Bone Marrow Mast Cell Infiltration Research Articles

Predicting the Clinical Course of Treatment with Midostaurin in Patients with Advanced Systemic Mastocytosis

Introduction: Advanced systemic mastocytosis (AdvSM) is characterized by presence of the KIT D816V mutation and variably other somatic mutations in the mast cell but also non-mast cell lineages, e.g. monocytes or eosinophils, in ≥80-90% of patients. Midostaurin is an approved multikinase/KIT inhibitor for treatment of AdvSM. The intricate landscape in assessment of response, resistance or progression, the occurrence of adverse events with its impact on dose modification and the recent approval of the specific KIT D816V inhibitor avapritinib contribute to complex decision-making. We here sought to characterize the most valuable baseline and on-treatment parameters for prediction of response and survival in midostaurin-treated patients with AdvSM. Methods: On basis of the ´German Registry on Disorders of Eosinophils and Mast Cells' (GREM), this retrospective-prospective analysis included 79 patients with AdvSM. Treatment was initiated between 2009 and 2022 accumulating into a 239 patient-years overall follow-up period. In addition to common serological, morphological, and molecular response parameters, we specifically examined the recurrent observation of an early flare-up in alkaline phosphatase (AP) levels, which was defined as a ≥25% AP increase within three months after treatment initiation, followed by a subsequent decline below baseline within six months. Results: Midostaurin was used in first-line (1L) or second and further lines (2L+; median 1 prior treatment line, range 0-4) in 63 (80%) and 16 (20%) patients, respectively. In 1L/2L+, median overall survival (OS) was 2.6/2.4 years. At baseline, the presence of additional somatic mutations in SRSF2 (n=36, 46%, HR 2.0 [1.2-3.6], P=0.014), ASXL1 (n=15, 19%, HR 2.0 [1.0-3.9], P=0.043), and EZH2 (n=6, 8%, HR 4.3 [1.7-11.3], P=0.003) significantly stratified patients according to their hazard ratio-weighted risk (median OS, 5.8 vs. 2.9 vs. 1.0 years; P<0.001). In 25 evaluable patients, the variant allele frequency in 72 additional somatic mutations remained stable (mean change 8%, absolute change >5% in 16/72 (22%) mutations). New mutations were identified in 9/25 (36%) patients during follow-up (Figure). Durable responses (complete, partial, clinical improvement) according to modified Valent criteria, IWG-MRT-ECNM criteria or Pure Pathological Response (PPR) criteria over a median duration between 12 and 24 months were achieved in 60%, 29% and 13% of patients, respectively. Within the first 12 months, duration of response was associated with an OS benefit ( P<0.001). An AP flare-up was observed in 22/79 (28%) patients, was paralleled by contemporaneous decrease of serum tryptase (median -35%, range -82 - 191%) and resulted into improved OS (median 5.8 vs. 2.2 years, P=0.007). Multivariable analysis identified the AP flare-up ( P=0.029), a ≥25% reduction of bone marrow (BM) mast cell (MC) infiltration ( P=0.046) and a ≥25% reduction of the KIT D816V expressed allele burden (EAB; P=0.034) at any time within the first 6 months as independent markers for improved OS (Table). Dynamic risk assessment of the independent parameters during follow-up allowed to abrogate a negative baseline risk-categorization. The initial dose was 200 mg/d (100 mg BID, including patients with a prespecified rapid dose escalation), 150 mg/d or 100 mg/d in 63/79 (80%), 2/79 (3%) and 14/79 (18%) patients, respectively. In the combined 150 mg and 100 mg cohorts, a dose increase to 200 mg/day was achieved in 9/16 (56%) patients. The 200 mg could be maintained at month 3, 6, 12, 24, and 36 in 50/63 (79%), 30/48 (63%), 23/34 (68%), 15/22 (68%) and 9/9 (100%) patients, respectively. Overall, 96 adverse events (AE) led to dose-adjustment (including temporary or permanent discontinuation). Hematologic and nonhematologic toxicities accounted for 24 (25%) and 36 (38%) of AEs with neutropenia (n=8, 8%) and nausea/emesis (n=22, 22%) being the most common AEs leading to dose-adjustment. Of note, the various dose levels had no impact on response or survival. Conclusions: Baseline mutations in SRSF2, ASXL1 and EZH2 conferred resistance to midostaurin. The various dose levels had no impact on response or survival. The on-treatment parameters AP flare-up, and a ≥25% reduction of BM MC infiltration and of KIT D816V EAB abrogated a negative baseline risk-categorization. No new safety signals occurred.

