Treatment of systemic mast cell disease with 2-chlorodeoxyadenosine

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.

Target Therapies for Systemic Mastocytosis: An Update

Systemic mastocytosis (SM) results from a clonal proliferation of abnormal mast cells (MCs) in extra-cutaneous organs. It could be divided into indolent SM, smoldering SM, SM with an associated hematologic (non-MC lineage) neoplasm, aggressive SM, and mast cell leukemia. SM is generally associated with the presence of a gain-of-function somatic mutation in KIT at codon 816. Clinical features could be related to MC mediator release or to uncontrolled infiltration of MCs in different organs. Whereas indolent forms have a near-normal life expectancy, advanced diseases have a poor prognosis with short survival times. Indolent forms should be considered for symptom-directed therapy, while cytoreductive therapy represents the first-line treatment for advanced diseases. Since the emergence of tyrosine kinase inhibitors (TKIs), KIT inhibition has been an attractive approach. Initial reports showed that only the rare KITD816V negative cases were responsive to first-line TKI imatinib. The development of new TKIs with activity against the KITD816V mutation, such as midostaurin or avapritinib, has changed the management of this disease. This review aims to focus on the available clinical data of therapies for SM and provide insights into possible future therapeutic targets.

Superior Efficacy of Midostaurin Over Cladribine in Advanced Systemic Mastocytosis: A Registry-Based Analysis

PURPOSE

On the basis of data from the German Registry on Disorders of Eosinophils and Mast Cells, we compared the efficacy of midostaurin and cladribine in patients with advanced systemic mastocytosis (AdvSM).

PATIENTS AND METHODS

Patients with AdvSM (n = 139) were treated with midostaurin only (n = 63, 45%), cladribine only (n = 23, 17%), or sequentially (midostaurin-cladribine, n = 30, 57%; cladribine-midostaurin, n = 23, 43%). Prognosis was assessed through the Mutation-Adjusted Risk Score (MARS). Besides the comparison of efficacy between midostaurin and cladribine on response (eg, organ dysfunction, bone marrow mast cell [MC] infiltration, and tryptase), overall survival (OS), and leukemia-free survival, we focused on the impact of treatment on involved non-MC lineages, for example, monocytes or eosinophils, and the KIT D816V expressed allele burden.

RESULTS

Midostaurin only was superior to cladribine only with effects from responses on MC and non-MC lineages conferring on a significantly improved OS (median 4.2 v 1.9 years, P = .033) and leukemia-free survival (2.7 v 1.3 years, P = .044) on the basis of a propensity score-weighted analysis of parameters included in MARS. Midostaurin compensated the inferior efficacy of cladribine in first- and second-line treatment. On midostaurin in any line, response of eosinophilia did not improve its baseline adverse prognostic impact, whereas response of monocytosis proved to be a positive on-treatment parameter. Multivariable analysis allowed to establish three risk categories (low/intermediate/high) through the combination of MARS and the reduction of the KIT D816V expressed allele burden of ≥ 25% at month 6 (median OS not reached v 3.0 years v 1.0 year; P < .001).

CONCLUSION

In this registry-based analysis, midostaurin revealed superior efficacy over cladribine in patients with AdvSM. In midostaurin-treated patients, the combination of baseline MARS and molecular response provided a compelling three-tier risk categorization (MARSv2.0) for OS.

Systemic Mastocytosis: Molecular Landscape and Implications for Treatment

Over the past decade, we have witnessed significant advances in the molecular characterization of systemic mastocytosis (SM). This has provided important information for a better understanding of the pathogenesis of the disease but has also practically impacted the way we diagnose and manage it. Advances in molecular testing have run in parallel with advances in therapeutic targeting of constitutive active KIT, the major driver of the disease. Therefore, assessing the molecular landscape in each SM patient is essential for diagnosis, prognosis, treatment, and therapeutic efficacy monitoring. This is facilitated by the routine availability of novel technologies like digital PCR and NGS. This review aims to summarize the pathogenesis of the disease, discuss the value of molecular diagnostic testing and how it should be performed, and provide an overview of present and future therapeutic concepts based on fine molecular characterization of SM patients.

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.

Relevant updates in systemic mastocytosis

Systemic Mastocytosis (SM) is a rare myeloproliferative neoplasm (MPN) that is characterized by a clonal proliferation of mast cells (MCs). The symptoms and clinical presentation of SM are the result of both MC proliferation as well as activation and degranulation, causing hyperactive and over-exaggerated hypersensitivity responses, as well as organ infiltration by pathogenic MCs. The clinical presentation and course of SM is varied and organ involvement can lead to significant morbidity and mortality in some cases. The subtypes of SM include indolent SM (ISM), smoldering SM (SSM), aggressive SM (ASM), SM with associated hematologic neoplasm (SM-AHN) and mast cell leukemia (MCL) and survival can range from normal in the case of ISM to months in MCL. The treatment of indolent forms of SM is largely focused on addressing symptom burden (B findings), while cytoreductive agents and more recently molecularly targeted agents are employed to reduce MC burden and reverse associated organ dysfunction (C findings). Although the pathogenesis of SM is multi-factorial, the acquisition of KIT D816 V is a relatively frequent mutational event and serves as the target of novel agents. The recent approval of midostaurin for the treatment of advanced SM has brought awareness to this disease and energized further drug development efforts. Expanding our understanding of the underlying molecular mechanisms of SM will continue to inform future therapeutic approaches.

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.

KIT D816V Positive Acute Mast Cell Leukemia Associated with Normal Karyotype Acute Myeloid Leukemia

Introduction

Mast cell (MC) leukemia (MCL) is extremely rare. We present a case of MCL diagnosed concomitantly with acute myeloblastic leukemia (AML).

