Search

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.

Background The Advanced Systemic Mastocytosis Symptom Assessment Form (AdvSM-SAF) was developed to evaluate symptoms of advanced systemic mastocytosis (AdvSM). This study aimed to psychometrically evaluate AdvSM-SAF scores and provide score interpretation guidelines. Methods The 10-item AdvSM-SAF was administered daily (scored as a seven-day average) in EXPLORER, an open-label Phase 1 study in AdvSM. Score distribution, reliability, construct-related validity, sensitivity to change, and interpretation guidelines were evaluated for AdvSM-SAF items, gastrointestinal symptom score (GSS), skin symptom score (SSS), and total symptom score (TSS). Results Thirty-one patients contributed to the analyses. At Baseline, the GSS, SSS, and TSS had adequate internal consistency (α > 0.7) and test-retest reliability (intraclass correlation coefficients >0.7). AdvSM-SAF scores were moderately to strongly correlated with variables as expected, and distinguished among clinically distinct groups. Observed relationships between change scores in the AdvSM-SAF and other assessments reflect evidence that AdvSM-SAF scores change in concert with other assessments designed to measure similar constructs. The magnitude of AdvSM-SAF weekly TSS mean change scores based on different anchor groupings was as expected (improvement > stable > worsening). Candidate clinically meaningful between-group difference estimates (GSS = 2–4, SSS = 2–3, and TSS = 4–7 points) and within-person change estimates (GSS = 6–9, SSS = 1–4, TSS = 9–14) for AdvSM-SAF weekly scores were generated. Conclusion The AdvSM-SAF produced reliable, construct-valid, and sensitive scores when administered in the target patient population. These results, along with its strong development history and evidence of content validity, indicate that the AdvSM-SAF is fit for the purpose of measuring treatment benefit in individuals with AdvSM.

Mast cell leukemia (MCL) is a very rare subtype of systemic mastocytosis (SM). We have identified 13 such patients (5.9%) among 218 patients with SM seen at our institution between 1994 and 2016. Patients with MCL had poor survival (median 31.6 months); response to various therapies was rare and not durable. Clinical course may be affected by concurrent associated hematologic neoplasm and different genetic profiles. More research is required to decipher this rare and enigmatic SM subtype.

Mastocytosis are myeloproliferative neoplasms commonly related to gain-of-function mutations involving the tyrosine kinase domain of KIT. We herein report a case of familial systemic mastocytosis with the rare KIT K509I germ line mutation affecting two family members: mother and daughter. In vitro treatment with imatinib, dasatinib and PKC412 reduced cell viability of primary mast cells harboring KIT K509I mutation. However, imatinib was more effective in inducing apoptosis of neoplastic mast cells. Both patients with familial systemic mastocytosis had remarkable hematological and skin improvement after three months of imatinib treatment, suggesting that it may be an effective front line therapy for patients harboring KIT K509I mutation.

We evaluate the haematopathologic features of systemic mastocytosis associated with acute myeloid leukaemia (SM-AML) and the prognostic role of c-KIT mutation. Total 11 patients were enrolled. Cytochemistry using toluidine blue and tryptase was positive, as was immunohistochemistry for CD117 and CD25 on clustered mast cells; however, CD2 was expressed in only nine cases. In 10 cases, RUNX1-RUNX1T1 fusion gene was detected, and one patient presented with a t(5;6)(q22;q23) translocation at diagnosis. The c-KIT mutation D816V was detected in six patients. Patients with c-KIT mutations had higher relapse and death rates than those without; 4/5 (80.0%) and 5/6 (83.3%) vs. 1/5 (20%) and 2/5 (40%), respectively. Overall survival was also significantly shorter in cases with, than those without, c-KIT mutations. To identify rare cases of SM-AML, which have a dismal prognosis, c-KIT mutation study and careful examination for the presence of clustered mast cell infiltration by immunochemistry should be performed.

