Utility of flow cytometric analysis of mast cells in the diagnosis and classification of adult mastocytosis

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.

Antibody-Based and Cell Therapies for Advanced Mastocytosis: Established and Novel Concepts

Advanced systemic mastocytosis (SM) is a heterogeneous group of myeloid neoplasms characterized by an uncontrolled expansion of mast cells (MC) in one or more internal organs, SM-induced tissue damage, and poor prognosis. Advanced SM can be categorized into aggressive SM (ASM), MC leukemia (MCL), and SM with an associated hematologic neoplasm (SM-AHN). In a vast majority of all patients, neoplastic cells display a KIT mutation, mostly D816V and rarely other KIT variants. Additional mutations in other target genes, such as SRSF2, ASXL1, or RUNX1, may also be identified, especially when an AHN is present. During the past 10 years, improved treatment approaches have led to a better quality of life and survival in patients with advanced SM. However, despite the availability of novel potent inhibitors of KIT D816V, not all patients enter remission and others relapse, often with a multi-mutated and sometimes KIT D816V-negative disease exhibiting multi-drug resistance. For these patients, (poly)chemotherapy, antibody-based therapies, and allogeneic hematopoietic stem cell transplantation may be viable treatment alternatives. In this article, we discuss treatment options for patients with drug-resistant advanced SM, including novel KIT-targeting drugs, antibody-based drugs, and stem cell-eradicating therapies.

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.

Multiparameter flow cytometry in the evaluation of myelodysplasia: Analytical issues: Recommendations from the European LeukemiaNet/International Myelodysplastic Syndrome Flow Cytometry Working Group

Multiparameter flow cytometry (MFC) is one of the essential ancillary methods in bone marrow (BM) investigation of patients with cytopenia and suspected myelodysplastic syndrome (MDS). MFC can also be applied in the follow-up of MDS patients undergoing treatment. This document summarizes recommendations from the International/European Leukemia Net Working Group for Flow Cytometry in Myelodysplastic Syndromes (ELN iMDS Flow) on the analytical issues in MFC for the diagnostic work-up of MDS. Recommendations for the analysis of several BM cell subsets such as myeloid precursors, maturing granulocytic and monocytic components and erythropoiesis are given. A core set of 17 markers identified as independently related to a cytomorphologic diagnosis of myelodysplasia is suggested as mandatory for MFC evaluation of BM in a patient with cytopenia. A myeloid precursor cell (CD34⁺ CD19^- ) count >3% should be considered immunophenotypically indicative of myelodysplasia. However, MFC results should always be evaluated as part of an integrated hematopathology work-up. Looking forward, several machine-learning-based analytical tools of interest should be applied in parallel to conventional analytical methods to investigate their usefulness in integrated diagnostics, risk stratification, and potentially even in the evaluation of response to therapy, based on MFC data. In addition, compiling large uniform datasets is desirable, as most of the machine-learning-based methods tend to perform better with larger numbers of investigated samples, especially in such a heterogeneous disease as MDS.

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.

Secondary basophilic leukemia in Ph-negative myeloid neoplasms: A distinct subset with poor prognosis

During progression of myeloid neoplasms, the basophil compartment may expand substantially and in some of these patients, a basophilic leukemia is diagnosed. In patients with Ph-chromosome+ chronic myeloid leukemia, acceleration of disease is typically accompanied by marked basophilia. In other myeloid neoplasms, secondary leukemic expansion of basophils is rarely seen. We report on 5 patients who suffered from a myelodysplastic syndrome, myeloproliferative neoplasm, or acute leukemia and developed a massive expansion of basophils during disease progression. In 4 of 5 patients, peripheral blood basophil counts reached 40%, and the diagnosis “secondary basophilic leukemia” was established. As assessed by flow cytometry, neoplastic basophils expressed CD9, CD18, CD25, CD33, CD63, PD-L1, CD123, and CLL-1. In addition, basophils were found to display BB1 (basogranulin), 2D7, tryptase and KIT. In 4 of 5 patients the disease progressed quickly and treatment with azacitidine was started. However, azacitidine did not induce major clinical responses, and all patients died from progressive disease within 3 Y. In in vitro experiments, the patients´ cells and the basophilic leukemia cell line KU812 showed variable responses to targeted drugs, including azacitidine, venetoclax, hydroxyurea, and cytarabine. A combination of venetoclax and azacitidine induced cooperative antineoplastic effects in these cells. Together, secondary basophilic leukemia has a poor prognosis and monotherapy with azacitidine is not sufficient to keep the disease under control for longer time-periods. Whether drug combination, such as venetoclax+azacitidine, can induce better outcomes in these patients remains to be determined in future clinical studies.

Establishing diagnostic criteria for mastocytosis in skin biopsies

AIMS

The diagnosis of mastocytosis in skin biopsies can be challenging - particularly in cases with very few mast cells. More diagnostic criteria are needed.

METHODS AND RESULTS

We analyzed 103 skin biopsies from patients with mastocytosis and compared them with biopsies from inflammatory skin lesions and normal skin. Using CD117 immunostaining, we determined the mast cell distribution pattern, the percentage of mast cells in the inflammatory infiltrate, and the mast cell count per mm². We found that a sheet-like or subepidermal distribution of mast cells was specific for mastocytosis. The most significant feature was the percentage of mast cells and not the mast cell count. We found that a mast cell percentage above 40% was fully specific in both adults and children but lacked sensitivity, especially in adults. In children, all cases with a percentage below 40% harbored a number of mast cells above 90 per mm², allowing a straightforward diagnosis. In adults, the diagnosis was more challenging and cases with less than 40% of mast cells could be diagnosed on account of a number of mast cells above 40 per mm², with 88.5% sensitivity and 95.2% specificity. Additional signs might be useful in difficult cases. However, CD25 immunostaining was not useful.