Proteomic and transcriptomic screening demonstrates increased mast cell–derived CCL23 in systemic mastocytosis

Systemic mastocytosis (SM) is a heterogeneous group of mast cell-driven diseases diagnosed by bone marrow sampling. However, there are a limited number of available blood disease biomarkers. Our aim was to identify mast cell-derived proteins that could potentially serve as blood biomarkers for indolent and advanced forms of SM. We performed a plasma proteomics screening coupled with single-cell transcriptomic analysis in SM patients and healthy subjects. Plasma proteomics screening identified 19 proteins upregulated in indolent disease compared to healthy, and 16 proteins in advanced disease compared to indolent. Among these, 5 proteins, CCL19, CCL23, CXCL13, IL-10, and IL-12Rβ1, were higher in indolent relative to healthy and in advanced disease compared to indolent. Single-cell RNA sequencing demonstrated that CCL23, IL-10, and IL-6 were selectively produced by mast cells. Notably, plasma CCL23 levels correlated positively with known markers of SM disease severity, namely tryptase levels, percentage bone marrow mast cell infiltration, and IL-6. CCL23 is produced predominantly by mast cellsin SM, and CCL23 plasma levels are associated withdisease severity, correlating positively with established markers ofdisease burden, thus suggesting that CCL23 is a specificSMbiomarker. In addition, the combination of CCL19, CCL23, CXCL13, IL-10, and IL-12Rβ1 may be useful fordefining disease stage.

Efficacy and safety of avapritinib in previously treated patients with advanced systemic mastocytosis

AbstractAdvanced systemic mastocytosis (AdvSM) is a rare myeloid neoplasm, driven by the KIT D816V mutation in >90% of patients. Avapritinib, a potent, highly selective D816V-mutant KIT inhibitor, is approved for treatment of adults with AdvSM by the US Food and Drug Administration, regardless of prior therapy, and the European Medicines Agency for patients with prior systemic therapy, based on EXPLORER (#NCT02561988; clinicaltrials.gov) and PATHFINDER (#NCT03580655; clinicaltrials.gov) clinical studies. We present latest pooled efficacy and safety analyses from patients who received ≥1 systemic therapy prior to avapritinib in EXPLORER/PATHFINDER. Overall response rate in response-evaluable patients (n = 31) was 71% (95% confidence interval: 52% to 86%; 22/31), including 19% (6/31) with complete remission (CR)/CR with partial recovery of peripheral blood counts (CRh). Median time to response was 2.3 months, median time to CR/CRh was 7.4 months, and median duration of response (DOR) was not reached. Reductions ≥50% in bone marrow mast cell infiltration (89%), KIT D816V variant allele fraction (66%), serum tryptase (89%), and reductions ≥35% in spleen size (70%) occurred in most patients. Median OS was not reached (median follow-up 17.7 months). Avapritinib was effective in all AdvSM subtypes, regardless of number/type of prior therapies or poor prognostic somatic mutations. Treatment-related adverse events (TRAEs) were observed in 94% of patients, most commonly grade 1/2; 57% had TRAEs of at least grade 3; 81% remained on treatment at 6 months. Avapritinib in adults with AdvSM who received prior systemic therapy was generally well tolerated, with high response rates regardless of prior systemic therapy.

An increased bone mineral density is an adverse prognostic factor in patients with systemic mastocytosis

