Systemic mastocytosis in adults: a review on prognosis and treatment based on 342 Mayo Clinic patients and current literature:

Challenges in Drug and Hymenoptera Venom Hypersensitivity Diagnosis and Management in Mastocytosis

Mastocytosis is a myeloproliferative neoplasm characterized by abnormal proliferation and activation of clonal mast cells typically bearing the KITD816V mutation. Symptoms manifest due to the release of bioactive mediators and the tissue infiltration by neoplastic mast cells. Mast cell activation symptoms include flushing, pruritus, urticaria, abdominal cramping, diarrhea, wheezing, neuropsychiatric symptoms, and anaphylaxis. Up to 50% of patients with mastocytosis report a history of provoked and unprovoked anaphylaxis, with Hymenoptera venom and drugs the most common culprits. NSAIDs, antibiotics, vaccines, perioperative medications, and radiocontrast media are often empirically avoided without evidence of reactions, depriving patients of needed medications and placing them at risk for unfavorable outcomes. The purpose of this review is to highlight the most common agents responsible for adverse drug reactions in patients with mastocytosis, with a review of current epidemiology, diagnosis, and management of drug hypersensitivity and Hymenoptera venom allergy.

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.

Measuring Symptom Severity and Quality of Life in Mastocytosis

Mastocytosis is a heterogeneous disease with a wide spectrum of signs, symptoms, and concomitant disorders, such as skin lesions, anaphylaxis, osteoporosis, gastrointestinal involvement, and organomegaly. Disease specificity for frequently reported symptoms, such as fatigue, headache, anxiety, and brain fog, is poorly defined and need to be addressed in further studies. Patients with CM and non-AdvSM are mostly affected by mast cell mediator-related symptoms, whereas in AdvSM symptoms also result from organ damage, which makes their assessment challenging. In this paper we discuss approaches currently used to measure symptom burden and QoL impairment in relation to the clinical phenotype.

Systemic mastocytosis with myeloid sarcoma and B-CLL: molecular and clonal heterogeneity in a rare case of SM-AHN with review of literature

BACKGROUND

Systemic mastocytosis (SM) is a rare myeloproliferative disease that results from a clonal proliferation of abnormal mast cells in one or more extra-cutaneous organs. Systemic mastocytosis with an associated hematological neoplasm (SM-AHN) is the second most common subgroup and is diagnosed when WHO criteria for both SM and a hematological neoplasm of non-mast cell lineage are met. The SM-AHN category as currently proposed is highly heterogeneous in terms of pathogenesis, clinical presentation, and prognosis.

CASE PRESENTATION

We present the first reported case of SM-AHN associated with two hematological malignancies of different lineages, a monocytic myeloid sarcoma and a B-cell chronic lymphatic leukemia. Cytogenetic and molecular analyses revealed a distinct clonal origin of the two associated malignancies. The SM-myeloid sarcoma clone demonstrated an abnormal karyotype, trisomy 8 and del(13)(q12.3q14.3), as well as mutations in KITD816V, DNMT3A and RUNX1. The DNMT3A mutation could be detected years before disease onset, supporting its potential role as early driver of leukemogenesis. No genetic aberrations could be identified in the CLL clone, which is assumed to present coincidentally.

CONCLUSIONS

This report highlights the importance of full diagnostic work-up in SM patients in whom an associated hematological malignancy is suspected. Moreover, the importance of genetic analysis is highlighted, as it provides additional insights in the underlying clonal pathogenesis of different phenotypes, can aid in risk stratification, and may help identify potential therapy targets.

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).

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.

Mast cell neoplasm: a challenging pathological diagnosis

Systemic mastocytosis (SM) is a myeloid neoplasm characterized by abnormal growth and accumulation of neoplastic mast cells in at least one extracutaneous site. Clinical presentation and course are variable, most patients developing an indolent disease and some, an aggressive/leukemic form. Because of its rarity, most physicians are unfamiliar with this disease and do not readily diagnose it. In the present retrospective study, the authors describe 12 patients diagnosed with mast cell neoplasm. Cases were selected from three institutions from Campinas and São Paulo City, Brazil. Morphological features and diagnostic pitfalls are emphasized. Patients' age ranged from 15 to 81 years (mean 51.6 years). Male and female were affected similarly (1:1). Ten patients were classified as aggressive systemic mastocytosis (SM), one patient as SM with an associated acute promyelocytic leukemia with t(15;17), and one patient with mast cell sarcoma. Most common clinical findings included anemia (9 patients), thrombocytopenia (3 patients) and skin lesions (3 patients). Bone marrow was involved in 11 patients at diagnosis, followed by skin (5 patients). Five morphological patterns were present: mast cell aggregates (5), plasmacytoid (4), monocytoid (2), spindle cell (2) and epithelioid/pleomorphic (1); two patients showed two histological patterns. In all cases neoplastic cells were positive for CD117/C-KIT. C-KIT D816V mutation was present in four patients, C-KIT K509I in two, and del(7q22) in one; in five cases no mutational status was available. Despite limited resources, basically morphology and a restricted immunohistochemical panel, it is possible to diagnose mast cell neoplasm. Of note, pathologist should recognize the different morphological variants of the disease and include the adequate markers when requesting immunohistochemical studies.