In core binding factor (CBF) acute myeloid leukaemia (AML), realtime quantitative PCR is useful to quantify the fusion transcript ratio (CBFβ-MYH11 and AML1-ETO, in case of inv(16) and t(8;21) respectively) in peripheral blood and bone marrow during the courses of chemotherapy, in order to monitor minimal residual disease (MRD). In two cases of CBF AML associated with systemic mastocytosis (SM), the persistence of mast cells and the detection of a high ratio of fusion transcript, in bone marrow, during the courses of chemotherapy, led us to determine whether the mast cell component of the disease carried the same molecular alterations as leukaemic blasts. We demonstrate that sorted mast cells carried CBF abnormality. These observations point out the lack of specificity of MRD monitoring by RQ-PCR in these exceptional AML cases with SM. Moreover, this suggests that leukaemic blasts and mast cells derive from a common malignant progenitor.

Gain-of-function D816V point mutation within the kinase domain of the transmembrane receptor KIT is found in the great majority of patients with systemic mastocytosis (SM) and is attractive therapeutic target. Twenty patients with SM were enrolled during 2003-2005 in phase II clinical trial with imatinib mesylate (400mg daily), a KIT inhibitor. Median time on therapy was 9 months (range, 0.5-44+). Only one patient, with D816V KIT mutation-negative FIP1L1-PDGFRalpha-negative SM-HES, achieved complete remission (now lasting for 44 months). Six other patients reported symptomatic improvement, including two with D816V KIT mutation-positive SM (one reported improvement in diarrhea and the other in fatigue). Other patients had no benefit. Imatinib was relatively well tolerated. Our study confirms that imatinib therapy does not result in appreciable clinical activity in patients with D816V mutation-positive SM, but may result in a significant benefit in occasional patient with D816V mutation-negative SM.

Among 23 cases of myeloproliferative neoplasms (MPNs) with an associated del(5q) seen at our institution, 14 (61%) fulfilled diagnostic criteria for primary myelofibrosis (PMF). Other diagnoses included polycythemia vera (PV; n=2), essential thrombocythemia (ET; n=1), post-ET myelofibrosis (n=1), systemic mastocytosis (SM; n=1), and MPN, unclassifiable (n=4). Compared to their del(5q)-negative counterparts, del(5q)-positive PMF cases were significantly more anemic (p

Systemic mastocytosis may be primary or be associated with other hematological malignancies, most commonly myeloid neoplasms. In contrast, the association of systemic mastocytosis with lymphoid neoplasms is comparatively rare, and in the absence of appropriate clinical vigilance the diagnosis may be missed. We report a case of aggressive systemic mastocytosis associated with chronic lymphocytic leukemia (SM-CLL), placing particular emphasis on the investigational algorithm used in establishing this diagnosis, and discussing key clinical considerations in the initiation of therapy.

Systemic mastocytosis is a myeloproliferative neoplasm with varying presentation that is caused by infiltration of neoplastic mast cells into extracutaneous tissues. Cytoreductive therapy is used to control organ dysfunction in aggressive systemic mastocytosis and is sometimes needed for control of severe refractory symptoms in patients with indolent disease. However, current standard cytoreductive agents are limited by their suboptimal degree and duration of response and associated significant toxicities, highlighting the need for novel treatments for systemic mastocytosis. Recent studies have identified CD30 as a therapeutic target in systemic mastocytosis, as CD30 is expressed on a majority of neoplastic mast cells. In this case series, the clinical outcomes of 4 patients with aggressive or indolent systemic mastocytosis treated with the anti-CD30 antibody‐drug conjugate brentuximab vedotin are reported. Two patients showed evidence of a response to treatment with a reduction in disease burden, 1 of which has demonstrated a durable response with ongoing benefit for more than 3 years. Treatment with brentuximab vedotin was well-tolerated with side effects that were effectively managed by dose modifications. The results presented suggest that brentuximab vedotin is active in systemic mastocytosis and can induce durable responses with a manageable toxicity profile.

