Detection of tryptase in cytoplasmic granules of basophils in patients with chronic myeloid leukemia and other myeloid neoplasms

Approach to Acute Myeloid Leukemia with Increased Eosinophils and Basophils

There is remarkable morphologic and genetic heterogeneity in acute myeloid leukemia (AML). In a small percentage of cases of AML, increased eosinophils and/or basophils are present in the bone marrow and sometimes in the peripheral blood. This is often a puzzling diagnostic situation but also an important finding that requires special investigation. Unique chromosomal rearrangements have been correlated with an increased number of eosinophils and basophils in AML. The identification of the underlying genetic lesion that promotes eosinophilia and basophilia can dramatically change both the prognosis and the treatment of the patient. Thus, clinicians must be vigilant in searching for the cause of eosinophilia and basophilia in patients with AML, since the different causes may lead to different treatments and survival outcomes. In this article, we examine the significance of increased eosinophils and/or basophils in the context of AML, provide guidance that simplifies the differential diagnosis, and give prognostic and therapeutic information about specific subtypes of AML associated with eosinophilia and/or basophilia. Evidence supporting personalized (molecularly targeted) therapy for these patients is also presented.

The Normal Range of Baseline Tryptase Should Be 1 to 15 ng/mL and Covers Healthy Individuals With HαT

Physiological levels of basal serum tryptase vary among healthy individuals, depending on the numbers of mast cells, basal secretion rate, copy numbers of the TPSAB1 gene encoding alpha tryptase, and renal function. Recently, there has been a growing debate about the normal range of tryptase because individuals with the hereditary alpha tryptasemia (HαT) trait may or may not be symptomatic, and if symptomatic, uncertainty exists as to whether this trait directly causes clinical phenotypes or aggravates certain conditions. In fact, most HαT-positive cases are regarded as asymptomatic concerning mast cell activation. To address this point, experts of the European Competence Network on Mastocytosis (ECNM) and the American Initiative in Mast Cell Diseases met at the 2022 Annual ECNM meeting and discussed the physiological tryptase range. Based on this discussion, our faculty concluded that the normal serum tryptase range should be defined in asymptomatic controls, inclusive of individuals with HαT, and based on 2 SDs covering the 95% confidence interval. By applying this definition in a literature screen, the normal basal tryptase in asymptomatic controls (HαT-positive persons included) ranges between 1 and 15 ng/mL. This definition should avoid overinterpretation, unnecessary referrals, and unnecessary anxiety or anticipatory fear of illness in healthy individuals.

Histology-based blood leukocyte profiling reveals parallel Th2 and Th17 signatures in seasonal allergic rhinitis

BACKGROUND

Allergic rhinitis (AR), a common condition in the westernized world, is suggested to be more immunologically complex than the archetypical 'Th2' inflammation. New approaches are needed to decode this complexity.

AIMS/OBJECTIVES

In this study, we explored a novel histology-based analysis for circulating blood leukocyte profiling in 16 patients with seasonal AR outside and during the pollen season.

MATERIAL AND METHODS

Leukocytes were purified with minimal ex-vivo artefacts, embedded into agarose-paraffin pellets for immunohistochemistry-based immune cell profiling. Blood leukocyte mapping was performed.

RESULTS

Samples collected during the pollen season had statistically increased eosinophils, neutrophils, monocytes, and CD8⁺ T-lymphocytes compared to the off-season baseline. In contrast, no change was observed for CD20⁺ B-lymphocytes and CD3⁺ T-lymphocytes. Subclassification of CD4⁺ T-helper cells demonstrated a parallel and significant expansion of Th2 and Th17-cells during the pollen season, while Th1-cells remained unchanged. Whereas absolute basophils numbers were unaltered, the basophil markers GATA2 and CPA3 increased during the pollen season.

CONCLUSIONS AND SIGNIFICANCE

This study introduces a novel and applicable method for systemic immune cell screening and provides further evidence of complex and parallel Th2 and Th17-immune signatures in seasonal AR. It also forwards GATA2 and CPA3 as potential biomarkers for ongoing allergic inflammation.

Chronic myeloid leukemia stem cells: targeting therapeutic implications

Chronic myeloid leukemia (CML) is a clonal myeloproliferative neoplasm driven by BCR-ABL1 oncoprotein, which plays a pivotal role in CML pathology, diagnosis, and treatment as confirmed by the success of tyrosine kinase inhibitor (TKI) therapy. Despite advances in the development of more potent tyrosine kinase inhibitors, some mechanisms particularly in terms of CML leukemic stem cell (CML LSC) lead to intrinsic or acquired therapy resistance, relapse, and disease progression. In fact, the maintenance CML LSCs in patients who are resistance to TKI therapy indicates the role of CML LSCs in resistance to therapy through survival mechanisms that are not completely dependent on BCR-ABL activity. Targeting therapeutic approaches aim to eradicate CML LSCs through characterization and targeting genetic alteration and molecular pathways involving in CML LSC survival in a favorable leukemic microenvironment and resistance to apoptosis, with the hope of providing a functional cure. In other words, it is possible to develop the combination therapy of TKs with drugs targeting genes or molecules more specifically, which is required for survival mechanisms of CML LSCs, while sparing normal HSCs for clinical benefits along with TKIs.

Behind the scenes with basophils: an emerging therapeutic target

Though basophils were originally viewed as redundant blood ‘mast cells’, the implementation of flow cytometry has established basophils as unique leukocytes with critical immunomodulatory functions. Basophils play an active role in allergic inflammation, autoimmunity, and hematological malignancies. They are distinguishable from other leukocytes by their characteristic metachromatic deep-purple cytoplasmic, round granules. Mature basophils are phenotypically characterized by surface expression of IL-3Rα (CD123); IL-3 drives basophil differentiation, degranulation, and synthesis of inflammatory mediators including type 2 cytokines. Basophil degranulation is the predominant source of histamine in peripheral blood, promoting allergic responses. Basophils serve as a bridge between innate and adaptive immunity by secreting IL-4 which supports eosinophil migration, monocyte differentiation into macrophages, B-cell activation, and CD4 T-cell differentiation into Th2 cells. Further, basophilia is a key phenomenon in myeloid neoplasms, especially chronic myeloid leukemia (CML) for which it is a diagnostic criterion. Increased circulating basophils, often with aberrant immunophenotype, have been detected in patients with CML and other myeloproliferative neoplasms (MPNs). The significance of basophils’ immunoregulatory functions in malignant and non-malignant diseases is an active area of research. Ongoing and future research can inform the development of immunotherapies that target basophils to impact allergic, autoimmune, and malignant disease states. This review article aims to provide an overview of basophil biology, identification strategies, and roles and dysregulation in diseases.

