Mastocytosis, MCAS, and Related Disorders-Diagnosis, Classification, and Therapy

Mastocytosis is a heterogeneous group of hematologic neoplasms defined by an accumulation of neoplastic mast cells (MC) in the skin, bone marrow, and other visceral organs [...].

[Cutaneous Manifestations in Mastocytosis: Update]

INTRODUCTION

Mastocytosis is characterized by the clonal expansion of morphological and immunophenotypically abnormal mast cells in different organs. The skin is the most frequently affected tissue. Virtually all children and more than 80% of adult patients with mastocytosis show cutaneous lesions.

MATERIAL AND METHODS

The present article describes the symptoms and signs in cutaneous mastocytosis, based on the review of recently published international consensus guidelines.

DISCUSSION

According to the 2016 World Health Organization classification, mastocytosis can be divided in cutaneous mastocytosis, systemic mastocytosis and mast cell sarcoma. Cutaneous mastocytosis is subclassified in three subtypes: maculopapular cutaneous mastocytosis, diffuse cutaneous mastocytosis and cutaneous astocytoma. Telangiectasia macularis eruptiva perstans is no longer considered a distinct entity.

CONCLUSION

Based on the age of onset, cutaneous manifestations of mastocytosis can be variable. The classification of cutaneous mastocytosis has recently been updated. Typically, in patients with childhood-onset mastocytosis, the disease occurs as cutaneous mastocytosis and shows spontaneous resolution around puberty. In contrast, adult patients, despite having also cutaneous lesions, often show systemic involvement and the course of the disease is usually chronic.

Multidisciplinary Management of Mastocytosis: Nordic Expert Group Consensus

Mastocytosis is a heterogeneous group of diseases defined by an increased number and accumulation of mast cells, and often also by signs and symptoms of mast cell activation. Disease subtypes range from indolent to rare aggressive forms. Mastocytosis affects people of all ages and has been considered rare; however, it is probably underdiagnosed with potential severe implications. Diagnosis can be challenging and symptoms may be complex and involve multiple organ-systems. In general it is advised that patients should be referred to centres with experience in the disease offering an individualized, multidisciplinary approach. We present here consensus recommendations from a Nordic expert group for the diagnosis and general management of patients with mastocytosis.

[Mastocytosis]

Mastocytosis is a heterogeneous disease with an increased number and activation of mast cells. Subtypes range from benign to rare aggressive forms, and the disease may affect people of all ages. The pathogenesis involves mutations in the KIT gene in both children and adult patients. Estimated prevalence is one per 10,000, but the disease is very likely underdiagnosed. The diagnosis may be challenging and patients may present to several medical specialties. This article presents an overview of clinical signs and symptoms as well as a diagnostic algorithm and treatment options of mastocytosis.

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.

[Mastocytosis--diagnostic criteria and treatment]

Mastocytosis is a heterogeneous group of rare diseases characterized by the proliferation and accumulation of mast cells in one or more organs such as the skin, bone marrow, liver, spleen, and lymph nodes. According to the WHO classification, mastocytosis is divided into seven subvariants. The symptoms are associated with mediator release and impaired organ function due to infiltration by neoplastic mast cells. There is a higher risk of anaphylactic shock; therefore education of the patients is very important. Patients may be asymptomatic. Symptomatic treatment is used in cutaneous mastocytosis and in indolent systemic mastocytosis. More aggressive subvariants of mastocytosis are treated with chemotherapy, targeted therapy, and bone marrow transplantation.

[Urticaria pigmentosa: a current approach]

The term urticaria pigmentosa (UP) denotes a heterogeneous group of disorders characterized by abnormal growth and accumulation of mast cells (MC) in the skin. Symptoms result from MC chemical mediator's release, pathologic infiltration of neoplastic MC in tissues or both. Multiple molecular, genetic and chromosomal defects seem contribute to an autonomous growth, but somatic c-kit D816V mutation is more frequently found, especially in systemic disease. The aim of this paper is to provide a current overview for a better understanding of the symptoms associated with this disease, to describe its classification, recent advances in its pathophysiology and its treatment.

[Mastocytosis: when should it be considered?]

Mast cell disorders are defined by the accumulation of mast cells in one or more organ systems. Cutaneous forms are mainly observed in children whereas systemic forms are predominant in adults. Mast cells cause symptoms by the release of proinflammatory mediators or by infiltration of various organs. The measurement of serum tryptase has opened the possibility of screening for mastocytosis, which must be taken into consideration in case of severe anaphylactic reactions. Definite diagnosis is established based on a biopsy of skin or bone marrow. An activating mutation of stem cell factor receptor c-kit is often found. Treatment is based on control of the symptoms triggered by mast cell degranulation. Moreover, novel treatment options targeting mast cell proliferation become available for clinical use.

