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

World Health Organization Classification and Diagnosis of Mastocytosis: Update 2023 and Future Perspectives

Experts of the European Competence Network on Mastocytosis (ECNM) and the American Initiative on Mast Cell Disorders have discussed and updated diagnostic criteria and the classification of mastocytosis, based on new insights in the field and data collected in recent years, mostly within ECNM registry projects in which studies on several thousand cases have been performed. Based on this proposal, the World Health Organization has updated its classification of mastocytosis. This article discusses the revised classification of mastocytosis in light of a rapidly moving field and the advent of new diagnostic parameters, new prognostication tools, and new therapies.

Kidney and urinary tract involvement in systemic mastocytosis

Systemic mastocytosis (SM) is a disorder of excessive mast cell accumulation in tissues due to a somatic gain-of-function mutation, commonly in the KIT gene, which prevents apoptosis of mast cells. Whereas bone marrow, skin, lymph nodes, spleen and gastrointestinal tract are commonly involved, kidneys are rarely involved directly by SM. However, there are increasing reports of indirect kidney involvement in patients with SM. Novel anti-neoplastic agents to treat advanced forms of SM include non-specific tyrosine kinase inhibitors, which are reported to be associated with kidney dysfunction in some patients. SM is also associated with immune-mediated glomerulonephritis (GN) such as mesangioproliferative GN, membranous nephropathy and diffuse proliferative GN. Kidney injury, in the form of monoclonal deposition disease and primary light chain amyloidosis, is reported in SM associated with plasma cell dyscrasia. In this narrative review we discuss the various ways kidneys (and the urinary tract) are involved in patients with SM.

Systemic mastocytosis in adults: 2023 update on diagnosis, risk stratification and management

OVERVIEW

Systemic mastocytosis (SM) results from clonal proliferation of mast cells (MC) in extracutaneous organs.

DIAGNOSIS

The major criterion is presence of multifocal MC clusters in the bone marrow and/or extracutaneous organs. Minor diagnostic criteria include elevated serum tryptase level, MC CD25/CD2/CD30 expression, and presence of activating KIT mutations.

RISK STRATIFICATION

Establishing SM subtype as per the International Consensus Classification/World Health Organization classification systems is an important first step. Patients either have indolent/smoldering SM (ISM/SSM) or advanced SM, including aggressive SM (ASM), SM with associated myeloid neoplasm (SM-AMN), and mast cell leukemia. Identification of poor-risk mutations (i.e., ASXL1, RUNX1, SRSF2, NRAS) further refines the risk stratification. Several risk models are available to help assign prognosis in SM patients.

MANAGEMENT

Treatment goals for ISM patients are primarily directed toward anaphylaxis prevention/symptom control/osteoporosis treatment. Patients with advanced SM frequently need MC cytoreductive therapy to reverse disease-related organ dysfunction. Tyrosine kinase inhibitors (TKI) (midostaurin, avapritinib) have changed the treatment landscape in SM. While deep biochemical, histological and molecular responses have been documented with avapritinib treatment, its efficacy as monotherapy against a multimutated AMN disease component in SM-AMN patients remains unclear. Cladribine continues to have a role for MC debulking, whereas interferon-α has a diminishing role in the TKI era. Treatment of SM-AMN primarily targets the AMN component, particularly if an aggressive disease such as acute leukemia is present. Allogeneic stem cell transplant has a role in such patients. Imatinib has a therapeutic role only in the rare patient with an imatinib-sensitive KIT mutation.

Secretory and Membrane-Associated Biomarkers of Mast Cell Activation and Proliferation

Mast cells (MCs) are immune cells distributed in many organs and tissues and involved in the pathogenesis of allergic and inflammatory diseases as a major source of pro-inflammatory and vasoactive mediators. MC-related disorders are heterogeneous conditions characterized by the proliferation of MC within tissues and/or MC hyper-reactivity that leads to the uncontrolled release of mediators. MC disorders include mastocytosis, a clonal disease characterized by tissue MC proliferation, and MC activation syndromes that can be primary (clonal), secondary (related to allergic disorders), or idiopathic. Diagnosis of MC disorders is difficult because symptoms are transient, unpredictable, and unspecific, and because these conditions mimic many other diseases. Validation of markers of MC activation in vivo will be useful to allow faster diagnosis and better management of MC disorders. Tryptase, being the most specific MC product, is a widely used biomarker of proliferation and activation. Other mediators, such as histamine, cysteinyl leukotrienes, and prostaglandin D2, are unstable molecules and have limitations in their assays. Surface MC markers, detected by flow cytometry, are useful for the identification of neoplastic MC in mastocytosis but, so far, none of them has been validated as a biomarker of MC activation. Further studies are needed to identify useful biomarkers of MC activation in vivo.

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

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

Comprehensive mastocytosis data analysis from a single center

Mastocytosis is a very rare disorder and is divided into three prognostically distinct variants by World Health Organization: Cutaneous mastocytosis (CM), systemic mastocytosis (SM), and mast cell sarcoma or localized mast cell (MC) tumors. The wide range of complaints may cause patients to consult various clinics, with resulting mis- or underdiagnosis. Therefore, cooperation between different subspecialties is of paramount importance. In this article, we have compiled 104 adult mastocytosis cases diagnosed and followed in our Hematology and other clinics. 86 (82.7%) of 104 patients had systemic mastocytosis. Osteoporosis, disease-related complications, and secondary malignancies are important topics in this group. We know that indolent form has great survival. But smoldering or aggressive mastocytosis has a poor prognosis. CM and indolent SM have a significantly better prognosis compared to aggressive SM (p < 0.001). We found that the presence of more than 25% of mast cells in the bone marrow, the presence of concomitant marrow dysplasia, and the presence of disease-related complications affect survival (p < 0.001). In addition to the WHO classification, the IPSM scoring system is indicative of the prognosis in this rare disease.