Cancer non-stem cells as a potent regulator of tumor microenvironment: a lesson from chronic myeloid leukemia

A limited subset of human leukemia cells has a self-renewal capacity and can propagate leukemia upon their transplantation into animals, and therefore, are named as leukemia stem cells, in the early 1990’s. Subsequently, cell subpopulations with similar characteristics were detected in various kinds of solid cancers and were denoted as cancer stem cells. Cancer stem cells are presently presumed to be crucially involved in malignant progression of solid cancer: chemoresitance, radioresistance, immune evasion, and metastasis. On the contrary, less attention has been paid to cancer non-stem cell population, which comprise most cancer cells in cancer tissues, due to the lack of suitable markers to discriminate cancer non-stem cells from cancer stem cells. Chronic myeloid leukemia stem cells generate a larger number of morphologically distinct non-stem cells. Moreover, accumulating evidence indicates that poor prognosis is associated with the increases in these non-stem cells including basophils and megakaryocytes. We will discuss the potential roles of cancer non-stem cells in fostering tumor microenvironment, by illustrating the roles of chronic myeloid leukemia non-stem cells including basophils and megakaryocytes in the pathogenesis of chronic myeloid leukemia, a typical malignant disorder arising from leukemic stem cells.

Genetic Regulation of Tryptase Production and Clinical Impact: Hereditary Alpha Tryptasemia, Mastocytosis and Beyond

Tryptase is a serine protease that is predominantly produced by tissue mast cells (MCs) and stored in secretory granules together with other pre-formed mediators. MC activation, degranulation and mediator release contribute to various immunological processes, but also to several specific diseases, such as IgE-dependent allergies and clonal MC disorders. Biologically active tryptase tetramers primarily derive from the two genes TPSB2 (encoding β-tryptase) and TPSAB1 (encoding either α- or β-tryptase). Based on the most common gene copy numbers, three genotypes, 0α:4β, 1α:3β and 2α:2β, were defined as “canonical”. About 4–6% of the general population carry germline TPSAB1-α copy number gains (2α:3β, 3α:2β or more α-extra-copies), resulting in elevated basal serum tryptase levels. This condition has recently been termed hereditary alpha tryptasemia (HαT). Although many carriers of HαT appear to be asymptomatic, a number of more or less specific symptoms have been associated with HαT. Recent studies have revealed a significantly higher HαT prevalence in patients with systemic mastocytosis (SM) and an association with concomitant severe Hymenoptera venom-induced anaphylaxis. Moreover, HαT seems to be more common in idiopathic anaphylaxis and MC activation syndromes (MCAS). Therefore, TPSAB1 genotyping should be included in the diagnostic algorithm in patients with symptomatic SM, severe anaphylaxis or MCAS.

Diagnosis, Classification and Management of Mast Cell Activation Syndromes (MCAS) in the Era of Personalized Medicine

Mast cell activation (MCA) is seen in a variety of clinical contexts and pathologies, including IgE-dependent allergic inflammation, other immunologic and inflammatory reactions, primary mast cell (MC) disorders, and hereditary alpha tryptasemia (HAT). MCA-related symptoms range from mild to severe to life-threatening. The severity of MCA-related symptoms depends on a number of factors, including genetic predisposition, the number and releasability of MCs, organs affected, and the type and consequences of comorbid conditions. In severe systemic reactions, MCA is demonstrable by a substantial increase of basal serum tryptase levels above the individual’s baseline. When, in addition, the symptoms are recurrent, involve more than one organ system, and are responsive to therapy with MC-stabilizing or mediator-targeting drugs, the consensus criteria for the diagnosis of MCA syndrome (MCAS) are met. Based on the etiology of MCA, patients can further be classified as having i) primary MCAS where KIT-mutated, clonal, MCs are detected; ii) secondary MCAS where an underlying IgE-dependent allergy or other reactive MCA-triggering pathology is found; or iii) idiopathic MCAS, where neither a triggering reactive state nor KIT-mutated MCs are identified. Most severe MCA events occur in combined forms of MCAS, where KIT-mutated MCs, IgE-dependent allergies and sometimes HAT are detected. These patients may suffer from life-threatening anaphylaxis and are candidates for combined treatment with various types of drugs, including IgE-blocking antibodies, anti-mediator-type drugs and MC-targeting therapy. In conclusion, detailed knowledge about the etiology, underlying pathologies and co-morbidities is important to establish the diagnosis and develop an optimal management plan for MCAS, following the principles of personalized medicine.

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.

Mast Cells in Peritoneal Fluid From Women With Endometriosis and Their Possible Role in Modulating Sperm Function

Endometriosis is a local pelvic inflammatory process, frequently associated with infertility, with altered function of immune-related cells in the peritoneal environment. Mast cells are known to be key players of the immune system and have been recently involved in endometriosis and in infertility, with their mediators directly suppressing sperm motility. In this study, we evaluated the mast cell population and their mediators in the peritoneal fluid of infertile patients with endometriosis and their impact on human sperm motility. Peritoneal fluids, collected by laparoscopy from 11 infertile patients with endometriosis and 9 fertile controls were evaluated for the presence of mast cells, tryptase levels and their effect on sperm motility. Furthermore, an in vitro model of mast cells-sperm interaction in peritoneal fluid was set up, using LAD2 cell line as a mast cell model, and analyzed from a functional as well as a morphological point of view. Mast cell peritoneal fluid population and its main mediator, tryptase, is more represented in endometriosis confirming an involvement of these cells in this disease. Anyway it appears unlikely that tryptase enriched peritoneal fluid, which fails to inhibit sperm motility, could contribute to endometriosis associated infertility. Despite of this, sperm interaction with the mast cell surface (LAD2) induced a significantly mast cell-degranulation response in the peritoneal fluid from endometriosis which could directly modulate sperm function other than motility. This evidence lead us to suppose that there is, between these elements, an interrelationship which deserves further studies.

Recent advances in our understanding of mast cell activation - or should it be mast cell mediator disorders?