Mastocytosis: a rare case of anaphylaxis in paediatric age and literature review

The term "mastocytosis" denotes a heterogeneous group of disorders characterised by abnormal growth and accumulation of mast cells (MC) in one or more organ systems. Symptoms result from MC chemical mediator's release, pathologic infiltration of neoplastic MC in tissues or both. Multiple molecular, genetic and chromosomal defects seem to contribute to an autonomous growth, but somatic c-kit D816V mutation is more frequently encountered, especially in systemic disease. We present a literature review of mastocytosis and a rare case report of an 18 month-old-girl with a bullous dermatosis, respiratory distress and anaphylaxis, as clinical manifestations of mastocytosis. The developments of accepted classification systems and novel useful markers allowed a re-evaluation and updating of the classification of mastocytosis. In paediatric age cutaneous forms of disease prevail and may regress spontaneously. SM is more frequently diagnosed in adults and is a persistent (clonal) disease of bone marrow. The clinical course in these patients is variable. Today diagnostic criteria for each disease variant are reasonably well defined. There are, however, peculiarities, namely in paediatric age, that makes the diagnostic approach difficult. Systemic disease may pose differential diagnostic problems resulting from multiple organ systems involvement. Conversely, the "unexplained" appearance of those symptoms with no skin lesions should raise the suspicion of MC disease. This case is reported in order to stress the clinical severity and difficult diagnostic approach that paediatric mastocytosis may assume.

Mastocytosis: state of the art

Mastocytosis is a neoplastic disease involving mast cells (MC) and their CD34+ progenitors. Symptoms in mastocytosis are caused by biological mediators released from MC and/or the infiltration of neoplastic MC in various organs, the skin and the bone marrow being predominantly involved. A WHO consensus classification for mastocytosis exists, which is widely accepted and includes three major categories: (1) Cutaneous mastocytosis (CM), a benign disease in which MC infiltration is confined to the skin, is preferentially seen in young children and exhibits a marked tendency to regress spontaneously. (2) Systemic mastocytosis (SM) which is commonly diagnosed in adults and includes four major subtypes: (i) indolent SM (ISM, the most common form involving mainly skin and bone marrow); (ii) a unique subcategory termed SM with an associated non-mast cell clonal hematological disease (SM-AHNMD); (iii) aggressive SM usually presenting without skin lesions, and (iv) MC leukemia, probably representing the rarest variant of human leukemias. (3) The extremely rare localized extracutaneous MC neoplasms, either presenting as malignancy (MC sarcoma) or as benign tumor termed extracutaneous mastocytoma. Diagnostic criteria for mastocytosis are available and are widely accepted. SM criteria include one major criterion (multifocal compact tissue infiltration by MC) and four minor criteria: (1) prominent spindling of MC; (2) atypical immunophenotype of MC with coexpression of CD2 and/or CD25 (antigens which have not been found to be expressed on normal/reactive MC); (3) activating (somatic) point mutations of the c-kit proto-oncogene usually involving exon 17, with the imatinib-resistant type D816V being most frequent, and (4) persistently elevated serum tryptase level (>20 ng/ml). To establish the diagnosis of SM, at least one major and one minor criterion, or at least three minor criteria, have to be fulfilled. The natural clinical course of mastocytosis is variable. Most patients, in particular those with CM and ISM, remain in an indolent stage over many years or even decades, while others, in particular those with aggressive SM, SM-AHNMD, or mast cell leukemia, show a progressive course, usually with a fatal outcome.

Diagnostic evaluation and classification of mastocytosis

During the past few years, mastocytosis research has reached important milestones, including the formulation of diagnostic criteria, definition of markers, and targeting of mutated KIT. Important aims for the future are to standardize diagnostic assays and techniques, and to achieve harmonization among centers as a basis for the design of multicenter clinical trials in SM, including the rare ASM and MCL subvariants.

Mastocytosis: The Great Masquerader

Variants of mastocytosis can present with puzzling cutaneous and systemic symptoms and signs that can result in an erroneous diagnosis of idiopathic urticaria or idiopathic anayphylaxis. The molecular basis of mastocytosis is now better understood, with updated classification based on distinct growth factor and oncogene abnormalities. Elicitation of a full history and careful attention to the skin examination will usually provide the clinician enough information to deduce that the condition is not simply chronic idiopathic urticaria.

Mastocytosis: pathology, genetics, and current options for therapy

Mast cell disorders are defined by an abnormal accumulation of tissue mast cells (MCs) in one or more organ systems. Symptoms in mastocytosis result from MC-derived mediators and, less frequently, from destructive infiltration of MCs. Cutaneous mastocytosis (CM) is a benign disease of the skin and may regress spontaneously. Systemic mastocytosis (SM) is a persistent disease in which a somatic c-kit mutation at codon 816 is usually detectable in MCs and their progenitors. The clinical course in these patients is variable ranging from asymptomatic for years to highly aggressive and rapidly devastating. The WHO discriminates five categories of SM: indolent SM (ISM), aggressive SM (ASM), SM with associated clonal hematological non-MC-lineage disease (AHNMD), and mast cell leukemia (MCL). The c-kit mutation D816V is quite common and may be found in all SM-categories. In SM-AHNMD, additional genetic abnormalities have been reported, whereas no additional defects are yet known for ASM or MCL. Patients with ISM and CM are treated with "mediator-targeting" drugs, whereas patients with ASM or MCL are candidates for cytoreductive therapy. The use of "Kit-targeting" tyrosine kinase inhibitors such as STI571 (Imatinib, Gleevec), has also been suggested. However, the D816V mutation of c-kit is associated with relative resistance against STI571. Therefore, these patients require alternative targeted drugs or new drug-combinations. In patients with SM-AHNMD, separate treatment plans for the SM-component and the AHNMD should be established. Examples include the use of STI571 in patients with SM plus hypereosinophilic syndrome (SM-HES) and the FIPL1/PDGFRA fusion gene target, or chemotherapy for eradication of AML in patients with SM-AML.

