Systemic Mastocytosis and Other Entities Involving Mast Cells: A Practical Review and Update

SOHO State of the Art Update and Next Questions: Current and Emerging Therapies for Systemic Mastocytosis

Systemic mastocytosis (SM) is a heterogeneous myeloid neoplasm, characterized by clonal proliferation of mast cells (MCs) in ≥ 1 extracutaneous organs, including the bone marrow (BM) and gastrointestinal tract. Aberrant MC proliferation is driven by mutation KIT D816V in ≈90-95% of SM patients. Indolent SM (ISM) is the most common SM subtype with various symptoms that can be severe. Advanced SM (AdvSM) has markedly poor prognosis. The advent of KIT inhibitors, targeting mutant KIT and neoplastic MCs, led to a paradigm shift in SM management and markedly improved outcomes. Midostaurin inaugurated the era of KIT inhibitors and was approved for AdvSM in 2017. Avapritinib is the first highly potent and selective inhibitor of KIT D816V that was approved to treat AdvSM and symptomatic ISM (platelets ≥ 50 × 109/L), in the US, in 2021 and 2023, respectively. Pooled analysis of the EXPLORER and PATHFINDER studies, assessing avapritinib in AdvSM, demonstrated rapid and profound reductions (≥ 50%) in markers of MC burden, high response rates (71-75%), and prolonged survival. In the PIONEER study, avapritinib significantly and rapidly improved symptoms/quality of life, and reduced markers of MC burden in ISM patients. The investigational agents bezuclastinib and elenestinib are highly potent and selective inhibitors of KIT D816V with minimal blood-brain barrier penetration. Bezuclastinib reduced markers of MC burden by ≥ 50% in ≈50% of AdvSM patients and ≈90-100% of nonAdvSM patients and reduced symptoms (≥ 50%) in the APEX and SUMMIT studies, respectively. Elenestinib demonstrated dose-dependent efficacy in reducing MC burden markers and improved symptoms in ISM patients in the HARBOR study.

Ocular and palpebral manifestations of mastocytosis: A prospective single-center study

BACKGROUND

Ocular discomfort has been described as a frequent symptom in patients with mastocytosis, a rare disease resulting from accumulation of mast cells in organs.

OBJECTIVES

This study aims to assess the frequency and describe the nature of ocular and palpebral abnormalities in mastocytosis patients.

PATIENTS AND METHODS

We conducted a prospective, single-center study in adult mastocytosis patients, who were systematically examined by a dermatologist and an ophthalmologist with determination of tear cytokine levels.

RESULTS

Twenty-one patients with a mean age of 60.7 ± 16.4 years were included. Nine patients presented with isolated cutaneous mastocytosis and 12 with indolent systemic mastocytosis. Seventeen patients (81.0%) presented with one or more eye symptoms. The most frequently reported symptoms were ocular itching (n = 12), dryness (n = 12), and excessive tearing (n = 9). Based on their Ocular Surface Disease Index scores, 11 patients (52.4%) were classified as having moderate orsevere ocular surface disease. Eye examination revealed dry eye disease in 11 patients (52.4%), associated with superficial punctate keratitis in two patients and posterior blepharitis in 10 patients (47.6%). Tear cytokine levels of interleukin (IL)-1RA and IL-6 were not significantly different in mastocytosis patients compared to controls and did not vary according to ocular symptoms.

CONCLUSION

Dry eye disease and blepharitis were frequently found in this cohort of mastocytosis patients. Ocular consultation may be considered in this population to initiate eye hydration measures.

A post-marketing pharmacovigilance study of avapritinib: Adverse event data mining and analysis based on the United States Food and Drug Administration Adverse Event Reporting System database

AIMS

Avapritinib was first approved by the FDA in January 2020 and represents the first precision-targeted drug for gastrointestinal stromal tumours. However, there is a lack of large-scale data relating to adverse events (AEs) related to its use. We aimed to explore the avapritinib-related AEs in real-world practice based on the post-marketing data.

METHODS

We extracted all avapritinib-related reports submitted to the FDA Adverse Event Reporting System (FAERS) by June 2022. Based on disproportionality analysis and Bayesian analysis, we then calculated the reporting odds ratio (ROR), proportional reporting ratio (PRR), information component (IC) and empirical Bayes geometric mean (EBGM) to evaluate whether there is a significant association between avapritinib and AEs. Gender, age and time to onset were comparable between haemorrhage/non-haemorrhage, serious/non-serious, death/non-death AEs, respectively.