PurposeSystemic mastocytosis (SM) is characterized by the expansion of clonal mast cells that infiltrate various organ systems. The extent of organ infiltration and subsequent organ damage distinguishes between indolent SM (ISM) defined by a nearly normal life expectancy and advanced SM (AdvSM) defined by poor prognosis. In ISM, measurement of the bone mineral density (BMD) frequently reveals osteoporosis. In contrast, the clinical implication of an increased BMD and osteosclerosis remains unclear.MethodsBMD was evaluated in 61 patients with mastocytosis (ISM, n = 29, 48%; AdvSM, n = 32, 52%). We correlated the prevalence of osteoporosis, increased BMD and osteosclerosis with clinical parameters, disease variant and prognosis.ResultsOsteoporosis was detected in 11/29 (38%) patients with ISM but only in 2/32 (6%) patients with AdvSM (p = 0.004). An increased BMD was detected in 1/29 (3%) patients with ISM and 24/32 (75%) patients with AdvSM (p < 0.001) while osteosclerosis was only detected in AdvSM patients (16/32, 50%). AdvSM patients with increased BMD had higher levels of bone marrow mast cell infiltration, higher serum tryptase and alkaline phosphatase levels compared to ISM as well as higher number of high-molecular risk mutations (p < 0.05). In addition, we found that the prognosis of AdvSM patients with increased BMD is inferior compared to those without increased BMD (median overall survival 3.6 years versus not reached, p = 0.031).ConclusionsOsteoporosis is a common feature in ISM but not in AdvSM. An increased BMD is frequently present in AdvSM but not in ISM and is associated with more advanced disease and inferior outcome.

An Increased Bone Mineral Density As an Adverse Prognostic Factor in Patients with Systemic Mastocytosis

Systemic mastocytosis (SM) is characterized by expansion of clonal mast cells that infiltrate various organ systems. The extent of organ infiltration and subsequent organ damage distinguishes between indolent SM (ISM) and advanced SM (AdvSM). ISM patients usually present with a low mast cell burden and have a nearly normal life expectancy while AdvSM patients have a high disease burden, multiple organ damage and poor prognosis. In ISM patients, measurement of the bone mineral density (BMD) frequently reveals osteopenia and osteoporosis (lumbar spine BMD T-score of ≤ −2.5 standard deviation [SD]). In contrast, the association between increased BMD and osteosclerosis, respectively, and the various SM subtypes is unclear. We therefore sought to evaluate the BMD in 61 patients (ISM, n = 29, 48%; AdvSM, n = 32, 52%) and correlated the prevalence of osteoporosis, increased BMD and osteosclerosis with clinical parameters and prognosis. All patients were scanned on the same 16 row CT Scanner (SOMATOM Emotion 16, Siemens Healthcare Sector, Forchheim, Germany). The results were expressed as T-score (SD below the mean of young healthy adults) and as Z-score (SD below the age- and gender-matched mean reference value). According to established WHO criteria, osteoporosis was defined as a lumbar spine BMD T-score of ≤ −2.5 SD. Increased BMD and osteosclerosis were defined as Z-score &gt; 1 SD and &gt; 2 SD, respectively. Osteoporosis was detected in 11/29 (38%) patients with ISM and 2/32 (6%) patients with AdvSM (p = 0.004). Bone marrow mast cell infiltration (median 10% versus 20%, p=0.035) and serum tryptase levels (median 31 µg/L versus 58 µg/L, p = 0.047) were significantly lower in ISM patients with osteoporosis as compared to those without osteoporosis (n=18, 62%). No significant differences were seen regarding age, gender, blood counts, and overall survival. An elevated BMD was detected in 1/29 (3%) patient with ISM and 24/32 (75%) patients with AdvSM (p &lt; 0.001) while osteosclerosis was only detected in AdvSM patients (16/32, 50%). AdvSM patients with increased BMD were older (median 77 years versus 68 years, p = 0.0043), had lower platelet counts (median 111 x 109/L versus 238 x 109/L, p = 0.041) and higher levels of bone marrow mast cell infiltration (50% versus 10%, p=0.002), serum tryptase (median 262 µg/L versus 62 µg/L, p = 0.003) and alkaline phosphatase (238 U/L versus 74 U/L, p &lt; 0.0001). In consequence, prognosis of AdvSM patients with increased BMD was significantly inferior as compared to those without increased BMD (median overall survival 3.6 years versus not reached, p = 0.031). In conclusion, i) osteoporosis is a common feature in ISM but not in AdvSM patients, ii) an increased BMD is frequent in AdvSM but not in ISM patients, iii) osteosclerosis is restricted to AdvSM patients, and iv) an elevated BMD is associated with a more aggressive phenotype and inferior survival (Figure A-B). Disclosures Fabarius: Novartis: Research Funding. Reiter:Novartis: Consultancy, Honoraria, Other: Travel reimbursement, Research Funding; Blueprint: Consultancy, Honoraria, Other: Travel reimbursement; Deciphera: Consultancy, Honoraria, Other: Travel reimbursement.

