The tryptase positive compact round cell infiltrate of the bone marrow (TROCI-BM): a novel histopathological finding requiring the application of lineage specific markers

Harmonization of Diagnostic Criteria in Mastocytosis for Use in Clinical Practice: WHO vs ICC vs AIM/ECNM

Mastocytosis is a clonal myeloid disorder defined by an increase and accumulation of mast cells (MCs) in one or multiple organ systems. The complex pathology of mastocytosis results in variable clinical presentations, courses, and outcomes. The World Health Organization (WHO) divides the disease into cutaneous mastocytosis (CM), several forms of systemic mastocytosis (SM), and MC sarcoma. In most patients with SM, a somatic KIT mutation, usually D816V, is identified. Patients diagnosed with CM or nonadvanced SM, including indolent SM, have a near-normal life expectancy, whereas those with advanced SM, including aggressive SM and MC leukemia, have limited life expectancy. Since 2001, a multidisciplinary consensus group consisting of experts from the European Competence Network on Mastocytosis and the American Initiative in Mast Cell Diseases has supported the field by developing diagnostic criteria for mastocytosis. These criteria served as the basis for the WHO classification of mastocytosis over 2 decades. More recently, an International Consensus Classification group proposed slightly modified diagnostic criteria and a slightly revised classification. In this article, these changes are discussed. Furthermore, we propose harmonization among the proposals of the American Initiative in Mast Cell Diseases/European Competence Network on Mastocytosis consensus group, WHO, and the International Consensus Classification Group. Such harmonization will facilitate comparisons of retrospective study results and the conduct of prospective trials.

Activated mast cells in periprosthetic joint infection-associated tissue

Background

Periprosthetic joint infection (PJI) is a devastating complication of total joint arthroplasty surgery. Increased densities of activated mast cells have been predicted to be present in PJI compared to non-infectious arthroplasty failure based on analysis of transcriptomic data, but their presence in PJI-associated periprosthetic tissues has not been visually confirmed.

Objective

This preliminary study investigated the presence and activation status of mast cells in periprosthetic tissues associated with PJI.

Methods

Periprosthetic tissues from five PJI cases and three arthroplasty failures due to instability and one due to stiffness were immunohistochemically stained using tryptase and microscopically evaluated to enumerate mast cells and evaluate overall activation status within tissue samples. Mast cell activation was evidenced by the release of tryptase into the extracellular space surrounding mast cells.

Results

Mast cells were found in all samples, with average cellular densities of 22 and 26 cells/mm2 tissue in PJI and uninfected samples, respectively (p, 0.6610). Apparent mast cell activation and degranulation was readily observed throughout each of the five PJI samples studied, but not in any of the uninfected samples studied.

Conclusion

While preliminary, these findings provide evidence for a role of mast cells in the immune response in PJI. Additional investigation of the role of mast cells during arthroplasty failure is warranted, providing a better understanding of underlying biology and informing potential diagnostic and treatment targets.

Systemic Mastocytosis in a Patient with BCR-ABL1-Positive Chronic Myeloid Leukemia in the Remission Phase

Systemic mastocytosis (SM) comprises a group of rare disorders resulting from tissue infiltration by pathological mast cells. In a percentage ranging from 5 to 40% in various patient series, SM appears to be associated with an accompanying hematologic neoplasm (SM-AHN). The coexistence of SM with chronic myelogenous leukemia (CML) is extremely rare with only 3 cases in the literature. The natural course of CML has changed dramatically over the past 2 decades with the use of tyrosine kinase inhibitors (TKIs). We report a case of diagnosing SM in a patient in complete molecular remission of CML after stopping TKI treatment.