Case Report

A 41-year-old woman presented with asthenia, anorexia, fever, epigastralgia, and diarrhea. She had a maculopapular skin rash, hepatosplenomegaly, retroperitoneal adenopathies, pancytopenia, 6% blast cells (BC) and 20% MC in the peripheral blood, elevated lactate dehydrogenase, cholestasis, hypoalbuminemia, hypogammaglobulinemia, and increased serum tryptase (184 μg/L). The bone marrow (BM) smears showed 24% myeloblasts, 17% promyelocytes, and 16% abnormal toluidine blue positive MC, and flow cytometry revealed 12% myeloid BC, 34% aberrant promyelocytes, a maturation blockage at the myeloblast/promyelocyte level, and 16% abnormal CD2−CD25+ MC. The BM karyotype was normal, and the KIT D816V mutation was positive in BM cells. The diagnosis of MCL associated with AML was assumed. The patient received corticosteroids, disodium cromoglycate, cladribine, idarubicin and cytosine arabinoside, high-dose cytosine arabinoside, and hematopoietic stem cell transplantation (HSCT). The outcome was favorable, with complete hematological remission two years after diagnosis and one year after HSCT.

Conclusions

This case emphasizes the need of an exhaustive laboratory evaluation for the concomitant diagnosis of MCL and AML, and the therapeutic options.

Midostaurin: A Multiple Tyrosine Kinases Inhibitor in Acute Myeloid Leukemia and Systemic Mastocytosis

Midostaurin (PKC412, Rydapt^®) is an oral multiple tyrosine kinase inhibitor. Main targets are the kinase domain receptor, vascular endothelial-, platelet derived-, and fibroblast growth factor receptor, stem cell factor receptor c-KIT, as well as mutated and wild-type FLT3 kinases. Midostaurin was approved by the Food and Drug Administration (FDA) and the European Medical Agency (EMA) for acute myeloid leukemia with activating FLT3 mutations in combination with intensive induction and consolidation therapy as well as aggressive systemic mastocytosis (ASM), systemic mastocytosis with associated hematological neoplasm (SM-AHN) or mast cell leukemia (MCL). Several clinical trials are active or are planned to further investigate the role of midostaurin in myeloid malignancies and mastocytosis.

Midostaurin treatment in FLT3-mutated acute myeloid leukemia and systemic mastocytosis

INTRODUCTION

A number of tyrosine kinase inhibitors (TKIs) have been developed that inhibit the constitutively activated kinase activity caused by activating tyrosine kinase mutations, such as FLT3 or KIT, thus interrupting signaling pathways. Currently, midostaurin is the only approved TKI as monotherapy for aggressive systemic mastocytosis (SM), SM with associated hematological neoplasm, or mast cell leukemia displaying a KIT mutation as well as in combination with standard intensive chemotherapy for adult patients with newly diagnosed FLT3-mutated acute myeloid leukemia (AML). Areas covered: We provide a concise review of the pharmacology, tolerability and clinical efficacy of midostaurin and emerging new treatment options for ASM and FLT3-mutated AML. Expert commentary: Currently, midostaurin is the only approved TKI in aggressive SM, SM with associated hematological neoplasm, or mast cell leukemia inducing responses including complete remissions. With regard to AML, midostaurin is the first drug to receive regulatory approval in this indication in the molecularly defined subgroup of AML with FLT3 mutations. By introduction of this new standard in AML with FLT3 mutations, the bare has been raised for future approvals of next generation FLT3 inhibitors which will be based increasingly on head to head comparisons with midostaurin.

Efficacy and safety of midostaurin in patients with advanced systemic mastocytosis: 10-year median follow-up of a phase II trial

Patients with advanced systemic mastocytosis (SM) (e.g. aggressive SM (ASM), SM with an associated hematologic neoplasm (SM-AHN) and mast cell leukemia (MCL)) have limited treatment options and exhibit reduced survival. Midostaurin is an oral multikinase inhibitor that inhibits D816V-mutated KIT, a primary driver of SM pathogenesis. We conducted a phase II trial of midostaurin 100 mg twice daily, administered as 28-day cycles, in 26 patients (ASM, n=3; SM-AHN, n= 17; MCL, n=6) with at least one sign of organ damage. During the first 12 cycles, the overall response rate was 69% (major/partial response: 50/19%) with clinical benefit in all advanced SM variants. With ongoing therapy, 2 patients achieved a complete remission of their SM. Midostaurin produced a ⩾50% reduction in bone marrow mast cell burden and serum tryptase level in 68% and 46% of patients, respectively. Median overall survival for the entire cohort was 40 months, and 18.5 months for MCL patients. Low-grade gastrointestinal side effects were common and manageable with antiemetics. The most frequent grade 3/4 nonhematologic and hematologic toxicities were asymptomatic hyperlipasemia (15%) and anemia (12%). With median follow-up of 10 years, no unexpected toxicities emerged. These data establish the durable activity and tolerability of midostaurin in advanced SM.