Molecular quantification of tissue disease burden is a new biomarker and independent predictor of survival in mastocytosis.

A high allele burden of the KIT D816V mutation in peripheral blood or bone marrow aspirates indicates multi-lineage hematopoietic involvement and has been associated with an aggressive clinical course of systemic mastocytosis. Since mast cells are substantially underrepresented in these liquid specimens, their mutation burden likely underestimates the tumor burden of the disease. We used a novel previously validated digital polymerase chain reaction (PCR) method for KIT D816V analysis to systematically analyze the mutation burden in formalin-fixed, paraffin-embedded bone marrow tissue sections of 116 mastocytosis patients (91 with indolent and 25 with advanced systemic mastocytosis), and to evaluate for the first time the clinical value of the tissue mutation burden as a novel biomarker. The KIT D816V mutation burden in the tissue was significantly higher and correlated better with bone marrow mast cell infiltration (r=0.68 vs. 0.48) and serum tryptase levels (r=0.68 vs. 0.58) compared to that in liquid specimens. Furthermore, the KIT D816V tissue mutation burden was: (i) significantly higher in advanced than in indolent systemic mastocytosis (P=0.001); (ii) predicted survival of patients in multivariate analyses independently; and (iii) was significantly reduced after response to cytoreductive therapy. Finally, digital PCR was more sensitive in detecting KIT D816V in bone marrow sections of indolent systemic mastocytosis patients than melting curve analysis after peptide nucleic acid-mediated PCR clamping (97% vs. 89%; P<0.05). In summary, digital PCR-based measurement of KIT D816V mutation burden in the tissue represents a novel biomarker with independent prognostic significance that can also be employed for monitoring disease progression and treatment response in systemic mastocytosis.

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/Rpos) 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/Rpos 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/Rpos 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.

Imatinib in systemic mastocytosis: a phase IV clinical trial in patients lacking exon 17 KIT mutations and review of the literature.

Resistance to imatinib has been recurrently reported in systemic mastocytosis (SM) carrying exon 17 KIT mutations. We evaluated the efficacy and safety of imatinib therapy in 10 adult SM patients lacking exon 17 KIT mutations, 9 of which fulfilled criteria for well-differentiated SM (WDSM). The World Health Organization 2008 disease categories among WDSM patients were mast cell (MC) leukemia (n = 3), indolent SM (n = 3) and cutaneous mastocytosis (n = 3); the remainder case had SM associated with a clonal haematological non-MC disease. Patients were given imatinib for 12 months −400 or 300 mg daily depending on the presence vs. absence of > 30% bone marrow (BM) MCs and/or signs of advanced disease–. Absence of exon 17 KIT mutations was confirmed in highly-purified BM MCs by peptide nucleic acid-mediated PCR, while mutations involving other exons were investigated by direct sequencing of purified BM MC DNA. Complete response (CR) was defined as resolution of BM MC infiltration, skin lesions, organomegalies and MC-mediator release-associated symptoms, plus normalization of serum tryptase. Criteria for partial response (PR) included ≥ 50% reduction in BM MC infiltration and improvement of skin lesions and/or organomegalies. Treatment was well-tolerated with an overall response rate of 50%, including early and sustained CR in four patients, three of whom had extracellular mutations of KIT, and PR in one case. This later patient and all non-responders (n = 5) showed wild-type KIT. These results together with previous data from the literature support the relevance of the KIT mutational status in selecting SM patients who are candidates for imatinib therapy.