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.

Patients with Systemic Mastocytosis (SM) need a highly sensitive diagnostic test for D816V detection of the KIT receptor gene.Along with histology/cytology and flow cytometry evaluation, bone marrow (BM) from 110 consecutive adult patients referred with a suspicion of SM to Multidisciplinary Outpatient Clinic for Mastocytosis in Verona were tested both by Amplification Refractory Mutation System Reverse Transcriptase quantitative real time Polymerase Chain Reaction (ARMS-RT-qPCR) and RT-PCR. +. Restriction Fragment Length Polymorphism (RFLP) followed by Denaturing-High Performance Liquid Chromatography (D-HPLC) and Sanger sequencing.ARMS-RT-qPCR identified D816V mutation in 77 patients, corresponding to 100% of cases showing CD25+ mast cells (MCs) whereas RT-PCR+RFLP/D-HPLC+sequencing revealed D816V mutations in 47 patients.According to the 2008 WHO criteria 75 SM, 1 Cutaneous Mastocytosis (CM), 1 monoclonal MC activation syndrome (MMAS), and 1 SM Associated with Haematologic Non-Mast Cell Disorder (SM-AHNMD) were diagnosed. Seventeen out 75 SM patients (23%) would have not satisfied sufficient WHO criteria on the basis of the sole RT-PCR+RFLP: these patients had significantly lower serum tryptase levels and amount of CD25+ MCs.Therefore, ARMS-RT-qPCR might result particularly useful, in patients that do not fulfil major BM histological criterion, for the recognition of indolent SM with a very low MC burden.

The concurrent development of chronic myeloid (CML) or myelomonocytic (CMML) leukemia in patients with systemic mastocytosis (SM) is a well recognized phenomenon. Although the leukemia often resembles CML in morphological and in clinical terms, a Ph-Chromosome-positive variant has not been reported in SM so far. We here describe a 43-year-old female patient with typical Ph-Chromosome-positive CML in whom a co-existing bone marrow mastocytosis, a special subvariant of SM, was diagnosed. RT-PCR analysis revealed the typical p210 kDa form of BCR/ABL in leukemic cells. The diagnosis SM was based on the typical focal aggregates of spindle-shaped mast cells (MC) in the bone marrow, expression of CD25 in MC, and the c-kit mutation D816V, which was detectable in microdissected bone marrow MC, but not in microdissected leukemic cells, suggesting the presence of two different (sub)clones of neoplastic cells. Therapy with the BCR/ABL-targeting drug Imatinib (STI571) resulted in complete cytogenetic remission of CML. Together, our case provides further evidence for the biologic diversity of leukemias that may occur in patients with SM. The exact knowledge of the pathology and target-profile of the associated leukemias in SM have important therapeutic implications.

Daily treatment of systemic mastocytosis with high-dose interferon-alfa often is not tolerated because of clinical or hematologic side effects. We report successful treatment of a patient with systemic mastocytosis, who was positive for the D816V mutation, with interferon alfa-2b at 10 million units three times per week. During 5 years of treatment, bone marrow infiltration by mast cells decreased from 50 to ≤5%, and there was a decrease (urinary N -methylhistamine excretion, 75%; serum tryptase concentration, 98%) or normalization (serum calcitonin value, urinary prostaglandin F 2α excretion) of mast cell mediators. Side effects included mild depression (untreated) and biochemical hypothyroidism easily managed with supplemental levothyroxine.

The c-kit mutation Asp-816-->Val is detectable not only in neoplastic mast cells (MCs) in patients with systemic mastocytosis (SM) but also in most associated hematologic non-MC lineage disease (AHNMD). In order to prove a monoclonal disease evolution we investigated DNA of pooled microdissected single cells for the presence of the mutation in a patient with SM and concomitant chronic myelomonocytic leukemia (CMML). LightCycler melting curve analysis and direct sequencing of nested polymerase chain reaction (PCR) products revealed the c-kit mutation in tryptase-positive MC and in leukemic CD15-positive cells in bone marrow infiltrates, but not in colonic epithelial cells, thus, suggesting a monoclonal evolution of SM and concurrent CMML on the basis of a somatic mutation in a common hematologic progenitor.