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

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

Proposed European Competence Network on Mastocytosis-American Initiative in Mast Cell Diseases (ECNM-AIM) Response Criteria in Advanced Systemic Mastocytosis

Advanced systemic mastocytosis (AdvSM) is characterized by the presence of KIT D816V and other somatic mutations (eg, in SRSF2, ASXL1, and RUNX1) in 95% and 60% to 70% of patients, respectively. The biological and clinical consequences of AdvSM include multilineage involvement (eg, associated hematologic neoplasm) in 60% to 80% of patients, variable infiltration and damage (C-findings) of predominantly bone marrow and visceral organs through affected mast cell (MC) and non-MC lineages, and elevated levels of serum tryptase. Recently, the treatment landscape has substantially changed with the introduction of the multikinase/KIT inhibitor midostaurin and the selective KIT D816V inhibitor avapritinib. In this review, we discuss the evolution of AdvSM response criteria that have been developed to better capture clinical benefit (eg, improved responses and progression-free and overall survival). We propose refined response criteria from European Competence Network on Mastocytosis and American Initiative in Mast Cell Diseases investigators that use a tiered approach to segregate the effects of histopathologic (eg, bone marrow MC burden, tryptase), molecular (eg, KIT D816V variant allele frequency), clinical (eg, C-findings), and symptom response on long-term outcomes. These response criteria require evaluation in future prospective clinical trials of selective KIT inhibitors and other novel agents.

Standards of Pathology in the Diagnosis of Systemic Mastocytosis: Recommendations of the EU-US Cooperative Group

Pathology plays a central role in the diagnosis of systemic mastocytosis (SM), its delineation from other neoplasms and reactive conditions, and in monitoring of SM under therapy. The morphologic hallmark of SM is the accumulation of spindle-shaped, hypogranulated mast cells (MCs) in bone marrow (BM) and other extracutaneous tissues. Four of the 5 World Health Organization-defined diagnostic criteria (ie, compact MC aggregates [=major criterion]; atypical MC morphology; activating KIT point mutations; aberrant expression of CD25 and/or CD2 and/or CD30 in MCs [=minor criteria]) can be addressed by the pathologist. The final classification of SM variants as either BM mastocytosis, indolent SM, smoldering SM, aggressive SM (ASM), SM with an associated hematologic neoplasm (SM-AHN), or MC leukemia (MCL) has important prognostic significance and requires the integration of certain morphological, clinical, radiological, and biochemical data, referred to as B- and C-findings. Substantial diagnostic challenges may be posed to the pathologist and clinician especially in the so-called advanced SM variants, that is, ASM, MCL, and SM-AHN. In this article, updated recommendations of the EU-US Cooperative Group regarding standards of pathology in the diagnosis of SM, presented during the year 2020 Working Conference held in September in Vienna, are reported.

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

Evidence in the recent literature suggests that the presentation spectrum of mast cell neoplasms is broad. In this article, we elaborate on recent data pertaining to minor diagnostic criteria of systemic mastocytosis (SM), including sensitive testing methods for detection of activating mutations in the KIT gene or its variants, and adjusted serum tryptase levels in cases with hereditary α-tryptasemia. We also summarize entities that require differential diagnosis, such as the recently reclassified SM subtype named bone marrow mastocytosis, mast cell leukemia (an SM subtype that can be acute or chronic); the rare morphological variant of all SM subtypes known as well-differentiated systemic mastocytosis; the extremely rare myelomastocytic leukemia and its differentiating features from mast cell leukemia; and mast cell activation syndrome. In addition, we provide a concise clinical update of the latest adjusted risk stratification model incorporating genomic data to define prognosis in SM and new treatments that were approved for advanced SM (midostaurin, avapritinib).

The Expressions of CD30 and CD123 of Mastocytosis in Taiwan

Mastocytosis is a rare disease with a low incidence in Asia-Pacific populations. CD30 and CD123 may have potential prognostic and therapeutic value, but the results are inconsistent. Because racial disparities may exist, we aim to evaluate the expressions of CD30 and CD123 in a series of mastocytosis cases in Taiwan. Twelve patients with systemic and 7 with cutaneous forms of mastocytosis were studied. The expressions of CD30 and CD123 were correlated with the clinical features of the patients. Eighty-three percent (10/12) of patients with systemic mastocytosis (SM) had an associated hematological neoplasm. Four of the SM patients had both "B" and "C" findings, and they had a median survival time of 0.9 months. CD30 expression was positive in 50% (6/12) of SM cases and 100% (6/6) of cutaneous mastocytosis cases. CD123 was expressed focally or weakly in only 2 SM-associated hematological neoplasm cases. The distribution of mastocytosis subtypes and the expression of CD30 and CD123 in Taiwan differed from those reported in North America and Europe. However, mastocytosis, especially indolent forms, is easily overlooked as its heterogeneous and nonspecific clinical manifestations. A high index of suspicion and improved diagnostic methods can be helpful.

Systemic Mastocytosis: Multidisciplinary Approach

Systemic mastocytosis (SM) is a heterogeneous group of diseases that affect almost exclusively adults and are defined by the proliferation and accumulation of clonal mast cells (MC) in various tissues. Disease subtypes range from indolent to rare aggressive forms. Although SM is classified as a rare disease, it is believed to be likely underdiagnosed. Major signs and symptoms mainly depend on MC activation and less frequent organ infiltration, typical of more aggressive variants. Diagnosis may be challenging, and symptoms can be aspecific and involve several organs. Therefore, it is advisable to refer patients to specialized centers, having sufficient knowledge of the disease, sensitive diagnostic procedures, offering a personalized and multidisciplinary diagnostic approach, including at least hematological, allergological, dermatological, and rheumatological evaluations. A precise and timely diagnosis is required for: a) adequate counseling of patients and their physicians; b) beginning of symptomatic treatment (anti-mediator therapy); c) prevention of severe manifestations of the disease (i.e., recurrent anaphylaxis, osteoporosis, and bone fractures); d) cytoreductive treatment of advanced SM variants. This review summarizes the disease's main manifestations and describes the ideal diagnostic approach for adult patients with suspected SM, giving physicians the main notions for correct patient diagnosis and management. This review also highlights the importance of a multidisciplinary approach in this very complex disease.