Clinical potential of midostaurin in advanced systemic mastocytosis

Advanced (Ad) systemic mastocytoses (SM) include aggressive SM (ASM) and mast cell leukemia (MCL) with or without an associated clonal hematological non-mast cell lineage disease (AHNMD). They are rare (<15%) but are associated with a poor prognosis due to rapid organ dysfunction. To date, responses to high-dose chemotherapy, cladribine, and imatinib were revealed to be suboptimal with a median survival time of 24 months. Midostaurin is a potent multikinase inhibitor including the most frequent KIT D816V mutation (>80%). We herein present a review of the most recent data of the use of midostaurin in AdSM. First, a multicenter Phase II study (CPKC412D2213) revealed an unprecedented overall response rate (ORR) of 69% regardless of KIT mutational status, with 38% of major response (MR) among 26 AdSM patients treated with midostaurin alone 200 mg daily. Second, a sponsor-initiated, multicenter, single-arm open Phase II study (CPKC412D2201) confirmed a high and durable ORR of 60% including 45% of MR among 89 AdSM patients. Finally, a French compassionate use program managed by the French Reference Centre for Mastocytosis allowed the treatment of almost a hundred AdSM patients to date in France since the CPKC412D2201 study closure. The outcome of the first 28 treated patients under cover of this on-going procedure revealed an ORR of 71% including 57% of MR. Most importantly, survival analysis revealed in comparison to a historical control cohort of AdSM patients who did not receive midostaurin a twofold lower risk of death (p=0.02) in midostaurin-treated patients. Side effects revealed were acceptable and manageable (mostly digestive). Midostaurin appears to be an effective and safe treatment of AdSM. However, its effect on the course of the AHNMD is less clear. For the future, combined therapy (hypomethylating agents, cladribine, mammalian target of rapamycin inhibitors, chemotherapy, and allogeneic bone marrow transplantation) may further improve long-term survival, particularly that of MCL and AdSM patients with AHNMD.

The clinical and molecular diversity of mast cell leukemia with or without associated hematologic neoplasm

Mast cell leukemia is a rare variant of advanced systemic mastocytosis characterized by at least 20% of mast cells in a bone marrow smear. We evaluated clinical and molecular characteristics of 28 patients with (n=20, 71%) or without an associated hematologic neoplasm. De novo mast cell leukemia was diagnosed in 16 of 28 (57%) patients and secondary mast cell leukemia evolving from other advanced systemic mastocytosis subtypes in 12 of 28 (43%) patients, of which 7 patients progressed while on cytoreductive treatment. Median bone marrow mast cell infiltration was 65% and median serum tryptase was 520 μg/L. C-findings were identified in 26 of 28 (93%) patients. Mutations in KIT (D816V, n=19; D816H/Y, n=5; F522C, n=1) were detected in 25 of 28 (89%) patients and prognostically relevant additional mutations in SRSF2, ASXL1 or RUNX1 (S/A/R^pos) in 13 of 25 (52%) patients. Overall response rate in 18 treatment-naïve patients was 5 of 12 (42%) on midostaurin and 1 of 6 (17%) on cladribine, and after switch 1 of 4 (25%) on midostaurin and 0 of 3 on cladribine, respectively. S/A/R^pos adversely affected response to treatment and progression to secondary mast cell leukemia (n=6) or acute myeloid leukemia (n=3) while on treatment (P<0.05). The median overall survival from mast cell leukemia diagnosis was 17 months as compared to 44 months in a control group of 124 patients with advanced systemic mastocytosis but without mast cell leukemia (P=0.03). In multivariate analyses, S/A/R^pos remained the only independent poor prognostic variable predicting overall survival (P=0.007). In conclusion, the molecular signature should be determined in all patients with mast cell leukemia because of its significant clinical and prognostic relevance.

Systemic mastocytosis in adults: 2017 update on diagnosis, risk stratification and management

Disease overview:Systemic mastocytosis (SM) results from a clonal proliferation of abnormal mast cells (MC) in one or more extra-cutaneous organs.

DIAGNOSIS

The major criterion is presence of multifocal clusters of morphologically abnormal MC in the bone marrow. Minor diagnostic criteria include elevated serum tryptase level, abnormal MC expression of CD25 and/or CD2, and presence of KITD816V. Risk stratification: The 2008 World Health Organization (WHO) classification of SM has been shown to be prognostically relevant. Classification of SM patients into indolent (SM), aggressive SM (ASM), SM associated with a clonal non-MC lineage disease (SM-AHNMD) and mast cell leukemia (MCL) subgroups is a useful first step in establishing prognosis.

MANAGEMENT

SM treatment is generally palliative. ISM patients have a normal life expectancy and receive symptom-directed therapy; infrequently, cytoreductive therapy may be indicated for refractory symptoms. ASM patients have disease-related organ dysfunction; interferon-α (±corticosteroids) can control dermatological, hematological, gastrointestinal, skeletal and mediator-release symptoms, but is hampered by poor tolerability. Similarly, cladribine has broad therapeutic activity, with particular utility when rapid MC debulking is indicated; the main toxicity is myelosuppression. Imatinib has a therapeutic role in the presence of an imatinib-sensitive KIT mutation or in KITD816-unmutated patients. Treatment of SM-AHNMD is governed primarily by the non-MC neoplasm; hydroxyurea has modest utility in this setting; there is a role for allogeneic stem cell transplantation in select cases. Investigational drugs: Recent data confirms midostaurin's significant anti-MC activity in patients with advanced SM. Am. J. Hematol. 91:1147-1159, 2016. © 2016 Wiley Periodicals, Inc.

Efficacy and Safety of Midostaurin in Advanced Systemic Mastocytosis

BACKGROUND

Advanced systemic mastocytosis comprises rare hematologic neoplasms that are associated with a poor prognosis and lack effective treatment options. The multikinase inhibitor midostaurin inhibits KIT D816V, a primary driver of disease pathogenesis.

METHODS

We conducted an open-label study of oral midostaurin at a dose of 100 mg twice daily in 116 patients, of whom 89 with mastocytosis-related organ damage were eligible for inclusion in the primary efficacy population; 16 had aggressive systemic mastocytosis, 57 had systemic mastocytosis with an associated hematologic neoplasm, and 16 had mast-cell leukemia. The primary outcome was the best overall response.