INTRODUCTION

An increasing number of patients present with multiple symptoms affecting many organs including the brain due to multiple mediators released by mast cells. These unique tissue immune cells are critical for allergic reactions triggered by immunoglobulin E (IgE), but are also stimulated (not activated) by immune, drug, environmental, food, infectious, and stress triggers, leading to secretion of multiple mediators often without histamine and tryptase. The presentation, diagnosis, and management of the spectrum of mast cell disorders are very confusing. As a result, neuropsychiatric symptoms have been left out, and diagnostic criteria made stricter excluding most patients. Areas covered: A literature search was performed on papers published between January 1990 and November 2018 using MEDLINE. Terms used were activation, antihistamines, atopy, autism, brain fog, heparin, KIT mutation, IgE, inflammation, IL-6, IL-31, IL-37, luteolin, mast cells, mastocytosis, mediators, mycotoxins, release, secretion, tetramethoxyluteolin, and tryptase. Expert opinion: Conditions associated with elevated serum or urine levels of any mast cell mediator, in the absence of comorbidities that could explain elevated levels, should be considered 'Mast Cell Mediator Disorders (MCMD).' Emphasis should be placed on the identification of unique mast cell mediators, and development of drugs or supplements that inhibit their release.

Proposed Diagnostic Algorithm for Patients with Suspected Mast Cell Activation Syndrome

Mast cell activation (MCA) accompanies diverse physiologic and pathologic processes and is one of the more frequently encountered conditions in medicine. MCA-related symptoms are usually mild and often transient. In such cases, histamine receptor blockers and other mediator-targeting drugs can usually control MCA. In severe cases, an MCA syndrome (MCAS) may be diagnosed. However, overt MCAS is an unusual condition, and many patients referred because of suspected MCAS are diagnosed with other diseases (autoimmune, neoplastic, or infectious) unrelated to MCA or suffer from MCA-related (eg, allergic) disorders and/or comorbidities without fulfilling criteria of an overt MCAS. These considerations are important as more and more patients are informed that they may have MCA or even MCAS without completing a thorough medical evaluation. In fact, in several instances, symptoms are misinterpreted as MCA/MCAS, and other clinically relevant conditions are not thoroughly pursued. The number of such referrals is increasing. To avoid such unnecessary referrals and to prevent misdiagnoses, we here propose a diagnostic algorithm through which a clinically relevant (systemic) MCA can be suspected and MCAS can subsequently be documented or excluded. In addition, the algorithm proposed should help guide the investigating care providers to consider the 2 principal diagnoses that may underlie MCAS, namely, severe allergy and systemic mastocytosis accompanied by severe MCA. Although validation is required, we anticipate that this algorithm will facilitate the management of patients with suspected MCAS.

The underestimated role of basophils in Ph+ chronic myeloid leukaemia

Chronic myeloid leukaemia (CML) is a hematopoietic neoplasm defined by the chromosome translocation t(9;22) and the related oncogene, BCR-ABL1. In most patients, leukaemic cells can be kept under control using BCR-ABL1-targeting drugs. However, many patients relapse which remains a clinical challenge. In particular, patients with advanced (accelerated or blast phase) CML have a poor prognosis. So far, little is known about molecular and cellular interactions and features that contribute to disease progression and drug resistance in CML. One key prognostic factor at diagnosis is marked basophilia. However, although basophils are well-known multifunctional effector cells, their impact in CML remains uncertain. In this article, we discuss the potential role of basophils as active contributors to disease evolution and progression in CML. In particular, basophils serve as a unique source of inflammatory, angiogenic and fibrogenic molecules, such as vascular endothelial growth factor or hepatocyte growth factor. In addition, basophils provide vasoactive substances, like histamine as well as the cytokine-degrading enzyme dipeptidyl-peptidase IV which may promote stem cell mobilization and the extramedullary spread of stem and progenitor cells. Finally, basophils may produce autocrine growth factors for myeloid cells. Understanding the role of basophils in CML evolution and progression may support the development of more effective treatment concepts.

Mast cells and cancer

Mast cells (MCs) are a potent proangiogenic factor in tumors, they product several pro-angiogenic factors such as fibroblast growth factor 2 (FGF-2), vascular epithelial growth factor (VEGF), tryptase and chymase. Tryptase is a serine protease classified as α-tryptase and β-tryptase, both produced by MCs. Tryptase degrades the tissues, playing an important role in angiogenesis and in the development of metastases. Serum tryptase increases with age, with increased damage to cells and risk of developing a malignancy and it could be considered the expression of a fundamental role of MCs in tumor growth or, on the contrary, in the antitumor response. Many biomarkers have been developed in clinical practice for improving diagnosis and prognosis of some neoplasms. Elevated tryptase levels are found in subgroups of patients with haematologic and solid cancers. In the current review, we want to update the perspectives of tryptase as a potential biomarker in daily practice in different neoplasms.

Proposed diagnostic criteria and classification of basophilic leukemias and related disorders

Basophils form a distinct cell lineage within the hematopoietic cell family. In various myeloid neoplasms, including chronic myeloid leukemia, basophilia is frequently seen. Acute and chronic basophilic leukemias, albeit rare, have also been described. However, no generally accepted criteria and classification of basophilic leukemias have been presented to date. To address this unmet need, a series of Working Conferences and other meetings were organized between March 2015 and March 2016. The current article provides a summary of consensus statements from these meetings, together with proposed criteria to delineate acute basophilic leukemia (ABL) from chronic basophilic leukemia (CBL) and primary forms of the disease where no preceding myeloid malignancy is detected, from the more common 'secondary' variants. Moreover, the term hyperbasophilia (HB) is proposed for cases with a persistent peripheral basophil count ⩾1000 per μl of blood. This condition, HB, is highly indicative of the presence of an underlying myeloid neoplasm. Therefore, HB is an important checkpoint in the diagnostic algorithm and requires a detailed hematologic investigation. In these patients, an underlying myeloid malignancy is often found and is then labeled with the appendix -baso, whereas primary cases of ABL or CBL are very rare. The criteria and classification proposed in this article should facilitate the diagnosis and management of patients with unexplained basophilia and basophil neoplasms in routine practice, and in clinical studies.

