Validation of dermatopathological criteria to diagnose cutaneous lesions of mastocytosis: importance of KIT D816V mutation analysis.

BACKGROUND: Cutaneous lesions of mastocytosis (CLM) are often subtle and may require biopsy. However, dermatohistopathological criteria for CLM remain undefined. OBJECTIVES: To establish criteria for CLM by validating histological and molecular parameters. METHODS: In skin samples from Caucasian patients with CLM and controls (atopic dermatitis, chronic urticaria, pruritus, tissue from tumor safety margin excisions), mast cell (MC) numbers, size, shape, distribution, immunostainability with a large panel of markers, pigmentation and presence of KIT D816V mutation were analysed. RESULTS: Forty-seven CLM patients (32 maculopapular cutaneous mastocytosis (MPCM), 15 mastocytomas) and 36 controls were included. Mastocytomas were easily identified by densely packed cuboidal MCs. In MPCM, skin MC density in CD117 stains was higher in CLM patients than in controls (P < 0.0001) and values correlated closely (r = 0.65, P < 0.0001) to results in tryptase stains. The optimized upper dermis cut-off number of 62 MC/mm2 had a sensitivity and specificity of 92% in both stainings, corresponding to approximately 12 MC/high power field (HPF). MC size was larger in MPCM than in controls (P = 0.01). Interstitial (= not perivascular or periadnexal) MCs and stronger basal pigmentation of the epidermis were indicative of MPCM (P < 0.0001 each) and clusters of >3 nucleated MC/HPF exclusively found in MCPM. Surface markers CD2, CD25 and CD30 stained T-lymphocytes, but only negligibly CLM MC. The KIT D816V mutation in formalin fixed paraffin embedded (FFPE) skin was evaluable in 87.5% of MCPM patients and had both 100% sensitivity and specificity. CONCLUSIONS: MPCM can be predicted by major and minor criteria combined in a scoring model. Presence of D816V mutation in FFPE skin and MC density > 27/HPF are >95%-specific major criteria for MPCM. MC densities 12/HPF, interstitial MC, clusters and basal pigmentation are minor criteria.

Drug-induced inhibition of phosphorylation of STAT5 overrides drug resistance in neoplastic mast cells.

Systemic mastocytosis (SM) is a mast cell (MC) neoplasm with complex pathology and a variable clinical course. In aggressive SM (ASM) and MC leukemia (MCL), responses to conventional drugs are poor and the prognosis is dismal. R763 is a multi-kinase inhibitor that blocks the activity of Aurora-kinase-A/B, ABL1, AKT and FLT3. We examined the effects of R763 on proliferation and survival of neoplastic MC. R763 produced dose-dependent inhibition of proliferation in the human MC lines HMC-1.1 (IC50 5-50 nM), HMC-1.2 (IC50 1-10 nM), ROSAKIT WT (IC50 1-10 nM), ROSAKIT D816V (IC50 50-500 nM) and MCPV-1.1 (IC50 100-1000 nM). Moreover, R763 induced growth inhibition in primary neoplastic MC in patients with ASM and MCL. Growth-inhibitory effects of R763 were accompanied by signs of apoptosis and a G2/M cell cycle arrest. R763 also inhibited phosphorylation of KIT, BTK, AKT and STAT5 in neoplastic MC. The most sensitive target appeared to be STAT5. In fact, tyrosine phosphorylation of STAT5 was inhibited by R763 at 10 nM. At this low concentration, R763 produced synergistic growth-inhibitory effects on neoplastic MC when combined with midostaurin or dasatinib. Together, R763 is a novel promising multi-kinase inhibitor that blocks STAT5 activation and thereby overrides drug-resistance in neoplastic MC.

Midostaurin: a magic bullet that blocks mast cell expansion and activation.