CONCLUSIONS

We confirmed that the criteria currently applied in the bone marrow were not appropriate for the skin. Accordingly, we developed an algorithm for the diagnosis of mastocytosis in skin biopsies with a high level of interrater reproducibility (mean kappa 0.8).

B-Cell Regeneration Profile and Minimal Residual Disease Status in Bone Marrow of Treated Multiple Myeloma Patients

B-cell regeneration during therapy has been considered as a strong prognostic factor in multiple myeloma (MM). However, the effects of therapy and hemodilution in bone marrow (BM) B-cell recovery have not been systematically evaluated during follow-up. MM (n = 177) and adult (≥50y) healthy donor (HD; n = 14) BM samples were studied by next-generation flow (NGF) to simultaneously assess measurable residual disease (MRD) and residual normal B-cell populations. BM hemodilution was detected in 41 out of 177 (23%) patient samples, leading to lower total B-cell, B-cell precursor (BCP) and normal plasma cell (nPC) counts. Among MM BM, decreased percentages (vs. HD) of BCP, transitional/naïve B-cell (TBC/NBC) and nPC populations were observed at diagnosis. BM BCP increased after induction therapy, whereas TBC/NBC counts remained abnormally low. At day+100 postautologous stem cell transplantation, a greater increase in BCP with recovered TBC/NBC cell numbers but persistently low memory B-cell and nPC counts were found. At the end of therapy, complete response (CR) BM samples showed higher CD19^- nPC counts vs. non-CR specimens. MRD positivity was associated with higher BCP and nPC percentages. Hemodilution showed a negative impact on BM B-cell distribution. Different BM B-cell regeneration profiles are present in MM at diagnosis and after therapy with no significant association with patient outcome.

Mast cells as a unique hematopoietic lineage and cell system: From Paul Ehrlich's visions to precision medicine concepts

The origin and functions of mast cells (MCs) have been debated since their description by Paul Ehrlich in 1879. MCs have long been considered 'reactive bystanders' and 'amplifiers' in inflammatory processes, allergic reactions, and host responses to infectious diseases. However, knowledge about the origin, phenotypes and functions of MCs has increased substantially over the past 50 years. MCs are now known to be derived from multipotent hematopoietic progenitors, which, through a process of differentiation and maturation, form a unique hematopoietic lineage residing in multiple organs. In particular, MCs are distinguishable from basophils and other hematopoietic cells by their unique phenotype, origin(s), and spectrum of functions, both in innate and adaptive immune responses and in other settings. The concept of a unique MC lineage is further supported by the development of a distinct group of neoplasms, collectively referred to as mastocytosis, in which MC precursors expand as clonal cells. The clinical consequences of the expansion and/or activation of MCs are best established in mastocytosis and in allergic inflammation. However, MCs have also been implicated as important participants in a number of additional pathologic conditions and physiological processes. In this article, we review concepts regarding MC development, factors controlling MC expansion and activation, and some of the fundamental roles MCs may play in both health and disease. We also discuss new concepts for suppressing MC expansion and/or activation using molecularly-targeted drugs.

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

BACKGROUND

In indolent systemic mastocytosis (ISM), several risk factors of disease progression have been identified. Previous studies, performed with limited patient numbers, have also shown that the clinical course in ISM is stable and comparable to that of cutaneous mastocytosis (CM). The aim of this project was to compare the prognosis of patients with ISM with that of patients with CM.

METHODS

We employed a dataset of 1993 patients from the registry of the European Competence Network on Mastocytosis (ECNM) to compare outcomes of ISM and CM.

RESULTS

We found that overall survival (OS) is worse in ISM compared to CM. Moreover, in patients with typical ISM, bone marrow mastocytosis (BMM), and smoldering SM (SSM), 4.1% of disease progressions have been observed (4.9% of progressions in typical ISM group, 1.7% in BMM, and 9.4% in SSM). Progressions to advanced SM were observed in 2.9% of these patients. In contrast, six patients with CM (1.7%) converted to ISM and no definitive progression to advanced SM was found. No significant differences in OS and event-free survival (EFS) were found when comparing ISM, BMM, and SSM. Higher risk of both progression and death was significantly associated with male gender, worse performance status, and organomegaly.

CONCLUSION

Our data confirm the clinical impact of the WHO classification that separates ISM from CM and from other SM variants.

Pharmacotherapy in Mast Cell Leukemia

INTRODUCTION

Mast cell leukemia (MCL) is one of the most aggressive forms of Systemic Mastocytosis (SM), a complex family of rare diseases, for which standard therapies are very few. MCL represents only <1% cases of SM and this is the reason why there are no specific clinical trials to better explore this disease. As a consequence, MCL is treated and grouped within other forms of SM, being all KIT-driven diseases; however, its KIT dysregulation leads to uncontrolled activation of mast cells (MCs), which correlates with forms of myeloid acute leukemia (AML).

AREAS COVERED

Different therapeutic approaches can be followed in the treatment of MCL. The authors look at both symptomatic therapies along with other approaches including targeted therapy. Further, the authors provide their expert opinion.