Updated Diagnostic Criteria and Classification of Mast Cell Disorders: A Consensus Proposal

Mastocytosis is a hematologic neoplasm characterized by expansion and focal accumulation of neoplastic mast cells (MC) in diverse organs, including the skin, bone marrow (BM), spleen, liver, and gastrointestinal tract. The World Health Organization classification divides the disease into prognostically distinct variants of cutaneous mastocytosis (CM) and systemic mastocytosis (SM). Although this classification remains valid, recent developments in the field and the advent of new diagnostic and prognostic parameters created a need to update and refine definitions and diagnostic criteria in MC neoplasms. In addition, MC activation syndromes (MCAS) and genetic features predisposing to SM and MCAS have been identified. To discuss these developments and refinements in the classification, we organized a Working Conference comprised of experts from Europe and the United States in August 2020. This article reports on outcomes from this conference. Of particular note, we propose adjustments in the classification of CM and SM, refinements in diagnostic criteria of SM variants, including smoldering SM and BM mastocytosis (BMM), and updated criteria for MCAS and other conditions involving MC. CD30 expression in MC now qualifies as a minor SM criterion, and BMM is now defined by SM criteria, absence of skin lesions and absence of B- and C-findings. A basal serum tryptase level exceeding 20 ng/mL remains a minor SM criterion, with recognition that hereditary alpha-tryptasemia and various myeloid neoplasms may also cause elevations in tryptase. Our updated proposal will support diagnostic evaluations and prognostication in daily practice and the conduct of clinical trials in MC disorders.

Precision Medicine in Systemic Mastocytosis

Mastocytosis is a rare hematological neoplasm characterized by the proliferation of abnormal clonal mast cells (MCs) in different cutaneous and extracutaneous organs. Its diagnosis is based on well-defined major and minor criteria, including the pathognomonic dense infiltrate of MCs detected in bone marrow (BM), elevated serum tryptase level, abnormal MCs CD25 expression, and the identification of KIT D816V mutation. The World Health Organization (WHO) classification subdivides mastocytosis into a cutaneous form (CM) and five systemic variants (SM), namely indolent/smoldering (ISM/SSM) and advanced SM (AdvSM) including aggressive SM (ASM), SM associated to hematological neoplasms (SM-AHN), and mast cell leukemia (MCL). More than 80% of patients with SM carry a somatic point mutation of KIT at codon 816, which may be targeted by kinase inhibitors. The presence of additional somatic mutations detected by next generation sequencing analysis may impact prognosis and drive treatment strategy, which ranges from symptomatic drugs in indolent forms to kinase-inhibitors active on KIT. Allogeneic stem cell transplant (SCT) may be considered in selected SM cases. Here, we review the clinical, diagnostic, and therapeutic issues of SM, with special emphasis on the translational implications of SM genetics for a precision medicine approach in clinical practice.

Systemic Mastocytosis: Advances in Diagnosis and Current Management

Mastocytosis is a rare hematologic disorder characterized by abnormal proliferation and accumulation of neoplastic mast cells in various body sites. Isolated skin involvement is termed cutaneous mastocytosis (CM) and the term systemic mastocytosis (SM) refers to multi-organ involvement, most commonly of the bone marrow, skin, liver, and spleen. A subset of patients with SM have an associated clonal hematologic neoplasm which is most commonly myelodysplastic syndrome, chronic myelomonocytic leukemia, or acute myelogenous leukemia and this entity is termed SM with associated hematological neoplasm (AHN). Bone marrow involvement is present in all patients regardless of the subtype of SM. The genetic hallmark of SM is a somatic gain-of-function point mutation within the KIT gene. Other molecular aberrations that have been reported include somatic mutations in TET2, SRSF2, ASXL1, CBL, RUNX1, and RAS and these are common in SM-AHN. The clinical presentation of SM can range from indolent to advanced depending on extent of mast cell burden and genetic profile. In the case of indolent SM, the goal of treatment is to control mediator release-related effects as well as to reduce mast cell burden. In the case of SM-AHN, therapy is primarily that of the AHN and allogeneic hematopoietic stem cell transplantation is the preferred therapy in suitable candidates.

Developing a standardized approach for assessing mast cells and eosinophils on tissue biopsies: A Work Group Report of the AAAAI Allergic Skin Diseases Committee

Mast cells and eosinophils are commonly found, expectedly or unexpectedly, in human tissue biopsies. Although the clinical significance of their presence, absence, quantity, and quality continues to be investigated in homeostasis and disease, there are currently gaps in knowledge related to what constitutes quantitatively relevant increases in mast cell and eosinophil number in tissue specimens for several clinical conditions. Diagnostically relevant thresholds of mast cell and eosinophil numbers have been proposed and generally accepted by the medical community for a few conditions, such as systemic mastocytosis and eosinophilic esophagitis. However, for other mast cell- and eosinophil-associated disorders, broad discrepancies remain regarding diagnostic thresholds and how samples are processed, routinely and/or specially stained, and interpreted and/or reported by pathologists. These discrepancies can obfuscate or delay a patient's correct diagnosis. Therefore, a work group was assembled to review the literature and develop a standardized consensus for assessing the presence of mast cells and eosinophils for a spectrum of clinical conditions, including systemic mastocytosis and cutaneous mastocytosis, mast cell activation syndrome, eosinophilic esophagitis, eosinophilic gastritis/enteritis, and hypereosinophilia/hypereosinophilic syndrome. The intent of this work group is to build a consensus among pathology, allergy, dermatology, hematology/oncology, and gastroenterology stakeholders for qualitatively and quantitatively assessing mast cells and eosinophils in skin, gastrointestinal, and bone marrow pathologic specimens for the benefit of clinical practice and patients.

Diagnosis of Primary Mast Cell Disorders in Anaphylaxis: Value of KIT D816V in Peripheral Blood

BACKGROUND

Anaphylaxis is frequent in patients suffering from primary mast cell disorders (PMCDs). In patients without mastocytosis in the skin (MIS) and a baseline serum tryptase (bST) less than 30 ng/mL, the diagnosis of PMCD is challenging. In these patients, detection of the KIT D816V mutation in peripheral blood (PB) has been suggested as screening tool for a PMCD.

OBJECTIVE

In this study, we investigated whether KIT D816V in PB can contribute to the decision to perform a bone marrow (BM) biopsy in patients with anaphylaxis without MIS and a bST less than 30 ng/mL.

METHODS

We selected 74 patients with severe anaphylaxis without MIS and a bST less than 30 ng/mL. All underwent a BM biopsy. KIT D816V mutation was quantified in both PB and BM using digital droplet polymerase chain reaction (ddPCR).

RESULTS

Diagnosis of a PMCD was established in 40 patients (54%). Median bST for patients with and without PMCD was, respectively, 9.5 ng/mL (range 4.2-27 ng/mL) and 4.9 ng/mL (range 2.2-20.3 ng/mL) (P <.001). KIT D816V in PB was detected in 16 out of 40 (40%) patients with PMCD. KIT D816V in BM was detected in 22 out of 40 (55%) patients with PMCD.