Additional Mutations in SRSF2, ASXL1 and/or RUNX1 Identify a High Risk Group of Patients with KIT D816V+ Advanced Systemic Mastocytosis

The presence of multiple additional mutations was recently reported in >90% of patients with KIT D816V+ advanced systemic mastocytosis (SM) (Schwaab et al., Blood 2013). In the vast majority of cases, additional mutations occur prior to KIT D816V indicating a multi-mutated stem cell disease with phenotype modification through KIT D816V (Jawhar et al., Leukemia 2015). We now sought to clarify the prognostic impact of individual mutations and the number of mutated genes in 70 multi-mutated patients with ISM (n=26), aggressive SM (ASM, n=34) and mast cell leukemia (MCL, n=10). All patients had an associated clonal hematologic non-mast-cell disease (AHNMD), such as a myelodysplastic/myeloproliferative syndrome unclassified (MDS/MPNu, n=28), chronic myelomonocytic leukemia (CMML, n=21), chronic eosinophilia leukemia (CEL, n=9), acute myeloid leukemia (AML, n=8) or primary mylofibrosis (PMF, n=4). Mutational analysis was performed by next-generation sequencing in the following genes: ASXL1, CBL, ETV6, EZH2, IDH2, JAK2, KRAS, NRAS, RUNX1, SF3B1, SRSF2, TET2 and U2AF1. The most frequently identified mutated genes were TET2 (n=33, 47% of cases), SRSF2 (n=30, 43%), ASXL1 (n=20, 29%), RUNX1 (n=16, 23%) and JAK2 (n=11, 16%). The molecular data were correlated with overall survival (OS), clinical characteristics (e.g. B- and C-findings), bone marrow (BM) findings, serum tryptase levels and KIT D816V allele burden in peripheral blood. With a median observation time of 3.7 years, 25 of 70 patients (36%) have died. Three-year OS probability was 71%. In univariate analysis, OS was adversely influenced by mutations in SRSF2 ([hazard ratio (HR) 5.9, 95% confidence interval (CI)] [2.2-15.4], p<0.0001), ASXL1 (HR 3.4 [1.5-7.7], p=0.002) and RUNX1 (HR 2.4 [1.1-5.4], p=0.03) but was not influenced by mutations in TET2 (p=0.3) or JAK2 (p=0.1). In multivariate analysis of the most frequently mutated genes, SRSF2 remained as the best independent poor risk marker for OS. Furthermore, inferior OS was significantly associated with the number of mutated genes in SRSF2/ASXL1/RUNX1 (S/A/R), with median OS not reached for 0 mutation (n=25), 3.9 years for 1 mutation (n=27) and 2.7 years for >=2 mutations (n=18). The 3-year OS was 90% in patients with 0 mutation, 73% in patients with 1 mutation and 42% in patients with >=2 mutations in the S/A/R gene panel. Pairwise significantly different OS probabilities were observed for the comparisons 0 vs. 1 mutation (HR 9.2 [2.0-42.3], p=0.001), 0 vs. >=2 mutations (HR 4.1 [1.9-8.8], p<0.0001) and 1 and >=2 mutations in the S/A/R gene panel (HR 2.5 [1.1-6.0], p=0.04) (Figure 1). Regarding clinical characteristics, the S/A/R mutation profile is significantly related to C-findings including hepatosplenomegaly, albumin <35g/L, alkaline phosphatase >150 IU/L, ascites and weight loss, and other important disease-related parameters including bone marrow mast cell infiltration, serum tryptase levels and KIT D816V+ allele burden. We therefore conclude that a) presence and number of mutations in the S/A/R gene panel are adversely associated with advanced disease and poor survival in KIT D816V+ SM patients and b) the inclusion of molecular markers should be considered in upcoming prognostic scoring systems for SM patients. [Display omitted] DisclosuresSchnittger:MLL: Equity Ownership. Meggendorfer:MLL Munich Leukemia Laboratory: Employment. Sotlar:Ludwig-Maximilians-University: Employment. Haferlach:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Valent:Bristol-Myers Squibb: Honoraria; Pfizer: Honoraria; Celgene: Honoraria; Ariad: Honoraria, Research Funding; Novartis: Consultancy, Honoraria, Research Funding. Cross:Qiagen: Consultancy, Honoraria, Research Funding; Ariad: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Honoraria, Research Funding.

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.

Indolent Mastocytosis in 159 Adults: Smoldering but Not Bone Marrow Only Variant Is Prognostically Significant.