Mast cell leukemia (MCL) is a rare form of systemic mastocytosis characterized by leukemic expansion of mostly immature mast cells, organ damage, drug-resistance, and a poor prognosis. Even when treated with chemotherapy, most patients have a life-expectancy of less than one year. However, there are rare patients with MCL in whom the condition is less aggressive and does not cause organ damage within a short time. In these patients, mast cells exhibit a more mature morphology when compared to acute MCL. A recently proposed classification suggests that these cases are referred to as chronic MCL. In the present article, we discuss clinical, histopathological and morphological aspects of acute and chronic MCL.

An increase in mast cell (MC) numbers in hemopoietic tissues may be associated with (a) primary neoplastic MC disease (mastocytosis); (b) non-mast cell lineage myelogenous disorders (myelodysplastic or myeloproliferative syndromes and myeloid leukemias); or (c) reactive, i.e. non-clonal states (MC hyperplasia and reactive mastocytosis). However, the histologic discrimination between hyperplastic states and neoplastic MC proliferative disorders is sometimes very difficult. MC hyperplasia is characterized by a diffuse increase in mature, round or spindle-shaped, metachromatic MC that are loosely scattered throughout the tissue and do not form dense focal infiltrates, even in states of marked hyperplasia. However, loosely scattered MC are also a prominent feature of many cases of myelodysplastic syndromes and acute leukemia involving the MC lineage. In contrast, the demonstration of dense, focal and/or diffuse MC infiltrates can be regarded as indicative of primary MC disease/mastocytosis. In addition to the highly diagnostic focal MC infiltrates, mastocytosis may also present with a predominantly diffuse or a mixed (diffuse and focal) infiltration pattern. The relatively rare diffuse pattern is usually dominated by atypical, often hypogranulated or even non-metachromatic MC and is associated with the aggressive or frankly malignant subtypes of systemic mastocytosis and MC leukemia. Although the demonstration of MC infiltrates in Giemsa-stained tissue sections is still very important for the diagnosis of mastocytosis, immunohistochemical techniques using antibodies against MC-associated antigens such as tryptase or c-kit (CD117) are essential for the identification of highly atypical, hypogranulated MC, especially in MC leukemia, and for the detection of small and even minute MC infiltrates.

Three cornerstones of mast cell development are an absolute dependence on the presence of stem cell factor, T-cell-independent and T-cell-dependent tissue mast cell populations derived from a single lineage, and a diversity of phenotypes for mature tissue mast cells as defined by immunohistochemical and biochemical properties. The in vivo biology of the mast cell in the mouse has been deduced through the availability of mice with genetic and induced gene disruptions, whereas limited but compatible findings for the human have been acquired through the study of patients with systemic mastocytosis and T-cell deficiency. The characteristics of mast cells recognized from these in situ circumstances can be used to establish culture systems for obtaining mouse and human mast cells from progenitor cell sources. These cells allow studies of receptor-mediated gene regulation by cytokines derived from both stromal cells and T cells.