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.

Cytogenetic and molecular aberrations and worse outcome for male patients in systemic mastocytosis

In systemic mastocytosis (SM), the clinical features and survival vary greatly. Patient-related factors determining the outcome in SM are largely unknown. Methods: We examined the impact of sex on the clinical features, progression-free survival (PFS), and overall survival (OS) in 3403 patients with mastocytosis collected in the registry of the European Competence Network on Mastocytosis (ECNM). The impact of cytogenetic and molecular genetic aberrations on sex differences was analyzed in a subset of patients. Results: Of all patients enrolled, 55.3% were females. However, a male predominance was found in a subset of advanced SM (AdvSM) patients, namely SM with an associated hematologic neoplasm (SM-AHN, 70%; p < 0.001). Correspondingly, organomegaly (male: 23% vs. female: 13%, p = 0.007) was more, whereas skin involvement (male: 71% vs. female: 86%, p = 0.001) was less frequent in males. In all patients together, OS (p < 0.0001) was significantly inferior in males, and also within the WHO sub-categories indolent SM, aggressive SM (ASM) and SM-AHN. PFS was significantly (p = 0.0002) worse in males when all patients were grouped together; due to low numbers of events, this significance persisted only in the subcategory smoldering SM. Finally, prognostically relevant cytogenetic abnormalities (10% vs. 5%, p = 0.006) or molecular aberrations (SRSF2/ASXL1/RUNX1 profile; 63% vs. 40%, p = 0.003) were more frequently present in males. Conclusions: Male sex has a major impact on clinical features, disease progression, and survival in mastocytosis. Male patients have an inferior survival, which seems related to the fact that they more frequently develop a multi-mutated AdvSM associated with a high-risk molecular background.

How "benign" is cutaneous mastocytosis? A Danish registry-based matched cohort study

BACKGROUND

There are limited estimates of the incidence rates (IRs) of mastocytosis, and only a few studies have addressed the long-term consequences of living with these diagnoses. Previous reports have shown that systemic mastocytosis is associated with leukemic transformations and an increased risk of death as opposed to cutaneous mastocytosis (CM) and indolent systemic mastocytosis (ISM), which have benign diagnoses with life expectancy rates similar to those of the background population.

OBJECTIVE

This study aimed to analyze the incidence and mortality of mastocytosis.

METHODS

A population-based matched cohort study of patients with mastocytosis between 1 January 1, 1977 and 31 December 31, 2014 was identified from the Danish National Health Registries. IRs of CM, ISM, and pediatric mastocytosis were highlighted. Survival estimates were compared with those of a healthy background population, using a Cox proportional hazard model.

RESULTS

A total of 1461 patients with mastocytosis were identified. The annual IR of overall mastocytosis was 1.1 per 100,000 person years (95% confidence interval [CI], 1.0-1.2). Among children, the IR was 1.8 per 100,000 person years (95% CI, 1.6-2.1). The prevalence of any comorbidity was twice as high among patients with mastocytosis compared with the population without mastocytosis (odds ratio: 2.1; 95% CI, 1.8-2.5). The Charlson Comorbidity Index-adjusted mortality among adult patients with mastocytosis was HRCutaneous Mastocytosis 1.2 (95% CI, 0.8-1.9), HRIndolent Systemic Mastocytosis 1.9 (95% CI 1.4-2.5), and HRSystemic Mastocytosis 4.2 (95%, CI 1.9-9.4), respectively.

CONCLUSION

Based on an entire nation, with free health care at the point of access, we estimated an annual IR of mastocytosis and its subgroups. We discovered that patients with ISM had an increased risk of death compared with the general population. Our data supported the overall benign nature of CM diagnosed after age 2 years.

A phase 2 study of brentuximab vedotin in patients with CD30-positive advanced systemic mastocytosis

There is an unmet need for effective therapies for advanced systemic mastocytosis (advSM). CD30 is expressed on the surface of neoplastic mast cells (MC) in more than 50% of patients with advSM. Brentuximab vedotin (BV) is a CD30-directed antibody-drug conjugate with preclinical evidence supporting both an antineoplastic effect and an attenuation of immunoglobulin E-associated mediator release. These observations are the basis for this phase 2 trial of BV monotherapy (1.8 mg/kg IV every 3 weeks up to 8 cycles) in patients with CD30-positive advSM. The primary objective was to determine the efficacy of BV according to International Working Group-Myeloproliferative Neoplasms Research and Treatment-European Competence Network on Mastocytosis (IWG-MRT-ECNM) response criteria. Secondary objectives included evaluation of safety, changes in bone marrow (BM) MC burden, serum tryptase level, flow cytometric quantification of MC surface expression of CD30, and self-reported symptom burden. The trial enrolled 10 patients with a diagnosis of CD30⁺ advSM (aggressive SM, SM with an associated hematologic neoplasm [SM-AHN], or mast cell leukemia [MCL]) with 1 or more signs of SM-related organ damage. According to IWG-MRT-ECNM criteria, none of the patients demonstrated better than stable disease with BV. In addition, there were no significant reductions in BM MC burden, serum tryptase levels, or MC surface expression of CD30. Self-reported symptom scores showed no durable improvement with BV treatment. We conclude that BV is not active as a single agent in CD30⁺ advSM. This trial was registered at www.clinicaltrials.gov as #NCT01807598.