Clinically relevant features in patients with systemic mastocytosis (SM) include the cosmetic burden of lesional skin, mediator-related symptoms, and organ damage resulting from mast cell (MC) infiltration in advanced forms of SM. Regardless of the SM variant, expansion of neoplastic MC in the skin and other organs is triggered by mutant forms of KIT, the most prevalent being D816V. Activation of MC with subsequent release of chemical mediators is often caused by IgE-dependent mechanisms in these patients. Midostaurin, also known as PKC412, blocks the kinase activity of wild-type KIT and KIT D816V, counteracts KIT-dependent growth of neoplastic MC, and inhibits IgE-dependent mediator secretion. Based on this activity-profile, the drug has been used for treatment of patients with advanced SM. Indeed, encouraging results have been obtained with the drug in a recent multi-center phase II trial in patients with advanced SM, with an overall response rate of 60% and a substantial decrease in the burden of neoplastic MC in various organs. Moreover, midostaurin improved the overall survival and relapse-free survival in patients with advanced SM compared with historical controls. In addition, midostaurin was found to improve mediator-related symptoms and quality of life, suggesting that the drug may also be useful in patients with indolent SM suffering from mediator-related symptoms resistant to conventional therapies or those with MC activation syndromes. Ongoing and future studies will determine the actual value of midostaurin-induced MC depletion and MC deactivation in these additional indications.

Proposed diagnostic criteria and classification of basophilic leukemias and related disorders.

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

Splenomegaly, elevated alkaline phosphatase and mutations in the SRSF2/ASXL1/RUNX1 gene panel are strong adverse prognostic markers in patients with systemic mastocytosis.

We evaluated the impact of clinical and molecular characteristics on overall survival (OS) in 108 patients with indolent (n=41) and advanced systemic mastocytosis (SM) (advSM, n=67). Organomegaly was measured by magnetic resonance imaging-based volumetry of the liver and spleen. In multivariate analysis of all patients, an increased spleen volume ⩾450 ml (hazard ratio (HR), 5.2; 95% confidence interval (CI), (2.1-13.0); P=0.003) and an elevated alkaline phosphatase (AP; HR 5.0 (1.1-22.2); P=0.02) were associated with adverse OS. The 3-year OS was 100, 77, and 39%, respectively (P<0.0001), for patients with 0 (low risk, n=37), 1 (intermediate risk, n=32) or 2 (high risk, n=39) parameters. For advSM patients with fully available clinical and molecular data (n=60), univariate analysis identified splenomegaly ⩾1200 ml, elevated AP and mutations in the SRSF2/ASXL1/RUNX1 (S/A/R) gene panel as significant prognostic markers. In multivariate analysis, mutations in S/A/R (HR 3.2 (1.1-9.6); P=0.01) and elevated AP (HR 2.6 (1.0-7.1); P=0.03) remained predictive adverse prognostic markers for OS. The 3-year OS was 76 and 38%, respectively (P=0.0003), for patients with 0-1 (intermediate risk, n=28) or 2 (high risk, n=32) parameters. We conclude that splenomegaly, elevated AP and mutations in the S/A/R gene panel are independent of the World Health Organization classification and provide the most relevant prognostic information in SM patients.

Additional mutations in SRSF2, ASXL1 and/or RUNX1 identify a high-risk group of patients with KIT D816V(+) advanced systemic mastocytosis.

Most patients with KIT D816V(+) advanced systemic mastocytosis (SM) are characterized by somatic mutations in additional genes. We sought to clarify the prognostic impact of such mutations. Genotype and clinical characteristics of 70 multi-mutated KIT D816V(+) advanced SM patients were included in univariate and multivariate analyses. The most frequently identified mutated genes were TET2 (n=33 of 70 patients), SRSF2 (n=30), ASXL1 (n=20), RUNX1 (n=16) and JAK2 (n=11). In univariate analysis, overall survival (OS) was adversely influenced by mutations in SRSF2 (P<0.0001), ASXL1 (P=0.002) and RUNX1 (P=0.03), but was not influenced by mutations in TET2 or JAK2. In multivariate analysis, SRSF2 and ASXL1 remained the most predictive adverse indicators concerning OS. Furthermore, we found that inferior OS and adverse clinical characteristics were significantly influenced by the number of mutated genes in the SRSF2/ASXL1/RUNX1 (S/A/R) panel (P<0.0001). In conclusion, the presence and number of mutated genes within the S/A/R panel are adversely associated with advanced disease and poor survival in KIT D816V(+) SM. On the basis of these findings, inclusion of molecular markers should be considered in upcoming prognostic scoring systems for patients with SM.