Long-term treatment with imatinib results in profound mast cell deficiency in Ph+ chronic myeloid leukemia

Although mast cells (MC) play an important role in allergic reactions, their physiologic role remains unknown. In mice, several models of MC-deficiency have been developed. However, no comparable human model is available. We examined the in vitro- and in vivo effects of the KIT-targeting drug imatinib on growth and development of human MC. Imatinib was found to inhibit stem cell factor (SCF)-induced differentiation of MC in long-term suspension cultures (IC50: 0.01 μM). Correspondingly, long-term treatment of chronic myeloid leukemia (CML) patients with imatinib (400 mg/day) resulted in a marked decrease in MC. In patients with continuous complete molecular response during therapy, bone marrow MC decreased to less than 5% of pre-treatment values, and also serum tryptase concentrations decreased significantly (pre-treatment: 32.0±11.1 ng/ml; post-therapy: 3.4±1.8, p<0.01). Other myeloid lineages, known to develop independently of KIT, were not affected by imatinib-therapy. Imatinib also produced a substantial decrease in MCdevelopment in mice. However, no clinical syndrome attributable to drug-induced MC-deficiency was recorded in our CML patients. Together, imatinib suppresses MC production in vitro and in vivo. However, drug-induced MC depletion is not accompanied by adverse clinical events, suggesting that MC are less relevant to homeostasis in healthy tissues than we assumed so far.

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.

Spectrum of mast cell activation disorders

Mast cell (MC) activation disorders present with multiple symptoms including flushing, pruritus, hypotension, gastrointestinal complaints, irritability, headaches, concentration/memory loss and neuropsychiatric issues. These disorders are classified as: cutaneous and systemic mastocytosis with a c-kit mutation and clonal MC activation disorder, allergies, urticarias and inflammatory disorders and mast cell activation syndrome (MCAS), idiopathic urticaria and angioedema. MCs are activated by IgE, but also by cytokines, environmental, food, infectious, drug and stress triggers, leading to secretion of multiple mediators. The symptom profile and comorbidities associated with these disorders, such as chronic fatigue syndrome and fibromyalgia, are confusing. We propose the use of the term 'spectrum' and highlight the main symptoms, useful diagnostic tests and treatment approaches.

Mast cell activation syndromes: definition and classification

Mast cell activation (MCA) occurs in a number of different clinical conditions, including IgE-dependent allergies, other inflammatory reactions, and mastocytosis. MCA-related symptoms may be mild, moderate, severe, or even life-threatening. The severity of MCA depends on a number of different factors, including genetic predisposition, the number and releasability of mast cells involved in the reaction, the type of allergen, presence of specific IgE, and presence of certain comorbidities. In severe reactions, MCA can be documented by a substantial increase in the serum tryptase level above baseline. When symptoms are recurrent, are accompanied by an increase in mast cell-derived mediators in biological fluids, and are responsive to treatment with mast cell-stabilizing or mediator-targeting drugs, the diagnosis of mast cell activation syndrome (MCAS) is appropriate. Based on the underlying condition, these patients can further be classified into i) primary MCAS where KIT-mutated, clonal mast cells are detected, ii) secondary MCAS where an underlying inflammatory disease, often in the form of an IgE-dependent allergy, but no KIT-mutated mast cells, is found, and iii) idiopathic MCAS, where neither an allergy or other underlying disease, nor KIT-mutated mast cells are detectable. It is important to note that in many patients with MCAS, several different factors act together to lead to severe or even life-threatening anaphylaxis. Detailed knowledge about the pathogenesis and complexity of MCAS, and thus establishing the exact final diagnosis, may greatly help in the management and therapy of these patients.

NI-1: a novel canine mastocytoma model for studying drug resistance and IgER-dependent mast cell activation

BACKGROUND

Advanced mast cell (MC) disorders are characterized by uncontrolled growth of neoplastic MC in various organs, mediator-related symptoms, and a poor prognosis. Kit mutations supposedly contribute to abnormal growth and drug resistance in these patients.

METHODS

We established a novel canine mastocytoma cell line, NI-1, from a patient suffering from MC leukemia.

RESULTS

NI-1 cells were found to form mastocytoma lesions in NOD/SCID IL-2Rgamma(null) mice and to harbor several homozygous Kit mutations, including missense mutations at nucleotides 107(C→T) and 1187(A→G), a 12-bp duplication (nucleotide 1263), and a 12-bp deletion (nucleotide 1550). NI-1 cells expressed several MC differentiation antigens, including tryptase, Kit, and a functional IgE receptor. Compared to the C2 mastocytoma cell line harboring a Kit exon 11 mutation, NI-1 cells were found to be less responsive against the Kit tyrosine kinase inhibitors (TKI) masitinib and imatinib, but were even more sensitive against proliferation-inhibitory effects of the mammalian target of rapamycin (mTOR) blocker RAD001 and PI3-kinase/mTOR blocker NVP-BEZ235. The Kit-targeting multikinase inhibitors PKC412 and dasatinib were also found to override TKI resistance in NI-1 cells, and produced growth inhibition with reasonable IC(50) values (<0.1 μM).

CONCLUSION

NI-1 may serve as a useful tool to investigate IgE-dependent reactions and mechanisms of abnormal growth and drug resistance in neoplastic MC in advanced mastocytosis.

Systemic mastocytosis

Systemic mastocytosis (SM) is a clonal disorder of hematopoietic system characterized by abnormal growth and accumulation of mast cells in various tissues. Its clinical spectrum ranges from mild disease to an aggressive course with life-threatening conditions. Some of the clinical signs or symptoms of SM (hyperhidrosis, syncope and hypotensive/tachycardiac attacks) require consideration of pheochromocytoma and carcinoid syndrome in the differential diagnosis. The diagnosis relies on the demonstration of mast cell aggregates in bone marrow or extracutaneous tissues. The World Health Organization categorizes SM into 6 variants: indolent SM, SM with associated clonal hematological nonmast cell lineage disease, aggressive SM, mast cell leukemia, mast cell sarcoma and extracutaneous mastocytosis. Patients with indolent SM have a favorable prognosis with a life expectancy comparable with the healthy population, and symptomatic treatment is usually sufficient. However, more aggressive forms may be life threatening, and cytoreductive treatment is indicated in most cases.