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.

The Spectrum of Aggressive Mastocytosis: A Workshop Report and Literature Review

Most cases of mastocytosis are indolent, usually cutaneous mastocytosis or indolent systemic mastocytosis (SM). Aggressive mast cell (MC) diseases are very rare and often fatal. They can develop de novo or due to progression of indolent forms and can present in different ways; either as MC sarcoma or as advanced SM which includes aggressive SM, MC leukemia, and SM with an associated hematological neoplasm. This review will describe these different aggressive forms of mastocytosis, illustrated by cases submitted to the workshop of the 18th Meeting of the European Association for Haematopathology, Basel 2016, organized by the European Bone Marrow Working Group. In addition, the diagnostic criteria for identifying myelomastocytic leukemia, an aggressive myeloid neoplasm with partial MC differentiation that falls short of the criteria for SM, and disease progression in patients with established mastocytosis are discussed.

Frequency and prognostic impact of KIT and other genetic variants in indolent systemic mastocytosis

Indolent systemic mastocytosis (ISM) patients have a normal life expectancy, except in the 5% to 10% of cases that progress to more advanced SM (advSM), which has a significantly poorer outcome. Mutations in genes other than KIT frequently found in myeloid neoplasms have been associated with a poorer outcome among advSM, whereas limited information exists about their frequency and prognostic impact in ISM. We investigated the frequency and prognostic impact of variants in 18 genes, found to be altered in advSM, in 322 ISM patients (median follow-up, 5.7 years) divided into discovery (n = 200) and validation (n = 122) cohorts. Overall, 71 genetic variants were detected in 55 of 322 (17%) patients. Mutated ISM cases, particularly those carrying ASXL1, RUNX1, and/or DNMT3A (A/R/D) pathogenic variant allele frequencies (VAFs) ≥ 30%, exhibited significantly shortened (P &lt; .001) progression-free survival (PFS) and overall survival (OS). Multivariate analysis showed that serum β2-microglobulin (sβ2M) levels &gt; 2.5 µg/mL (hazard ratio [HR], 9.8; P = .001), together with a KIT D816V VAF ≥ 1% in bone marrow (BM) (HR, 10.1; P = .02) and pathogenic variants of A/R/D VAFs ≥ 30% (HR, 4.2; P = .02), were the best combination of independent predictors for PFS. In turn, A/R/D gene pathogenic VAF ≥ 30% was the only independent predictor for OS (HR, 51.8; P &lt; .001). Based on these variables, 2 scoring systems were constructed for risk stratification of ISM at diagnosis with significantly different 10-year PFS (100%, 91%, 0% for scores of 0, 1, ≥2, respectively) and OS (100% and 50% for scores of 0 and 1) rates.

LncRNA PLAC2 upregulates p53 to induce hepatocellular carcinoma cell apoptosis

It is known that lncRNA PLAC2 can inhibit glioma. This study explored the function of PLAC2 in hepatocellular carcinoma (HCC). Our data showed that PLAC2 expression in HCC was not affect by HCV and HBV infection, while PLAC2 levels were significantly lower in HCC tissues comparing to non-cancer tissues. Low PLAC2 levels in HCC tissues were associated with low overall 5-year survival rate. P53 mRNA was also downregulated in HCC and positively correlated with PLAC2. PLAC2 overexpression caused upregulated p53 and increase cancer cell apoptosis. P53 overexpression failed to affect PLAC2. In addition, p53 silencing reduced the effects of PLAC2 overexpression. Therefore, PLAC2 upregulated p53 to mediate cancer cell apoptosis.

Relevant updates in systemic mastocytosis

Systemic Mastocytosis (SM) is a rare myeloproliferative neoplasm (MPN) that is characterized by a clonal proliferation of mast cells (MCs). The symptoms and clinical presentation of SM are the result of both MC proliferation as well as activation and degranulation, causing hyperactive and over-exaggerated hypersensitivity responses, as well as organ infiltration by pathogenic MCs. The clinical presentation and course of SM is varied and organ involvement can lead to significant morbidity and mortality in some cases. The subtypes of SM include indolent SM (ISM), smoldering SM (SSM), aggressive SM (ASM), SM with associated hematologic neoplasm (SM-AHN) and mast cell leukemia (MCL) and survival can range from normal in the case of ISM to months in MCL. The treatment of indolent forms of SM is largely focused on addressing symptom burden (B findings), while cytoreductive agents and more recently molecularly targeted agents are employed to reduce MC burden and reverse associated organ dysfunction (C findings). Although the pathogenesis of SM is multi-factorial, the acquisition of KIT D816 V is a relatively frequent mutational event and serves as the target of novel agents. The recent approval of midostaurin for the treatment of advanced SM has brought awareness to this disease and energized further drug development efforts. Expanding our understanding of the underlying molecular mechanisms of SM will continue to inform future therapeutic approaches.