RESULTS

The overall response rate was 60% (95% confidence interval [CI], 49 to 70); 45% of the patients had a major response, which was defined as complete resolution of at least one type of mastocytosis-related organ damage. Response rates were similar regardless of the subtype of advanced systemic mastocytosis, KIT mutation status, or exposure to previous therapy. The median best percentage changes in bone marrow mast-cell burden and serum tryptase level were -59% and -58%, respectively. The median overall survival was 28.7 months, and the median progression-free survival was 14.1 months. Among the 16 patients with mast-cell leukemia, the median overall survival was 9.4 months (95% CI, 7.5 to not estimated). Dose reduction owing to toxic effects occurred in 56% of the patients; re-escalation to the starting dose was feasible in 32% of those patients. The most frequent adverse events were low-grade nausea, vomiting, and diarrhea. New or worsening grade 3 or 4 neutropenia, anemia, and thrombocytopenia occurred in 24%, 41%, and 29% of the patients, respectively, mostly in those with preexisting cytopenias.

CONCLUSIONS

In this open-label study, midostaurin showed efficacy in patients with advanced systemic mastocytosis, including the highly fatal variant mast-cell leukemia. (Funded by Novartis Pharmaceuticals and others; ClinicalTrials.gov number, NCT00782067.).

Pharmacological treatment options for mast cell activation disease

Mast cell activation disease (MCAD) is a term referring to a heterogeneous group of disorders characterized by aberrant release of variable subsets of mast cell (MC) mediators together with accumulation of either morphologically altered and immunohistochemically identifiable mutated MCs due to MC proliferation (systemic mastocytosis [SM] and MC leukemia [MCL]) or morphologically ordinary MCs due to decreased apoptosis (MC activation syndrome [MCAS] and well-differentiated SM). Clinical signs and symptoms in MCAD vary depending on disease subtype and result from excessive mediator release by MCs and, in aggressive forms, from organ failure related to MC infiltration. In most cases, treatment of MCAD is directed primarily at controlling the symptoms associated with MC mediator release. In advanced forms, such as aggressive SM and MCL, agents targeting MC proliferation such as kinase inhibitors may be provided. Targeted therapies aimed at blocking mutant protein variants and/or downstream signaling pathways are currently being developed. Other targets, such as specific surface antigens expressed on neoplastic MCs, might be considered for the development of future therapies. Since clinicians are often underprepared to evaluate, diagnose, and effectively treat this clinically heterogeneous disease, we seek to familiarize clinicians with MCAD and review current and future treatment approaches.

Mastocytosis: the puzzling clinical spectrum and challenging diagnostic aspects of an enigmatic disease

Mastocytosis is a complex disorder characterized by the accumulation of abnormal mast cells (MC) in the skin, bone marrow and/or other visceral organs. The clinical manifestations result from MC-derived mediators and, less frequently, from destructive infiltration of MCs. Patients suffer from a variety of symptoms including pruritus, flushing and life-threatening anaphylaxis. Whilst mastocytosis is likely to be suspected in a patient with typical skin lesions [i.e. urticaria pigmentosa (UP)], the absence of cutaneous signs does not rule out the diagnosis of this disease. Mastocytosis should be suspected in cases of recurrent, unexplained or severe insect-induced anaphylaxis or symptoms of MC degranulation without true allergy. In rare cases, unexplained osteoporosis or unexplained haematological abnormalities can be underlying feature of mastocytosis, particularly when these conditions are associated with elevated baseline serum tryptase levels. The diagnosis is based on the World Health Organization criteria, in which the tryptase level, histopathological and immunophenotypic evaluation of MCs and molecular analysis are crucial. A somatic KIT mutation, the most common of which is D816V, is usually detectable in MCs and their progenitors. Once a diagnosis of systemic mastocytosis (SM) is made, it is mandatory to assess the burden of the disease, its activity, subtype and prognosis, and the appropriate therapy. Mastocytosis comprises seven different categories that range from indolent forms, such as cutaneous and indolent SM, to progressive forms, such as aggressive SM and MC leukaemia. Although prognosis is good in patients with indolent forms of the disease, patients with advanced categories have a poor prognosis.

Response of patients with indolent systemic mastocytosis to tamoxifen citrate

We examined whether tamoxifen citrate at 20mg/day for 1 year had a beneficial effect on laboratory findings, bone marrow mastocytosis, common clinical symptoms, or quality-of-life assessment for 5 women and 2 men with indolent systemic mastocytosis. Tamoxifen was well tolerated. We found significant reductions in the platelet count, serum alkaline phosphatase, and 24-h urinary excretion of N-methylhistamine and significant increases in serum lactate dehydrogenase and (excluding 2 patients taking aspirin) in 24-h urinary excretion of 11β-prostaglandin F2α. Overall, no change occurred in percent involvement of bone marrow by mastocytosis. Symptom scores were mild and did not change during the treatment. The 36-Item Short Form Health Survey scores for quality of life physical and mental components showed no marked changes. Tamoxifen, an older, nonhematotoxic medication, has limited activity in systemic mastocytosis at the dosage used in this study.

Long-term efficacy and safety of cladribine (2-CdA) in adult patients with mastocytosis

Mastocytosis (M) is a clonal myeloid-disabling disorder for which no curative therapy is currently available. Cladribine (2-chlorodeoxyadenosine [2-CdA]) is a synthetic purine analog cytoreductive treatment, for which efficacy is mostly reported in advanced M. Here we report, with a long-term follow-up period (>10 years) efficacy and safety in 68 adult patients with M (36 [53%] had indolent M and 32 [47%] had advanced M) treated by 2-CdA (0.14 mg/kg in infusion or subcutaneously, days 1-5; repeated at 4-12 weeks until 1 to 9 courses). Median 2-CdA courses number was 3.7 (1-9). The overall response rate was 72% (complete remission [R]/major/partial R: 0%/47%/25%) and according to indolent/advanced M was 92% (major/partial R: 56%/36%) and 50% (major/partial R: 37.5%/12.5%), respectively. Clinical improvement was observed for 10 of 11 mediator release and 6 of 7 mast cell infiltration-related symptoms including urticaria pigmentosa and organomegaly (P < .02). Serum tryptase levels decreased (P = .01). Median durations of response were 3.71 (0.1-8) and 2.47 (0.5-8.6) years for indolent and aggressive M, respectively. The most frequent grade 3/4 toxicities were lymphopenia (82%), neutropenia (47%), and opportunistic infections (13%). 2-CdA appears to provide a significant efficacy with some toxicity in various M subtypes, mostly in indolent M, refractory to multiple symptomatic therapies.