Definitions, criteria and global classification of mast cell disorders with special reference to mast cell activation syndromes: a consensus proposal

Activation of tissue mast cells (MCs) and their abnormal growth and accumulation in various organs are typically found in primary MC disorders also referred to as mastocytosis. However, increasing numbers of patients are now being informed that their clinical findings are due to MC activation (MCA) that is neither associated with mastocytosis nor with a defined allergic or inflammatory reaction. In other patients with MCA, MCs appear to be clonal cells, but criteria for diagnosing mastocytosis are not met. A working conference was organized in 2010 with the aim to define criteria for diagnosing MCA and related disorders, and to propose a global unifying classification of all MC disorders and pathologic MC reactions. This classification includes three types of 'MCA syndromes' (MCASs), namely primary MCAS, secondary MCAS and idiopathic MCAS. MCA is now defined by robust and generally applicable criteria, including (1) typical clinical symptoms, (2) a substantial transient increase in serum total tryptase level or an increase in other MC-derived mediators, such as histamine or prostaglandin D(2), or their urinary metabolites, and (3) a response of clinical symptoms to agents that attenuate the production or activities of MC mediators. These criteria should assist in the identification and diagnosis of patients with MCAS, and in avoiding misdiagnoses or overinterpretation of clinical symptoms in daily practice. Moreover, the MCAS concept should stimulate research in order to identify and exploit new molecular mechanisms and therapeutic targets.

Standards and impact of hematopathology in myelodysplastic syndromes (MDS)

The diagnosis, classification, and prognostication of patients with myelodysplastic syndromes (MDS) are usually based on clinical parameters, analysis of peripheral blood and bone marrow smears, and cytogenetic determinants. However, a thorough histologic and immunohistochemical examination of the bone marrow is often required for a final diagnosis and exact classification in these patients. Notably, histology and immunohistology may reveal dysplasia in megakaryocytes or other bone marrow lineages and/or the presence of clusters of CD34-positive precursor cells. In other cases, histology may reveal an unrelated or co-existing hematopoietic neoplasm, or may support the conclusion the patient is suffering from acute myeloid leukemia rather than MDS. Moreover, histologic investigations and immunohistology may reveal an increase in tryptase-positive cells, a coexisting systemic mastocytosis, or bone marrow fibrosis, which is of prognostic significance. To discuss diagnostic algorithms, terminologies, parameters, and specific issues in the hematopathologic evaluation of MDS, a Working Conference involving a consortium of US and EU experts, was organized in June 2010. The outcomes of the conference and resulting recommendations provided by the faculty, are reported in this article. These guidelines should assist in the diagnosis, classification, and prognostication in MDS in daily practice as well as in clinical trials.

Standards and impact of hematopathology in myelodysplastic syndromes (MDS)

The diagnosis, classification, and prognostication of patients with myelodysplastic syndromes (MDS) are usually based on clinical parameters, analysis of peripheral blood and bone marrow smears, and cytogenetic determinants. However, a thorough histologic and immunohistochemical examination of the bone marrow is often required for a final diagnosis and exact classification in these patients. Notably, histology and immunohistology may reveal dysplasia in megakaryocytes or other bone marrow lineages and/or the presence of clusters of CD34-positive precursor cells. In other cases, histology may reveal an unrelated or co-existing hematopoietic neoplasm, or may support the conclusion the patient is suffering from acute myeloid leukemia rather than MDS. Moreover, histologic investigations and immunohistology may reveal an increase in tryptase-positive cells, a coexisting systemic mastocytosis, or bone marrow fibrosis, which is of prognostic significance. To discuss diagnostic algorithms, terminologies, parameters, and specific issues in the hematopathologic evaluation of MDS, a Working Conference involving a consortium of US and EU experts, was organized in June 2010. The outcomes of the conference and resulting recommendations provided by the faculty, are reported in this article. These guidelines should assist in the diagnosis, classification, and prognostication in MDS in daily practice as well as in clinical trials.

Elevated tryptase levels selectively cluster in myeloid neoplasms: a novel diagnostic approach and screen marker in clinical haematology

BACKGROUND

Recent data suggest that tryptase, a mast cell enzyme, is expressed in neoplastic cells in myeloid leukaemias. In several of these patients, increased serum tryptase levels are detectable.

MATERIALS AND METHODS

We have determined serum tryptase levels in 914 patients with haematological malignancies, including myeloproliferative disorders (n = 156), myelodysplastic syndromes (MDS, n = 241), acute myeloid leukaemia (AML, n = 317), systemic mastocytosis (SM, n = 81), non-Hodgkin's lymphoma (n = 59) and acute lymphoblastic leukaemia (n = 26). Moreover, tryptase was measured in 136 patients with non-neoplastic haematological disorders, 102 with non-haematological disorders and 164 healthy subjects.

RESULTS

In healthy subjects, the median serum tryptase was 5.2 ng mL(-1). Elevated serum tryptase levels were found to cluster in myeloid neoplasm, whereas almost all patients with lymphoid neoplasms exhibited normal tryptase. Among myeloid neoplasms, elevated tryptase levels (> 15 ng mL(-1)) were recorded in > 90% of patients with SM, 38% with AML, 34% with CML and 25% with MDS. The highest tryptase levels, often > 1000 ng mL(-1), were found in advanced SM and core-binding-factor leukaemias. In most patients with non-neoplastic haematological disorders and non-haematological disorders analysed in our study, tryptase levels were normal, the exception being a few patients with end-stage kidney disease and helminth infections, in whom a slightly elevated tryptase was found.

CONCLUSIONS

In summary, tryptase is a new diagnostic marker of myeloid neoplasms and a useful test in clinical haematology.

Targeting of mTOR is associated with decreased growth and decreased VEGF expression in acute myeloid leukaemia cells

BACKGROUND

The mammalian target of rapamycin (mTOR) has recently been implicated in leukaemic cell growth, tumour-associated angiogenesis and expression of vascular endothelial growth factor (VEGF). We examined whether mTOR plays a role as regulator of growth and VEGF-expression in acute myeloid leukaemia (AML). Three mTOR-targeting drugs, rapamycin, everolimus (RAD001) and CCI-779, were applied. The effects of these drugs on growth, survival, apoptosis and VEGF expression in primary AML cells and various AML cell lines were examined.

MATERIALS AND METHODS

Growth of AML cells and AML-derived cell lines was assessed by (3)H-thymidine incorporation, survival was examined by light- and electron microscopy, by Tunel assay and by AnnexinV-staining, and the expression of VEGF by Northern blotting, RT-PCR and ELISA.