CONCLUSIONS

In patients without MIS and a bST less than < 30 ng/mL who experience anaphylaxis, determination of KIT D816V mutation in PB is of limited help in deciding when to proceed to a BM biopsy. Therefore, KIT D816V in PB mutation analysis should be interpreted together with scoring tools to make a better assessment in identifying patients who should undergo BM biopsy.

Mast cell differentiation of leukemic blasts in diverse myeloid neoplasms: A potential pre-myelomastocytic leukemia condition

INTRODUCTION

Myeloid neoplasm with blasts showing mast cell (MC)-differentiation and MC-component less than 10% of all nucleated cells but not fulfilling the criteria for systemic mastocytosis with associated hematological neoplasm (SM-AHN) or myelomastocytic leukemia (MML) has not been described in the literature. Herein, we report a study of diverse myeloid malignancies with blasts showing MC-differentiation but not meeting the criteria for SM-AHN or MML. We also evaluated the utility of flow-cytometric immunophenotyping (FCI) in the characterization of immature-MCs (iMCs).

METHODS

We identified nine patients of myeloid neoplasms and studied their morphological, FCI, immunohistochemistry, cytogenetic and molecular characteristics. We also compared the immunophenotypic features of MCs from patient samples with control samples.

RESULTS

The study included patients with newly-diagnosed acute myeloid leukemia (n = 4), chronic myelomonocytic leukemia (n = 1), and chronic myeloid leukemia on follow-up (n = 4) showing MC differentiation in leukemic-blasts. These patients had mildly increased MCs (range, 0.5%-3%) in bone-marrow morphology, including immature-forms and did not meet the criteria for either SM-AHN or MML. On FCI, iMCs were positive for bright-CD117, heterogeneous-CD34, dim-to-negative-HLADR, and moderate-CD203c expression. Expression-levels of CD123 and CD38 were higher (p < 0.001) but CD33 and CD45 were lower in iMCs compared to mature-MC from control samples (p = 0.019 and p = 0.0037).

CONCLUSION

We reported a rare finding of MC differentiation of leukemic blasts in diverse myeloid neoplasms and proposed it as a potential pre-myelomastocytic leukemia condition. We described the distinct immunophenotypic signature of immature-MCs using commonly used markers and highlighted the utility of FCI for the diagnosis of this entity.

Systemic mastocytosis in adults: 2021 Update on diagnosis, risk stratification and management

OVERVIEW

Systemic mastocytosis (SM) results from a clonal proliferation of abnormal mast cells (MC) in extra-cutaneous organs.

DIAGNOSIS

The major criterion is presence of multifocal clusters of spindled MC in the bone marrow. Minor diagnostic criteria include elevated serum tryptase level, abnormal MC CD25 expression, and presence of KITD816V mutation.

RISK STRATIFICATION

Establishing SM subtype as per the World Health Organization classification system is an important first step. Broadly, patients either have indolent/smoldering SM (ISM/SSM) or advanced SM, the latter includes aggressive SM (ASM), SM with associated hematological neoplasm (SM-AHN), and mast cell leukemia (MCL). Identification of poor-risk mutations (ie, ASXL1, RUNX1, SRSF2, NRAS) further refines the risk stratification. Recently, clinical and hybrid clinical-molecular risk models have been developed to more accurately assign prognosis in SM patients.

MANAGEMENT

Treatment goals for ISM patients are primarily directed towards anaphylaxis prevention/symptom control/osteoporosis treatment. Patients with advanced SM frequently need MC cytoreductive therapy to ameliorate disease-related organ dysfunction. High response rates have been seen with small-molecule inhibitors that target mutant-KIT, including midostaurin (Food and Drug Administration approved) or avapritinib (investigational). Other options for MC cytoreduction include cladribine or interferon-α, although head-to-head comparisons are lacking. Treatment of SM-AHN primarily targets the AHN component, particularly if an aggressive disease such as acute myeloid leukemia is present. Allogeneic stem cell transplant can be considered in such patients, or in those with relapsed/refractory advanced SM. Imatinib has a limited therapeutic role in SM; effective cytoreduction is limited to those with imatinib-sensitive KIT mutations.

Acute aleukemic mast cell leukemia: Report of a case and review of the literature

Mast Cell Leukemia (MCL) is the rarest form of systemic mastocytosis, a rare group of neoplastic disease that result from clonal proliferation of mast cells and their accumulation in one or more organ systems. The diagnosis of MCL is made by meeting the World Health Organization (WHO) 2017 criteria. MCL is further subclassified as leukemic or aleukemic based on presence or absence of circulating mast cells in the peripheral blood and acute versus chronic based on presence or absence of findings indicative of impaired organ function due to mast cell infiltration. A 64-year-old Hispanic male presented with myalgia, diarrhea, urticarial rash, back pain, and fulminant disseminated intravascular coagulation. Bone marrow examination, supplemented by immunohistochemistry results, fulfilled the WHO criteria for the diagnosis of MCL. To the best of our knowledge, this is the first documented case of aleukemic acute MCL in a Hispanic patient.

Pleomorphic mastocytoma associated with loss of chromosome 5, PDGFRA, and HRAS mutations: A case of cutaneous mastocytosis with severe atypia and indolent behavior

A 21-year-old female presented with a 5-year history of an erythematous papule on her right breast. The biopsy showed a dense, dermal nodular infiltrate, extending focally into the subcutaneous tissue. The infiltrate was composed predominantly of pleomorphic cells with bi-lobed, multi-lobed, horseshoe, or ring-shaped nuclei. There was a smaller subset of monomorphous cells characterized by a round, reniform, or elongated single-lobed nucleus. Accompanying cells included few foamy histiocytes, lymphocytes, and numerous scattered eosinophils. No necrosis, vascular invasion, or ulceration was present. The pleomorphic and monomorphic granular cells were positive for Giemsa stain as well as for tryptase, CD117, CD68, CD2, and CD30 immunohistochemistry and negative for S100, CD1a, myeloperoxidase, lysozyme, and CD56. Clinical examination was negative for any additional similar lesions and serum tryptase was within normal limits. The bone marrow was not biopsied. In addition, fluorescent in situ hybridization revealed multiple clones with loss of number 5 chromosome and PDGFRA and HRAS mutations. The lesion did not recur or progress after a 6-year clinical follow-up. To our full knowledge, we report the first case of pleomorphic mastocytoma with loss of chromosome 5 and PDGFRA and HRAS mutations.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