The Data Registry of the European Competence Network on Mastocytosis (ECNM): Set Up, Projects, and Perspectives

Mastocytosis is a unique hematologic neoplasm with complex biology and pathology and a variable clinical course. The disease can essentially be divided into cutaneous mastocytosis (CM) and systemic mastocytosis (SM). In adults, SM is diagnosed in most cases and manifests as either indolent or advanced disease. Patients with advanced SM have an unfavorable prognosis with reduced survival. However, so far, little is known about the prevalence of various categories of SM and about prognostic factors. In an attempt to learn more about the behavior and evolution of various forms of CM and SM, the European Competence Network on Mastocytosis (ECNM) initiated a mastocytosis registry in 2012. In this article, the set up and start phase of this registry are described. Until 2018, more than 3000 patients from 12 countries and 25 centers have been enrolled. In a majority of all patients, robust follow-up data and relevant clinical end points are available. Using this data set, a series of registry projects have been launched, with the aim to validate previously identified diagnostic and prognostic variables and to identify new disease-related and patient-related parameters in various forms of mastocytosis. Moreover, the core data set of the registry will be useful to establish multiparametric scoring systems through which prognostication and individualized management of patients with mastocytosis should improve in the foreseeable future.

Receptor Tyrosine Kinase-Targeted Cancer Therapy

In the past two decades, several molecular targeted inhibitors have been developed and evaluated clinically to improve the survival of patients with cancer. Molecular targeted inhibitors inhibit the activities of pathogenic tyrosine kinases. Particularly, aberrant receptor tyrosine kinase (RTK) activation is a potential therapeutic target. An increased understanding of genetics, cellular biology and structural biology has led to the development of numerous important therapeutics. Pathogenic RTK mutations, deletions, translocations and amplification/over-expressions have been identified and are currently being examined for their roles in cancers. Therapies targeting RTKs are categorized as small-molecule inhibitors and monoclonal antibodies. Studies are underway to explore abnormalities in 20 types of RTK subfamilies in patients with cancer or other diseases. In this review, we describe representative RTKs important for developing cancer therapeutics and predicting or evaluated resistance mechanisms.

Loss of epigenetic regulator TET2 and oncogenic KIT regulate myeloid cell transformation via PI3K pathway

Mutations in KIT and TET2 are associated with myeloid malignancies. We show that loss of TET2-induced PI3K activation and -increased proliferation is rescued by targeting the p110α/δ subunits of PI3K. RNA-Seq revealed a hyperactive c-Myc signature in Tet2-/- cells, which is normalized by inhibiting PI3K signaling. Loss of TET2 impairs the maturation of myeloid lineage-derived mast cells by dysregulating the expression of Mitf and Cebpa, which is restored by low-dose ascorbic acid and 5-azacytidine. Utilizing a mouse model in which the loss of TET2 precedes the expression of oncogenic Kit, similar to the human disease, results in the development of a non-mast cell lineage neoplasm (AHNMD), which is responsive to PI3K inhibition. Thus, therapeutic approaches involving hypomethylating agents, ascorbic acid, and isoform-specific PI3K inhibitors are likely to be useful for treating patients with TET2 and KIT mutations.

Drug-induced inhibition of phosphorylation of STAT5 overrides drug resistance in neoplastic mast cells

Systemic mastocytosis (SM) is a mast cell (MC) neoplasm with complex pathology and a variable clinical course. In aggressive SM (ASM) and MC leukemia (MCL) responses to conventional drugs are poor and the prognosis is dismal. R763 is a multi-kinase inhibitor that blocks the activity of Aurora-kinase-A/B, ABL1, AKT and FLT3. We examined the effects of R763 on proliferation and survival of neoplastic MC. R763 produced dose-dependent inhibition of proliferation in the human MC lines HMC-1.1 (IC₅₀ 5-50 nM), HMC-1.2 (IC₅₀ 1-10 nM), ROSA^{KIT WT} (IC₅₀ 1-10 nM), ROSA^{KIT D816V} (IC₅₀ 50-500 nM) and MCPV-1.1 (IC₅₀ 100-1000 nM). Moreover, R763 induced growth inhibition in primary neoplastic MC in patients with ASM and MCL. Growth-inhibitory effects of R763 were accompanied by signs of apoptosis and a G2/M cell cycle arrest. R763 also inhibited phosphorylation of KIT, BTK, AKT and STAT5 in neoplastic MC. The most sensitive target appeared to be STAT5. In fact, tyrosine phosphorylation of STAT5 was inhibited by R763 at 10 nM. At this low concentration, R763 produced synergistic growth-inhibitory effects on neoplastic MC when combined with midostaurin or dasatinib. Together, R763 is a novel promising multi-kinase inhibitor that blocks STAT5 activation and thereby overrides drug-resistance in neoplastic MC.

Natural history and treatment of cutaneous and systemic mastocytosis

INTRODUCTION

Mastocytosis, a heterogeneous group of disorders, is characterized by an abnormal increase in the number of mast cells that is limited to the skin (cutaneous mastocytosis), involving extracutaneous tissues (systemic mastocytosis), or presenting as solid tumours (mastocytoma and mast cell sarcoma). Recent studies estimate that 1 in 10,000 people are diagnosed with mastocytosis. Although prompt diagnosis and appropriate management are crucial, little is known about the natural history and currently there are no established management guidelines. We have conducted a systematic review to assess the natural history and management of different mastocytosis subtypes.