Systemic mastocytosis (SM) is a heterogeneous disease, vast majority of these patients have a gain of function mutation in the gene encoding the tyrosine kinase KIT (KIT(D816V)). A small subset of SM patients with KIT(D816V) mutation require cytoreductive therapy. In these patients, tyrosine kinase inhibitors (TKIs) have been actively investigated over the last decade because of codon 816 KIT mutations causing constitutive activation of tyrosine kinase activity of the molecule. The main question has been whether the success story with imatinib in chronic myeloid leukemia (CML), another disease associated with a constitutively active tyrosine kinase, could be mimicked in mastocytosis. However, the results from various TKIs in SM with KIT(D816V) mutation have been disappointing to date. Only a few of the TKIs sufficiently block KIT(D816V) activity and have shown promising clinical results. The data from these studies indicate that, apart from KIT(D816V), other kinase targets and target pathways may play a role in disease evolution and progression, especially in patients with SM with an associated clonal hematological non-mast cell lineage disease (SM-AHNMD). Imatinib is effective in patients with increased mast cells and eosinophils associated with FIP1L1/PDGFRA+ (e.g., myeloid neoplasm with eosinophilia and rearrangement of PDGFRA) or rare patients with SM associated with KIT mutations outside of exon 17. This review will focus on the KIT receptor, KIT mutations, and the effects of the mutations in SM. The preclinical and clinical activities of FDA approved TKIs (for CML) as well as novel TKIs in SM will be evaluated.

Dasatinib has been reported to potently inhibit juxtamembrane domain mutant KIT(D816V) autophosphorylation and KIT-dependent activation of down stream signaling important for cell growth and survival of neoplastic cells. Additionally, dasatinib induced apoptosis in mast cell and leukemia cell lines expressing KIT(D816V). Here, we present the first case report of long-term hematologic and molecular remission achieved with combined treatment with chemotherapy and dasatinib in a patient with systemic mastocytosis (SM) and acute myeloid leukemia (AML) with mutant KIT(D816V) expression. A 50-year-old male presented with pancytopenia, organomegaly, lymphadenopathy, and lytic bone lesions in the pelvis. The patient was found to have systemic mastocytosis (SM) and acute myelogeneous leukemia (AML) positive for KIT(D816V) and therefore diagnosed with SM with an associated clonal hematological non-mast cell lineage disease (SM-AHNMD). Both primary CD34+ cells containing myeloblasts and CD34- cells containing mastocytes obtained from the diagnostic BM lost viability markedly by in vitro dasatinib treatment. In addition, dasatinib diminished activity of STAT5, STAT3, AKT and ERK and attenuated the levels of c-KIT. The patient achieved a hematologic complete remission (HCR) by two induction chemotherapies with residual mastocytes. Dasatinib (70mg PO bid, days 1-4) was added to consolidation treatments composed of four cycles of high dose cytarabine and was then continued as maintenance therapy (50mg PO bid). Periodic bone marrow (BM) aspirate/biopsies (eight over 18 months) were performed. The patient remained in HCR, and the mastocyte burden decreased by 50%. The bone lytic lesions improved. The KIT(D816V)mutation progressively decreased and became undetectable in the last three BM analyses. This result was confirmed by an independent laboratory showing a lack of c-KIT mutation in both CD34+ cells and CD34- cells in the last BM. No significant adverse effects of dasatinib occurred. Dasatinib has in vitro and in vivo efficacy in SM-AML patients with KIT(D816V) mutation. Along with chemotherapy, dasatinib should be considered in these patients particularly if they cannot undergo allogeneic stem cell transplantation for this poor prognostic AML.

Systemic mastocytosis (SM) comprises a heterogeneous group of disorders characterized by infiltration of bone marrow and other tissues by neoplastic mast cells. A subset of patients with SM has associated hematologic malignancy usually of myeloid origin and comprises an entity termed systemic mastocytosis with associated clonal hematological non-mast cell lineage disease (SM-AHNMD) by the current WHO classification. Reports of clonal lymphoid malignancies associated with SM are rare. We describe a patient who was simultaneously diagnosed with indolent SM and a plasma cell dyscrasia fitting the definition of monoclonal gammopathy of undetermined significance (MGUS). We also discuss the pathologic interaction between the neoplastic mast cells of SM and the lymphoid/plasma cell malignancy when these two entities coexist.