Mastocytosis

Systemic mast cell disorders in most instances appear to be clonal disorders of the mast cell and its progenitor. Symptoms result from a pathological release of mast cell mediators and a destructive mast cell infiltration. Cutaneous mastocytosis is most frequently seen in children and may regress. Systemic mastocytosis (SM) is a persistent disease. A somatic c-kit mutation at codon 816 is often detectable in haematopoietic cells. The clinical course of mastocytosis is variable, ranging from indolent to aggressive. Five categories of disease are recognized: Indolent SM, aggressive SM, SM with associated clonal haematological non-mast cell-lineage disease (AHNMD) and mast cell leukaemia (MCL). In SM-AHNMD, additional genetic abnormalities have been reported. Patients with cutaneous or indolent systemic disease are treated symptomatically. Patients with aggressive disease are candidates for cytoreductive therapy. The use of 'Kit-targeting' tyrosine kinase inhibitors are best selected following a mutational analysis of c-kit. For instance, the D816V mutation appears to be associated with relative resistance against imatinib. However, imatinib has been used with success in patients with SM-hypereosinophilic syndrome (HES) and the FIPL1/PDGFRA fusion gene and in a patient with mastocytosis with a mutation outside of codon 816. The value of bone marrow transplantation remains under investigation.

[Mastocytosis, classification, biological diagnosis and therapy]

In mast cell (MC) disorders (mastocytosis), clinical symptoms are caused by the release of chemical mediators from MCs, the pathologic infiltration of neoplastic MCs in tissues, or both. Cutaneous mastocytosis is a benign disease in which MC infiltration is confined to the skin. In pediatric cases cutaneous mastocytosis might regress spontaneously. Systemic mastocytosis (SM) is more frequently diagnosed in adults and is a persistent (clonal) disease of bone marrow-derived myelomastocytic progenitors. The somatic c-kit mutation D816V is found in the majority of such patients. The natural clinical course in SM is variable. Whereas most patients remain at the indolent stage for many years, some have aggressive SM (ASM) at diagnosis. Other patients have an associated clonal hematologic none MC lineage disease (AHNMD). MC leukemia (MCL) is a rare disease variant characterized by circulating MCs and fatal disease progression. Two important diagnostic clues in SM are an increased serum tryptase level and the presence of abnormal mast cells in the bone marrow. The current review provides an overview of mastocytosis and its subvariants, the new classification of these diseases, a practical guide for the biological diagnosis and advances and future directions in therapy of these pathologies.

Diagnosis and classification of mast cell proliferative disorders: delineation from immunologic diseases and non–mast cell hematopoietic neoplasms

In mast cell (MC) disorders (mastocytosis), clinical symptoms are caused by the release of chemical mediators from MCs, the pathologic infiltration of neoplastic MCs in tissues, or both. Cutaneous mastocytosis is a benign disease in which MC infiltration is confined to the skin. In pediatric cases cutaneous mastocytosis might regress spontaneously. Systemic mastocytosis (SM) is more frequently diagnosed in adults and is a persistent (clonal) disease of bone marrow-derived myelomastocytic progenitors. The somatic c-kit mutation D816V is found in the majority of such patients. The natural clinical course in SM is variable. Whereas most patients remain at the indolent stage for many years, some have aggressive SM (ASM) at diagnosis. Other patients have an associated clonal hematologic non-MC lineage disease (AHNMD). MC leukemia (MCL) is a rare disease variant characterized by circulating MCs and fatal disease progression. The diagnoses of ASM, SM-AHNMD, and MCL might be confused with a variety of endocrinologic, vascular, or immunologic disorders. It is therefore of particular importance to be aware of the possibility of an underlying (malignant) MC disease in patients with unexplained vascular instability, unexplained (anaphylactoid) shock, idiopathic flushing, diarrhea, headache, and other symptoms that might be mediator related. An important diagnostic clue in such cases is an increased serum tryptase level. The current review provides an overview of mastocytosis and its subvariants and a practical guide that might help to delineate mastocytosis from unrelated systemic disorders.