Abstract 2906Poster Board II-882 Background:The World Health Organization (WHO) classification system recognizes indolent SM (ISM) as an entity characterized by low systemic mast cell (MC) burden but frequent skin involvement. The WHO system also recognizes 2 provisional ISM sub-variants: smoldering SM (SSM) and bone marrow (BM) mastocytosis (BMM). The two are respectively characterized by increased systemic MC burden (presence of ≥ 2 ‘B-findings') and BM MC infiltration in the absence of skin or multiorgan visceral lesions. The prognostic relevance of this sub-classification remains unclear. Methods:The study population was drawn from a larger cohort of 342 adult SM patients (Blood. 2009 Jun 4;113(23):5727). Clinical data and BM histology were reviewed, and the diagnosis of ISM and its subclassification confirmed per the 2008 WHO proposal. The primary objectives of the study were to: (i) describe the clinical characteristics of a large cohort of ISM patients, within the context of the WHO classification; (ii) evaluate the prevalence of molecular and cytogenetic abnormalities; (iii) evaluate whether ISM subclassification is prognostically relevant on the basis of survival and risk of transformation to acute leukemia or aggressive SM (ASM).Results: (i) Clinical characteristics:159 ISM patients were evaluated (69 males; median age 49 years, range 19-84); 22 (14%) had SSM, 36 (23%) BMM, and 101 (63%) ‘ISM-other' (ISMo). By definition, ‘B-findings' were absent in BMM patients. ‘B-findings' in SSM (and ISMo) patients was as follows: hepatosplenomegaly and/or lymphadenopathy 91% (21%), BM MC >30% or serum tryptase level >200ng/mL 68% (8%), and hypercellular BM or dysmyelopoiesis without cytopenias 50% (2%). SSM patients were older (p<0.01) and more frequently displayed constitutional symptoms (p<0.01), and anemia (p<0.01). MC mediator-release symptoms (p=0.01), including anaphylaxis (p<0.01), were more frequent in BMM. The following MC-mediators were studied: serum tryptase (57%), beta prostaglandin F2alpha (45%), urine methylhistamine (32%), and urine histamine (21%) – significant differences were noted amongst the ISM subgroups with the following relationship: SSM>ISMo>BMM (p<0.01). (ii) Molecular and cytogenetic abnormalities:Complete karyotype information was available for 55 patients; only 1 patient (with ISMo) had an abnormal karyotype. Fifty nine patients were screened for KITD816V and JAK2V617F; JAK2V617F was universally absent, and distribution of KITD816V was not significantly different amongst the ISM subgroups: SSM (100%), BMM (92%), and ISMo (69%). (iii) Survival and risk of disease transformation:At a median follow of 27 months (range <1-417), 26 deaths were recorded (ISMo 14, SSM 10, and BMM 2), and the combined median survival was 198 months: ISMo 301 months, SSM 120 months, and BMM (not reached) (p<0.01; Figure). Transformation to acute leukemia and ASM was seen in 1 patient (SSM) and 3 patients (2 SSM and 1 ISMo), respectively. Conclusions:Among WHO-defined ISM patients, SSM is associated with significantly shorter survival whereas BMM and ISMo are prognostically similar. If these observations are confirmed by others, consideration may be given to classifying SSM as a distinct subcategory of SM, instead of a sub-variant of ISM as it currently stands. [Display omitted] Disclosures:No relevant conflicts of interest to declare.

Clinical, Biological, and Molecular Characteristics of Well-Differentiated Systemic Mastocytosis: a study in 18 Patients by Spanish Network on Mastocytosis (REMA)