EXPERT OPINION

In the scenario of mast cell leukemia treatment, the key approach to achieve clinical results is, more than other similar pathologies, personalizing the therapy. It could be interesting or desirable to introduce for instance KIT mutant forms as minor criteria for the diagnosis of advanced SM, considering the small patient population with MCL and the relatively large panel of activating mutations for KIT and other important proteins involved in MCs' regulation.

Identification and Immunophenotypic Characterization of Normal and Pathological Mast Cells

Mast cells (MCs) are secretory cells that are central players in human allergic disease and immune responses. With the exception of a few pathological situations, MCs are usually present at relatively low frequencies in most tissues. Since their first description, MCs in tissues were identified mostly using their morphological characteristics and their typical coloration when stained with aniline dyes. However, increasing availability of highly specific antibodies now permits the use of fluorescence-based flow cytometry as the method of choice for the quantification, characterization, and purification of cells in suspension. This technique allows for a rapid analysis of thousands of events and for the identification of cells present at frequencies as low as one event in 10⁶ unwanted cells. This method also permits for simultaneous characterization of multiple antigens at a single cell level, which is ideal in order to study rare populations of cells like MCs. Here we describe the basis of flow cytometry-based immunophenotyping applied to the study of MC. The protocol focuses on the study of human MCs present in body fluids (mainly bone marrow) but can easily be adapted to studying MCs from other tissues and species.

International prognostic scoring system for mastocytosis (IPSM): a retrospective cohort study

BACKGROUND

The WHO classification separates mastocytosis into distinct variants, but prognostication remains a clinical challenge. The aim of this study was to improve prognostication for patients with mastocytosis.

METHODS

We analysed data of the registry of the European Competence Network on Mastocytosis including 1639 patients (age 17-90 years) diagnosed with mastocytosis according to WHO criteria between Jan 12, 1978, and March 16, 2017. Univariate and multivariate analyses with Cox regression were applied to identify prognostic variables predicting survival outcomes and to establish a prognostic score. We validated this International Prognostic Scoring System in Mastocytosis (IPSM) with data of 462 patients (age 17-79 years) from the Spanish network Red Española de Mastocitosis diagnosed between Jan 22, 1998, and Nov 2, 2017.

FINDINGS

The prognostic value of the WHO classification was confirmed in our study (p<0·0001). For patients with non-advanced mastocytosis (n=1380), we identified age 60 years or older (HR 10·75, 95% CI 5·68-20·32) and a concentration of alkaline phosphatase 100 U/L or higher (2·91, 1·60-5·30) as additional independent prognostic variables for overall survival. The resulting scoring system divided patients with non-advanced mastocytosis into three groups: low (no risk factors), intermediate 1 (one risk factor), and intermediate 2 (two risk factors). Overall survival and progression-free survival differed significantly among these groups (p<0·0001). In patients with advanced mastocytosis (n=259), age 60 years or older (HR 2·14, 95% CI 1·42-3·22), a concentration of tryptase 125 ng/mL or higher (1·81, 1·20-2·75), a leukocyte count of 16 × 10⁹ per L or higher (1·88, 1·27-2·79), haemoglobin of 11 g/dL or lower (1·71, 1·13-2·57), a platelet count of 100 × 10⁹ per L or lower (1·63, 1·13-2·34), and skin involvement (0·46, 0·30-0·69) were prognostic variables. Based on these variables, a separate score for advanced mastocytosis with four risk categories was established, with significantly different outcomes for overall survival and progression-free survival (p<0·0001). The prognostic value of both scores was confirmed in 413 patients with non-advanced disease and 49 with advanced mastocytosis from the validation cohort.

INTERPRETATION

The IPSM scores for patients with non-advanced and advanced mastocytosis can be used to predict survival outcomes and guide treatment decisions. However, the predictive value of the IPSM needs to be confirmed in forthcoming trials.

FUNDING

Austrian Science Fund, Deutsche Forschungsgemeinschaft, Koeln Fortune Program, Charles and Ann Johnson Foundation, Instituto de Salud Carlos III, Fondos FEDER, Research-Foundation Flanders/Fonds Wetenschappelijk Onderzoek, Clinical Research-Fund of the University Hospitals Leuven, and Research-Foundation Flanders/Fonds Wetenschappelijk Onderzoek.

Identification of a leukemia-initiating stem cell in human mast cell leukemia

Mast cell leukemia (MCL) is a highly fatal malignancy characterized by devastating expansion of immature mast cells in various organs. Although considered a stem cell disease, little is known about MCL-propagating neoplastic stem cells. We here describe that leukemic stem cells (LSCs) in MCL reside within a CD34⁺/CD38⁻ fraction of the clone. Whereas highly purified CD34⁺/CD38⁻ cells engrafted NSG_hSCF mice with fully manifesting MCL, no MCL was produced by CD34⁺/CD38⁺ progenitors or the bulk of KIT⁺/CD34⁻ mast cells. CD34⁺/CD38⁻ MCL cells invariably expressed CD13 and CD133, and often also IL-1RAP, but did not express CD25, CD26 or CLL-1. CD34⁺/CD38⁻ MCL cells also displayed several surface targets, including CD33, which was homogenously expressed on MCL LSC in all cases, as well as the D816V mutant form of KIT. Whereas CD34⁺/CD38⁻ cells were resistant against single drugs, exposure to combinations of CD33-targeting and KIT-targeting drugs resulted in LSC-depletion and markedly reduced engraftment in NSG_hSCF mice. Together, MCL LSCs are CD34⁺/CD38⁻ cells that express distinct profiles of markers and target antigens. Characterization of MCL LSCs should facilitate their purification and should support the development of LSC-eradicating curative treatment approaches in this fatal type of leukemia.