A phase 2 study of brentuximab vedotin in patients with CD30-positive advanced systemic mastocytosis

There is an unmet need for effective therapies for advanced systemic mastocytosis (advSM). CD30 is expressed on the surface of neoplastic mast cells (MC) in more than 50% of patients with advSM. Brentuximab vedotin (BV) is a CD30-directed antibody-drug conjugate with preclinical evidence supporting both an antineoplastic effect and an attenuation of immunoglobulin E-associated mediator release. These observations are the basis for this phase 2 trial of BV monotherapy (1.8 mg/kg IV every 3 weeks up to 8 cycles) in patients with CD30-positive advSM. The primary objective was to determine the efficacy of BV according to International Working Group-Myeloproliferative Neoplasms Research and Treatment-European Competence Network on Mastocytosis (IWG-MRT-ECNM) response criteria. Secondary objectives included evaluation of safety, changes in bone marrow (BM) MC burden, serum tryptase level, flow cytometric quantification of MC surface expression of CD30, and self-reported symptom burden. The trial enrolled 10 patients with a diagnosis of CD30⁺ advSM (aggressive SM, SM with an associated hematologic neoplasm [SM-AHN], or mast cell leukemia [MCL]) with 1 or more signs of SM-related organ damage. According to IWG-MRT-ECNM criteria, none of the patients demonstrated better than stable disease with BV. In addition, there were no significant reductions in BM MC burden, serum tryptase levels, or MC surface expression of CD30. Self-reported symptom scores showed no durable improvement with BV treatment. We conclude that BV is not active as a single agent in CD30⁺ advSM. This trial was registered at www.clinicaltrials.gov as #NCT01807598.

Pharmacotherapy in Mast Cell Leukemia

INTRODUCTION

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

AREAS COVERED

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

EXPERT OPINION

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

The clinical and pathological panoply of systemic mastocytosis

Mastocytosis is a rare disease with varied presentation, myriad symptomatology and variable prognosis. Most patients present with cutaneous disease and mediator-related symptomatology with a small subset having systemic disease (systemic mastocytosis, SM). A subset of the latter develops synchronous or metachronous haematologic neoplasms (SM-AHN), most commonly chronic myelomonocytic leukaemia (CMML). Advanced systemic mastocytosis (ASM) is seen in a relatively small number of patients and is usually associated with organ dysfunction, and may present with hepatosplenomegaly, lymphadenopathy and ascites with progression to leukaemic transformation (mast cell leukaemia/acute myeloid leukaemia) occurring in a few patients. This paper discusses the clinical and pathologic features of the entire spectrum of SM in adults.

The Spectrum of Aggressive Mastocytosis: A Workshop Report and Literature Review

Most cases of mastocytosis are indolent, usually cutaneous mastocytosis or indolent systemic mastocytosis (SM). Aggressive mast cell (MC) diseases are very rare and often fatal. They can develop de novo or due to progression of indolent forms and can present in different ways; either as MC sarcoma or as advanced SM which includes aggressive SM, MC leukemia, and SM with an associated hematological neoplasm. This review will describe these different aggressive forms of mastocytosis, illustrated by cases submitted to the workshop of the 18th Meeting of the European Association for Haematopathology, Basel 2016, organized by the European Bone Marrow Working Group. In addition, the diagnostic criteria for identifying myelomastocytic leukemia, an aggressive myeloid neoplasm with partial MC differentiation that falls short of the criteria for SM, and disease progression in patients with established mastocytosis are discussed.

Highly Aggressive CD4-Positive Mast Cell Leukaemia (Leukaemic Variant) Associated with Isolated Trisomy 19 and Hemophagocytosis by Neoplastic Mast Cells: A Case Report with Challenging Experience and Review

Background

Mast cell leukaemia is a unique disease among hematopoietic neoplasms, being one of the rarest leukaemia subtypes. In addition, its prompt diagnosis is usually challenging. This is due to its heterogeneity in clinical presentations and cytomorphological and immunophenotypical features together with potential associations with other hematologic neoplasms which can complicate the condition and delay accurate diagnosis. To the best of our knowledge, this is the first case report of CD4-positive mast cell leukaemia.

Case Presentation

A 39-year-old male presented with acute onset of fever, abdominal pain, and generalized body aches of two-week duration. Peripheral blood smear showed circulating blasts (13%) with coarsely basophilic granulation. Bone marrow (BM) aspirate showed extensive infiltration with immature mast cells of blast-like morphology with trilineage dysplasia and evident hemophagocytic activity exhibited by histiocytes and neoplastic mast cells. BM biopsy was diffusely infiltrated with many atypical mast cells positive for CD45, CD117, mast cell tryptase, CD25, and CD4 with partial positivity for CD7 and CD30. Cytogenetics showed an abnormal karyotype: 47, XY, +1947, XY, +19[13]/46, XY[9]. Molecular analysis revealed a KIT D816V mutation consistent with a diagnosis of systemic mastocytosis, mast cell leukaemia.

Conclusion

The expression of T-cell associated markers by abnormal mast cells is well documented; however, CD4 and CD7 expression have not previously been described in association with mast cell leukaemia. Coexpression of CD2, CD4, CD7, and CD30 by the mast cells particularly in skin lesions may provoke misinterpretation as a cutaneous T-cell neoplasm. To the best of our knowledge, this is the first report of CD4-positive mast cell leukaemia. Moreover, hemophagocytic mast cell leukaemia is a very rare morphologic variant, and possible correlation between this finding and expression of CD4 by neoplastic mast cells is a topic for further investigation.

Immunophenotype of pediatric-onset mastocytosis does not correlate with clinical course

BACKGROUND

Pediatric mastocytosis differs from adult mastocytosis in its presentation and clinical course. However, the data regarding the immunophenotypic characterization of mast cells in children are limited. Our objective was to evaluate the immunophenotype of mast cells in pediatric mastocytosis and correlate it with the clinical course.

METHODS

Biopsy specimens of children with cutaneous mastocytosis were retrieved from the institutions of pathology and were stained for CD25, CD2, and CD30. The percentage of mast cells and the staining intensity were correlated with the clinical data.

RESULTS

Twenty-five biopsy specimens were included in the study. Patients' average age was 15.4 at presentation and 37.5 months at biopsy performance. Clinical presentations included maculopapular cutaneous mastocytosis in 79% and mastocytoma in 21% of cases. CD25, CD2, and CD30 were positive in 60%, 44%, and 84% of the biopsy specimens, respectively. The staining score was significantly higher for CD30 as compared to those for CD25 and CD2 (P = 0.02). No correlation was found between the immunophenotype and the clinical form or course of disease.