Protease profile of normal and neoplastic mast cells in the human bone marrow with special emphasis on systemic mastocytosis

Mast cells (MC) are immune cells that produce a variety of mediators, such as proteases, that are important in the body's immune responses. MC proteases have pronounced multifunctionality and in many respects determine the biological characteristics of the organ-specific MC population. Although, increased numbers of MC are one of the objective mastocytosis signs, a detailed assessment of the proteases biogenesis and excretion mechanisms in the bone marrow (BM) has not yet been carried out. Here, we performed an analysis of the expression of proteases in patients with various forms of systemic mastocytosis. We presented data on intracellular protease co-localization in human BM MCs and discussed their implication in secretory pathways of MCs in the development of the disease. Systemic mastocytosis, depending on the course, is featured by the formation of definite profiles of specific proteases in various forms of atypical mast cells. Intragranular accumulation of tryptase, chymase and carboxypeptidases in the hypochromic phenotype of atypical mast cells is characterized. Characterization of MC proteases expression during mastocytosis can be used to refine the MC classification, help in a prognosis, and increase the effectiveness of targeted therapy.

Tryptase Positivity in Chronic Myeloid Leukemia With Marked Basophilia

Chronic myeloid leukemia (CML) is the most common chronic myeloproliferative disorder, which was the first to be described and understood at a molecular level. Marked basophilia can be seen in CML and other neoplastic and reactive processes. Tryptase is a serine protease that is mainly expressed in mast cells, whereas basophils express only trace amounts of the enzyme. Therefore, it has always been regarded as a specific marker for mast cells.

We report a case of a 41-year-old male who had been diagnosed with CML eight years ago, and, interestingly, his most recent bone marrow biopsy demonstrated an accelerated phase of the disease with a significant increase of basophils count. These basophils were immunoreactive with tryptase along with CD123.

In the literature, this phenomenon of tryptase immunoreactivity by basophils has been described in association with CML, primary myelofibrosis, and myelodysplastic syndrome. Therefore, our finding supports these data and suggests that tryptase should not be regarded as a specific marker for mast cells when approaching various myeloid neoplasms including CML.

A Rare Case of Systemic Mastocytosis with Associated Hematologic Neoplasm (SM-AHN) Involving Chronic Myeloid Leukemia: A Case Report and Literature Review

BACKGROUND Single or multiple cell line dysplasia is a characteristic feature of myelodysplastic syndrome. However, significant dysgranulopoiesis is not a feature of chronic myeloid leukemia (CML). Systemic mastocytosis (SM) with an associated hematologic neoplasm (SM-AHN) comprises 5% to 40% of cases of SM. All types of hematologic neoplasms have been previously reported, although CML has been rarely encountered. CASE REPORT A 28-year-old male presented with a 3-month-history of weight loss and massive splenomegaly. Peripheral blood revealed marked leukocytosis, shift to left with 13% blasts. There was evident dysgranulopoiesis that raised a provisional diagnosis of myelodysplastic/myeloproliferative neoplasm. Bone marrow (BM) examination revealed granulocytic hyperplasia with 10% blasts and significant dysgranulopoiesis. Unexpectedly, cytogenetic analysis revealed t(9;22) with BCR/ABL1 rearrangement, diagnostic of chronic myeloid leukemia in an accelerated phase. The patient was started on dasatinib 100 mg upfront, however, he failed to respond, with increasing leukocytosis. Repeat BM examination showed persistence of the findings with 8% blasts. At this time, aggregates of mast cells with aberrant expression of CD25 were elicited, thus concluding the diagnosis of SM-AHN. The patient failed multiple lines of treatment (dasatinib, nilotinib, hydroxyurea, cytarabine subcutaneous, 6-mercaptopurine and interferon) and progressed to the blast phase a few months later. CONCLUSIONS We report an unusual case of CML, presented with significant dysgranulopoiesis with an aggressive clinical course including SM uncovered during the disease course with subsequent transformation to the blast phase. The different biological behavior of this case underscores the need for studies on a larger number of cases to explore the significance of the aforementioned coexistent features.