Systemic mastocytosis in adults: 2015 update on diagnosis, risk stratification, and management

DISEASE OVERVIEW

Systemic mastocytosis (SM) results from a clonal proliferation of abnormal mast cells (MC) in one or more extracutaneous organs.

DIAGNOSIS

The major criterion is presence of multifocal clusters of morphologically abnormal MC in the bone marrow. Minor diagnostic criteria include elevated serum tryptase level, abnormal MC expression of CD25 and/or CD2, and presence of KITD816V.

RISK STRATIFICATION

The 2008 World Health Organization classification of SM has been shown to be prognostically relevant. Classification of SM patients into indolent SM (ISM), aggressive SM (ASM), SM associated with a clonal non-MC lineage disease (SM-AHNMD), and mast cell leukemia (MCL) subgroups is a useful first step in establishing prognosis.

MANAGEMENT

SM treatment is generally palliative. ISM patients have a normal life expectancy and receive symptom-directed therapy; infrequently, cytoreductive therapy may be indicated for refractory symptoms. ASM patients have disease-related organ dysfunction; interferon-α (+/-corticosteroids) can control dermatological, hematological, gastrointestinal, skeletal, and mediator-release symptoms, but is hampered by poor tolerability. Similarly, cladribine has broad therapeutic activity, with particular utility when rapid MC debulking is indicated; the main toxicity is myelosuppression. Imatinib has a therapeutic role in the presence of an imatinib-sensitive KIT mutation or in KITD816-unmutated patients. Treatment of SM-AHNMD is governed primarily by the non-MC neoplasm; hydroxyurea has modest utility in this setting; there is a role for allogeneic stem cell transplantation in select cases. Investigational Drugs: Recent data confirms midostaurin's significant anti-MC activity in patients with advanced SM.

Systemic mastocytosis in adults: 2013 update on diagnosis, risk stratification, and management

DISEASE OVERVIEW

Systemic mastocytosis (SM) results from a clonal proliferation of abnormal mast cells (MC) in one or more extracutaneous organs.

DIAGNOSIS

The major criterion is presence of multifocal clusters of morphologically abnormal MC in the bone marrow. Minor diagnostic criteria include elevated serum tryptase level, abnormal MC expression of CD25 and/or CD2, and presence of KITD816V.

RISK STRATIFICATION

The 2008 World Health Organization (WHO) classification of SM has been shown to be prognostically relevant. Classification of SM patients into indolent (SM), aggressive SM (ASM), SM associated with a clonal non-MC lineage disease (SM-AHNMD) and mast cell leukemia (MCL) subgroups is a useful first step in establishing prognosis.

MANAGEMENT

SM treatment is generally palliative. ISM patients have a normal life expectancy and receive symptom-directed therapy; infrequently, cytoreductive therapy may be indicated for refractory symptoms. ASM patients have disease-related organ dysfunction; interferon-α (±corticosteroids) can control dermatological, hematological, gastrointestinal, skeletal, and mediator-release symptoms, but is hampered by poor tolerability. Similarly, cladribine has broad therapeutic activity, with particular utility when rapid MC debulking is indicated; the main toxicity is myelosuppression. Imatinib has a therapeutic role in the presence of an imatinib-sensitive KIT mutation or in KITD816-unmutated patients. Treatment of SM-AHNMD is governed primarily by the non-MC neoplasm; hydroxyurea has modest utility in this setting.

INVESTIGATIONAL DRUGS

Dasatinib's in vitro anti- KITD816V activity has not translated into significant therapeutic activity in most SM patients. In contrast, recently updated data confirms Midostaurin's significant anti-MC activity in patients with advanced SM.

Thalidomide in systemic mastocytosis: results from an open-label, multicentre, phase II study

Mastocytosis can lead to organ failure as well as systemic symptoms that can be disabling, with considerable deterioration in quality of life. Beside symptomatic treatments, interferon-α and purine analogues have been shown to be effective but complete or long-term remission is rarely obtained with these drugs. We conducted a phase II, multicentre, study to investigate thalidomide in severely symptomatic indolent and aggressive systemic mastocytosis. Twenty patients were enrolled of whom 16 were analysed for response. The overall response rate was 56%. Responses were observed in the skin in 61% of patients with a significant decrease in the pruritus score. Mast cell mediator-related symptoms responded in 71% of cases and 25% of aggressive systemic mastocytosis patients had a response in terms of B/C findings (borderline/cytoreduction needed). Bone marrow mast cell infiltration decreased in five of the eight evaluable patients. There was no significant improvement in the AFIRMM (Association Française pour les Initiatives de Recherche sur le Mastocyte et Les Mastocytoses), Quality of Life or Hamilton scores. Grade 3-4 toxicities consisted of peripheral neuropathy (11%) and myelosuppression (neutropenia: 5%; thrombocytopenia: 11%). In conclusion, thalidomide might be useful in mastocytosis and in the treatment of mast cell-related symptoms. It might be considered in selected patients, taking into account the benefit/risk balance and the individual patient evaluation.