CONCLUSIONS

Our results confirm that CD30 is a sensitive marker for pediatric-onset mastocytosis. Nevertheless, its expression does not correlate with clinical subtype or clinical course. The sensitivity of CD25 is higher than that of CD2 in skin lesions.

Multidisciplinary Challenges in Mastocytosis and How to Address with Personalized Medicine Approaches

Mastocytosis is a hematopoietic neoplasm defined by abnormal expansion and focal accumulation of clonal tissue mast cells in various organ-systems. The disease exhibits a complex pathology and an equally complex clinical behavior. The classification of the World Health Organization (WHO) divides mastocytosis into cutaneous forms, systemic variants, and localized mast cell tumors. In >80% of patients with systemic mastocytosis (SM), a somatic point mutation in KIT at codon 816 is found. Whereas patients with indolent forms of the disease have a normal or near-normal life expectancy, patients with advanced mast cell neoplasms, including aggressive SM and mast cell leukemia, have a poor prognosis with short survival times. In a majority of these patients, multiple somatic mutations and/or an associated hematologic neoplasm, such as a myeloid leukemia, may be detected. Independent of the category of mastocytosis and the serum tryptase level, patients may suffer from mediator-related symptoms and/or osteopathy. Depending on the presence of co-morbidities, the symptomatology in such patients may be mild, severe or even life-threatening. Most relevant co-morbidities in such patients are IgE-dependent allergies, psychiatric, psychological or mental problems, and vitamin D deficiency. The diagnosis and management of mastocytosis is an emerging challenge in clinical practice and requires vast knowledge, a multidisciplinary approach, and personalized medicine procedures. In this article, the current knowledge about mastocytosis is reviewed with special emphasis on the multidisciplinary aspects of the disease and related challenges in daily practice.

Single-cell analysis reveals the KIT D816V mutation in haematopoietic stem and progenitor cells in systemic mastocytosis

Background

Systemic mastocytosis (SM) is a haematological disease characterised by organ infiltration by neoplastic mast cells. Almost all SM patients have a mutation in the gene encoding the tyrosine kinase receptor KIT causing a D816V substitution and autoactivation of the receptor. Mast cells and CD34⁺ haematopoietic progenitors can carry the mutation; however, in which progenitor cell subset the mutation arises is unknown. We aimed to investigate the distribution of the D816V mutation in single mast cells and single haematopoietic stem and progenitor cells.

Methods

Fluorescence-activated single-cell index sorting and KIT D816V mutation assessment were applied to analyse mast cells and >10,000 CD34⁺ bone marrow progenitors across 10 haematopoietic progenitor subsets. In vitro assays verified cell-forming potential.

Findings

We found that in SM 60–99% of the mast cells harboured the KIT D816V mutation. Despite increased frequencies of mast cells in SM patients compared with control subjects, the haematopoietic progenitor subset frequencies were comparable. Nevertheless, the mutation could be detected throughout the haematopoietic landscape of SM patients, from haematopoietic stem cells to more lineage-primed progenitors. In addition, we demonstrate that FcεRI⁺ bone marrow progenitors exhibit mast cell-forming potential, and we describe aberrant CD45RA expression on SM mast cells for the first time.

Interpretation

The KIT D816V mutation arises in early haematopoietic stem and progenitor cells and the mutation frequency is approaching 100% in mature mast cells, which express the aberrant marker CD45RA.

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

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

The new tool "KIT" in advanced systemic mastocytosis

Mastocytosis is a rare disease characterized by KIT-driven expansion and accumulation of neoplastic mast cells in various tissues. Although mediator symptoms related to mast cell activation can impose a symptom burden in cutaneous disease and across the spectrum of systemic mastocytosis subtypes, the presence of an associated hematologic neoplasm and/or organ damage denotes advanced disease and the potential for increased morbidity and mortality. In addition to the revised 2016 World Health Organization classification of mastocytosis, a new diagnostic and treatment toolkit, tethered to enhanced molecular characterization and monitoring, is poised to transform the management of patients with advanced systemic mastocytosis (advSM). Although the efficacy of midostaurin and novel selective KIT D816V inhibitors, such as avapritinib (BLU-285), have validated KIT as a therapeutic target, the clinical and biologic heterogeneity of advSM requires that we reimagine the blueprint for tackling these diseases and use tools that move beyond KIT-centric approaches.

Mastocytosis: from a Molecular Point of View

Mast cells (MCs) are physiologically activated by binding of stem cell factor (SCF) to the extracellular domains of the Kit receptor. This binding increases the proliferation and prolongs the survival of normal mature MCs, as well as intensifies the release of mediators. In mastocytosis, somatic mutations of the coding Kit gene cause autocrine dysregulation and lead to constitutive KIT activation even in the absence of its ligand SCF. Clinical symptoms are caused by MC-mediator release and/or infiltration of MCs into tissues. Aberrant KIT activation may result in increased production of MCs in the skin and extracutaneous organs. Depending on the affected organ(s), the disease can be divided into cutaneous mastocytosis (CM), systemic mastocytosis (SM), and localized MC tumors. The updated classification of WHO discriminates between several distinct subvariants of CM and SM. While the prognosis in CM and indolent SM (ISM) is excellent with (almost) normal life expectancy, the prognosis in aggressive SM (ASM) and MC leukemia (MCL) is dismal. The symptoms may comprise urticaria, angioedema, flush, pruritus, abdominal pain, diarrhea, hypotension, syncope, and musculoskeletal pain and are the results of MC infiltration and mediator release into target organs, i.e., the skin, gastrointestinal tract, liver, spleen, lymph nodes, and bone marrow. Mastocytosis differs from a lot of other hematological disorders because its pathology is not only based on the lack of normal function of a specific pathway or of a specific cell type but additionally is a proliferative disease. Currently available treatments of mastocytosis include symptomatic, antimediator and cytoreductive targeted therapies.