Mastocytosis: classification, diagnosis, and clinical presentation

Mastocytosis comprises several diseases characterized by an abnormal increase in tissue mast cells. Cutaneous mastocytosis (CM) is the most common form of mastocytosis, affects predominantly children, and presents as a mast cell hyperplasia limited to the skin. Systemic mastocytosis (SM) comprises multiple distinct entities in which mast cells in filtrate the skin and/or other organs. The diagnosis of SM is based on the presence of one major criterion and one minor criterion or three minor criteria. Major criteria include the presence of multifocal dense infiltrates of > 15 mast cells in bone marrow and/or other extracutaneous organs. Four minor criteria include the presence of elevated serum alpha-tryptase levels > 20 ng/mL, the expression of CD2 and CD25 surface markers in c-kit-positive mast cells from bone marrow or other organs, the presence of a c-kit mutations on bone marrow and/or other tissues mast cells, and the presence of > 25% abnormal spindle-shaped mast cells in bone marrow and/or tissues. Symptoms of CM include pruritus, flushing urticaria, and dermatographism. Symptoms of SM include cutaneous symptoms in association with syncope, gastric distress, nausea and vomiting, diarrhea, bone pain, and neuropsychiatric symptoms. Activating and nonactivating mutations of c-kit (Asp816Val) are seen in adult SM and in some pediatric CM (Gly839Lys), indicating a clonal dysregulation. There is no cure for mastocytosis but the majority of pediatric CM regress at puberty. Women with mastocytosis are fertile and pregnancy and delivery have been successful by blocking mast cell-mediated symptoms. Symptomatic treatment aimed at reducing the effect of mediators is effective with antihistamines and mast cell-stabilizing agents such as sodium cromolyn. To reduce mast cell burden, interferon alpha, steroids, and purine analogs have been used with varying results. Future directions include tyrosine kinase inhibitors and bone marrow transplant.

Clinical, genetic, and therapeutic insights into systemic mast cell disease

PURPOSE OF REVIEW

Mast cell disease is markedly heterogeneous in its underlying molecular pathogenesis, clinical presentation, natural history, and specific treatment. Skin-only disease (cutaneous mastocytosis) is infrequent in adults and systemic mastocytosis may be broadly classified as an indolent or aggressive variant based on the absence or presence of impaired organ function. Urticaria pigmentosa and mast cell mediator release symptoms can occur in all categories of mast cell disease and may not be prognostically detrimental. The purpose of this review is to summarize current concepts and recent advances in the pathogenesis and treatment of adult mast cell disease.

RECENT FINDINGS

A series of laboratory investigations has revealed that mast cell disease is a clonal stem cell disorder, and at least two genes (c-kit and PDGFRA) with pathogenetically relevant mutations have been identified. FIP1L1-PDGFRA+ mast cell disease responds completely to imatinib mesylate. Both Asp816Val c-kit+ and molecularly undefined cases have been shown to respond to 2-chlorodeoxyadenosine therapy after failing treatment with interferon-alpha.

SUMMARY

A partial molecular classification of mast cell disease is now possible; Asp816Val c-kit+, FIP1L1-PDGFRA+, and molecularly undefined cases. Such molecular classification is therapeutically relevant.

Chronic Myelogenous Leukemia and Myeloproliferative Disease

In Section I, Dr. Stephen O’Brien reviews the latest data on the clinical use of imatinib (STI571, Gleevec, Glivec) in CML. His review focuses on the use of imatinib in newly diagnosed chronic phase patients and summarizes cytogenetic and molecular response data, as well as use of the agent at high doses and in combination with other drugs. A brief summary of the prospective international Phase III studies that are currently ongoing is also provided, and the issues of resistance and definition of suboptimal therapeutic response are also covered. Finally, therapeutic decision-making and treatment strategy are considered.

In Section II, Dr. Ayalew Tefferi considers the latest developments in the biology and therapy of myeloid metaplasia/myelofibrosis. Dr. Tefferi covers what is currently understood of the biology of the disease and reviews established therapies for the condition as well as novel agents that are being used in clinical trials. The development of optimal management strategies for the disease is considered.

In Section III, Dr. Peter Valent reviews the classification of mast cell proliferative disorders and covers the clinical and pathological presentation of this group of neoplasms. He reviews the state-of-the-art regarding the molecular biology of mastocytosis along with diagnostic criteria and novel treatment concepts.

Mast cell proliferative disorders: current view on variants recognized by the World Health Organization

The term mastocytosis covers a heterogeneous group of disorders characterized by the abnormal growth and accumulation of MCs in one or more organ systems. Clinical symptoms occur from the release of chemical mediators or pathologic infiltration of MCs. CM typically presents as UP and is a benign disease confined to the skin. In many cases, particularly in children, this disease regresses spontaneously. By contrast, SM is a clonal persistent disease of MC-committed or precommitted hematopoietic progenitors. In most of these patients, the transforming c-kit mutation Asp-816-Val is detectable. The clinical course in SM is variable. Many cases remain in an indolent stage over decades. In a few patients, significant organopathy is found, and this may lead to the diagnosis of aggressive SM. In other patients, AHNMD is diagnosed. MCL is a rare form of SM characterized by leukemic spread of MCs in the marrow and blood and rapid progression. In contrast to indolent SM, patients with MCL or aggressive SM often present without UP-like skin lesions. Patients with indolent SM should be treated with mediator-targeting drugs but not with cytoreductive drugs. By contrast, patients with aggressive SM or MCL are candidates for cytoreductive therapy. Some patients with aggressive SM may benefit from IFNalpha2b. Patients with rapid progression or MCL are candidates for more aggressive treatment, including cladribine, chemotherapy, and stem cell transplantation. In patients with SM-AHNMD, the SM should be treated as if no AHNMD is present, and the AHNMD should be treated as if no SM had been diagnosed.