METHODS

A systematic review and meta-analysis were conducted using the PubMed and Ovid database of studies published in English and French over the last fifteen years, from January 2001 to December 2016. Keywords 'Cutaneous mastocytosis', 'Systemic mastocytosis', 'pathophysiology', 'clinical course', 'prognosis', 'drug therapy', and 'therapy' were searched. Rate of complete resolution was subjected to pooled analysis for different mastocytosis subtypes. Meta-analysis was conducted using Stata version 12.0.

RESULTS

We reviewed 634 papers, of which 5 were included in the analysis of resolution, and 138 were included in the assessment of management. Pooled estimate for rate of complete resolution varied depending on the mastocytosis subtype. In cutaneous mastocytosis, the complete resolution rate for mastocytoma was 10% per year (95% CI: 4.8%, 15.1%) while the rate for urticaria pigmentosa was 1.9% per year (95% CI: -0.5%, 4.3%). Diffuse cutaneous mastocytosis and systemic mastocytosis subtypes did not show evidence of complete resolution in the studies reviewed. Treatment of cutaneous and systemic mastocytosis is purely symptomatic with topical corticosteroids, antihistamines, omalizumab and imatinib being common choices.

CONCLUSION

Rate of resolution of mastocytosis is only shown in urticaria pigmentosa and mastocytoma. Better management guidelines are required to improve the health of these patients.

Patient-reported disease-specific quality-of-life and symptom severity in systemic mastocytosis

BACKGROUND

Presently, no validated data exist on symptom severity and disease-specific quality-of-life (QoL) for patients with mastocytosis. Simultaneously, clinical trials and drug application processes increasingly mandate reporting patients' perspectives on symptoms and QoL. We report on the development and validation of the mastocytosis quality-of-life questionnaire (MQLQ) and the mastocytosis symptom assessment form (MSAF).

METHODS

Both outcome measures were developed in a standardized stepwise method, starting with the identification of items in focus groups (n = 12), item reduction and subsequent cross-sectional validation in a 63% female cohort of 164 adult patients with indolent systemic mastocytosis.

RESULTS

The MSAF reveals that fatigue is the severest mastocytosis symptom while the MQLQ indicates that fear of anaphylaxis mostly impacts QoL. Cross-sectional validity was assessed by correlating both individual domains and the total scores of the MQLQ and MSAF with independent measures of mastocytosis. The total scores of both the MQLQ (P < 0.001; Spearman's r: 0.568) and the MSAF (P < 0.001; Spearman's r: 0.559) correlated significantly with the consensus on physician-scored mediator symptoms. The MQLQ domains displayed a high internal consistency (Cronbach's alpha: 0.841-0.958) and the domains 'bones', 'skin symptoms' and 'anaphylaxis' differed significantly between patients with and without osteoporosis, urticaria pigmentosa or anaphylaxis, respectively (P < 0.001).

CONCLUSIONS

The MQLQ is the first disease-specific QoL questionnaire for mastocytosis and is complemented by the MSAF, a short and convenient symptom scoring form. Both patient-reported outcome measures are valid, reliable and discriminate between patients with different disease characteristics, making them useful instruments for clinical research.

KIT D816V–mutated bone marrow mesenchymal stem cells in indolent systemic mastocytosis are associated with disease progression

Acquisition of the KIT D816V mutation in an early pluripotent progenitor cell confers ISM cases a greater risk for disease progression. Despite the early acquisition of the KIT mutation, onset of clinical symptoms of ISM is often delayed to middle adulthood.

The role of Lin28b in myeloid and mast cell differentiation and mast cell malignancy

Mast cells (MCs) are critical components of the innate immune system and important for host defense, allergy, autoimmunity, tissue regeneration and tumor progression. Dysregulated MC development leads to systemic mastocytosis (SM), a clinically variable but often devastating family of hematologic disorders. Here we report that induced expression of Lin28, a heterochronic gene and pluripotency factor implicated in driving a fetal hematopoietic program, caused MC accumulation in adult mice in target organs such as the skin and peritoneal cavity. In vitro assays revealed a skewing of myeloid commitment in LIN28B-expressing hematopoietic progenitors, with increased levels of LIN28B in common myeloid and basophil-MC progenitors altering gene expression patterns to favor cell fate choices that enhanced MC specification. In addition, LIN28B-induced MCs appeared phenotypically and functionally immature, and in vitro assays suggested a slowing of MC terminal differentiation in the context of LIN28B upregulation. Finally, interrogation of human MC leukemia samples revealed upregulation of LIN28B in abnormal MCs from patients with SM. This work identifies Lin28 as a novel regulator of innate immune function and a new protein of interest in MC disease.