RESULTS

Rapamycin was found to counteract growth in the AML cell lines U937 and KG1a as well as in primary AML cells in 14/18 patients examined. The effects of rapamycin and its derivatives were dose-dependent (IC(50): 10 pM-100 nM). It was also found that exposure to mTOR-targeting drugs resulted in apoptosis and in decreased expression of VEGF in leukaemic cells.

CONCLUSIONS

mTOR-targeting drugs exert antileukaemic effects on AML cells in vitro through multiple actions, including direct inhibition of proliferation, induction of apoptosis and suppression of VEGF. Based on this study and other studies, mTOR can be regarded as a potential drug target in AML.

Diagnostic and prognostic value of new biochemical and immunohistochemical parameters in chronic myeloid leukemia

Chronic myeloid leukemia (CML) is a stem-cell disease characterized by multilineage expansion of clonal BCR/ABL+ cells. Transformation from chronic into accelerated and blast phase of CML is usually associated with drug resistance and is accompanied by typical clinical and/or laboratory features, such as splenomegaly, increase in precursor cells, disturbed megakaryopoiesis, basophilia or marrow fibrosis. Because of new treatment options, early recognition of disease-acceleration is of importance. In this article, we review most recent developments in diagnostic procedures employing basophil-related biochemical and histopathological markers. These tests are useful to quantitate basophil-lineage cells in the peripheral blood in CML, to determine and quantify basophilia in the bone marrow, and to detect focal accumulations of blast cells and megakaryocytes as well as increased angiogenesis and fibrosis in bone marrow sections. Application of these markers may assist in determining the phase of disease and may help to better predict the prognosis in individual patients.

Mixed-lineage eosinophil/basophil crisis in MDS: a rare form of progression

BACKGROUND

Basophilic crisis and eosinophilia are well recognized features of advanced chronic myeloid leukaemia. In other myeloid neoplasms, however, transformation with marked basophilia and eosinophilia is considered unusual.

DESIGN

We examined the long-term follow-up of 322 patients with de novo myelodysplastic syndromes (MDS) to define the frequency of basophilic, eosinophilic and mixed lineage (basophilic and eosinophilic) transformation.

RESULTS

Of all patients, only one developed mixed lineage crisis (>or= 20% basophils and >or= 20% eosinophils). In this patient, who initially suffered from chronic myelomonocytic leukaemia, basophils increased to 48% and eosinophils up to 31% at the time of progression. Mixed lineage crisis was not accompanied by an increase in blast cells or organomegaly. The presence of BCR/ABL and other relevant fusion gene products (FIP1L1/PDGFRA, AML1/ETO, PML/RAR alpha, CBF beta/MYH11) were excluded by PCR. Myelomastocytic transformation/myelomastocytic leukaemia and primary mast cell disease were excluded by histology, KIT mutation analysis, electron microscopy and immunophenotyping. Basophils were thus found to be CD123+, CD203c+, BB1+, KIT- cells, and to express a functional IgE-receptor. Among the other patients with MDS examined, 4(1.2%) were found to have marked basophilia (>or= 20%) and 7(2.1%) were found to have massive eosinophilia ( >or= 20%), whereas mixed-lineage crisis was detected in none of them.

CONCLUSIONS

Mixed basophil/eosinophil crisis may develop in patients with MDS but is an extremely rare event.

Targeting of heat shock protein 32 (Hsp32)/heme oxygenase-1 (HO-1) in leukemic cells in chronic myeloid leukemia: a novel approach to overcome resistance against imatinib

Resistance toward imatinib and other BCR/ABL tyrosine kinase inhibitors remains an increasing clinical problem in the treatment of advanced stages of chronic myeloid leukemia (CML). We recently have identified the heat shock protein 32 (Hsp32)/heme oxygenase-1 (HO-1) as a BCR/ABL-dependent survival molecule in CML cells. We here show that silencing Hsp32/HO-1 in CML cells by an siRNA approach results in induction of apoptosis. Moreover, targeting Hsp32/HO-1 by either pegylated zinc protoporphyrine (PEG-ZnPP) or styrene maleic acid-micelle-encapsulated ZnPP (SMA-ZnPP) resulted in growth inhibition of BCR/ABL-transformed cells. The effects of PEG-ZnPP and SMA-ZnPP were demonstrable in Ba/F3 cells carrying various imatinib-resistant mutants of BCR/ABL, including the T315I mutant, which exhibits resistance against all clinically available BCR/ABL tyrosine kinase inhibitors. Growth-inhibitory effects of PEG-ZnPP and SMA-ZnPP also were observed in the CML-derived human cell lines K562 and KU812 as well as in primary leukemic cells obtained from patients with freshly diagnosed CML or imatinib-resistant CML. Finally, Hsp32/HO-1-targeting compounds were found to synergize with either imatinib or nilotinib in producing growth inhibition in imatinib-resistant K562 cells and in Ba/F3 cells harboring the T315I mutant of BCR/ABL. In summary, these data show that HO-1 is a promising novel target in imatinib-resistant CML.

Gastrointestinal manifestations of dermatologic disorders

The skin and the gastrointestinal tract may be affected concurrently by the same diseases. Pathogenetically, these conditions may be primarily dermatologic diseases involving the gastrointestinal (GI) tract or systemic diseases involving the skin, GI tract, and liver simultaneously. The correct diagnosis of such conditions relies on the ability of the gastroenterologist to recognize the underlying dermatologic disorder. The goal of this clinical review article is to increase gastroenterologists' awareness and understanding of some of these conditions. Case vignettes are presented and the relevant literature reviewed for epidermolysis bullosa, mastocytosis, hereditary hemorrhagic telangiectasia, and melanoma. This review focuses on increasing gastroenterologists' ability to recognize, diagnose, comprehend, and manage patients with these dermatologic conditions who have GI manifestations. Advances in molecular genetics that provide insight into the underlying pathophysiology and histopathology of these lesions are highlighted.

Systemic mastocytosis: a concise clinical and laboratory review

CONTEXT

Systemic mastocytosis is characterized by abnormal growth and accumulation of neoplastic mast cells in various organs. The clinical presentation is varied and may include skin rash, symptoms related to release of mast cell mediators, and/or organopathy from involvement of bone, liver, spleen, bowel, or bone marrow.

OBJECTIVE

To concisely review pathogenesis, disease classification, clinical features, diagnosis, and treatment of mast cell disorders.