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.

Bone Marrow Expression of Mast Cell Disorders

Mast cell disorders comprise a heterogeneous group of rare diseases, the diagnosis of which still remains a challenge. Bone marrow analysis constitutes the most appropriate site for screening systemic involvement in mastocytosis. Morphologic, immunohistochemical, flow cytometric immunophenotyping, and molecular studies should be routinely performed for diagnostic/prognostic purposes in experienced reference centers during the diagnostic workup in suspected systemic mastocytosis. The authors review the most relevant characteristics of bone marrow expression of mast cell disorders as well as the different methodological approaches to be applied to perform an objective and reproducible diagnosis and classification of mastocytosis and other mast cell disorders.

CD44 is a RAS/STAT5-regulated invasion receptor that triggers disease expansion in advanced mastocytosis

The Hermes receptor CD44 is a multifunctional adhesion molecule that plays an essential role in the homing and invasion of neoplastic stem cells in various myeloid malignancies. Although mast cells (MCs) reportedly express CD44, little is known about the regulation and function of this receptor in neoplastic cells in systemic mastocytosis (SM). We found that clonal CD34⁺/CD38^- stem cells, CD34⁺/CD38⁺ progenitor cells, and CD117⁺⁺/CD34^- MCs invariably express CD44 in patients with indolent SM (ISM), SM with an associated hematologic neoplasm, aggressive SM, and MC leukemia (MCL). In addition, all human MCL-like cell lines examined (HMC-1, ROSA, and MCPV-1) displayed cytoplasmic and cell-surface CD44. We also found that expression of CD44 in neoplastic MCs depends on RAS-MEK and STAT5 signaling and increases with the aggressiveness of SM. Correspondingly, higher levels of soluble CD44 were measured in the sera of patients with advanced SM compared with ISM or cutaneous mastocytosis and were found to correlate with overall and progression-free survival. To investigate the functional role of CD44, a xenotransplantation model was employed using severe combined immunodeficient (SCID) mice, HMC-1.2 cells, and a short hairpin RNA (shRNA) against CD44. In this model, the shRNA-mediated knockdown of CD44 resulted in reduced MC expansion and tumor formation and prolonged survival in SCID mice compared with HMC-1.2 cells transduced with control shRNA. Together, our data show that CD44 is a RAS-MEK/STAT5-driven MC invasion receptor that correlates with the aggressiveness of SM. Whether CD44 can serve as therapeutic target in advanced SM remains to be determined in forthcoming studies.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Mast Cell Disease Assessment by Flow Cytometric Analysis

Mast cells are present at a low frequency in bone marrow, rendering high-sensitivity multiparametric flow cytometric analysis an ideal method to assess antigen expression on mast cells. This article discusses the normal antigen expression profile of mast cells, established criteria to identify neoplastic mast cells, and new immunophenotypic markers and approaches to identify the presence of neoplastic mast cells in cases of mastocytosis.

Characterization of Mast Cell Activation Syndrome

BACKGROUND

Mast cell activation syndrome (MCAS), a recently recognized nonneoplastic mast cell disease driving chronic multisystem inflammation and allergy, appears prevalent and thus important. We report the first systematic characterization of a large MCAS population.

METHOD

Demographics, comorbidities, symptoms, family histories, physical examination and laboratory findings were reviewed in 298 retrospective and 115 prospective patients with MCAS. Blood samples from prospective subjects were examined by flow cytometry for clonal mast cell disease and tested for cytokines potentially driving the monocytosis frequent in MCAS.

RESULTS

Demographically, white females dominated. Median ages at symptom onset and diagnosis were 9 and 49 years, respectively (range: 0-88 and 16-92, respectively) and median time from symptom onset to diagnosis was 30 years (range: 1-85). Median numbers of comorbidities, symptoms, and family medical issues were 11, 20, and 4, respectively (range: 1-66, 2-84, and 0-33, respectively). Gastroesophageal reflux, fatigue and dermatographism were the most common comorbidity, symptom and examination finding. Abnormalities in routine laboratories were common and diverse but typically modest. The most useful diagnostic markers were heparin, prostaglandin D2, histamine and chromogranin A. Flow cytometric and cytokine assessments were unhelpful.

CONCLUSIONS

Our study highlights MCAS׳s morbidity burden and challenging heterogeneity. Recognition is important given good survival and treatment prospects.

Update on Mastocytosis (Part 1): Pathophysiology, Clinical Features, and Diagnosis

Mastocytosis is a term used to describe a heterogeneous group of disorders characterized by clonal proliferation of mast cells in various organs. The organ most often affected is the skin. Mastocytosis is a relatively rare disorder that affects both sexes equally. It can occur at any age, although it tends to appear in the first decade of life, or later, between the second and fifth decades. Our understanding of the pathophysiology of mastocytosis has improved greatly in recent years, with the discovery that somatic c-kit mutations and aberrant immunophenotypic features have an important role. The clinical manifestations of mastocytosis are diverse, and skin lesions are the key to diagnosis in most patients.