Systemic mastocytosis (SM) may rarely be associated with lymphoproliferative disorders. In such cases, the relationship between the neoplastic mast cells and the malignant lymphocytes remains unclear. We describe a patient with indolent SM whose bone marrow showed evidence of low-grade B-cell lymphoma. By detecting the activating KIT mutation D816V in the microdissected bone marrow mast cells, but not in the neoplastic B-lymphocytes, we demonstrate the distinct clonal origins of the mastocytosis and lymphoma when these two entities coexist. We also highlight the clinical and pathologic differences between SM associated with lymphoid as opposed to myeloid neoplasms and discuss their pathogenesis.

In systemic mastocytosis with associated clonal, hematological non-mast cell lineage disease (SM-AHNMD), mast cell infiltration of the bone marrow coexists with a hematologic neoplasm, usually of myeloid origin. Activating KIT gene mutations are universally present in these neoplastic mast cells. When SM is associated with AML, the leukemic cells commonly carry the t(8;21)(q22;q22) core binding factor translocation. The precise relationship between neoplastic mast cells and the leukemic clone has remained unclear. By target FISH analysis, we demonstrate t(8;21) in the bone marrow mast cells of a patient with systemic mastocytosis associated with t(8;21) AML, thus, proving the origin of these neoplastic mast cells from the leukemic clone. We also show that after successful allogeneic hematopoietic stem cell transplantation, these neoplastic bone marrow mast cells can persist without adverse consequences and gradually decline with time.

Aggressive systemic mastocytosis (ASM) is a hematopoietic neoplasm characterized by infiltration of visceral organs by neoplastic mast cells (MCs) with consecutive organopathy and respective clinical and laboratory findings (so called C-Findings). Whereas, it is generally appreciated that patients with ASM are candidates for pharmacological intervention, no ideal drug or drug combination have been identified yet. One drug proposed to work in ASM is interferon alpha-2b (IFN-alpha2b). However, little is known so far about the quality of responses to IFN-alpha2b and actual response rates. We here report on five ASM patients treated with either a combination of IFN-alpha2b (3x3 million units per week) and prednisolone (n=4), or IFN-alpha2b alone (n=1). During therapy, two of the five patients showed a major response defined by complete resolution of C-Finding(s), one a partial response (partial regression of C-Findings), and one a stable disease (no changes in C-Findings). In one patient, progression to mast cell leukemia was seen after 3 months. In contrast to the other patients, this patient exhibited10% MCs in his bone marrow (bm) smear at first presentation. In summary, our data confirm beneficial effects of IFN-alpha2b (plus prednisolone) for a group of patients with ASM, whereas patients with mast cell leukemia may require more aggressive therapy. Prospective trials with more patients are now required to further document these drug effects and to better define subgroups of patients with ASM who show good and long-lasting responses to IFN-alpha2b.

Twenty to thirty-three percent of systemic mast cell disease (SMCD) patients have some degree of peripheral blood and/or bone marrow eosinophilia. While the clonality of SMCD was established by identification of the pathogenic c-kit Asp816 to Val (D816V) mutation in sorted cells of different hematopoietic lineages, this mutation has not previously been demonstrated in eosinophils from SMCD patients. In the current study, we demonstrate the D816V mutation in purified eosinophils from two patients with aggressive, eosinophilia-associated SMCD, thus proving that the eosinophils are clonal and not reactive in nature. The clinical implications of this finding are discussed.

The aberrant co-expression of CD2 and CD25 antigens is the immunophenotypic hallmark of neoplastic mast cells, and has been consistently identified on bone marrow mast cells from patients with indolent mast cell disease (MCD). We prospectively analyzed the bone marrow mast cell immunophenotype by multiparametric flow cytometry (FC) for 33 MCD cases, to examine the role of CD2 and CD25 expression in establishing diagnosis, detecting histologically occult bone marrow mast cell infiltration, and assessing treatment response. While CD25 was almost uniformly expressed, only 6 of 13 patients with indolent MCD, 1 of 8 with aggressive MCD, 2 of 7 with MCD and an associated hematological disorder, and none of the 2 patients with either mast cell leukemia or smoldering systemic mastocytosis, expressed CD2. One of three patients with cutaneous mastocytosis had an aberrant CD2+/CD25+ mast cell population suggesting histologically occult bone marrow involvement. CD25 expression was lost in one patient who achieved complete histologic remission with therapy, but not in two patients who achieved a partial remission. In conclusion, CD25, but not CD2, is a reliable marker for neoplastic mast cells, and CD25 expression indicates histologically occult bone marrow infiltration and residual disease after therapy.