Unmasking mastocytosis

Mastocytosis is a cutaneous disorder that may progress to a life-threatening, multi-organ systemic disease. Adults are more likely to experience systemic disease than children. A discussion of the disease process, treatment modalities, and practical strategies for patient care is presented.

Mastocytosis: current concepts in diagnosis and treatment

Mastocytosis consists of a group of disorders characterized by a pathologic increase in mast cells in tissues including skin, bone marrow, liver, spleen, and lymph nodes. Mastocytosis is a rare disease. Because of this, general practitioners have limited exposure to its clinical manifestations, diagnosis, classification, and management. Diagnosis of mastocytosis is suspected on clinical grounds and is established by histopathologic examination of involved tissues such as skin and bone marrow. The most common clinical sign of mastocytosis is the presence of typical skin lesions of urticaria pigmentosa. Most patients experience symptoms related to mast cell mediator release, and prevention of the effects of these mediators on tissues constitutes the major therapeutic goal in the management of mastocytosis. Despite recent advances in knowledge about the pathophysiology, diagnosis, and classification of mastocytosis, a curative treatment for mastocytosis does not now exist. Management of patients within all categories of mastocytosis includes: (1) a careful counseling of patients (parents in pediatric cases) and care providers, (2) avoidance of factors triggering acute mediator release, (3) treatment of acute mast cell mediator release, (4) treatment of chronic mast cell mediator release, and if indicated (5) an attempt to treat organ infiltration by mast cells. The goal of this manuscript is to provide an overview of the mediators produced and released by mast cells, the diagnostic criteria for the different variants of mastocytosis, and the treatment options currently available.

Spectrum of associated clonal hematologic non-mast cell lineage disorders occurring in patients with systemic mastocytosis

Systemic mastocytosis (SM) is a myeloproliferative disease affecting multipotent and/or mast cell-committed hematopoietic progenitor cells. In a significant subgroup of patients (10-35%), an associated clonal hematologic non-mast cell lineage disorder (AHNMD) occurs. These AHNMDs can be classified according to recently established WHO criteria. Most AHNMDs resemble myeloid malignancies such as acute myeloid leukemia, myeloproliferative disorders or myelodysplastic syndromes. In only a few cases, lymphoproliferative disorders are diagnosed. Patients with SM-AHNMD have a less favorable prognosis concerning survival when compared to indolent SM. No general guidelines for the treatment of patients with SM-AHNMD have been established so far. A reasonable straightforward approach may be to treat the AHNMD in those patients in the same way as if no coexisting SM exists.

Cutaneous mastocytosis -- clinical heterogeneity

Cutaneous mastocytosis (CM) encompasses several distinct patterns of disease which can be distinguished by the type of skin lesions, age of onset, familial occurrence, noncutaneous involvement, associated c-kit mutations, and prognosis. A clear distinction of the type of CM in individual patients has important implications regarding patient management and prognosis.

Smouldering mastocytosis: a novel subtype of systemic mastocytosis with slow progression

Systemic mastocytosis (SM) is a clonal disease that shows an either indolent or an aggressive clinical course. Utilizing established criteria, indolent SM can readily be discriminated from the rare aggressive subvariants of SM in most cases. In a small group of patients, however, clinical and laboratory parameters are indicative of slow progression without signs of aggressive disease or an associated hemopoietic neoplasm. These SM patients exhibit a high burden of mast cells, hypercellular marrow and organomegaly. Because of the 'intermediate' course and uncertain prognosis, these cases have been referred to as smouldering SM. In the present article, we discuss clinical and laboratory findings in smouldering SM and review the current literature. In addition, the pathophysiology of this novel subtype of SM is discussed.

Kit and c-kit mutations in mastocytosis: a short overview with special reference to novel molecular and diagnostic concepts

Mastocytosis is a heterogeneous group of hematopoietic disorders characterized by abnormal growth and accumulation of mast cells (MC) in one or more organs. Clinical symptoms occur as a result of the release of chemical mediators and/or of pathologic infiltration of MC in various tissues. Although the initial events leading to mastocytosis have not yet been unraveled, acquired alterations in the c-kit gene coding for the receptor of stem cell factor (SCF), a major cytokine involved in MC growth, have been described in a significant number of patients. Of particular interest are point mutations resulting in a constitutively activated SCF receptor. Such mutations are probably involved in the abnormal (SCF-independent) proliferation of MC in these patients. New therapeutic strategies may be envisaged to inhibit the deregulated kinase activity of these mutant forms of c-kit.

Mastocytosis

Mastocytosis represents a heterogeneous group of clinical disorders resulting from the infiltration of mast cells in the skin and other organs. Although mastocytosis was first described over 130 years ago, the pathophysiologic mechanisms responsible for this disease have been identified only recently. This article discusses the salient clinical features of the disease, the mechanisms responsible for its development, and provides treatment approaches that have proven useful for managing patients with this disorder.