FLOCK cluster analysis of mast cell event clustering by high-sensitivity flow cytometry predicts systemic mastocytosis

OBJECTIVES

In our high-sensitivity flow cytometric approach for systemic mastocytosis (SM), we identified mast cell event clustering as a new diagnostic criterion for the disease.

METHODS

To objectively characterize mast cell gated event distributions, we performed cluster analysis using FLOCK, a computational approach to identify cell subsets in multidimensional flow cytometry data in an unbiased, automated fashion.

RESULTS

FLOCK identified discrete mast cell populations in most cases of SM (56/75 [75%]) but only a minority of non-SM cases (17/124 [14%]). FLOCK-identified mast cell populations accounted for 2.46% of total cells on average in SM cases and 0.09% of total cells on average in non-SM cases (P < .0001) and were predictive of SM, with a sensitivity of 75%, a specificity of 86%, a positive predictive value of 76%, and a negative predictive value of 85%.

CONCLUSIONS

FLOCK analysis provides useful diagnostic information for evaluating patients with suspected SM, and may be useful for the analysis of other hematopoietic neoplasms.

Systemic Mastocytosis: Clinical Update and Future Directions

Systemic mastocytosis (SM) is defined as the accumulation of abnormal mast cells (MC) in 1 or more extracutaneous tissues. Symptoms are due to either MC activation or organ infiltration and vary depending on disease subtype. More benign forms of SM, such as indolent SM, result in a life expectancy similar to the general population, while more aggressive subtypes, such as MC leukemia (MCL), have a median survival measured on the order of months. Treatment of indolent SM is directed at controlling the symptoms associated with MC activation. In advanced forms, such as aggressive SM and MCL, agents targeting MC proliferation such as KIT tyrosine kinase inhibitors, cladribine, and thalidomide may be provided. Newer agents based on preclinical rationale are also being actively investigated. However, the only potentially curative therapy for aggressive SM/MCL remains hematopoietic stem cell transplantation. Given that SM is a relatively rare disease, clinicians are often underprepared to evaluate, diagnose, and effectively treat this clinically heterogeneous condition. Here we seek to familiarize clinicians with this orphan disease and review current and future treatment approaches.

Chronic mast cell leukemia: a novel leukemia-variant with distinct morphological and clinical features

Mast cell leukemia (MCL) is a rare form of systemic mastocytosis characterized by leukemic expansion of mostly immature mast cells, organ damage, drug-resistance, and a poor prognosis. Even when treated with chemotherapy, most patients have a life-expectancy of less than one year. However, there are rare patients with MCL in whom the condition is less aggressive and does not cause organ damage within a short time. In these patients, mast cells exhibit a more mature morphology when compared to acute MCL. A recently proposed classification suggests that these cases are referred to as chronic MCL. In the present article, we discuss clinical, histopathological and morphological aspects of acute and chronic MCL.

Mast cell leukemia: a review

SUMMARY 

Mast cell leukemia (MCL) is a rare subtype of systemic mastocytosis. In MCL the numbers of mast cells exceed 19% of nucleated cells in bone marrow and/or 10% of circulating leukocytes in peripheral blood. Primary MCL must be distinguished from secondary MCL evolving from another subvariant of systemic mastocytosis or from mast cell sarcoma. Acute MCL with a poor prognosis is distinguished from the more indolent chronic MCL. Serum tryptase is significantly elevated in almost all MCL patients and activating point mutations at codon 816 of KIT (usually KIT D816V) are encountered in about 70%. Regarding differential diagnosis, other ‘tryptase-positive’ or ‘metachromatic’ leukemias must be considered, including myelomastocytic leukemia and tryptase-positive acute myeloid leukemia but also acute and chronic basophilic leukemias.

The immunophenotype of mast cells and its utility in the diagnostic work-up of systemic mastocytosis

SM comprises a heterogeneous group of disorders, characterized by an abnormal accumulation of clonal MCs in 1 or more tissues, frequently involving the skin and BM. Despite the fact that most adult patients (>90%) carry the same genetic lesion (D816V KIT mutation), the disease presents with multiple variants with very distinct clinical and biologic features, a diverse prognosis, and different therapeutic requirements. Recent advances in the standardization of the study of BM MC by MFC allowed reproducible identification and characterization of normal/reactive MCs and their precursors, as well as the establishment of the normal MC maturational profiles. Analysis of large groups of patients versus normal/reactive samples has highlighted the existence of aberrant MC phenotypes in SM, which are essential for the diagnosis of the disease. In turn, 3 clearly distinct and altered maturation-associated immunophenotypic profiles have been reported recently in SM, which provide criteria for the distinction between ISM patients with MC-restricted and multilineage KIT mutation; thus, immunphenotyping also contributes to prognostic stratification of ISM, particularly when analysis of the KIT mutation on highly purified BM cells is not routinely available in the diagnostic work-up of the disease.