DATA SOURCES

Pertinent literature emerging during the last 20 years in the field of mast cell disorders.

CONCLUSIONS

The cornerstone of diagnosis is careful bone marrow histologic examination with appropriate immunohistochemical studies. Ancillary tests such as mast cell immunophenotyping, cytogenetic/molecular studies, and serum tryptase levels assist in confirming the diagnosis. Patients with cutaneous disease or with low systemic mast cell burden are generally managed symptomatically. In the patients requiring mast cell cytoreductive therapy, treatment decisions are increasingly being guided by results of molecular studies. Most patients carry the kit D816V mutation and are predicted to be resistant to imatinib mesylate (Gleevec) therapy. In contrast, patients carrying the FIP1L1-PDGFRA mutation achieve complete responses with low-dose imatinib therapy. Other therapeutic options include use of interferon-alpha, chemotherapy (2-chlorodeoxyadenosine), or novel small molecule tyrosine kinase inhibitors currently in clinical trials.

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.

Identification of heat shock protein 32 (Hsp32) as a novel survival factor and therapeutic target in neoplastic mast cells

Systemic mastocytosis (SM) is a myeloid neoplasm characterized by increased survival and accumulation of neoplastic mast cells (MCs). In most patients, the D816V-mutated variant of KIT is detectable. We report here that heat shock protein 32 (Hsp32), also known as heme oxygenase-1 (HO-1), is a novel KIT-inducible survival factor in neoplastic MCs. As assessed by reverse transcription-polymerase chain reaction (RT-PCR), immunocytochemistry, and Western blotting, the KIT D816V(+) MC line HMC-1.2 as well as highly enriched primary neoplastic MCs were found to express Hsp32 mRNA and the Hsp32 protein. Moreover, KIT D816V and stem cell factor (SCF)-activated wild-type KIT were found to induce Hsp32 promoter activity, expression of Hsp32 mRNA, and expression of the Hsp32 protein in Ba/F3 cells. Correspondingly, the KIT D816V-targeting drug PKC412 decreased the expression of Hsp32 as well as proliferation/survival in neoplastic MCs. The inhibitory effects of PKC412 on the survival of HMC-1.2 cells were counteracted by the HO-1 inductor hemin or lentiviral-transduced HO-1. Moreover, 2 Hsp32-targeting drugs, pegylated zinc protoporphyrin (PEG-ZnPP) and styrene maleic acid copolymer micelle-encapsulated ZnPP (SMA-ZnPP), were found to inhibit proliferation and to induce apoptosis in neoplastic MCs. Furthermore, both drugs were found to cooperate with PKC412 in producing growth inhibition. Together, these data show that Hsp32 is an important survival factor and interesting new therapeutic target in neoplastic MCs.

Diagnostic Value of Tryptase in Anaphylaxis and Mastocytosis

Serum (or plasma) levels of total and mature tryptase measurements are recommended in the diagnostic evaluation of systemic anaphylaxis and systemic mastocytosis, but their interpretation must be considered in the context of a complete workup of each patient. Total tryptase levels generally reflect the increased burden of mast cells in patients with all forms of systemic mastocytosis (indolent systemic mastocytosis, smoldering systemic mastocytosis, systemic mastocytosis associated with a hematologic clonal non-mast cell disorder, aggressive systemic mastocytosis, and mast cell leukemia) and the decreased burden of mast cells associated with cytoreductive therapies in these disorders. Causes of an elevated total tryptase level other than systemic mastocytosis must be considered, however, and include systemic anaphylaxis, acute myelocytic leukemia, various myelodysplastic syndromes, hypereosinophilic syndrome associated with the FLP1L1-PDGFRA mutation, end-stage renal failure, and treatment of onchocerciasis. Mature (beta) tryptase levels generally reflect the magnitude of mast cell activation and are elevated during most cases of systemic anaphylaxis, particularly with parenteral exposure to the inciting agent.

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

AIMS

Compact tryptase-positive round cell infiltrates of the bone marrow (TROCI-BM) are very rare histopathological findings and may pose challenging problems with regard to the cell type involved (either mast cells or basophilic granulocytes) and the exact diagnosis.

METHODS

A selected panel of immunohistochemical markers against mast cell and basophil related antigens, including CD25, CD34, CD117/Kit, and the 2D7 antigen (which is found only in basophilic granulocytes) on a total of 410 routinely processed bone marrow biopsy specimens (including 88 cases of systemic mastocytosis (SM), 20 cases of chronic myeloid leukaemia (CML), 92 cases of myeloid neoplasms other than CML, and 210 controls with normal/reactive bone marrows).

RESULTS

In total, 17 cases with TROCI-BM could be identified: 11 SM (including two cases of well-differentiated SM and two mast cell leukaemias; MCL), 2 myelomastocytic leukaemia (MML), 2 CML with excess of basophils (secondary basophilic leukaemia (CMLba)), and 2 tryptase positive acute myeloid leukaemia (AML). Regarding the cell types involved, TROCI-BM cells were found to express CD117/Kit in all cases of SM and MCL. In MML and tryptase postitive AML, TROCI-BM cells were found to coexpress CD34 and Kit. The basophil specific antigen 2D7 was only detected in CD34/Kit negative TROCI-BM cells in two patients with CMLba. The activating point mutation D816V was detected in 8/11 patients with SM but not in any of the other haematological malignancies.

CONCLUSIONS

In summary, a total of six rare myeloid neoplasms may present with a novel immunohistochemical phenomenon tentatively termed TROCI-BM.

Evaluation of neoplastic human mast cells by tryptase-immunoelectron microscopy

AIMS

To analyse and characterize the ultrastructural morphology of normal tissue mast cells (MC) and neoplastic bone marrow MC.

METHODS

We have examined the ultrastructure and cytomorphological features of MC derived from cord blood cells, neoplastic bone marrow MC in patients with systemic mastocytosis (SM, n = 4), myelomastocytic leukaemia (MML, n = 2), mast cell leukaemia (MCL, n = 2) and tryptase-positive acute myeloid leukaemia (AML, n = 4).