Long-term efficacy and safety of cladribine (2-CdA) in adult patients with mastocytosis

Mastocytosis (M) is a clonal myeloid-disabling disorder for which no curative therapy is currently available. Cladribine (2-chlorodeoxyadenosine [2-CdA]) is a synthetic purine analog cytoreductive treatment, for which efficacy is mostly reported in advanced M. Here we report, with a long-term follow-up period (>10 years) efficacy and safety in 68 adult patients with M (36 [53%] had indolent M and 32 [47%] had advanced M) treated by 2-CdA (0.14 mg/kg in infusion or subcutaneously, days 1-5; repeated at 4-12 weeks until 1 to 9 courses). Median 2-CdA courses number was 3.7 (1-9). The overall response rate was 72% (complete remission [R]/major/partial R: 0%/47%/25%) and according to indolent/advanced M was 92% (major/partial R: 56%/36%) and 50% (major/partial R: 37.5%/12.5%), respectively. Clinical improvement was observed for 10 of 11 mediator release and 6 of 7 mast cell infiltration-related symptoms including urticaria pigmentosa and organomegaly (P < .02). Serum tryptase levels decreased (P = .01). Median durations of response were 3.71 (0.1-8) and 2.47 (0.5-8.6) years for indolent and aggressive M, respectively. The most frequent grade 3/4 toxicities were lymphopenia (82%), neutropenia (47%), and opportunistic infections (13%). 2-CdA appears to provide a significant efficacy with some toxicity in various M subtypes, mostly in indolent M, refractory to multiple symptomatic therapies.

Mast Cell Activation Disease and Microbiotic Interactions

PURPOSE

This article reviews the diagnostically challenging presentation of mast cell activation disease (MCAD) and current thoughts regarding interactions between microbiota and MCs.

METHODS

A search for all studies on interactions between mast cells, mast cell activation disease, and microbiota published on pubmed.gov and scholar.google.com between 1960 and 2015 was conducted using the search terms mast cell, mastocyte, mastocytosis, mast cell activation, mast cell activation disease, mast cell activation syndrome, microbiome, microbiota. A manual review of the references from identified studies was also conducted. Studies were excluded if they were not accessible electronically or by interlibrary loan.

FINDINGS

Research increasingly is revealing essential involvement of MCs in normal human biology and in human disease. Via many methods, normal MCs-present sparsely in every tissue-sense their environment and reactively exert influences that, directly and indirectly, locally and remotely, improve health. The dysfunctional MCs of the "iceberg" of MCAD, on the other hand, sense abnormally, react abnormally, activate constitutively, and sometimes (in mastocytosis, the "tip" of the MCAD iceberg) even proliferate neoplastically. MCAD causes chronic multisystem illness generally, but not necessarily, of an inflammatory ± allergic theme and with great variability in behavior among patients and within any patient over time. Furthermore, the range of signals to which MCs respond and react include signals from the body's microbiota, and regardless of whether an MCAD patient has clonal mastocytosis or the bulk of the iceberg now known as MC activation syndrome (also suspected to be clonal but without significant MC proliferation), dysfunctional MCs interact as dysfunctionally with those microbiota as they interact with other human tissues, potentially leading to many adverse consequences.

IMPLICATIONS

Interactions between microbiota and MCs are complex at baseline. The potential for both pathology and benefit may be amplified when compositionally variant microbiota interact with aberrant MCs in various types of MCAD. More research is needed to better understand and leverage these interactions.

Eosinophilia and bone lesion as clinical manifestations of aggressive systemic mastocytosis

We report a patient with aggressive systemic mastocytosis (SM), who exhibited eosinophilia and unusual destructive bone lesions. A 43-year-old female was referred to our hospital because of a vertebral compression fracture, multiple lytic bone lesions, and eosinophilia in February 2011. A diagnosis of aggressive SM was made on the basis of abnormal mast cells in the bone marrow, high serum tryptase levels, and multiple lytic bone lesions including vertebral compression fractures. Polymerase chain reaction and subsequent sequencing of its products to identify mutations of c-kit yielded negative results and imatinib mesylate failed to improve the SM of the patient. She was then treated with interferon-α, with considerable improvement of the disease, although severe myelosuppression prevented the continued administration of a sufficient dose of this agent. In August 2011, the patient suddenly developed paraplegia of the lower extremities. Magnetic resonance imaging demonstrated epidural mass lesions at the levels from Th9 to Th11, compressing the spinal cord. Emergent laminectomy and subsequent irradiation of the tumors were performed without improvement of the paraplegia. Histopathologic examination of the epidural tumors, from samples obtained intraoperatively, confirmed the diagnosis of SM. She was further treated with dasatinib and then cladribine without obvious improvement, although the latter reduced the eosinophilia to some extent ; however, she died of sepsis in September 2011.

Delayed diagnosis of adult indolent systemic mastocytosis

Systemic mastocytosis (SM) is a rare, heterogeneous disorder characterized by infiltration and accumulation of mast cells within multiple organs, most commonly the skin. Given the rarity of the disease and the fact that many of its symptoms are shared by more common disorders, a diagnosis may be delayed or hindered. These patients have an elevated risk of developing potentially life-threatening anaphylactoid reactions, thus underscoring the importance of keeping SM in mind as a differential diagnosis when a patient presents with chronic, itchy skin lesions and a history of multiple allergic reactions to bites, drugs, and anesthesia. We present a case illustrating that features of SM common to many disorders may hinder or delay its diagnosis.