Refined diagnostic criteria and classification of mast cell leukemia (MCL) and myelomastocytic leukemia (MML): a consensus proposal

Mast cell leukemia (MCL), the leukemic manifestation of systemic mastocytosis (SM), is characterized by leukemic expansion of immature mast cells (MCs) in the bone marrow (BM) and other internal organs; and a poor prognosis. In a subset of patients, circulating MCs are detectable. A major differential diagnosis to MCL is myelomastocytic leukemia (MML). Although criteria for both MCL and MML have been published, several questions remain concerning terminologies and subvariants. To discuss open issues, the EU/US-consensus group and the European Competence Network on Mastocytosis (ECNM) launched a series of meetings and workshops in 2011-2013. Resulting discussions and outcomes are provided in this article. The group recommends that MML be recognized as a distinct condition defined by mastocytic differentiation in advanced myeloid neoplasms without evidence of SM. The group also proposes that MCL be divided into acute MCL and chronic MCL, based on the presence or absence of C-Findings. In addition, a primary (de novo) form of MCL should be separated from secondary MCL that typically develops in the presence of a known antecedent MC neoplasm, usually aggressive SM (ASM) or MC sarcoma. For MCL, an imminent prephase is also proposed. This prephase represents ASM with rapid progression and 5%-19% MCs in BM smears, which is generally accepted to be of prognostic significance. We recommend that this condition be termed ASM in transformation to MCL (ASM-t). The refined classification of MCL fits within and extends the current WHO classification; and should improve prognostication and patient selection in practice as well as in clinical trials.

Flow cytometric immunophenotypic analysis of systemic mastocytosis involving bone marrow

CONTEXT

Mast cells of systemic mastocytosis (SM) have aberrant immunophenotypes that are useful for their detection by flow cytometry immunophenotyping.

OBJECTIVES

To assess the usefulness of CD2, CD25, and other antigens for establishing the diagnosis of SM in bone marrow using flow cytometry immunophenotyping.

DESIGN

We studied 50 bone marrow aspirates of patients with SM using flow cytometry immunophenotyping. The bone marrow aspirates were stained with antibodies specific for CD2, CD25, CD35, CD59, CD63, and CD69. For the detection of CD2 and CD25, antibodies conjugated with phycoerythrin (PE) or fluorescein isothiocyanate (FITC) were compared. CD45-PerCP and CD117-APC were used for gating. Data were acquired on FACS Calibur cytometers and analyzed using CellQuest software.

RESULTS

CD2 and CD25 were positive in 41 of 50 (82%) and 45 of 50 (90%) SM cases, respectively. For CD2, the PE-conjugated antibody yielded better sensitivity than the FITC-conjugated antibody (31 of 40 [78%] versus 28 of 40 [70%]). For CD25, PE-conjugated and FITC-conjugated antibodies showed similar detection sensitivity, although the intensity of expression was brighter with CD25-PE. Compared with immunohistochemistry, flow cytometry immunophenotyping was superior for detecting CD2 (14 of 23 [61%] versus 9 of 23 [39%]). Other antigens frequently overexpressed in SM were CD35 (43 of 50 [86%]), CD59 (46 of 50 [92%]), CD63 (43 of 49 [88%]), and CD69 (39 of 48 [81%]).

CONCLUSIONS

Flow cytometry immunophenotyping is a rapid and sensitive technique for characterizing mast cells in bone marrow aspirate specimens. The use of PE-conjugated antibodies for CD2 and CD25 improves the detection rate (CD2) or facilitates analysis (CD25); therefore, PE-conjugated antibodies are suggested. Antibodies reactive with CD35, CD59, CD63, and CD69 are also helpful in detecting SM in bone marrow.

Mast cell-mediated and associated disorders in pregnancy: a risky game with an uncertain outcome?

During pregnancy, the maternal organism is under the influence of tremendous endocrine as well as immunological changes as an adaptation to the implanted and developing fetus. In most cases, the maternal adaptations to pregnancy ensure both, the protection against harmful pathogens and the tolerance toward the growing semi-allogeneic fetus. However, under certain circumstances the unique hormonal milieu during pregnancy is causative of a shift into an unfavorable direction. Of particular importance are cellular disorders previous to pregnancy that involve cell types known for their susceptibility to hormones. One interesting cell type is the mast cell (MC), one of the key figures in allergic disorders. While physiological numbers of MCs were shown to positively influence pregnancy outcome, at least in mouse models, uncontrolled augmentations in quantity, and/or activation can lead to pregnancy complications. Women that have the desire of getting pregnant and been diagnosed with MC mediated disorders such as urticaria and mastocytosis or chronic inflammatory diseases in which MCs are involved, including atopic dermatitis, asthma, or psoriasis, may benefit from specialized medical assistance to ensure a positive pregnancy outcome. In the present review, we address the course of pregnancy in women affected by MC mediated or associated disorders.

Identification and immunophenotypic characterization of normal and pathological mast cells

Mast cells (MCs) are secretory cells that are central players in human allergic disease and immune responses. With the exception of a few pathological situations, MCs are usually present at relatively low frequencies in most tissues. Since their first description, MCs in tissues were identified mostly using their morphological characteristics and their typical coloration when stained with aniline dyes. However, increasing availability of highly specific antibodies now permits the use of fluorescence-based flow cytometry as the method of choice for the quantification, characterization, and purification of cells in suspension. This technique allows for a rapid analysis of thousands of events and for the identification of cells present at frequencies as low as one event in 10(6) unwanted cells. This method also permits for simultaneous characterization of multiple antigens at a single-cell level, which is ideal in order to study rare populations of cells like MCs. Here we describe the basis of flow cytometry-based immunophenotyping applied to the study of MC. The protocol focuses on the study of human MCs present in body fluids (mainly bone marrow) but can easily be adapted to study MCs from other tissues and species.

Immunology and clinical manifestations of non-clonal mast cell activation syndrome

There is a spectrum of disorders that clinically manifest as a result of mast cell activation. A non-clonal form has emerged in the literature where many of the clinical features of systemic mastocytosis are shared despite having a distinct mast cell biology. In this review, we summarize key features of the science behind mast cell activation relevant to what is now known as non-clonal mast cell activation syndrome (nc-MCAS). We highlight the clinical manifestations of nc-MCAS with a focus on diagnosis and treatment.