Clinical varieties of mastocytoses

Varieties of the clinical features of mastocytoses, also called mastocytosis syndrome, are presented. The disease is characterized by excessive accumulation of mast cells, their proliferation and action in the skin and other organs, even in the central nervous system. The mastocytosis syndrome was known as early as the second half of the 19th century under the term urticaria pigmentosa, and was histologically confirmed by the presence in the dermis of metachromatic cells, i.e. Ehrlich mast cells with red-purple cytoplasmic granules visible with Giemsa or toluidine blue stains. The mastocytosis syndrome was then supposed to be a benign chronic dermatosis of childhood with spontaneous regression by adolescence. The clinically pathognomonic symptoms of Darier's sign (urtication of primary skin lesion upon rubbing) and flushing help in the diagnosis of mastocytosis syndrome. In the 1950s, there was a progression in the diagnosis of systemic mastocytosis achieved by scientists and clinicians of various specialties. Upon the discovery of many mast cell released mediators (heparin, histamine, leukotrienes, prostaglandins, proteases, cytokines), receptor functions, relationship to IgE, anaphylatoxin, etc., they were recognized as triggers of various clinical features of the mastocytosis syndrome. In this paper, different forms of cutaneous and systemic mastocytosis are described, with special reference to 'mastocytosis mucocutanea haemorrhagica' observed by one of the authors in a female infant and followed from 6 months till 2.5 years of age. The patient showed practically all the diverse forms of cutaneous mastocytosis: urticaria pigmentosa, papular, nodular, tumorous-like melanoma, vesiculobullous, erythrodermic, telangiectasia eruptiva maculosa perstans. She also suffered from nasal and rectal hemorrhage, conjunctival suggillations, plaque-like infiltrations of the glossal, oropharyngeal and laryngotracheal mucosa, episodes of flushing, and transitory apnea. It is emphasized that the diagnosis of mastocytosis syndrome may be difficult for its mimicking various other diseases. The occurence of mastocytosis syndrome from the neonatal period through adult and old age, and possibilities of symptomatic treatment and prevention of sudden death or fatalities are discussed. Familial occurrence of mastocytosis syndrome and new genetic studies that may prove highly useful for understanding the etiopathogenesis of mastocytosis syndrome are described.

Diagnostic criteria and classification of mastocytosis: a consensus proposal

The term 'mastocytosis' denotes a heterogeneous group of disorders characterized by abnormal growth and accumulation of mast cells (MC) in one or more organ systems. Over the last 20 years, there has been an evolution in accepted classification systems for this disease. In light of such developments and novel useful markers, it seems appropriate now to re-evaluate and update the classification of mastocytosis. Here, we propose criteria to delineate categories of mastocytosis together with an updated consensus classification system. In this proposal, the diagnosis cutaneous mastocytosis (CM) is based on typical clinical and histological skin lesions and absence of definitive signs (criteria) of systemic involvement. Most patients with CM are children and present with maculopapular cutaneous mastocytosis (=urticaria pigmentosa, UP). Other less frequent forms of CM are diffuse cutaneous mastocytosis (DCM) and mastocytoma of skin. Systemic mastocytosis (SM) is commonly seen in adults and defined by multifocal histological lesions in the bone marrow (affected almost invariably) or other extracutaneous organs (major criteria) together with cytological and biochemical signs (minor criteria) of systemic disease (SM-criteria). SM is further divided into the following categories: indolent systemic mastocytosis (ISM), SM with an associated clonal hematologic non-mast cell lineage disease (AHNMD), aggressive systemic mastocytosis (ASM), and mast cell leukemia (MCL). Patients with ISM usually have maculopapular skin lesions and a good prognosis. In the group with associated hematologic disease, the AHNMD should be classified according to FAB/WHO criteria. ASM is characterized by impaired organ-function due to infiltration of the bone marrow, liver, spleen, GI-tract, or skeletal system, by pathologic MC. MCL is a 'high-grade' leukemic disease defined by increased numbers of MC in bone marrow smears (>or=20%) and peripheral blood, absence of skin lesions, multiorgan failure, and a short survival. In typical cases, circulating MC amount to >or=10% of leukocytes (classical form of MCL). Mast cell sarcoma is a unifocal tumor that consists of atypical MC and shows a destructive growth without (primary) systemic involvement. This high-grade malignant MC disease has to be distinguished from a localized benign mastocytoma in either extracutaneous organs (=extracutaneous mastocytoma) or skin. Depending on the clinical course of mastocytosis and development of an AHNMD, patients can shift from one category of MC disease into another. In all categories, mediator-related symptoms may occur and may represent a serious clinical problem. All categories of mastocytosis should be distinctively separated from reactive MC hyperplasia, MC activation syndromes, and a more or less pronounced increase in MC in myelogenous malignancies other than mastocytosis. Criteria proposed in this article should be helpful in this regard.

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

The diagnosis of bone marrow (BM) involvement in mastocytosis has mainly been based on conventional histology. Nevertheless, in recent years, three major methodological advances have been made: the measurement of serum tryptase levels, the immunohistochemical assessment of mast cell (MC) tryptase, and the immunophenotypical characterization of BMMC using flow cytometry (FCM). The most characteristic immunophenotypic feature in mastocytosis is the coexpression of CD2 and CD25 antigens, which are never present in normal BMMC and constitute a phenotypic hallmark of BMMC in adult mastocytosis. Such observations would support the need to include the immunophenotypic analysis of MC in the diagnosis of mastocytosis.