RESULTS

In total, 3120 cases related to avapritinib were documented in the FAERS database, and 44% were reported within 30 days of commencing avapritinib. A total of 331 different AE signals were detected, and no significant differences between males and females was identified. Although the number of AEs associated with an abnormal skin texture and executive dysfunction was small, the signal intensity is high, suggesting that these events are strongly correlated with avapritinib. Subgroup analysis showed that elderly male patients were more likely to suffer from serious AEs compared to females (P < .01), but there was no significant difference between the haemorrhage group and the non-haemorrhage group. Analysis of fatalities due to avapritinib-related AEs indicated that sex, age and time-to-onset were all significantly related to death (P < .05).

CONCLUSION

Our study provides a more precise description of the incidence and characteristics of AEs after using avapritinib, clinicians should be particularly careful when prescribing avapritinib to elderly male patients, especially within the 30 days.

Treatment refractory mast cell leukemia with dominant gastrointestinal manifestation and concomitant skin symptoms: A case report

BACKGROUND

Mast cell leukemia (MCL), a subtype of systemic mastocytosis (SM), is an extremely rare clinical entity characterized by a very poor prognosis. Chemotherapy, tyrosine kinase inhibitors, and allogeneic hematopoietic cell transplantation are the only treatment options, but they cannot provide the desired outcomes in most cases of MCL. However, other types of SM can be successfully treated. The disease has no specific manifestation, but gastroenterological symptoms are present in most cases.

CASE SUMMARY

The authors, hereby, report a case of a 46-year-old female patient diagnosed with MCL-the rarest subtype of SM. The patient presented to the gastroenterology clinic with multiple, various, and unspecific gastroenterological symptoms. Concomitance of skin lesions significantly contributed to a relatively prompt diagnosis. The serum tryptase level was extremely high and bone the marrow aspirate showed an infiltration of atypical mast cells. The disease was rapidly progressive and primary refractory to chemotherapy and the patient succumbed to the illness about a month after the initiation of treatment.

CONCLUSION

Despite its "hematological nature", MCL, in most cases presents dominantly with unspecific gastroenterological symptoms. Thus, a high disease awareness among physicians other than hematologists is necessary to improve treatment outcomes. Serum tryptase level, due to its non-invasive nature and easy access, may serve as an initial step to estimate the probability of mastocytosis.

T-cell immune profile in blood of systemic mastocytosis: Association with disease features

BACKGROUND

Systemic mastocytosis (SM) is a heterogeneous disease characterized by an expansion of KIT-mutated mast cells (MC). KIT-mutated MC display activated features and release MC mediators that might act on the tumour microenvironment and other immune cells. Here, we investigated the distribution of lymphocyte subsets in blood of patients with distinct subtypes of SM and determined its association with other disease features.

METHODS

We studied the distribution of TCD4+ and TCD4- cytotoxic cells and their subsets, as well as total NK- and B cells, in blood of 115 SM patients-38 bone marrow mastocytosis (BMM), 67 indolent SM (ISM), 10 aggressive SM (ASM)- and 83 age-matched healthy donors (HD), using spectral flow cytometry and the EuroFlow Immunomonitoring panel, and correlated it with multilineage KITD816V, the alpha-tryptasemia genotype (HαT) and the clinical manifestations of the disease.

RESULTS

SM patients showed decreased counts (vs. HD) of TCD4- cytotoxic cells, NK cells and several functional subsets of TCD4+ cells (total Th1, Th2-effector memory, Th22-terminal effector and Th1-like Tregs), together with increased T-follicular-helper and Th1/Th17-like Treg counts, associated with different immune profiles per diagnostic subtype of SM, in multilineal versus MC-restricted KITD816V and in cases with a HαT+ versus HαT- genotype. Unique immune profiles were found among BMM and ISM patients with MC-restricted KITD816V who displayed HαT, anaphylaxis, hymenoptera venom allergy, bone disease, pruritus, flushing and GI symptoms.

CONCLUSION

Our results reveal altered T- and NK-cell immune profiles in blood of SM, which vary per disease subtype, the pattern of involvement of haematopoiesis by KITD816V, the HαT genotype and specific clinical manifestations of the disease.