High-sensitivity flow cytometric analysis for the evaluation of systemic mastocytosis including the identification of a new flow cytometric criterion for bone marrow involvement

We used high-sensitivity flow cytometry to assess 93 bone marrow aspirates for involvement by systemic mastocytosis. Aberrant CD2/CD25 expression by CD117-gated mast cells was seen in 34 samples (37%), with the majority of mast cells expressing both markers (n = 23; 68%). In 24 cases, a discrete population of mast cells within the CD117-bright gate correlated with a positive morphologic finding in the biopsy, even in the absence of an aberrant immunophenotype. A discrete CD117-bright population, when considered a positive criterion, increases analytic sensitivity from 77% to 95%, exceeding the sensitivity of morphologic analysis (69% for aspirate and 85% for biopsy). We conclude that flow cytometry is a sensitive and specific test for the presence of systemic mastocytosis, particularly when the presence of a discrete CD117-positive mast cell population is regarded as a diagnostic criterion.

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.

Systemic Mastocytosis With Associated Clonal Hematologic Nonmast Cell Lineage Disease: A Clinicopathologic Review

Systemic mastocytosis (SM) is a heterogeneous disease with 6 subtypes, including systemic mastocytosis with associated clonal hematologic nonmast cell lineage disease (SM-AHNMD). Bone marrow biopsy specimens show multifocal aggregates of mast cells with predominantly spindle-shaped morphology associated with a myeloid or, less frequently, a lymphoproliferative neoplasm defined by World Health Organization criteria. Neoplastic mast cells abnormally express CD2 and/or CD25, which may be detected by flow cytometry or immunohistochemistry. The pathogenesis of SM-AHNMD is not well understood; however, combined KIT tyrosine kinase receptor mutations and additional genetic events in myeloid stem cells may have a pathogenic role. Reactive mast cell hyperplasia, monocytic/histiocytic proliferations, SM without sufficient criteria for a diagnosis of AHNMD, atypical mast cells associated with PDGFRA rearrangements, and other tryptase-positive myeloid proliferations should be excluded. Overall, the prognosis is poor and largely related to the AHNMD. Cytoreductive therapies, splenectomy, allogeneic bone marrow transplant, and tyrosine kinase inhibitors, excluding imatinib, may have potential efficacy in the treatment of these diseases.

CD25 Is Expressed by Canine Cutaneous Mast Cell Tumors but not by Cutaneous Connective Tissue Mast Cells

Canine cutaneous mast cell tumors (MCT) of different histological grades have distinct biological behaviors. However, little is known about underlying molecular mechanisms that lead to tumor development and increasing malignancy with higher tumor grade. Recent studies have identified the interleukin-2 receptor (IL-2R) subunits CD25 and CD2 as markers that distinguish nonneoplastic from neoplastic mast cells in human systemic mastocytosis. In this study, their potential as a marker for canine MCT and their possible impact on MCT carcinogenesis were evaluated. mRNA expression levels of both genes were compared between grade 1 ( n = 12) and grade 3 ( n = 8) MCT, and protein expression levels of CD25 were compared in 90 MCT of different tumor grades. mRNA expression levels of both CD25 and CD2 were upregulated in grade 3 MCT. In contrast, CD25 protein was expressed by fewer tumor cells and at decreased levels in grade 3 tumors, while most grade 1 MCT had strong CD25 protein expression. Moreover, CD25 was not expressed by nonneoplastic, resting cutaneous mast cells, while few presumably activated mast cells in tissue samples from dogs with allergic dermatitis had weak CD25 expression. Taken together, these findings suggest that CD25 may play a critical role in early MCT development and may be a stimulatory factor in grade 1 MCT, while grade 3 MCT seem to be less dependent on CD25. Because of the low number of CD25-positive tumor cells in high-grade tumors, the usefulness of CD25 as a tumor marker is, however, questionable.

Blood CD34-c-Kit+ cell rate correlates with aggressive forms of systemic mastocytosis and behaves like a mast cell precursor

Mastocytosis is a heterogeneous disease characterized by the accumulation of mast cells in one or more organs. Our objective was to identify a peripheral mast cell precursor and assess its variation rate in mastocytosis. A peripheral blood phenotypic analysis was performed among 50 patients with mastocytosis who were enrolled in a prospective multicentric French study, and the phenotypic analysis results of the patients were compared with those of healthy donors. The rate of peripheral blood CD34(-)c-Kit(+) cells correlated with the severity of mastocytosis. This cellular population was isolated from healthy donors as well as from patients with systemic mastocytosis. After 30 days of culture, the CD34(-)c-Kit(+) cells gave birth to mature mast cells, indicating that this cellular population constitutes a mast cell circulating precursor. Monitoring peripheral CD34(-)c-Kit(+) cells by flow cytometry could be a useful and low-invasive tool to determine the disease severity and the relapses and to assess treatment efficiency.