Identification of bromodomain-containing protein-4 as a novel marker and epigenetic target in mast cell leukemia.

Advanced systemic mastocytosis (SM) is a life-threatening neoplasm characterized by uncontrolled growth and accumulation of neoplastic mast cells (MCs) in various organs and a poor survival. So far, no curative treatment concept has been developed for these patients. We identified the epigenetic reader bromodomain-containing protein-4 (BRD4) as novel drug target in aggressive SM (ASM) and MC leukemia (MCL). As assessed by immunohistochemistry and PCR, neoplastic MCs expressed substantial amounts of BRD4 in ASM and MCL. The human MCL lines HMC-1 and ROSA also expressed BRD4, and their proliferation was blocked by a BRD4-specific short hairpin RNA. Correspondingly, the BRD4-targeting drug JQ1 induced dose-dependent growth inhibition and apoptosis in HMC-1 and ROSA cells, regardless of the presence or absence of KIT D816V. In addition, JQ1 suppressed the proliferation of primary neoplastic MCs obtained from patients with ASM or MCL (IC50: 100-500 nm). In drug combination experiments, midostaurin (PKC412) and all-trans retinoic acid were found to cooperate with JQ1 in producing synergistic effects on survival in HMC-1 and ROSA cells. Taken together, we have identified BRD4 as a promising drug target in advanced SM. Whether JQ1 or other BET-bromodomain inhibitors are effective in vivo in patients with advanced SM remains to be elucidated.

KIT mutation analysis in mast cell neoplasms: recommendations of the European Competence Network on Mastocytosis.

Although acquired mutations in KIT are commonly detected in various categories of mastocytosis, the methodologies applied to detect and quantify the mutant type and allele burden in various cells and tissues are poorly defined. We here propose a consensus on methodologies used to detect KIT mutations in patients with mastocytosis at diagnosis and during follow-up with sufficient precision and sensitivity in daily practice. In addition, we provide recommendations for sampling and storage of diagnostic material as well as a robust diagnostic algorithm. Using highly sensitive assays, KIT D816V can be detected in peripheral blood leukocytes from most patients with systemic mastocytosis (SM) that is a major step forward in screening and SM diagnosis. In addition, the KIT D816V allele burden can be followed quantitatively during the natural course or during therapy. Our recommendations should greatly facilitate diagnostic and follow-up investigations in SM in daily practice as well as in clinical trials. In addition, the new tools and algorithms proposed should lead to a more effective screen, early diagnosis of SM and help to avoid unnecessary referrals.

Molecular profiling of myeloid progenitor cells in multi-mutated advanced systemic mastocytosis identifies KIT D816V as a distinct and late event.

To explore the molecular profile and its prognostic implication in systemic mastocytosis (SM), we analyzed the mutation status of granulocyte-macrophage colony-forming progenitor cells (CFU-GM) in patients with KIT D816V(+) indolent SM (ISM, n=4), smoldering SM (SSM, n=2), aggressive SM (ASM, n=1), SM with associated clonal hematologic non-mast cell lineage disorder (SM-AHNMD, n=5) and ASM-AHNMD (n=7). All patients with (A)SM-AHNMD (n=12) carried 1-4 (median 3) additional mutations in 11 genes tested, most frequently TET2, SRSF2, ASXL1, CBL and EZH2. In multi-mutated (A)SM-AHNMD, KIT D816V(+) single-cell-derived CFU-GM colonies were identified in 8/12 patients (median 60%, range 0-95). Additional mutations were identified in CFU-GM colonies in all patients, and logical hierarchy analysis indicated that mutations in TET2, SRSF2 and ASXL1 preceded KIT D816V. In ISM/SSM, no additional mutations were detected and CFU-GM colonies were exclusively KIT D816V(-). These data indicate that (a) (A)SM-AHNMD is a multi-mutated neoplasm, (b) mutations in TET2, SRSF2 or ASXL1 precede KIT D816V in ASM-AHNMD,

Proposed diagnostic algorithm for patients with suspected mastocytosis: a proposal of the European Competence Network on Mastocytosis.