RESULTS

Based on their ultrastructure and morphology, four distinct cell types could be delineated: (i) mature well-granulated tissue MC exhibiting a round central nucleus; (ii) atypical MC type I with oval nuclei, hypogranulated cytoplasm, and prominent surface projections; (iii) immature atypical MC with bi- or polylobed nuclei (atypical MC type II = promastocytes); and (iv) metachromatic blasts. Type I atypical MC were detected in a patient with indolent SM, whereas type II MC and metachromatic blasts were primarily found in MML, MCL and tryptase-positive AML. In all samples examined, the identity of MC could be reconfirmed by immunoelectron microscopy, irrespective of the stage of cell maturation or the disease variant, all types of MC contained tryptase in their cytoplasmic granules.

CONCLUSION

Immunoelectron microscopy may be a helpful approach in confirming the identity of neoplastic MC in myeloid neoplasms.

PKC412 inhibits in vitro growth of neoplastic human mast cells expressing the D816V-mutated variant of KIT: comparison with AMN107, imatinib, and cladribine (2CdA) and evaluation of cooperative drug effects

In most patients with systemic mastocytosis (SM), including aggressive SM and mast cell leukemia (MCL), neoplastic cells express the oncogenic KIT mutation D816V. KIT D816V is associated with constitutive tyrosine kinase (TK) activity and thus represents an attractive drug target. However, imatinib and most other TK inhibitors fail to block the TK activity of KIT D816V. We show that the novel TK-targeting drugs PKC412 and AMN107 counteract TK activity of D816V KIT and inhibit the growth of Ba/F3 cells with doxycycline-inducible expression of KIT D816V as well as the growth of primary neoplastic mast cells and HMC-1 cells harboring this KIT mutation. PKC412 was a superior agent with median inhibitory concentration (IC(50)) values of 50 to 250 nM without differences seen between HMC-1 cells exhibiting or lacking KIT D816V. By contrast, AMN107 exhibited more potent effects in KIT D816V(-) HMC-1 cells. Corresponding results were obtained with Ba/F3 cells exhibiting wild-type or D816V-mutated KIT. The growth-inhibitory effects of PKC412 and AMN107 on HMC-1 cells were associated with induction of apoptosis and down-regulation of CD2 and CD63. PKC412 was found to cooperate with AMN107, imatinib, and cladribine (2CdA) in producing growth inhibition in HMC-1, but synergistic drug interactions were observed only in cells lacking KIT D816V. Together, PKC412 and AMN107 represent promising novel agents for targeted therapy of SM.

Expression of angiogenic factors in chronic myeloid leukaemia: role of the bcr/abl oncogene, biochemical mechanisms, and potential clinical implications

Chronic myeloid leukaemia (CML) is a stem cell disease characterized by an increased production and accumulation of clonal BCR/ABL-positive cells in haematopoietic tissues. The chronic phase of CML is inevitably followed by an accelerated phase of the disease, with consecutive blast crisis. However, depending on genetic stability, epigenetic events, and several other factors, the clinical course and survival appear to vary among patients. Recent data suggest that angiogenic cytokines such as vascular endothelial growth factor (VEGF), are up-regulated in CML, and play a role in the pathogenesis of the disease. These factors appear to be produced and released in leukaemic cells in patients with CML. In line with this notion, increased serum-levels of angiogenic growth factors are measurable in CML patients. In this study we provide an overview of angiogenic growth factors expressed in CML cells, discuss the possible pathogenetic role of these cytokines, the biochemical basis of their production in leukaemic cells, and their potential clinical implications.

Systemic mastocytosis with associated clonal haematological non-mast cell lineage diseases: a histopathological challenge

AIMS

Although systemic mastocytosis (SM) with an associated clonal haematological non-mast cell lineage disease (SM-AHNMD) is a major subtype of SM, little is known about its frequency among myelogenous neoplasms, and mastocytosis in particular, or about AHNMD subtype frequencies.

METHODS

Approximately 19500 routine bone marrow biopsies were evaluated. Immunostaining with antibodies against tryptase, KIT, and CD25 and molecular analysis for detection of C-KIT point mutations were performed in approximately 550/4100 myelogenous malignancies including mastocytosis, almost all subtypes of myelodysplastic syndrome (MDS), myelodysplastic/myeloproliferative syndrome (MDS/MPD), MPD, and acute myeloid leukaemia (AML).

RESULTS

SM was rare-it was diagnosed in only 64 bone marrows (0.3%) and made up 1.5% of myelogenous tumours. SM-AHNMD was the second most frequent subtype (20). SM-AHNMD was never included in the clinical differential diagnoses and was confirmed histologically in most cases only after appropriate immunostaining. The abnormal mast cell phenotype was confirmed by immunohistochemical demonstration of tryptase and CD25 coexpression. The following associated haematological neoplasms were found: MDS/MPS, AML, MPS, MDS, plasma cell myeloma, and unclassifiable myelogenous malignancy. C-KIT point mutations were detected in 16 of 20 cases.

CONCLUSIONS

SM-AHNMD can be diagnosed histologically in bone marrow trephines only after immunostaining with antibodies against tryptase, KIT, and CD25. Eighteen of 20 AHNMDs were of myeloid origin. C-KIT point mutations were present in 16 of 20 cases. The prognostic relevance of detecting SM associated with another haematological neoplasm remains unclear, but mast cell resistance to most cytoreductive agents is of major importance for treatment planning.

The distribution of mast cells in the human area postrema

The topography and phenotype of mast cells in the human area postrema, together with correlation between mast-cell density and microvessel density (MVD), were analysed in 16 brains. Transverse serial sections of formalin-fixed, paraffin-embedded brainstems were stained with toluidine blue and alcian blue/safranin stainings, and with anti-tryptase and anti-CD31 monoclonal antibodies. The mean (+/- SD) numbers of mast cells per section were 1.3 +/- 0.8 and 1.2 +/- 0.7 with toluidine blue and alcian blue/safranin, respectively, whereas anti-tryptase monoclonal antibody showed a mean of 5.1 +/- 2.4 cells. Mast cells were alcian blue- and safranin-positive in 56%, because of the coexistence of low-sulphated (blue-staining) and high-sulphated (red-staining) granules. No significant linear correlation between mast-cell density (4.9 mm(-2)) and MVD (114.5 mm(-2)) was found (r(2) = 0.19, P = 0.09). Mast cells were frequently located close to blood vessels (55%) (33% to venules, 22% to arterioles), indicating that their products play a role in the regulation of blood flow and in vessel permeability in the area postrema. Mast cells were located subependymally in 44% and close to the dorsal aspect of the nucleus of the tractus solitarius in 31%, suggesting a subregional distribution.