BACKGROUND: Well-differentiated systemic mastocytosis (WDSM) has recently been described as a novel form of mast cell disease. WDSM is characterized by a marked increase of bone marrow (BM) mast cells, usually with compact aggregates, with normal phenotype and morphology as well as the absence of the typical D816V somatic KIT mutation.OBJECTIVE: To describe and compare clinical, morphological, biological and molecular characteristics in a group of 18 patients who fullfilled criteria for WDSM with a group of 32 patients with indolent systemic mastocytosis (ISM).PATIENTS AND METHODS: All the patients were diagnosed on the basis of BM aspirate and biopsy findings after they were thought to have a systemic mastocytosis. A rigorous skin examination together with a clinical work-up and a complete laboratory analysis including peripheral blood count, routine biochemistry and serum tryptase levels were performed. The Mann-Whitney U and the chi-square tests were used to assess the statistical differences of continuous and categorical variables, respectively.RESULTS: WDSM patients were 4 males and 14 females with a median (range) age of 24 years (2–72) at diagnosis. Median (range) age at the time of the first observation of skin lesions was 2 years (0–41). In 16 of the 18 patients (89%), skin lesions appeared under the age of 14, five of them being younger than 1 year old. All the WDSM patients had skin involvement but the typical maculo-papular lesions were found only in 18% of patients while in the remaining 82% of cases, cutaneous lesions were plaques or nodules. Interestingly, 78% of WDSM patients had cutaneous neck involvement in contrast with only 13% in the ISM group (p<0.001). There were no significant differences in mast cell mediators-related symptoms such as pruritus, flushing, abdominal pain or diahrrea between the two groups while anaphylactic reactions were significantly more frequent in the WDSM group than in the ISM group (59% vs 19%, p=0.004). Overall, bone loss was found in 38% and 37% of WDSM and ISM patients, respectively. Among all the biochemical parameters analyzed, only median serum cholesterol (mg/dL), ferritin (ng/mL) and tryptase levels (ng/mL) were significantly lower in patients with WDSM when compared to ISM patients (150 vs 168.5, p=0.043; 31.3 vs 56.6, p=0.004; 11 vs 31.6, p<0.001; respectively). There were no significant differences in the median percentage of mast cells in the BM study as assesed by flow cytometry between both groups (0.055% in WDSM group and 0.08% in ISM group). In contrast, the presence of both fibrosis and lymphoid aggregates in the BM biopsy were more frequent in patients with ISM than in patients with WDSM (52% vs 0%, p<0.001; 55% vs 14%, p=0.01; respectively). Somatic KIT mutation at codon 816 was found in 31 of the 32 ISM patients (97%) while only in one (6%) WDSM patient (p<0.001). Additionally, 2 WDSM patients were found to carry variant mutations at codons other than at codon 816 (N819Y and I817V, respectively). From the remaining 15 WDSM patients, clonality of mast cell population was demonstrated by human androgen receptor (HUMARA) assay in the 5 female patients in whom the assay was made.CONCLUSIONS: WDSM is a variant of systemic mastocytosis with several characteristics that are distinguishable from ISM, such as:early onset of skin lesions,atypical skin involvement (plaques or nodules and cutaneous neck involvement),frequent anaphylactic episodes,lower serum tryptase levels than ISM despite no differences in BM mast cell infiltration, andinfrequent detection of typical activating D816V KIT mutation.

Delineation of Patterns of Bone Marrow Mast Cell Infiltration in Systemic Mastocytosis: Value of CD25, Correlation With Subvariants of the Disease, and Separation From Mast Cell Hyperplasia

Delineation of Patterns of Bone Marrow Mast Cell Infiltration in Systemic Mastocytosis: Value of CD25, Correlation With Subvariants of the Disease, and Separation From Mast Cell Hyperplasia

A phase II study of AMN107, a novel tyrosine kinase inhibitor, administered to patients (pts) with systemic mastocytosis (SM)

6588 Background: SM is a clonal hematologic disorder associated with a constitutive activation of c-kit based on point mutations of this tyrosine kinase and is characterized by mast cell infiltration of extracutaneous organs. AMN107 is a novel aminopyrimidine which potently inhibits Bcr-Abl, as well as the PDGFR and c-kit kinases. Methods: This phase II, open-label study was designed to evaluate the safety and efficacy of AMN107 (400 mg bid). SM pts meeting specific disease criteria and with a clinical indication for treatment were enrolled. Preliminary data are presented for the first 23 pts accrued prior to September 1, 2005. Results: The median age was 49 (range 33–78) yrs and the median time from diagnosis of SM was 27 (range 1 to 292) months. For those with data available, 13/17 pts had a c-kit D816V mutation in bone marrow cells. The median exposure to AMN107 was 144 days. Treatment is ongoing for 18 (78%) pts; 5 (22%) discontinued, 3 (13%) for adverse events and 2 (9%) withdrew consent. Three (13%) responses were reported (2 incomplete remissions and 1 minor response), based on serum tryptase, bone marrow mast cell infiltration and improvement of clinical symptoms. Baseline mutation data are available for 2 of the 3 responding pts and revealed the c-kit D816V mutation. Anemia was reported in 2 (9%) pts. Non-hematologic toxicities in ≥10% of pts were headache in 12 (52%) pts (Gr 3/4 in 2; 9%), fatigue in 9 (39%) pts (Gr 3/4 in 1; 4%), nausea in 8 (35%) pts, vomiting in 7 (30%) pts, pruritus in 7 (30%) pts (Gr 3/4 in 2; 9%), muscle spasms in 6 (26%) pts (Gr 3/4 in 1; 4%), diarrhea in 5 (22%) pts (Gr 3/4 in 1; 4%), upper abdominal pain, rash in 5 (22%) pts each, dizziness, pain in extremities in 4 (17%) pts each (Gr 3/4 in 1; 4% each), dyspnea, myalgia, in 4 (17%) pts each, increased ALAT in 4 (17%) pts (Gr 3/4 in 2; 9%), bone pain, abdominal pain, cough, hard feces, pustular rash in 3 (13%) pts each, and hypotension in 3 (13%) pts (Gr 3/4 in 2; 9%). There were no deaths. Conclusions: These data suggest that AMN107 has clinical activity and an acceptable safety and tolerability profile in pts with SM. [Table: see text]