Mutations of Kit at position D816 have been implicated in mastocytosis, acute myeloid leukaemia and germ cell tumours. Expression of this mutant Kit in cell lines results in factor-independent growth, differentiation and increased survival in vitro and tumourigenicity in vivo. Mutant D816VKit and wild-type Kit were expressed in murine primary haemopoietic cells and grown in stem cell factor (SCF) or the absence of factors. Expression of D816VKit did not lead to transformation as assessed by a colony assay, but resulted in enhanced differentiation of cells when compared to control cells. D816VKit induced an increase in the number of cells differentiating along the megakaryocyte lineage in the absence of factors. SCF had an added effect with an increase in differentiation of mast cells. Expression of wild-type Kit in the presence of SCF also failed to cause transformation and induced differentiation of mast cells and megakaryocytes. We conclude that constitutive expression of D816VKit in primary haemopoietic cells is not a sufficient transforming stimulus but leads to the survival and maturation of cells whose phenotype is influenced by the presence of SCF.

Systemic mastocytosis (SM) is a clonal hematologic disease showing abnormal growth and accumulation of mast cells (MC) in visceral organs with or without skin involvement. The clinical course in SM is variable. In fact, indolent and aggressive variants have been described. In addition, SM patients may acquire an associated hematologic clonal non-MC lineage disease (AHNMD). In some cases, hematologic parameters are indicative of slowly progressing SM although the clinical course remains indolent over years. These cases have been referred to as smouldering SM. We report on a smouldering patient presenting with typical skin lesions, hypercellular marrow with focal MC aggregates, persistent leukocytosis (20,000-30,000/microl) with eosinophilia (5-10%), marked lymphadenopathy, and splenomegaly. The C-KIT mutation Asp-816-Val confirmed the diagnosis of SM. The clinical picture remained stable during an observation period of 10 years without signs of progression to an AHNMD or a high grade MC disease. These data show that some patients with SM can remain in a clinically indolent smouldering state over years even when presenting with marked eosinophilia and lymphadenopathy.

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

Mastocytosis is a term used for a group of disorders characterized by abnormal growth and accumulation of tissue mast cells (MC) in one or more organ systems. In patients with systemic mastocytosis (SM) the clinical course may be indolent or aggressive or even complicated by leukemic progression or an associated clonal hematologic non mast cell lineage disease (AHNMD). However, at first presentation (diagnosis) it may be difficult to define the category of disease and the prognosis. We report on a 48-year-old female patient with SM with urticaria pigmentosa-like skin lesions and mediator-related symptoms. She was found to have splenomegaly, a high infiltration grade (MC) in bone marrow biopsies (>30%), mild anemia, and a high serum tryptase level (>500 ng/ml). In addition, she exhibited discrete histologic signs of myeloproliferation in the 'non-affected' marrow and monoclonal blood cells established by C-KIT 2468A-->T mutation (Asp-816-Val) -analysis and HUMARA assay. Despite these findings, however, the clinical course was stable over years and no AHNMD or organ impairment developed. Because of the 'intermediate' clinical signs and absence of progression to aggressive disease, we proposed the term 'smouldering mastocytosis'.

A 43-year-old man with extensive systemic mastocytosis with poor prognostic indicators but no overt hematologic abnormality is described. This patient's clinical presentation and course are consistent with the newly proposed ‘smoldering mastocytosis’ category. Long-term follow-up of patients is needed to determine whether they may be at higher risk for progression into more aggressive categories.