Classes of c-KIT activating mutations: proposed mechanisms of action and implications for disease classification and therapy

Mutations causing constitutive activation of KIT have been shown to be causative in some forms of mastocytosis, and several types of mutations have been associated with myeloproliferative disorders (MPDs), acute myelogenous leukemia (AML), sinonasal lymphomas, and gastrointestinal stromal tumors (GIST). We divide these activating mutation into two types - 'regulatory type' mutations, which affect regulation of the kinase molecule, and 'enzymatic pocket type' mutations, which alter the amino acid sequence directly forming the enzymatic site. KIT inhibitors have been suggested as therapeutic drugs for these conditions, but different types of activating mutations respond differentially to KIT inhibitors, so classification of individuals on the basis of specific mutations is necessary to guide therapy.

Morphologic properties of neoplastic mast cells: delineation of stages of maturation and implication for cytological grading of mastocytosis

In the present study, cytological properties of bone marrow mast cells (MC) were analyzed and correlated with clinical parameters in 69 patients with systemic mastocytosis (SM). Based on cytomorphological features, four distinct cell types were recorded: (i) typical tissue MC (round cells, well granulated, round central nuclei); (ii) atypical MC exhibiting elongated cytoplasmic extensions, oval nuclei with excentric position, and a hypogranulated cytoplasm with focal granule accumulation ('atypical MC type I'); (iii) atypical MC with bi- or multilobed nuclei ('atypical MC type II'); and (iv) metachromatically granulated blast-like cells. In the majority of cases with SM, the percentage of MC in bone marrow (bm) smears was less than 5% (of all nucleated bm cells), and the predominant types were typical MC or atypical MC type I. In a smaller group of patients, the percentage of MC was greater than 5% and a significant subset of MC (>or=10%) were classified as 'metachromatic blasts' and/or atypical MC type II. These patients had a significantly shorter survival (P<0.05) and most of them were found to lack UP-like skin lesions. A percentage of MC>or=20% was invariably associated with the diagnosis 'mast cell leukemia'. Multivariate analysis confirmed the prognostic value of the cytology in SM and identified the percentage of MC (of all nucleated bm cells) as an independent prognostic variable. These data suggest that cytomorphological assessment of bm MC in SM is an important diagnostic approach that may help to delineate between variants of the disease.

Myelomastocytic overlap syndromes: biology, criteria, and relationship to mastocytosis

Although mast cells (MC) appear to be myeloid cells, MC lineage involvement in myelogenous malignancies has been described only rarely. Based on clonal evolution, biology of afflicted cells, and disease criteria, three major groups of patients have been recognized: The first meets criteria for both diagnoses 'systemic mastocytosis' and 'associated hematologic clonal non-mast cell lineage disease (AHNMD)'. In such patients, myeloproliferative (MPS) or myelodysplastic syndromes (MDS), or acute myeloid leukemia (AML) is diagnosed apart from mastocytosis. In a second group of patients, large numbers of very immature MC-lineage cells (metachromatically granulated blast-like cells) are detectable, but the criteria to diagnose mastocytosis are not met. These patients have advanced myeloid neoplasms (MDS or MPS with blast cell increase, or AML) and variably suffer from mediator-related symptoms (flush, GI-tract ulcer, diarrhoea, coagulopathy). In some cases, the disease mimics mast cell- or basophilic leukemia. In contrast to basophilic leukemia, however, the metachromatic cells are strongly KIT+ and tryptase+. In contrast to true mast cell leukemia (MCL), MC do not form multifocal dense infiltrates in the bone marrow. Also, MC lack CD2 and CD25, and the C-KIT mutation Asp-816-Val. We propose the term 'myelomastocytic leukemia' or 'myelodysplastic mast cell syndrome' for these cases. In a third group of patients, myeloid neoplasms (MDS, MPS, AML) show constitutive expression of MC-associated antigens (tryptase, histamine) or mastocytosis-related gene defects (mutated C-KIT) without significant increase in metachromatic cells or criteria of mastocytosis. Whether these neoplasms display aberrant gene expression (or gene defects) or represent 'pre-pre-mast cell leukemias', remains unknown.

Mastocytosis: molecular mechanisms and clinical disease heterogeneity

Systemic mastocytosis has one unifying feature: an unexplained and pathologic increase in mast cells in specific tissues. This observation, along with clinical disease heterogeneity has long suggested that mastocytosis is a disease of complex etiology. At the same time, the last decade has witnessed significant progress in identifying the critical elements that regulate mast cell growth and development. Human mast cells are now known to arise from CD34(+) progenitors, particularly under the influence of stem cell factor (SCF). This information in turn led to the critical observation that a substantial number of patients with mastocytosis exhibit activating mutations in c-kit, the receptor for SCF. And while this observation may well be key in understanding mastocytosis, this mutation alone does not explain all heterogeneity. It now appears that other influences such as genetic polymorphisms within the host may influence the course of disease in those with KIT mutations; and that the search for additional molecular events capable of creating disease diversity must continue.

