

RESULTS

A total of 101 adult patients with mastocytosis (74.3% women; mean age, 47.7 ± 13.5 years) were included. Half of the interviewed patients (50.6%) reported disease-related impairments in everyday life, and 42.4% stated a psychological burden. MC-QoL questionnaire scores showed a broad distribution, with a mean total score at a "mild" impairment level (mean total score, 34.7 ± 22.5). One-third of patients felt moderately (22.8%) or severely (13.9%) impaired, whereas one-third reported no impairment at all (30.7%). Symptoms of mast cell activation and perceived food intolerance had the highest impact on HRQOL. Higher age, higher body mass index, higher tryptase level, and longer duration of symptoms, as well as current drug therapy and pathological bone density, were each associated with reduced HRQOL.

CONCLUSIONS

A high level of suffering and strong associations between impairments and symptom-related factors indicate the importance of addressing patients' concerns and adequate symptom management in mastocytosis.

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

OVERVIEW

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

DIAGNOSIS

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

RISK STRATIFICATION

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

MANAGEMENT

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

Proceedings from the Inaugural American Initiative in Mast Cell Diseases (AIM) Investigator Conference

The American Initiative in Mast Cell Diseases (AIM) held its inaugural investigator conference at Stanford University School of Medicine in May 2019. The overarching goal of this meeting was to establish a Pan-American organization of physicians and scientists with multidisciplinary expertise in mast cell disease. To serve this unmet need, AIM envisions a network where basic, translational, and clinical researchers could establish collaborations with both academia and biopharma to support the development of new diagnostic methods, enhanced understanding of the biology of mast cells in human health and disease, and the testing of novel therapies. In these AIM proceedings, we highlight selected topics relevant to mast cell biology and provide updates regarding the recently described hereditary alpha-tryptasemia. In addition, we discuss the evaluation and treatment of mast cell activation (syndromes), allergy and anaphylaxis in mast cell disorders, and the clinical and biologic heterogeneity of the more indolent forms of mastocytosis. Because mast cell disorders are relatively rare, AIM hopes to achieve a coordination of scientific efforts not only in the Americas but also in Europe by collaborating with the well-established European Competence Network on Mastocytosis.

Clinical Impact of Skin Lesions in Mastocytosis: A Multicenter Study of the European Competence Network on Mastocytosis

Mastocytosis is a rare neoplasm characterized by the expansion and accumulation of mast cells in various organ systems. Systemic mastocytosis (SM) may or may not present with cutaneous lesions. To examine the frequency and clinical impact of cutaneous involvement, data on 1,510 patients with mastocytosis collected in the registry of the European Competence Network on Mastocytosis were analyzed. Cutaneous involvement was found in 1,195 of 1,510 patients (79.1%). Of these, 286 had cutaneous mastocytosis, and 721 had SM with skin involvement. Adult patients with skin involvement who did not have a bone marrow examination (n = 188) were defined as having mastocytosis in the skin. In 315 patients, SM without skin involvement was found. The percentage of cases with cutaneous involvement was higher in indolent SM (100%) and smoldering SM (87.9%) compared to aggressive SM (46.8%) or mast cell leukemia (38.5%). After a median follow-up of 5.6 years, no patient with cutaneous mastocytosis had died, but 2.6% of the patients with mastocytosis in the skin, 5.7% of the patients with SM with skin involvement, and 28.95% of the patients with SM without skin involvement had died. Overall survival was longer in patients with skin involvement (cutaneous mastocytosis and/or mastocytosis in the skin and/or SM with skin involvement) than in patients with SM without skin involvement (P < 0.0001). These data argue for a thorough examination of both the skin and bone marrow in adult patients with mastocytosis.

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.

Catching the clinical and biological diversity for an appropriate therapeutic approach in systemic mastocytosis

Systemic mastocytosis (SM) is a rare disease calling for integrated approaches involving onco-hematologic competences for appropriate clinical management and treatment. The wide variability of manifestations and disease course claims for an accurate risk stratification, currently relying on the appraisal of the benefit/risk ratio of treatment modalities within indolent and advanced variants according to WHO classification. More objective parameters are progressively incorporated and integrated into comprehensive models, on which to support the adoption of therapeutic strategies, since the mere clinical distinction between mediator-related signs/symptoms and “true” organ damage can sometimes be complicated. The development of novel targeted drugs is progressively extending the therapeutic alternatives available, which ranges from conventional agents such as interferon and cladribine, to the more modern approach based on KIT inhibition. Ultimately, the choice of the most appropriate therapy should be rationalized on the basis of the clinical picture and molecular data. The focus of the present review is on the areas still open in the current evaluation of SM patients, particularly when considering the need of a treatment.

Cutaneous mastocytosis: A dermatological perspective

Mastocytosis is a rare disease characterised by expansion and collection of clonal mast cells in various organs including the skin, bone marrow, spleen, lymph nodes and gastrointestinal tract. The prevalence of mastocytosis has been estimated to be one in 10 000, while the estimated incidence is one per 100 000 people per year. Cutaneous mastocytosis is classified into (i) maculopapular cutaneous mastocytosis, also known as urticaria pigmentosa; (ii) diffuse cutaneous mastocytosis; and (iii) mastocytoma of the skin. In adults, cutaneous lesions are usually associated with indolent systemic mastocytosis and have a chronic evolution. Paediatric patients, on the contrary, have often cutaneous manifestations without systemic involvement and usually experience a spontaneous regression. Diagnosis of cutaneous mastocytosis may be challenging due to the rarity of the disease and the overlap of cutaneous manifestations. This short review describes pathogenesis and clinical aspects of cutaneous mastocytosis with a focus on diagnosis and currently available therapies.

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.