Interleukin-9 (IL-9) and NPM-ALK each generate mast cell hyperplasia as single 'hit' and cooperate in producing a mastocytosis-like disease in mice

Mast cell neoplasms are characterized by abnormal growth and focal accumulation of mast cells (MC) in one or more organs. Although several cytokines, including stem cell factor (SCF) and interleukin-9 (IL-9) have been implicated in growth of normal MC, little is known about pro-oncogenic molecules and conditions triggering differentiation and growth of MC far enough to lead to the histopathological picture of overt mastocytosis. The anaplastic lymphoma kinase (ALK) has recently been implicated in growth of neoplastic cells in malignant lymphomas. Here, we describe that transplantation of NPM-ALK-transplanted mouse bone marrow progenitors into lethally irradiated IL-9 transgenic mice not only results in lymphoma-formation, but also in the development of a neoplastic disease exhibiting histopathological features of systemic mastocytosis, including multifocal dense MC-infiltrates, occasionally with devastating growth in visceral organs. Transplantation of NPM-ALK-transduced progenitors into normal mice or maintenance of IL-9-transgenic mice without NPM-ALK each resulted in MC hyperplasia, but not in mastocytosis. Neoplastic MC in mice not only displayed IL-9, but also the IL-9 receptor, and the same was found to hold true for human neoplastic MC. Together, our data show that neoplastic MC express IL-9 receptors, that IL-9 and NPM-ALK upregulate MC-production in vivo, and that both'hits' act in concert to induce a mastocytosis-like disease in mice. These data may have pathogenetic and clinical implications and fit well with the observation that neoplastic MC in advanced SM strongly express NPM and multiple "lymphoid" antigens including CD25 and CD30.

Advances and controversies in the diagnosis, pathogenesis, and treatment of systemic mastocytosis

The term systemic mastocytosis (SM) encompasses a group of hematopoietic malignancies characterized by excessive proliferation of neoplastic mast cells that accumulate in the bone marrow and visceral organs. Most patients with SM, particularly those who present with aggressive clinical courses, carry somatic mutations of the v-kit Hardy-Zuckerman 4 feline sarcoma viral oncogene homolog (KIT) gene. KIT mutations are considered central events in the pathogenesis of SM and serve as diagnostic markers and putative therapeutic targets. The heterogeneity in the clinical course of patients with SM and recent advances in the genetic and immunophenotypic characterization of neoplastic mast cells may help to improve current diagnostic, taxonomic, and therapeutic approaches in SM.

Primary role of multiparametric flow cytometry in the diagnostic work-up of indolent clonal mast cell disorders

BACKGROUND

According to the World Health Organization (WHO) classification the diagnosis of systemic mastocytosis (SM) relies on bone marrow (BM) examination and is based on one major and four minor criteria. Herein, we used WHO criteria to compare flow cytometry (FC) with other available techniques in the diagnosis of SM after BM examination.

METHODS

We analyzed a cohort of 95 patients with suspect SM. All patients underwent comprehensive BM examination by using cytology, immunohistochemistry, FC and molecular study for mutation of c-Kit and serum tryptase dosage. FC evaluation was based on a combination of monoclonal antibodies, specifically CD25/CD2/CD45/CD34/CD117.

RESULTS

Seventy-four out of ninety-five patients were diagnosed with indolent SM (n = 59) or monoclonal mast cell activation syndrome (n = 15) because satisfying less than 3 minor criteria. Thirty-nine out of these seventy-four patients fulfilled the major histological criterion, whereas the presence of a minor criterion was assessed by FC, molecular study, cytology, and tryptase level in 70/74, 52/67, 56/74, and 42/74 patients, respectively. FC showed higher sensitivity than IHC in detection of CD25+ mast cells (MC) (92.9% vs. 73.8%; P = 0.019), especially in the absence of the major histological criterion (90.5% vs. 47.6%; P = 0.003). Moreover, CD2 expression was documented by FC and IHC in 97.1% and 35.3% of cases, respectively (P < 0.001).

CONCLUSIONS

FC showed the best sensitivity for identifying abnormal MC compared to other techniques, especially in cases with low MC burden. Therefore, we hope for a major role of FC in the diagnostic work-up of clonal MC disorders.

Aberrant expression of CD30 in neoplastic mast cells in high-grade mastocytosis

Systemic mastocytosis either presents as aggressive neoplasm with short survival time or indolent systemic mastocytosis with normal life expectancy. In both instances, neoplastic mast cells usually harbor the D816V-mutated variant of KIT. Phenotypically, mast cells in systemic mastocytosis usually express CD25. However, no robust marker that discriminates between aggressive and indolent variants of systemic mastocytosis has been identified yet. We here report that CD30, also known as Ki-1 antigen, is expressed in neoplastic mast cells in a majority of patients with advanced systemic mastocytosis (11/13, 85%), whereas in most patients with indolent systemic mastocytosis (12/45, 27%; P<0.001), only a few if any mast cells stained positive for CD30. These results could be confirmed by TissueFAXS analysis in subsets of patients with indolent systemic mastocytosis (n=7) and advanced systemic mastocytosis (n=4; P=0.008). The mast cell leukemia cell line HMC-1, derived from a patient with aggressive systemic mastocytosis also expressed the CD30 protein. In addition, we were able to detect CD30 mRNA in HMC-1 cells as well as in bone marrow biopsy samples in patients with systemic mastocytosis. In contrast, CD30 transcripts could not be detected in bone marrow biopsies in cases of reactive mast cell hyperplasia and in various other myeloid neoplasms. In conclusion, CD30 is preferentially expressed in neoplastic mast cells in advanced mast cell neoplasms. Upregulated expression of CD30 in advanced systemic mastocytosis may thus be employed as a potential marker for grading systemic mastocytosis in hematopathology.