Expression of CD25, mast cell markers and T-cell markers in eosinophilic esophagitis

While eosinophilic esophagitis (EOE) is defined by histologic presence of eosinophils, a few studies have established the presence of mast cells in EOE and even shown their correlation with symptom persistence despite resolution of eosinophils. Expression of aberrant mast cell markers CD25 and CD2 have not been studied in EOE. This study quantifies the number of hotspot cells per high power field expressing CKIT/CD117, tryptase, CD25, CD2 and CD3 by immunohistochemical stains in endoscopic esophageal biopsies of the following three cohorts: (1) established and histologically confirmed EOE, (2) suspected EOE with biopsies negative for eosinophils, and (3) no history of or suspicion for EOE with histologically unremarkable biopsies. In this study, mast cells were highlighted by CKIT and tryptase in EOE, and not seen in other clinically mimicking cases. There were also significantly higher densities of CD25 and pan-T-cell marker staining in EOE cases. These findings suggest an inflammatory cellular milieu in EOE, beyond just eosinophils, that can be demonstrated by immunohistochemistry, and that invite further study into the role that these cells may play in EOE.

Fifth Edition of the World Health Classification of Tumors of the Hematopoietic and Lymphoid Tissue: Myeloid Neoplasms

In this manuscript, we review myeloid neoplasms in the fifth edition of the World Health Organization classification of hematolymphoid tumors (WHO-HEM5), focusing on changes from the revised fourth edition (WHO-HEM4R). Disease types and subtypes have expanded compared with WHO-HEM4R, mainly because of the expansion in genomic knowledge of these diseases. The revised classification is based on a multidisciplinary approach including input from a large body of pathologists, clinicians, and geneticists. The revised classification follows a hierarchical structure allowing usage of family (class)-level definitions where the defining diagnostic criteria are partially met or a complete investigational workup has not been possible. Overall, the WHO-HEM5 revisions to the classification of myeloid neoplasms include major updates and revisions with increased emphasis on genetic and molecular drivers of disease. The most notable changes have been applied to the sections of acute myeloid leukemia and myelodysplastic neoplasms (previously referred to as myelodysplastic syndrome) with incorporation of novel, disease-defining genetic changes. In this review we focus on highlighting the updates in the classification of myeloid neoplasms, providing a comparison with WHO-HEM4R, and offering guidance on how the new classification can be applied to the diagnosis of myeloid neoplasms in routine practice.

Mast Cell Leukemia: An Update with a Practical Review

Mast cell leukemia (MCL) is the leukemic form of SM with at least 20% mostly immature mast cells on bone marrow aspirate. MCL may develop de novo, in the absence of a prior SM, or it may represent a progression from a previous SM. MCL may be sub-divided into the more frequent, aggressive acute form with signs of organ damage (C-findings) and the chronic form lacking C-findings and presenting a more stable course, although over time, progression to acute MCL is common. The 2022 WHO subtype of MCL with an associated hematological neoplasm was renamed MCL with an associated myeloid neoplasm in the 2022 International Consensus Classification (ICC). The relevance of the distinction between the leukemic and aleukemic forms based on the percentage of circulating mast cells is a matter of debate. The current knowledge on MCL is restricted mainly to single reports or case series with a limited number of larger studies. Our aim is to provide a comprehensive overview of this rare disease in terms of clinical manifestations, morphology, phenotype, molecular characteristics, differential diagnosis, outcome and treatment. A general overview on mastocytosis is also included.

Mast cell evaluation in gastrointestinal biopsies: should we be counting? A critical review and practical guide for the surgical pathologist

Mast cells are residents of the tubular gastrointestinal (GI) tract, where they play an important role in host defence and other vital functions. Dysregulation of mast cells has been implicated in the pathogenesis of several neoplastic, inflammatory, and functional disorders, some of which may manifest with GI symptoms. Surgical pathologists must therefore confront when and how to evaluate GI biopsies for mast cells, and whether such decisions should be based on morphologic criteria, clinical context, or direct request from clinical colleagues. The pathologist's role in evaluation of mast cell infiltrates is best defined in the diagnosis of systemic mastocytosis, where the utility of morphologic assessment coupled with ancillary studies is well established. In contrast, in nonneoplastic mast cell disorders such as mast cell activation syndrome, irritable bowel syndrome, or so-called 'mastocytic enterocolitis', a role for histopathology, if any, is controversial. Despite this, pathologists have seen a sharp increase in requests for mast cell quantification in the latter setting, despite these requests not being supported by published evidence. Moreover, what constitutes a 'normal' number of mast cells in a luminal GI biopsy is not well established. As a result, there is considerable variation in how these requests are handled in practice. This review evaluates and summarizes the published evidence relating to mast cell evaluation in endoscopic GI biopsies in various clinical scenarios, with a goal of providing practical, evidence-based guidance for the surgical pathologist when approached with requests for mast cell quantification in GI biopsies.