Bone Marrow Expression of Mast Cell Disorders

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

Preclinical human models and emerging therapeutics for advanced systemic mastocytosis

Mastocytosis is a term used to denote a group of rare diseases characterized by an abnormal accumulation of neoplastic mast cells in various tissues and organs. In most patients with systemic mastocytosis, the neoplastic cells carry activating mutations in KIT Progress in mastocytosis research has long been hindered by the lack of suitable in vitro models, such as permanent human mast cell lines. In fact, only a few human mast cell lines are available to date: HMC-1, LAD1/2, LUVA, ROSA and MCPV-1. The HMC-1 and LAD1/2 cell lines were derived from patients with mast cell leukemia. By contrast, the more recently established LUVA, ROSA and MCPV-1 cell lines were derived from CD34⁺ cells of non-mastocytosis donors. While some of these cell lines (LAD1/2, LUVA, ROSA^{KIT WT} and MCPV-1) do not harbor KIT mutations, HMC-1 and ROSA^{KIT D816V} cells exhibit activating KIT mutations found in mastocytosis and have thus been used to study disease pathogenesis. In addition, these cell lines are increasingly employed to validate new therapeutic targets and to screen for effects of new targeted drugs. Recently, the ROSA^{KIT D816V} subclone has been successfully used to generate a unique in vivo model of advanced mastocytosis by injection into immunocompromised mice. Such a model may allow in vivo validation of data obtained in vitro with targeted drugs directed against mastocytosis. In this review, we discuss the major characteristics of all available human mast cell lines, with particular emphasis on the use of HMC-1 and ROSA^{KIT D816V} cells in preclinical therapeutic research in mastocytosis.

Prevalence of CD30 immunostaining in neoplastic mast cells: A retrospective immunohistochemical study

Mastocytosis is a rare disease characterized by clonal neoplastic proliferation of mast cells (MCs). It ranges from skin lesions as cutaneous mastocytosis (CM) which may spontaneously regress to highly aggressive neoplasms with multiorgan involvement corresponding to some aggressive systemic mastocytosis (ASM), mast cell leukemia (MCL), and/or mast cell sarcoma (MCS).There is increasing evidence of CD30 expression in neoplastic MCs of the bone marrow. This expression has been described almost exclusively in aggressive forms of systemic mastocytosis (SM).The aim of the present study is to evaluate CD30 expression both in cutaneous and systemic forms of mastocytosis. Forty-two mastocytosis cases were reviewed, including cutaneous (n = 29) and systemic (n = 13) forms to assess the prevalence of CD30 expression. Thirty-nine out of 42 (92.8%) cases were CD30 positive. In cases of CM, 28/29 (96.5%) cases were CD30 positive, 11/13 cases of SM (84.6%) were positive for CD30. MCs in normal skin biopsies and in urticaria lesions were CD30-negative. This study found that CD30 is also frequently expressed in CM as well as in systemic forms. This finding is a major departure from the prevailing concept that CD30 expression is often related to aggressive systemic forms of mastocytosis.

Mast cell sarcoma: new cases and literature review

Mast cell sarcoma (MCS) is a rare form of mastocytosis characterized by the presence of solid tumor(s) comprising malignant mast cells that harbor destructive infiltration capability and metastatic potential. Here, we present an extensive literature review and report on 23 cases of MCS, including 3 new cases from the French National Reference Center for Mastocytosis. From our analysis, it appears that MCS can occur at any age. It can manifest de novo or, to a lesser extent, may evolve from a previously established mastocytosis. Bone tumor is a frequent manifestation, and symptoms of mast cell activation are rare. Histological diagnosis can be difficult because MCS is frequently composed of highly atypical neoplastic mast cells and can thus mimic other tumors. Unexpectedly, the canonical KIT D816V mutation is found in only 21% of MCS; therefore, complete KIT gene sequencing is required. The prognosis of patients with MCS is poor, with a median survival time of less than 18 months, and progression to mast cell leukemia is not unusual. Because conventional chemotherapies usually fail, the role of targeted therapies and bone marrow transplantation warrants further investigation in such aggressive neoplasms.

CD30 Expression Is Rare in Myeloid Leukemia Cutis: A Study of 55 Cases and Implications for Routine Diagnostic Algorithms

Expression of CD30 in blastoid cutaneous infiltrates typically signifies a CD30 lymphoproliferative disorder, often requiring minimal immunohistochemical workup, if clinically consonant. However, myeloid and other hematologic malignancies often express CD30. We retrospectively examined the prevalence of CD30 expression in 41 patients (median age 59) and 55 biopsies with the diagnosis of leukemia cutis (LC) to determine whether an extensive immunohistochemical workup is warranted in all large, round cell CD30 cutaneous infiltrates. Each patient had refractory or recurrent disease, the histologic presence of a large mononuclear cell infiltrate, and varied cytogenetics. CD30 mononuclear cells within the infiltrate ranged from rare to many in 22 biopsies (22/55). In 18 biopsies, CD30 cells were interpreted as lymphocytic based on morphology, strong cytoplasmic and Golgi staining for CD30, and negative CD34 and CD117 staining. One case showing 3+ staining of lymphocytes was identified as a posttransplant lymphoproliferative disorder. The second 3+ case was favored to represent a subset of CD30-positive acute myeloid leukemia. Three other cases with 1+ membranous and cytoplasmic staining were interpreted as myeloid leukemia. In conclusion, CD30 positivity in myeloid leukemia in the skin is rare and does not often exhibit the strong membranous (2+ or 3+) and/or Golgi staining seen in reactive lymphocytes. Acute myeloid leukemia or myeloid LC may occasionally show 1+ (and rarely 2-3+) cytoplasmic/membranous or nonspecific blush nuclear CD30 labeling. Strong diffuse staining for CD30 should prompt consideration of a reactive lymphoid/lymphoproliferative process, and, when the clinical likelihood of CD30 LC is low, may obviate the need for further immunohistochemistry.

Understanding CD30 biology and therapeutic targeting: a historical perspective providing insight into future directions

CD30 is a member of the tumor necrosis factor receptor superfamily. It is characteristically expressed in certain hematopoietic malignancies, including anaplastic large cell lymphoma and Hodgkin lymphoma, among others. The variable expression of CD30 on both normal and malignant lymphoid cells has focused research efforts on understanding the pathogenesis of CD30 upregulation, its contribution to lymphomagenesis through anti-apoptotic mechanisms, and its effect on cell survival. Given the restriction of CD30 to certain tumor types, the logical extension of this has been to attempt to exploit it as a therapeutic target. The efficacy of naked anti-CD30 antibodies in practice was, however, modest. Moreover, combinations with bacterial toxins and radioimmunoconjugates have also had limited success. The development of the antibody-drug compound brentuximab vedotin (BV), however, has rejuvenated interest in CD30 as a tumor target. Phase I and II clinical trials in Hodgkin lymphoma, peripheral T-cell lymphoma, cutaneous T cell lymphoma, and even CD30-expressing B-cell lymphomas, have shown the compound is well tolerated, but more importantly, able to deliver meaningful disease control even in patients with multiply relapsed or refractory disease. FDA approval has been granted for its use in relapsed Hodgkin lymphoma and systemic anaplastic large cell lymphoma. A recent phase III trial of BV in cutaneous T-cell lymphoma has confirmed its superiority to standard of care therapies. In this manuscript, we explore the history of CD30 as a tumor marker and as a therapeutic target, both in the laboratory and in the clinic, with a view to understanding future avenues for further study.