Mastocytosis is an emerging differential diagnosis in patients with more or less specific mediator-related symptoms. In some of these patients, typical skin lesions are found and the diagnosis of mastocytosis can be established. In other cases, however, skin lesions are absent, which represents a diagnostic challenge. In the light of this unmet need, we developed a diagnostic algorithm for patients with suspected mastocytosis. In adult patients with typical lesions of mastocytosis in the skin, a bone marrow (BM) biopsy should be considered, regardless of the basal serum tryptase concentration. In adults without skin lesions who suffer from mediator-related or other typical symptoms, the basal tryptase level is an important parameter. In those with a slightly increased tryptase level, additional investigations, including a sensitive KIT mutation analysis of blood leucocytes or measurement of urinary histamine metabolites, may be helpful. In adult patients in whom (i) KIT D816V is detected and/or (ii) the basal serum tryptase level is clearly increased (>25-30 ng/ml) and/or (iii) other clinical or laboratory features suggest the presence of 'occult' mastocytosis or another haematologic neoplasm, a BM investigation is recommended. In the absence of KIT D816V and other signs or symptoms of mastocytosis or another haematopoietic disease, no BM investigation is required, but the clinical course and tryptase levels are monitored in the follow-up. In paediatric patients, a BM investigation is usually not required, even if the tryptase level is increased. Although validation is required, it can be expected that the algorithm proposed herein will facilitate the management of patients with suspected mastocytosis and help avoid unnecessary referrals and investigations.

Refined diagnostic criteria and classification of mast cell leukemia (MCL) and myelomastocytic leukemia (MML): a consensus proposal.

Mast cell leukemia (MCL), the leukemic manifestation of systemic mastocytosis (SM), is characterized by leukemic expansion of immature mast cells (MCs) in the bone marrow (BM) and other internal organs; and a poor prognosis. In a subset of patients, circulating MCs are detectable. A major differential diagnosis to MCL is myelomastocytic leukemia (MML). Although criteria for both MCL and MML have been published, several questions remain concerning terminologies and subvariants. To discuss open issues, the EU/US-consensus group and the European Competence Network on Mastocytosis (ECNM) launched a series of meetings and workshops in 2011-2013. Resulting discussions and outcomes are provided in this article. The group recommends that MML be recognized as a distinct condition defined by mastocytic differentiation in advanced myeloid neoplasms without evidence of SM. The group also proposes that MCL be divided into acute MCL and chronic MCL, based on the presence or absence of C-Findings. In addition, a primary (de novo) form of MCL should be separated from secondary MCL that typically develops in the presence of a known antecedent MC neoplasm, usually aggressive SM (ASM) or MC sarcoma. For MCL, an imminent prephase is also proposed. This prephase represents ASM with rapid progression and 5%-19% MCs in BM smears, which is generally accepted to be of prognostic significance. We recommend that this condition be termed ASM in transformation to MCL (ASM-t). The refined classification of MCL fits within and extends the current WHO classification; and should improve prognostication and patient selection in practice as well as in clinical trials.

Predictors of clinical effectiveness of Hymenoptera venom immunotherapy.