Myelomastocytic leukemia: histopathological features, diagnostic criteria and differential diagnosis

Myelomastocytic leukemia (MML) is an extremely rare myeloid overlap-neoplasm that belongs to the group of tryptase-positive (T+) myeloid neoplasms. Main differential diagnoses include aggressive systemic mastocytosis (ASM), in particular ASM in transformation; mast cell leukemia; T+ acute myeloid leukemia (T+ AML); acute basophilic leukemia and chronic basophilic leukemia. MML exhibits both proliferative and dysplastic features and is characterized by prominent differentiation into the mast cell lineage in an advanced myeloid neoplasm, usually primary or secondary AML. While the histological key feature of MML is a diffuse increase in neoplastic cells expressing mast cell-related antigens like tryptase and CD117 (KIT), the most important cytomorphological finding in bone marrow (BM) and peripheral blood (PB) is the metachromatically granulated blast cell (= metachromatic blast). In contrast to systemic mastocytosis (SM), MML neither shows activating point mutations at codon 816 of KIT nor the aberrant expression of CD25 by mast cells is seen. MML can only be diagnosed when tryptase-staining is performed on BM biopsy specimens, PB and BM smears are investigated for presence of metachromatic blasts and other T+ leukemias have been excluded.

The serum tryptase test: an emerging robust biomarker in clinical hematology

During the past few years, a number of molecular markers have been developed in clinical hematology, most of them related to specific gene defects. However, there is also an unmet need to develop novel serologic parameters to improve diagnostics and prognostication in daily practice. Among these, the serum tryptase appears to be a most reliable biomarker of myeloid neoplasms. Elevated tryptase levels are found in subgroups of patients with mastocytosis, myelodysplastic syndrome, myeloproliferative neoplasm, acute myeloid leukemia, chronic myeloid leukemia and chronic eosinophilic leukemia. In these patients, the tryptase level is of diagnostic and/or prognostic significance. In mastocytosis, an elevated tryptase level is a minor criterion of systemic disease and in BCR-ABL1(+) chronic myeloid leukemia, elevated tryptase at diagnosis correlates with treatment responses and overall survival. In patients with elevated tryptase, the enzyme also serves as follow-up parameter and can be employed to measure treatment-responses. In the current article, we review and update the perspectives of tryptase and provide recommendations for use of this conventional biomarker in daily practice.

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.

SCF/C-KIT signaling modulates tryptase expression in acute myeloid leukemia cells

Tryptase is a serine protease with a variety of biological functions. Recently, elevated serum tryptase has been detected in certain patients with acute myeloid leukemia (AML). However, the underlying mechanism for the regulation of tryptase expression remains elusive. In this study, we aimed to investigate the role of stem cell factor (SCF)/C-KIT signaling in regulating the expression of tryptase in AML cells. We found a significant positive correlation between tryptase and C-KIT expression levels in AML patients. Furthermore, real-time PCR, Western blot and ELISA analysis showed that SCF upregulated tryptase mRNA and protein expression in U937 cells, and that this effect was abolished by pretreatment with PD98059 and SB230580. In addition, levels of phosphorylated ERK1/2 and p38MAPK correlated with tryptase levels. Taken together, these data suggest that the expression of tryptase is regulated by SCF/C-KIT signaling via the ERK1/2 and p38MAPK pathways.

[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.

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.

[Mastocytosis and eosinophilic leukemia: diagnostics and classification]

Mastocytosis and myeloid eosinophilic neoplasms are rare diseases of the bone marrow and are often a diagnostic challenge for hematopathologists. In mastocytosis, compact mast cell infiltrates represent the main diagnostic criterion and for myeloid eosinophilic neoplasms, eosinophilic granulocytes dominate the histological picture. Both disease groups include phenotypically and prognostically very different entities which are each defined by WHO criteria. For systemic mastocytosis (SM), a differentiation between indolent and aggressive or even leukemic forms is of prognostic importance. In indolent variants of SM, a local and/or systemic, usually reactive increase in eosinophilic granulocytes (SM-eo) is often observed. In contrast, an increase in neoplastic eosinophils is often observed in advanced SM, predominantly in diseases designated SM with associated non-mastocytic hematological neoplasms (SM-AHNMD), e.g. in SM with chronic eosinophilic leukemia (SM-CEL). Apart from mastocytoses, immunophenotypically aberrant tissue mast cells are only observed in certain rare forms of myeloid neoplasms with eosinophilia, in particular in myeloproliferative neoplasms (MPN-eo) with cytogenic anomalies in the platelet-derived growth factor receptor (PDGFR). The World Health Organization (WHO) classification of eosinophilic leukemias, however, fulfils the morphological and clinical requirements in a limited way only and needs an update.