[Mastocytosis. Review of the literature and description of clinical cases]

The term mastocytosis (MC) encompasses a group of rare diseases characterized by the tumorous proliferation of clonal mast cells and the infiltration of one or several organs. The clinical picture of MC is extremely diverse from skin lesions that can spontaneously regress to the aggressive disease forms associated with organ dysfunction and short survival. Nowadays, the 2008 WHO classification identifies 7 MC subtypes. The disease is diagnosed on the basis of its clinical manifestations and detection of tumorous mast cell infiltrations via morphological, immunohistochemical, immunophenotypic, genetic, and molecular examinations. Abnormal mast cells are characterized by the atypical morphology and pathological expression of CD25 and CD2 antigens. Enhanced serum tryptase activity is a common sign in all MC subtypes. More than 90% of the patients have D816V KIT mutations in the mast cells. This paper reviews the literature. Three cases are described as a clinical example in patients with different MC subtypes.

Mast cell sarcoma: a rare and potentially under-recognized diagnostic entity with specific therapeutic implications

Mast cell sarcoma is a rare, aggressive neoplasm composed of cytologically malignant mast cells presenting as a solitary mass. Previous descriptions of mast cell sarcoma have been limited to single case reports, and the pathologic features of this entity are not well known. Here, we report three new cases of mast cell sarcoma and review previously reported cases. Mast cell sarcoma has a characteristic morphology of medium-sized to large epithelioid cells, including bizarre multinucleated cells, and does not closely resemble either normal mast cells or the spindle cells of systemic mastocytosis. One of our three cases arose in a patient with a remote history of infantile cutaneous mastocytosis, an association also noted in one previous case report. None of our three cases were correctly diagnosed as mast cell neoplasms on initial pathological evaluation, suggesting that this entity may be under-recognized. Molecular testing of mast cell sarcoma has not thus far detected the imatinib-resistant KIT D816V mutation, suggesting that recognition of these cases may facilitate specific targeted therapy.

Advanced systemic mastocytosis: the impact of KIT mutations in diagnosis, treatment, and progression

Apart from indolent systemic mastocytosis (SM), which is associated with a favorable prognosis, other subtypes of SM (SM with associated clonal hematologic non–mast cell lineage disease, aggressive SM, and mast cell leukemia – collectively referred to in this review as advanced SM) can be debilitating. The complexity of SM makes both the diagnosis and design of response criteria challenging for clinical studies. The tyrosine kinase KIT has been shown to play a crucial role in the pathogenesis of SM and has been a focal point in the development of targeted therapy. Mutations within various domains of the KIT receptor that lead to constitutive activation have been identified in patients, and those involving the activation loop of the KIT receptor are the mutations most frequently detected in patients with mastocytosis. Aberrant activation of the KIT receptor results in increased production of mast cells in extracutaneous organs that may lead to organ failure or early death. This review discusses the diagnosis and management of patients with advanced SM, including the relevance of KIT in this disease, potential therapies targeting this kinase, and criteria for measuring responses to these therapies.

Thalidomide in systemic mastocytosis: results from an open-label, multicentre, phase II study

Mastocytosis can lead to organ failure as well as systemic symptoms that can be disabling, with considerable deterioration in quality of life. Beside symptomatic treatments, interferon-α and purine analogues have been shown to be effective but complete or long-term remission is rarely obtained with these drugs. We conducted a phase II, multicentre, study to investigate thalidomide in severely symptomatic indolent and aggressive systemic mastocytosis. Twenty patients were enrolled of whom 16 were analysed for response. The overall response rate was 56%. Responses were observed in the skin in 61% of patients with a significant decrease in the pruritus score. Mast cell mediator-related symptoms responded in 71% of cases and 25% of aggressive systemic mastocytosis patients had a response in terms of B/C findings (borderline/cytoreduction needed). Bone marrow mast cell infiltration decreased in five of the eight evaluable patients. There was no significant improvement in the AFIRMM (Association Française pour les Initiatives de Recherche sur le Mastocyte et Les Mastocytoses), Quality of Life or Hamilton scores. Grade 3-4 toxicities consisted of peripheral neuropathy (11%) and myelosuppression (neutropenia: 5%; thrombocytopenia: 11%). In conclusion, thalidomide might be useful in mastocytosis and in the treatment of mast cell-related symptoms. It might be considered in selected patients, taking into account the benefit/risk balance and the individual patient evaluation.

Diagnosis and treatment of mast cell disorders: practical recommendations

CONTEXT AND OBJECTIVE The term mastocytosis covers a group of rare disorders characterized by neoplastic proliferation and accumulation of clonal mast cells in one or more organs. The aim of this study was to assess the principal elements for diagnosing and treating these disorders. DESIGN AND SETTING Narrative review of the literature conducted at Grupo Fleury, São Paulo, Brazil. METHODS This study reviewed the scientific papers published in the PubMed, Embase (Excerpta Medica Database), Lilacs (Literatura Latino-Americana e do Caribe em Ciências da Saúde) and Cochrane Library databases that were identified using the search term "mastocytosis." RESULTS The clinical presentation of mastocytosis is remarkably heterogeneous and ranges from skin lesions that may regress spontaneously to aggressive forms associated with organ failure and short survival. Currently, seven subtypes of mastocytosis are recognized through the World Health Organization classification system for hematopoietic tumors. These disorders are diagnosed based on clinical manifestations and on identification of neoplastic mast cells using morphological, immunophenotypic, genetic and molecular methods. Abnormal mast cells display atypical and frequently spindle-shaped morphology, and aberrant expression of the CD25 and CD2 antigens. Elevation of serum tryptase is a common finding in some subtypes, and more than 90% of the patients present the D816V KIT mutation in mast cells. CONCLUSION Here, we described the most common signs and symptoms among patients with mastocytosis and suggested a practical approach for the diagnosis, classification and initial clinical treatment of mastocytosis.