BACKGROUND: Treatment failure during venom immunotherapy (VIT) may be associated with a variety of risk factors, of which the relative importance is unknown. OBJECTIVE: Our aim was to evaluate the association of baseline serum tryptase concentration (BTC), mastocytosis in the skin (MIS) and of other parameters with the frequency of objective systemic reactions during in-hospital sting challenge (SC). METHODS: In this observational retrospective study, we enrolled 1532 patients (1609 cases due to double SC) with established honeybee or vespid venom allergy who had undergone VIT and a subsequent SC. Data were collected on various putative risk factors. Adult-onset MIS and/or a BTC > 20.0 µg/L was defined as clinical indicators of systemic mastocytosis. Relative rates were calculated with logistic regression models. RESULTS: Ninety-eight patients (6.4%) presented with MIS and/or BTC > 20.0 µg/L. 104 cases (6.5%) developed objective generalized symptoms during SC. In the absence of MIS, a BTC ≤ 20 µg/L did not increase the risk for VIT failure. The most important factors associated with a worse outcome were ACE inhibitor medication (OR 5.24, 95% CI 1.83-13.00, P < 0.001), honeybee venom allergy (OR 5.09, 95% CI 3.17-8.15, P < 0.001), systemic allergic reaction during VIT (OR 3.07, 95% CI 1.79-5.14, P < 0.001), and a substantial likelihood to suffer from SM (OR 2.74, 95% CI 1.37-5.22, P = 0.003), whereas a double VIT (OR 0.51, 95% CI 0.27-0.90, P = 0.027) and a longer duration of therapy (OR 0.68 per treatment month, 95% CI 0.50-0.93, P = 0.017) reduced the failure rate. CONCLUSION: The magnitude of therapeutic success correlates with type of venom, duration of therapy, and venom dose. Adult-onset MIS and/or a BTC > 20 µg/L is a significant, albeit not the strongest determinant for VIT failure. According to its odds ratio, ACE inhibitor therapy appears to be associated with the highest risk for VIT failure.

Prognostic impact of blast cell counts in dysplastic bone marrow disorders (MDS and CMML I) with concomitant fibrosis.

In a retrospective study, 43 patients with dysplastic neoplasms of the bone marrow (myelodysplastic syndromes and myelodysplastic/myeloproliferative-overlap neoplasms) associated with marked (grades 2-3) fibrosis were examined. Histopathologic and morphologic findings as well as cytogenetic and molecular results were correlated with clinical endpoints. Multilineage dysplasia (34 of 43 patients, 79 %) and hypercellular bone marrow (64 %) were found in most patients. In ten of 35 patients, poor risk karyotypes according to the International Prognostic Scoring System (IPSS) were recorded. The JAK2 V617F mutation was detected in four of 30 patients (13 %), and the KIT D816V mutation was found in two of 30 patients (6 %). Patients were mainly treated with palliative drugs and best supportive care. After an observation time of 1-41 (median 21) months, ten of 43 patients (23 %) had developed a secondary acute leukemia. The median survival of all 43 patients was 21.4 months (range 1.8-88.2 months). Of all prognostic parameters examined, the blast cell count at diagnosis was found to be a most reliable and most predictive marker concerning survival and leukemia progression. This confirms previous studies in dysplastic bone marrow neoplasms without fibrosis.

Oncostatin M is a FIP1L1/PDGFRA-dependent mediator of cytokine production in chronic eosinophilic leukemia.

BACKGROUND: Chronic eosinophilic leukemia (CEL) is a myeloproliferative neoplasm characterized by expansion of neoplastic eosinophils, tissue infiltration, and organ damage. In a subset of these patients, the FIP1L1/PDGFRA (F/P) oncoprotein is detectable. F/P exhibits constitutive tyrosine kinase activity and activates a number of signaling pathways. So far, however, little is known about the role of F/P-dependent proteins in the pathogenesis of CEL. METHODS: A screen for F/P-dependent cytokines was performed in growth factor-dependent human cell lines lentivirally transduced with F/P. Signal transduction pathways were characterized in Ba/F3 cells with doxycycline-inducible expression of F/P and in EOL-1 cells. Cytokine expression was confirmed in patients' material by immunohistochemistry, immunofluorescence, and confocal microscopy. Gene expression analysis, proliferation assays, and chemotaxis assays were used to elucidate paracrine interactions between neoplastic eosinophils and stromal cells. RESULTS: We show that F/P upregulates expression of oncostatin M (OSM) in various cell line models in a STAT5-dependent manner. Correspondingly, neoplastic eosinophils in the bone marrow were found to overexpress OSM. OSM derived from F/P + cells stimulated proliferation of stromal cells. Moreover, OSM-containing supernatants from F/P + cells were found to upregulate production of stromal cell-derived factor-1 (SDF-1)/CXCL12 in human fibroblasts. SDF-1, in turn, induced migration of EOL-1 cells in a dose-dependent manner. CONCLUSIONS: We have identified a F/P-driven paracrine interaction between neoplastic eosinophils and stromal cells that may contribute to tissue fibrosis and accumulation of neoplastic eosinophils in CEL.