Clinical and histopathological aspects of cutaneous mastocytosis

The organ most frequently involved in mastocytosis is the skin. Cutaneous mastocytosis (CM) is classified according to clinical presentation and is further defined by onset of disease. CM tends to appear early in life but adult onset CM occurs. CM in children has a low incidence of systemic involvement whereas systemic mastocytosis occurs in >25% of CM in adults. Almost all patients with CM belong into the indolent category of the consensus revised classification (Valent et al., Diagnostic criteria and classification of mastocytosis: a consensus proposal. Leukemia Research 2001;25:603-625.) and thus have a good prognosis. CM of infancy and childhood frequently involutes spontaneously, CM of adults does not. The prevalence of the disease is unknown and familiar occurrence is very rare.

Mastocytosis and the skin

The most frequent site of organ involvement in individuals with any form of mastocytosis is the skin. Cutaneous lesions include urticaria pigmentosa, mastocytoma, diffuse and erythematous cutaneous mastocytosis, and telangiectasia macularis eruptiva perstans. The major histologic feature is an increase in the number of mast cells in the dermis. Treatment depends on the type of skin lesions.

Treatment of systemic mast cell disorders

The heterogeneous nature of disease manifestations in mastocytosis requires the individualization of therapy to each patient's clinical presentation and prognosis. The mainstay of treatment for most categories of mastocytosis are H1 and H2 antihistamines with the addition of corticosteroids for more severe symptoms. This article presents a summary of treatment strategies for indolent and aggressive forms of mastocytosis along with a discussion of future therapeutic directions.

A proposed classification of mastocytosis incorporating molecular genetics

As an understanding of the molecular genetic causes of different forms of mastocytosis is developed, the therapy of choice may depend on the specific genetic abnormalities expressed by a patient's neoplastic mast cells. The authors propose a new classification system for mastocytosis that incorporates both molecular-genetic and clinical data. This system provides a theoretic framework for mast cell researchers and helps practicing physicians in estimating prognosis and determining therapeutic options for individual patients.

Clinical and biologic diversity of leukemias occurring in patients with mastocytosis

Patients with systemic mast cell (MC) disease, but not those with cutaneous mastocytosis, are at a high risk (10-30%) to develop life-threatening myelogenous malignancies. In a significant proportion of cases, myeloid leukemias occur. Using conventional criteria, such leukemias resemble acute myeloid leukemia (AML), chronic myeloid leukemia (CML), or myelomonocytic leukemia (CMML). Mast cell leukemia (MCL) may also occur. Myeloid leukemias (AML, CML, CMML) can develop in indolent or aggressive mastocytosis (skin lesions present or absent) with a variable prephase of MC disease. By contrast, MCL (typically without skin lesions) often develops on a "de novo" basis, and, if at all recognized, a prephase resembling (malignant) mastocytosis, is short. MCL differs from myeloid leukemias (AML, CML, CMML) by morphologic and phenotypic cellular characteristics. In fact, MCL are strongly tryptase-positive, c-kit-positive, myeloperoxidase (MPO) -negative neoplasms with variable metachromasia and chloroacetate esterase expression, whereas an MPO-positive, tryptase-negative phenotype supports the diagnosis of a myeloid non-MC lineage disease. Thus, MCL, but also myeloid non-MC lineage leukemias can develop in patients with (systemic) mastocytosis. Little is known, however, about the pathophysiologic basis of co-evolution. In the present article, the concomitant occurrence of mastocytosis and leukemia is discussed in the light of the literature and of concepts proposed to explain the biologic basis of this phenomenon.

[Mastocytosis--a review illustrated by two case reports]

BACKGROUND

Mastocytosis includes a range of disorders characterised by accumulation of tissue mast cells. These are derived from pluripotent haematopoietic stem cells. Recent research has improved the understanding of the mastocytosis pathogenesis. Organ manifestations and symptoms are highly variable.

MATERIAL AND METHODS

Two cases of systemic mast cell disease are presented.

RESULTS

One patient had urticaria pigmentosa and systemic mast cell disease; the other had systemic mast cell disease and myelodysplastic changes in the bone marrow.

INTERPRETATION

The two cases illustrate different manifestations and different prognosis for various types of mastocytosis.

Mastocytosis with skin manifestations: current status

AIM

To review our present knowledge about mastocyte origin, mastocytosis classification and management.

METHODS

Literature review.

RESULTS

Mastocytoses are chronic and recurrent disorders with symptoms which might either be limited only to the skin or to internal organs as well. The mastocytes, coming from bone marrow progenitor cells, migrate to tissues where they participate in inflammation and in cellular immunity as well as in the metabolism of connective and osseous tissues. Their proliferation causes the appearance of mastocytoses. The classification of the clinical manifestations of the mastocytoses into cutaneous, reactive (under the influence of the degranulator factors) and systemic disease, facilitates dialog among clinicians. Determination of prognosis and appropriate therapeutic regimens depend on individual features.

CONCLUSIONS

Mastocytosis diagnosis is verified by histological study of skin lesion biopsy material. Management is symptomatic and unfortunately does not eradicate the disease.