Proteasome inhibition upregulates Bim and induces caspase-3-dependent apoptosis in human mast cells expressing the Kit D816V mutation

The majority of patients with systemic mastocytosis exhibit a D816V mutation in the activating loop of the Kit receptor expressed on mast cells. The Kit ligand regulates mast cell survival by transcriptional repression of the proapoptotic BH3-only protein Bim and by promoting Bim phosphorylation that makes it vulnerable for proteasomal-dependent degradation. We investigated here whether prevention of Bim degradation by a proteasomal inhibitor, MG132, would induce apoptosis in mast cells with the D816V mutation. Human umbilical cord blood-derived mast cells (CBMCs) with wild-type (wt) Kit and two different subclones of the human mast cell line-1 (HMC-1) were used for the study: HMC-1.1 with the V560G mutation in the juxtamembrane domain and HMC-1.2 carrying the V560G mutation together with the D816V mutation. MG132 at 1 μM induced apoptosis in all cell types, an effect accompanied by increased BH3-only proapoptotic protein Bim. The raise of Bim was accompanied by caspase-3 activation, and a caspase-3 inhibitor reduced MG132-induced apoptosis. Further, MG132 caused a reduction of activated Erk, a negative regulator of Bim expression, and thus Bim upregulation. We conclude that decreased phosphorylation and increased levels of Bim overcome the prosurvival effect of the D816V mutation and that the results warrant further investigations of the clinical effects of proteasomal inhibition in systemic mastocytosis.

Therapeutic targeting of c-KIT in cancer

INTRODUCTION

Mutated forms of the receptor tyrosine kinase c-KIT are "drivers" in several cancers and are attractive targets for therapy. While benefits have been obtained from use of inhibitors of KIT kinase activity such as imatinib, especially in gastrointestinal stromal tumours (GIST), primary resistance occurs with certain oncogenic mutations. Furthermore, resistance frequently develops due to secondary mutations. Approaches to addressing both of these issues as well as combination therapies to optimise use of KIT kinase inhibitors are discussed.

AREAS COVERED

This review covers the occurrence of oncogenic KIT mutations in different cancers and the molecular basis of their action. The action of KIT kinase inhibitors, especially imatinib, sunitinib, dasatinib and PKC412, on different primary and secondary mutants is discussed. Outcomes of clinical trials in GIST, acute myeloid leukaemia (AML), systemic mastocytosis and melanoma and their implications for future directions are considered.

EXPERT OPINION

Analysis of KIT mutations in individual patients is an essential prerequisite to the use of kinase inhibitors for therapy, and monitoring for development of secondary mutations that confer drug resistance is necessary. However, it is unlikely that KIT inhibitors alone can lead to cure. KIT mutations alone do not seem to be sufficient for transformation; thus identification and co-targeting of synergistic oncogenic pathways should lead to improved outcomes.

Death from mast cell leukemia: a young patient with longstanding cutaneous mastocytosis evolving into fatal mast cell leukemia

   Mastocytosis is a broad term used for a group of disorders characterized by accumulation of mast cells in the skin with or without extracutaneous involvement. The clinical spectrum of the disease varies from only cutaneous lesions to highly aggressive systemic involvement such as mast cell leukemia. Mastocytosis can present from birth to adulthood. In children, mastocytosis is usually benign, and there is a good chance of spontaneous regression at puberty, unlike adult-onset disease, which is generally systemic and more severe. Moreover, individuals with systemic mastocytosis may be at risk of developing hematologic malignancies. We describe a girl who presented to us with a solitary mastocytoma at age 5 and later developed maculopapular cutaneous mastocytosis. At age 23, after an episode of anaphylactic shock, a bone marrow examination revealed mast cell leukemia. She ultimately died despite aggressive chemotherapy and bone marrow transplantation.

Childhood mastocytosis

PURPOSE OF REVIEW

Important advances have been achieved in recent years in adult mastocytosis. However, our knowledge about childhood mastocytosis is limited because invasive tests are not routinely performed in children. We ignore the frequency of systemic involvement in childhood mastocytosis, its outcome, and which are the main clinical and laboratory parameters associated with persistence into adult mastocytosis and its severity.

RECENT FINDINGS

Childhood mastocytosis is a clonal mast cell disease, with different activating mutations in the KIT gene discovered in most patients. Serum tryptase is the best marker for mast cell burden in children, and, at baseline, correlates well with the severity of symptoms in childhood mastocytosis. Systemic mastocytosis definitely may occur in children, but bone marrow studies to demonstrate a systemic involvement are not routinely performed nor recommended; it can be estimated that around 30% of children may have bone marrow involvement as demonstrated by showing aggregates of mast cells or by flow cytometry of mast cells expressing the aberrant CD25 marker.

SUMMARY

A new and improved classification of childhood mastocytosis is needed, and should be based on the correlation of clinical manifestations, morphology of mast cells in the skin, and the predicted outcome of the disease. The current classifications of childhood mastocytosis do not address any of these important issues.