[Mastocytosis and eosinophilic leukemia: diagnostics and classification]. / Mastozytosen und myeloische Neoplasien mit Eosinophilie: Diagnostik und Klassifikation.

Mastocytosis and myeloid eosinophilic neoplasms are rare diseases of the bone marrow and are often a diagnostic challenge for hematopathologists. In mastocytosis, compact mast cell infiltrates represent the main diagnostic criterion and for myeloid eosinophilic neoplasms, eosinophilic granulocytes dominate the histological picture. Both disease groups include phenotypically and prognostically very different entities which are each defined by WHO criteria. For systemic mastocytosis (SM), a differentiation between indolent and aggressive or even leukemic forms is of prognostic importance. In indolent variants of SM, a local and/or systemic, usually reactive increase in eosinophilic granulocytes (SM-eo) is often observed. In contrast, an increase in neoplastic eosinophils is often observed in advanced SM, predominantly in diseases designated SM with associated non-mastocytic hematological neoplasms (SM-AHNMD), e.g. in SM with chronic eosinophilic leukemia (SM-CEL). Apart from mastocytoses, immunophenotypically aberrant tissue mast cells are only observed in certain rare forms of myeloid neoplasms with eosinophilia, in particular in myeloproliferative neoplasms (MPN-eo) with cytogenic anomalies in the platelet-derived growth factor receptor (PDGFR). The World Health Organization (WHO) classification of eosinophilic leukemias, however, fulfils the morphological and clinical requirements in a limited way only and needs an update.

Systemic mastocytosis: progressive evolution of an occult disease into fatal mast cell leukemia: unique findings on an unusual hematological neoplasm.

Systemic mastocytosis (SM) may be associated with a clonal hematopoietic non-mast cell-lineage disease (AHNMD). SM and AHNMD even may be clonally related. This report contributes to a better understanding of the different morphological aspects of SM by demonstrating that various AHNMDs can be detected in one patient during the course of disease. Routinely processed biopsy specimens of bone marrow and spleen removed from a 63-year-old man were investigated including a broad panel of immunohistochemical stainings. KIT codon 816 mutation analysis was carried out by melting point analysis of nested PCR products amplified from DNA of pooled microdissected mast cells. The histomorphological features of the initial bone marrow showed diffuse infiltration by hairy cell leukemia (HCL). Occult SM was only detected retrospectively by demonstration of a slight diffuse increase in loosely scattered, spindle-shaped mast cells carrying the activating point mutation KIT ( D816V ). In the second bone marrow, core biopsy removed about two years later HCL had been completely eradicated, while a diagnosis of SM-AHNMD with multifocal compact mast cell infiltrates associated with a myeloproliferative neoplasm (MPN) and significant increase in eosinophilic granulocytes was established. The third and last bone marrow biopsy specimen lacked the features of both MPN and HCL but showed progression into a secondary mast cell leukemia (MCL) with a focal sarcomatous component. To the best of the authors' knowledge, this is the first description of a case of SM-AHNMD with coexisting hematological neoplasms of lymphatic and myeloid origin initially presenting as occult disease and terminating as secondary MCL.

Evaluation of mast cell activation syndromes: impact of pathology and immunohistology.