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.

Evaluation of the WHO criteria for the classification of patients with mastocytosis

Diagnosis and classification of mastocytosis is currently based on the World Health Organization (WHO) criteria. Here, we evaluate the utility of the WHO criteria for the diagnosis and classification of a large series of mastocytosis patients (n=133), and propose a new algorithm that could be routinely applied for refined diagnosis and classification of the disease. Our results confirm the utility of the WHO criteria and provide evidence for the need of additional information for (1) a more precise diagnosis of mastocytosis, (2) specific identification of new forms of the disease, (3) the differential diagnosis between cutaneous mastocytosis vs systemic mastocytosis, and (4) improved distinction between indolent systemic mastocytosis and aggressive systemic mastocytosis. Based on our results, a new algorithm is proposed for a better diagnostic definition and prognostic classification of mastocytosis, as confirmed prospectively in an independent validation series of 117 mastocytosis patients.

Systemic Mastocytosis

An unusual disease, mastocytosis challenges the pathologist with a variety of morphologic appearances and heterogeneous clinical presentations ranging from skin manifestations (pruritus, urticaria, dermatographism) to systemic signs and symptoms indicative of mast cell mediator release, including flushing, hypotension, headache, and anaphylaxis among others. In this article, we focus on recognizing the cytology, histopathology, clinical features, and prognostic implications of systemic mastocytosis, a clonal and neoplastic mast cell proliferation infiltrating extracutaneous organ(s) with or without skin involvement. Diagnostic pitfalls are reviewed with ancillary studies to help unmask the mast cell and exclude morphologic mimics.

Phenotypic heterogeneity, novel diagnostic markers, and target expression profiles in normal and neoplastic human mast cells

Mast cells (MC) are specialized immune cells that play a key role in anaphylactic reactions. Growth, differentiation, and function of these cells are regulated by a complex network of cytokines, surface receptors, signaling molecules, the microenvironment, and the genetic background. A number of previous and more recent data suggest that MC are heterogeneous in terms of cytokine-regulation, expression of cytoplasmic and cell surface antigens, and response to ligands. MC heterogeneity is often organ-specific and is considered to be related to MC plasticity, disease-associated factors, and the maturation stage of the cells. The stem cell factor (SCF) receptor KIT (CD117) is expressed on all types of MC independent of maturation and activation-status. In systemic mastocytosis (SM), KIT is often expressed in MC in a mutated and constitutively activated form. In these patients, MC aberrantly display CD2 and CD25, diagnostic markers of neoplastic MC in all SM variants. In advanced SM, MC co-express substantial amounts of CD30, whereas CD2 expression on MC may be decreased compared to indolent SM. Other surface molecules, such as CD63 or CD203c, are overexpressed on neoplastic MC in SM, and are further upregulated upon cross-linking of the IgE receptor. Some of the cell surface antigens expressed on MC or their progenitors may serve as therapeutic targets in the future. These targets include CD25, CD30, CD33, CD44, and CD117/KIT. The current article provides an overview on cell surface antigens and target receptors expressed by MC in physiologic and reactive tissues, and in patients with SM, with special reference to phenotypic heterogeneity and clinical implications.