International Working Group-Myeloproliferative Neoplasms Research and Treatment (IWG-MRT) & European Competence Network on Mastocytosis (ECNM) consensus response criteria in advanced systemic mastocytosis

Systemic mastocytosis (SM) is characterized by accumulation of neoplastic mast cells and is classified into indolent and aggressive forms. The latter include aggressive SM (ASM), mast cell leukemia (MCL), and SM associated with a myeloid neoplasm wherein 1 or both disease compartments exhibit advanced features. These variants, henceforth collectively referred to as advanced SM for the purposes of this report, are typically characterized by organ damage and shortened survival duration. In contrast to indolent SM, in which symptoms are usually managed by noncytotoxic antimediator therapy, cytoreduction is usually necessary for disease control in advanced SM. Unfortunately, current drug treatment of these patients rarely results in complete clinical and histopathologic remissions or improved survival time. Previously defined response criteria were adapted to the heterogeneous presentations of advanced SM and the limited effects of available drugs. However, recent advances in understanding the molecular pathogenesis of SM and the corresponding prospect in targeted therapy make it a priority to modify these criteria. Our current study is the product of an international group of experts and summarizes the challenges in accomplishing this task and forwards a new proposal for response criteria, which builds on prior proposals and should facilitate response evaluation in clinical trials.

Mast cell leukemia

Mast cell leukemia (MCL) is a very rare form of aggressive systemic mastocytosis accounting for < 1% of all mastocytosis. It may appear de novo or secondary to previous mastocytosis and shares more clinicopathologic aspects with systemic mastocytosis than with acute myeloid leukemia. Symptoms of mast cell activation-involvement of the liver, spleen, peritoneum, bones, and marrow-are frequent. Diagnosis is based on the presence of ≥ 20% atypical mast cells in the marrow or ≥ 10% in the blood; however, an aleukemic variant is frequently encountered in which the number of circulating mast cells is < 10%. The common phenotypic features of pathologic mast cells encountered in most forms of mastocytosis are unreliable in MCL. Unexpectedly, non-KIT D816V mutations are frequent and therefore, complete gene sequencing is necessary. Therapy usually fails and the median survival time is < 6 months. The role of combination therapies and bone marrow transplantation needs further investigation.

Mast Cell Leukaemia: c-KIT Mutations Are Not Always Positive

Mast cell leukemia (MCL) is a rare and aggressive disease with poor prognosis and short survival time. D816V c-KIT mutation is the most frequent molecular abnormality and plays a crucial role in the pathogenesis and development of the disease. Thus, comprehensive diagnostic investigations and molecular studies should be carefully carried out to facilitate the therapeutic choice. A MCL patient's case with rare phenotypic and genotypic characteristics is described with review of major clinical biological and therapeutic approaches in MCL.

Mast cells and eosinophils in mastocytosis, chronic eosinophilic leukemia, and non-clonal disorders

Mast cells and eosinophils often travel in the same biologic circles. In non-clonal states, such as allergic and inflammatory conditions, cell-to-cell contact and the pleiotropic actions of multiple cytokines and chemokines, derived from local tissues or mast cells themselves, foster the co-recruitment of these cells to the same geographic cellular niche. While eosinophils and mast cells serve critical roles as part of the host immune response and in maintenance of normal homeostasis, these cell types can undergo neoplastic transformation due to the development of clonal molecular abnormalities that arise in early hematopoietic progenitors. The dysregulated tyrosine kinases, D816V KIT and FIP1L1-PDGFRA, are the prototypic oncogenic lesions resulting in systemic mastocytosis (SM) and chronic eosinophilic leukemia, respectively. We review the pathobiology of these myeloproliferative neoplasms (MPNs) with a focus on the relationship between mast cells and eosinophils, and discuss murine models, which further elucidate how the phenotype of these diseases can be influenced by stem cell factor (SCF) and expression of the potent eosinophilopoietic cytokine, interleukin-5 (IL-5). Therapy of SM and FIP1L1-PDGFRA-positive disease and the prognostic relevance of increased peripheral blood and tissue mast cells in hematolymphoid malignancies will also be addressed.

Systemic mastocytosis in adults: 2012 Update on diagnosis, risk stratification, and management

DISEASE OVERVIEW

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

DIAGNOSIS

The major criterion is presence of multifocal clusters of morphologically abnormal MC in the bone marrow. Minor diagnostic criteria include elevated serum tryptase level, abnormal MC expression of CD25 and/or CD2, and presence of KITD816V.

RISK STRATIFICATION

The prognostic relevance of the 2008 World Health Organization (WHO) classification of SM has recently been confirmed. Classification of SM patients into indolent (SM), aggressive SM (ASM), SM associated with a clonal non-MC lineage disease (SM-AHNMD) and mast cell leukemia (MCL) subgroups is a useful first step in establishing prognosis.

MANAGEMENT

SM treatment is generally palliative. ISM patients have a normal life expectancy and receive symptom-directed therapy; infrequently, cytoreductive therapy may be indicated for refractory symptoms. ASM patients have disease-related organ dysfunction; interferon-α (±corticosteroids) can control dermatological, hematological, gastrointestinal, skeletal, and mediator-release symptoms, but is hampered by poor tolerability. Similarly, cladribine has broad therapeutic activity, with particular utility when rapid MC debulking is indicated; the main toxicity is myelosuppression. Imatinib has a therapeutic role in the presence of an imatinib-sensitive KIT mutation or in KITD816-unmutated patients. Treatment of SM-AHNMD is governed primarily by the non-MC neoplasm; hydroxyurea has modest utility in this setting.