Mast cell activation syndromes (MCAS) are clinically defined disease states with a largely unknown morphological background. Since mastocytosis may be associated with MCAS, it is crucial in every patient to document or exclude mastocytosis by appropriate histological, molecular, and serological investigations of tissues/organs that are commonly involved in mastocytosis like skin, mucosa of the gastrointestinal tract and bone marrow. Accordingly, histopathological investigation including immunohistological stains is crucial to reach the final diagnosis in such patients and to classify MCAS into primary MCAS, which can present with or without evidence of overt mastocytosis, or secondary MCAS, where an underlying disease with or without tissue inflammation is detected. Cases without evidence of mastocytosis, monoclonal mast cells, or any underlying disease should be termed idiopathic MCAS. When the activating point mutant KIT D816V is detectable but criteria for diagnosis of mastocytosis are not completely met, a so-called (mono)clonal MCAS as a subvariant of primary MCAS should be diagnosed.

Differential diagnoses of systemic mastocytosis in routinely processed bone marrow biopsy specimens: a review.

Diagnosis of systemic mastocytosis (SM) is mainly based on the morphological demonstration of compact mast cell infiltrates in various tissue sites. In almost all patients such infiltrates are detected in the bone marrow. Reliable immunohistochemical markers for the diagnosis and grading of SM have been established, but various differential diagnoses including myeloproliferative neoplasms, basophilic and eosinophilic leukemias may be very difficult to delineate. Even more challenging is the recognition of hematological neoplasms with signs of mast cell differentiation but not fulfilling diagnostic criteria for SM, especially the rare myelomastocytic leukemia. It is also important to separate the reactive state of mast cell hyperplasia from indolent variants of SM, especially those with a very low degree of bone marrow infiltration and absence of compact mast cell infiltrates. When the lymphocytic component of the SM infiltrate is very prominent, SM may be confused with an indolent lymphoma, especially lymphoplasmacytic lymphoma which almost always shows a marked reactive increase in mast cells. In aggressive and leukemic variants of SM, mast cells may be very atypical and devoid of metachromatic granules. This hypogranulation can be regarded as cellular atypia and may lead to the misdiagnosis aspect of monocytic leukemia or histiocytic neoplasm. Regarding immunohistochemical anomalies, mast cells in aggressive and leukemic SM have been found to express CD30 (Ki1-antigen). Thus, anaplastic large cell lymphoma or Hodgkin's disease may first be considered rather than SM. There is increasing evidence that most patients with long-standing adult-type urticaria pigmentosa-like skin lesions have in fact indolent SM. Therefore, such skin lesions are an important clue to the correct diagnosis in these patients. However, in aggressive or leukemic SM skin lesions are usually absent and then the correct diagnosis relies on an appropriate investigation of bone marrow biopsy specimens using both SM-related immunohistochemical markers (tryptase, KIT, CD25, CD30) but also markers excluding potential differential diagnoses. Investigation for presence of the activating KIT point mutation D816V is very helpful to establish a correct diagnosis of SM in all the difficult cases exhibiting a low degree of bone marrow infiltration or puzzling morphological findings.

KIT(D816V+) systemic mastocytosis associated with KIT(D816V+) acute erythroid leukaemia: first case report with molecular evidence for same progenitor cell derivation.

A case of systemic mastocytosis associated with a clonal haematological non-mast cell lineage disease (SM-AHNMD), where the associated disease is acute erythroid leukaemia (erythroid/myeloid type), is reported. Interestingly, molecular studies showed the KIT(D816V+) mutation not only in the mast cells, but also in the myeloid blast population and the leukaemic erythroid cells. As is the case with most erythroid leukaemias, the patient had a very aggressive clinical course and died shortly after diagnosis. It is believed that this is the first reported case of systemic mastocytosis with erythroid leukaemia where the KIT(D816V+) mutation was detected in all three cell types. Molecular findings provide evidence for derivation of these seemingly morphologically distinct lesions from the same clonal precursor cell. From a practice standpoint, this case illustrates the importance of definitively diagnosing the associated non-mast cell lineage disease due to its prognostic implications.