Mastocytosis: an unusual clonal disorder of bone marrow-derived hematopoietic progenitor cells

Mastocytosis, an unusual disorder of bone marrow-derived, clonally transformed hematopoietic progenitor cells, exhibits a broad spectrum of clinical and morphologic features ranging from a self-limiting benign disorder (ie, juvenile cutaneous mastocytosis) to highly aggressive neoplasms like mast cell leukemia. Principally, mastocytosis should be divided in 2 main subentities: cutaneous mastocytosis and systemic mastocytosis mainly involving the bone marrow. Mastocytosis is a morphologic diagnosis and should not be diagnosed on the basis of clinical findings alone. Pathologists need to be aware of the disease and its mimickers. Application of the defined diagnostic criteria can confirm or exclude mastocytosis in most cases. Use of antibodies against tryptase, CD117 (KIT), and CD25 is recommended in every suspected case. Because most cases of systemic mastocytosis show a very low degree of infiltration of the bone marrow, antitryptase and anti-CD117 are of major importance for screening and quantification of mast cells, in particular to detect even small compact infiltrates as the only major diagnostic criterion for mastocytosis. Expression of CD25 on mast cells is defined as a minor diagnostic criterion and is usually seen only in mastocytosis but not in reactive states of mast cell hyperplasia.

Increased mast cell number in human hypertensive nephropathy

Mast cells have recently been related to nonallergic chronic organ damage and fibrosis. In the present study, we analyzed mast cell number, localization, and maturation in the kidney of a relatively unique group of middle-aged accident victims with primary essential hypertension and in normotensive controls (n=8 per group, Caucasians, predominantly male). Hypertensive kidneys showed a significantly higher degree of arteriolosclerosis. However, glomerular and tubulointerstitial matrix accumulation did not differ significantly to normotensive controls indicating a relatively early stage of hypertensive nephropathy. Using toluidine blue staining, renal mast cell number was found to be fivefold higher in hypertensive subjects compared with normotensive controls. Mast cells were primarily located in the peritubular interstitial spaces, some perivascular, but not in glomeruli. In a series of immunohistological staining studies, mast cell maturation grading showed that expression of early hematopoietic precursor cell marker CD34 did not differ between both groups. In contrast, mast cells were mostly positive for IgE receptor, tryptase, and chymase indicating a mature, differentiated cell phenotype in hypertensive nephropathy. Renal expression of stem cell factor was markedly upregulated in primary hypertension. Kidney macrophage and lymphocyte numbers were similar in both groups. In conclusion, human hypertensive kidney disease shows an early and conspicuous upregulation of stem cell factor along with an increased number of mature mast cells. The results suggest that renal mast cell accumulation may play a role in the pathogenesis of human hypertensive nephropathy.

Diagnostic value of histology and immunohistochemistry in myelodysplastic syndromes

The histologic and immunohistochemical analysis of the bone marrow yields important information for the diagnosis of myelodysplastic syndromes (MDS), thereby often exceeding the information obtained by cytological analysis of smears. Notably, tissue-fibrosis, angiogenesis, or the abnormal localization of megakaryocytes and CD34+ progenitor cells can only be assessed histologically. Many of these parameters are also of prognostic significance. Moreover, evaluation of bone marrow histology is of crucial importance in cases with dry-tap or blood-contaminated marrow-smears, especially in hypoplastic states. Histologic/immunohistochemical investigation of the bone marrow therefore is strongly recommended for patients with (suspected) MDS, the minimum marker-panel suggested being CD31, CD34, and tryptase.

Standards and standardization in mastocytosis: consensus statements on diagnostics, treatment recommendations and response criteria

Although a classification for mastocytosis and diagnostic criteria are available, there remains a need to define standards for the application of diagnostic tests, clinical evaluations, and treatment responses. To address these demands, leading experts discussed current issues and standards in mastocytosis in a Working Conference. The present article provides the resulting outcome with consensus statements, which focus on the appropriate application of clinical and laboratory tests, patient selection for interventional therapy, and the selection of appropriate drugs. In addition, treatment response criteria for the various clinical conditions, disease-specific symptoms, and specific pathologies are provided. Resulting recommendations and algorithms should greatly facilitate the management of patients with mastocytosis in clinical practice, selection of patients for therapies, and the conduct of clinical trials.