INVESTIGATIONAL DRUGS

Dasatinib's in vitro anti-KITD816V activity has not translated into significant therapeutic activity in most SM patients. In contrast, preliminary data suggest that Midostaurin may produce significant decreases in MC burden in some patients.

Systemic mastocytosis in adults: 2011 update on diagnosis, risk stratification, and management

DISEASE OVERVIEW

Systemic mastocytosis (SM) results from a clonal proliferation of abnormal mast cells (MC) in one or more extracutaneous organs.

DIAGNOSIS

The major criterion is presence of multifocal clusters of morphologically abnormal MC in the bone marrow. Minor diagnostic criteria include elevated serum tryptase level, abnormal MC expression of CD25 and/or CD2, and presence of KITD816V.

RISK STRATIFICATION

The prognostic relevance of the 2008 World Health Organization (WHO) classification of SM has recently been confirmed. Classification of SM patients into indolent (SM), aggressive SM (ASM), SM associated with a clonal non-MC lineage disease (SM-AHNMD), and mast cell leukemia (MCL) subgroups is a useful first step in establishing prognosis.

RISK-ADAPTED THERAPY

SM treatment is generally palliative. ISM patients have a normal life expectancy and receive symptom-directed therapy; infrequently, cytoreductive therapy may be indicated for refractory symptoms. ASM patients have disease-related organ dysfunction; interferon-α (±corticosteroids) can control dermatological, hematological, gastrointestinal, skeletal, and mediator-release symptoms, but is hampered by poor tolerability. Similarly, cladribine has broad therapeutic activity, with particular utility when rapid MC debulking is indicated; the main toxicity is myelosuppression. Imatinib has a therapeutic role in the presence of an imatinib-sensitive KIT mutation or in KITD816-unmutated patients. Treatment of SM-AHNMD is governed primarily by the non-MC neoplasm; hydroxyurea has modest utility in this setting. Dasatinib's in vitro anti- KITD816V activity has not translated into significant therapeutic activity in most SM patients. In contrast, preliminary data suggest that Midostaurin may produce significant decreases in MC burden in some patients.

In vitro and in vivo growth-inhibitory effects of cladribine on neoplastic mast cells exhibiting the imatinib-resistant KIT mutation D816V

OBJECTIVE

In most patients with systemic mastocytosis (SM), including aggressive SM (ASM) and mast cell (MC) leukemia (MCL), neoplastic cells express the oncogenic KIT mutation D816V, which confers resistance to imatinib. Cladribine (2CdA) is a nucleoside analog that has been introduced as a promising agent for treatment of advanced SM.

MATERIALS AND METHODS

We examined the in vitro effects of 2CdA on growth of neoplastic MC, and the in vivo effects of 2CdA (0.13 mg/kg/day intravenously, days 1-5; three to eight cycles) in seven patients with advanced SM.

RESULTS

Cladribine was found to inhibit growth of primary MC and the MC line HMC-1 in a dose-dependent manner, with lower IC(50) values recorded in HMC-1.2 cells harboring KIT D816V (IC(50): 10 ng/mL) compared to HMC-1.1 cells lacking KIT D816V (IC(50): 300 ng/mL). In two patients with progressive smoldering SM, 2CdA produced a long-lasting response with a sustained decrease in serum tryptase levels, whereas in patients with progressive ASM or MCL, 2CdA showed little if any effects. The drug was well-tolerated in most cases. However, one patient developed a massive generalized purulent long-lasting skin rash. The antiproliferative effects of 2CdA on MC were found to be associated with morphologic signs of apoptosis and caspase cleavage. Cladribine did not counteract the kinase activity of KIT D816V or KIT-downstream signaling molecules.

CONCLUSIONS

Cladribine may be a promising agent for treatment of progressive smoldering KIT D816V(+) SM. In rapidly progressing ASM or MCL, additional or alternative drugs are required to induce long-lasting antineoplastic effects.

Cladribine inhibits a diltiazem-induced increase in red blood cell purine nucleotide concentrations in a zebrafish model

Minimizing drug interactions is paramount to improving the efficacy and tolerability of cancer therapy. The zebrafish represents an innovative cancer model due to highly conserved genetics and inherent capacity for high-throughput chemical screening. This pilot study extends the utility of the zebrafish to a preclinical model for pharmacodynamics by examining the interaction of the nucleoside analogue, cladribine with the calcium channel blocker, diltiazem. Cladribine (0.7-3.5 mM) and/or diltiazem (2.4 mM), was injected intraperitoneally into adult zebrafish and red blood cell (RBC) lysates were assayed by HPLC for levels of purine nucleotides (e.g. ATP), potential biomarkers of cardiovascular health. Diltiazem increased RBC ATP concentrations, which were inhibited by co-injection of cladribine. These results suggest a novel drug interaction and highlight the feasibility of the zebrafish as an in vivo model for pharmacodynamic studies.

Cytoreductive therapy in 108 adults with systemic mastocytosis: Outcome analysis and response prediction during treatment with interferon-alpha, hydroxyurea, imatinib mesylate or 2-chlorodeoxyadenosine

Cytoreductive therapy in systemic mastocytosis (SM) includes several drugs whose individual merit has not been well characterized. We retrospectively studied 108 Mayo Clinic patients who met the 2008 WHO diagnostic criteria for SM and received at least one cytoreductive drug. The numbers of patients who were evaluable for response to treatment with interferon-alpha with or without prednisone (IFN-alpha), hydroxyurea (HU), imatinib mesylate (IM) or 2-chlorodeoxyadenosine (2-CdA) were 40, 26, 22, and 22, respectively. The corresponding overall (major) response rates, according to recently published consensus criteria, were 53% (18%), 19% (0%), 18% (9%), and 55% (37%). The respective overall response rates in indolent SM, aggressive SM and SM associated with another clonal hematological nonmast cell lineage disease (SM-AHNMD) were 60%, 60%, 45% for IFN-alpha, 0, 0, 21% for HU, 14%, 50%, 9% for IM and 56%, 50%, 55% for 2-CdA. The absence of mast cell mediator release symptoms in IFN-alpha-treated patients and presence of circulating immature myeloid cells in 2-CdA-treated patients predicted inferior response. TET2 mutational status did not influence treatment response. Although the major response rates with these four cytoreductive agents were still suboptimal and HU was mainly used in patients with SM-AHNMD, the current study favors 2-CdA or IFN-alpha as first-line current therapy in SM and identifies patients who are likely to respond to such therapy.