Targeted Treatment Options in Mastocytosis

Mastocytosis refers to a heterogeneous group of disorders resulting from the clonal proliferation of abnormal mast cells and their accumulation in the skin (cutaneous mastocytosis when only in the skin, CM) or in various organs (systemic mastocytosis, SM). This leads to a wide variety of clinical manifestations resulting from excessive mediator release in CM and benign forms of SM (indolent SM, ISM) and from tissue mast cell infiltration causing multiorgan dysfunction and failure in more aggressive subtypes (aggressive SM, ASM, or mast cell leukemia). In addition, SM may be associated with hematological neoplasms (AHN). While treatment of ISM primarily aims at symptom management with anti-mediator therapies, cytoreductive and targeted therapies are needed to control the expansion of neoplastic mast cells in advanced forms of SM, in order to improve overall survival. Mast cell accumulation results from a gain-of-function mutation (mostly the D816V mutation) within the KIT tyrosine kinase domain expressed by mast cells and additional genetic and epigenetic mutations may further determine the features of the disease (ASM and AHN). Consequently, tyrosine kinase inhibitors and targeted therapies directed against the oncogenic signaling machinery downstream of KIT are attractive therapeutic approaches. A better understanding of the relative contribution of these genetic and epigenetic events to the molecular pathogenesis of mastocytosis is of particular interest for the development of targeted therapies and therefore to better choose patient subgroups that would best benefit from a given therapeutic strategy.

Use of the Total Cancer Care System to Enrich Screening for CD30-Positive Solid Tumors for Patient Enrollment Into a Brentuximab Vedotin Clinical Trial: A Pilot Study to Evaluate Feasibility

Background

One approach to identify patients who meet specific eligibility criteria for target-based clinical trials is to use patient and tumor registries to prescreen patient populations.

Objective

Here we demonstrate that the Total Cancer Care (TCC) Protocol, an ongoing, observational study, may provide a solution for rapidly identifying patients with CD30-positive tumors eligible for CD30-targeted therapies such as brentuximab vedotin.

Methods

The TCC patient gene expression profiling database was retrospectively screened for CD30 gene expression determined using HuRSTA-2a520709 Affymetrix arrays (GPL15048). Banked tumor tissue samples were used to determine CD30 protein expression by semiquantitative immunohistochemistry. Statistical comparisons of Z- and H-scores were performed using R statistical software (The R Foundation), and the predictive value, accuracy, sensitivity, and specificity of CD30 gene expression versus protein expression was estimated.

Results

As of March 2015, 120,887 patients have consented to the institutional review board–approved TCC Protocol. A total of 39,157 fresh frozen tumor specimens have been collected, from which over 14,000 samples have gene expression data available. CD30 RNA was expressed in a number of solid tumors; the highest median CD30 RNA expression was observed in primary tumors from lymph node, soft tissue (many sarcomas), lung, skin, and esophagus (median Z-scores 1.011, 0.399, 0.202, 0.152, and 1.011, respectively). High level CD30 gene expression significantly enriches for CD30-positive protein expression in breast, lung, skin, and ovarian cancer; accuracy ranged from 72% to 79%, sensitivity from 75% to 100%, specificity from 70% to 76%, positive predictive value from 20% to 40%, and negative predictive value from 95% to 100%.

Conclusions

The TCC gene expression profiling database guided tissue selection that enriched for CD30 protein expression in a number of solid tumor types. Such an approach may improve screening efficiency for enrolling patients into biomarker-based clinical trials.

Advances in the Classification and Treatment of Mastocytosis: Current Status and Outlook toward the Future

Mastocytosis is a term used to denote a heterogeneous group of conditions defined by the expansion and accumulation of clonal (neoplastic) tissue mast cells in various organs. The classification of the World Health Organization (WHO) divides the disease into cutaneous mastocytosis, systemic mastocytosis, and localized mast cell tumors. On the basis of histomorphologic criteria, clinical parameters, and organ involvement, systemic mastocytosis is further divided into indolent systemic mastocytosis and advanced systemic mastocytosis variants, including aggressive systemic mastocytosis and mast cell leukemia. The clinical impact and prognostic value of this classification has been confirmed in numerous studies, and its basic concept remains valid. However, refinements have recently been proposed by the consensus group, the WHO, and the European Competence Network on Mastocytosis. In addition, new treatment options are available for patients with advanced systemic mastocytosis, including allogeneic hematopoietic stem cell transplantation and multikinase inhibitors directed against KIT D816V and other key signaling molecules. Our current article provides an overview of recent advances in the field of mastocytosis, with emphasis on classification, prognostication, and emerging new treatment options in advanced systemic mastocytosis. Cancer Res; 77(6); 1261-70. ©2017 AACR.

Mastocytosis: 2016 updated WHO classification and novel emerging treatment concepts

Over the past few years, substantial advances have been made in understanding the pathogenesis, evolution, and complexity of mast cell neoplasms. New diagnostic and prognostic parameters and novel therapeutic targets with demonstrable clinical impact have been identified. Several of these new markers, molecular targets, and therapeutic approaches have been validated and translated into clinical practice. At the same time, the classification of mastocytosis and related diagnostic criteria have been refined and updated by the consensus group and the World Health Organization (WHO). As a result, more specific therapies tailored toward prognostic subgroups of patients have been developed. Emerging treatment concepts use drugs directed against KIT and other relevant targets in neoplastic mast cells and will hopefully receive recognition by health authorities in the near future. This article provides an overview of recent developments in the field, with emphasis on the updated WHO classification, refined criteria, additional prognostic parameters, and novel therapeutic approaches. Based on these emerging concepts, the prognosis, quality of life, and survival of patients with advanced mastocytosis are expected to improve in the coming years.