Advanced mast cell disease: an Italian Hematological Multicenter experience

The aim of the study is to evaluate clinical features, treatments and outcome of patients with systemic mast cell disease (MCD) who arrived to the attention of hematologists. A retrospective study was conducted over 1995-2006 in patients admitted in 18 Italian hematological divisions. Twenty-four cases of advanced MCD were collected: 12 aggressive SM (50%), 8 mast cell leukemia (33%), 4 SM with associated clonal non-mast cell-lineage hematologic disease (17%). Spleen and liver were the principal extramedullary organ involved. The c-kit point mutation D816V was found in 13/18 patients in which molecular biology studies were performed (72%). Treatments were very heterogeneous: on the whole Imatinib was administered in 17 patients, alpha-Interferon in 8, 2-CdA in 3; 2 patients underwent allogeneic hematopoietic stem cell transplantation. The overall response rate to Imatinib, the most frequently employed drugs, was of 29%, registering one complete remission and four partial remission; all responsive patients did not present D816V c-kit mutation. Overall three patients (12%) died for progression of disease. We conclude that MCD is characterized by severe mediator-related symptoms but with a moderate mortality rate. D816V c-kit mutation is frequent and associated with resistance against Imatinib. Because of the rarity of these forms, an effective standard of care is lacking. More data are needed to find new and successful therapeutic strategies.

KIT and mastocytosis

KIT is a receptor tyrosine kinase that is functionally relevant for hematopoiesis, mast cell development and function, gametogenesis and melanogenesis. Normal KIT signaling requires binding to stem cell factor, and PI3K-Akt is one of the putative effector pathways. In humans, germline loss-of-function KIT mutations have been associated with piebaldism - an autosomal dominant condition characterized by depigmented patches of skin and hair. Gain-of-function KIT mutations are usually acquired and have been associated with myeloid malignancies including core binding factor acute myeloid leukemia and systemic mastocytosis (SM), germ cell tumors, gastrointestinal stromal tumors and sinonasal T cell lymphomas. KITD816V is the most prevalent KIT mutation in mast cell disease and occurs in more than 90% of the cases that fulfill the World Health Organization diagnostic criteria for SM. However, its precise pathogenetic contribution is not well understood. In clinical practice, SM is considered either indolent or aggressive depending on the respective absence or presence of symptomatic target organ dysfunction aside from skin disease. In general, conventional therapy for SM is suboptimal, and efforts are under way to develop and employ small molecule drugs that target mutant KIT.

Gastrointestinal manifestations of dermatologic disorders

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

Mastocytosis: advances in diagnosis and treatment

Mastocytosis is characterized by pathologic mast cell accumulation and activation in tissues. Establishment of objective histopathologic and molecular criteria for diagnosis of mastocytosis has allowed sensitive detection of mast cells with aberrant features in patients presenting with suspected mast cell activation symptoms. Frequent detection of the D816V c-kit tyrosine kinase mutation in mastocytosis has led to evaluation of small-molecular-weight tyrosine kinase inhibitors as mast cell cytoreductive agents. In vitro experiments, however, showed that mast cells carrying the D816V c-kit mutation were resistant to the prototypical tyrosine kinase inhibitor imatinib. Efficacy of newer generation tyrosine inhibitors in mast cell disease is currently being evaluated.

Systemic mastocytosis: a concise clinical and laboratory review

CONTEXT

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

OBJECTIVE

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

DATA SOURCES

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

CONCLUSIONS

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

KIT D816V-associated systemic mastocytosis with eosinophilia and FIP1L1/PDGFRA-associated chronic eosinophilic leukemia are distinct entities

BACKGROUND

The broad and overlapping clinical manifestations of D816V KIT-associated systemic mastocytosis with eosinophilia and FIP1L1/PDGFRA-associated chronic eosinophilic leukemia (CEL), coupled with the increase in activated eosinophils and mast cells seen in both disorders, have led to confusion in the nomenclature. It is of paramount importance, however, to distinguish between these 2 groups of patients because of differences in clinical sequelae, prognoses, and selection of treatment.

OBJECTIVE

We thus sought to identify clinical and laboratory features that could be used to distinguish these 2 diagnoses.

METHODS

We compared 12 patients with D816V-positive systemic mastocytosis with eosinophilia with 17 patients with FIP1L1/PDGFRA-positive CEL. Distinguishing features were used to create a risk factor scoring system.

RESULTS

This system correctly classified 16 of 17 FIP1L1/PDGFRA-positive patients with CEL and all 12 patients with systemic mastocytosis with eosinophilia. Thirty-four FIP1L1/PDGFRA-positive patients described in the literature were also classified using this system, and although a complete set of data was not available for any of the historical patients, 21 were correctly classified.

CONCLUSION

These results reinforce the hypothesis that the FIP1L1/PDGFRA gene fusion and D816V-KIT mutation cause distinct clinical syndromes.

CLINICAL IMPLICATIONS

This novel diagnostic approach should prove helpful in clinical practice in the evaluation of patients with increased mast cells and peripheral eosinophilia.