Delineation of Patterns of Bone Marrow Mast Cell Infiltration in Systemic Mastocytosis

In most cases, the diagnosis of systemic mastocytosis (SM) is based on histomorphologic evaluation of the bone marrow. We analyzed mast cell (MC) infiltration patterns in 57 cases of SM and 31 cases of mast cell hyperplasia (MCH). Tryptase immunohistochemical analysis was used for MC detection and CD25 to distinguish neoplastic from normal MCs. The following infiltration patterns were found: I, diffuse interstitial; II, focal, dense; III, focal, dense with an additional diffuse component, located preferentially around focal infiltrates; IV, focal, dense with an additional diffuse component evenly distributed throughout; and V, diffuse, dense. In 29 cases of MCH, MCs formed the type I pattern. The majority of SM cases exhibited patterns II to V; type IV was the most frequent (n = 36). Type V was seen in 3 cases of MC leukemia and 1 case of smoldering SM. In 1 case of SM, type I infiltration was found; the SM diagnosis was based on 3 minor SM criteria. Our data show that the infiltration pattern in SM correlates with the disease subtype and should be recognized as an important aspect in the histomorphologic evaluation of the bone marrow.

Delineation of Patterns of Bone Marrow Mast Cell Infiltration in Systemic Mastocytosis : Value of CD25, Correlation With Subvariants of the Disease, and Separation From Mast Cell Hyperplasia

Delineation of Patterns of Bone Marrow Mast Cell Infiltration in Systemic Mastocytosis : Value of CD25, Correlation With Subvariants of the Disease, and Separation From Mast Cell Hyperplasia

FIP1L1-PDGFRA fusion: prevalence and clinicopathologic correlates in 89 consecutive patients with moderate to severe eosinophilia

AbstractA novel oncogenic mutation (FIP1L1-PDGFRA), which results in a constitutively activated platelet-derived growth factor receptor-α (PDGFRA), has been invariably associated with a primary eosinophilic disorder. The current study examines both the prevalence and the associated clinicopathologic features of this mutation in a cohort of 89 adult patients presenting with an absolute eosinophil count (AEC) of higher than 1.5 × 109/L. A fluorescence in situ hybridization (FISH)–based strategy was used to detect FIP1L1-PDGFRA in bone marrow cells. None of 8 patients with reactive eosinophilia displayed the abnormality, whereas the incidence of FIP1L1-PDGFRA in the remaining 81 patients with primary eosinophilia was 14% (11 patients). None (0%) of 57 patients with the hypereosinophilic syndrome (HES) but 10 (56%) of 19 patients with systemic mast cell disease associated with eosinophilia (SMCD-eos) carried the specific mutation. The bone marrow mast cell infiltration pattern in FIP1L1-PDGFRA+ SMCD-eos was distinctly diffuse with loose tumoral aggregates. Treatment with low-dose imatinib (100 mg/d) produced complete and durable responses in all 8 FIP1L1-PDGFRA+ cases treated. In contrast, only 40% partial response rate was seen in 10 HES cases. FIP1L1-PDGFRA is a relatively infrequent but treatment-relevant mutation in primary eosinophilia that is indicative of an underlying systemic mastocytosis.

Bone marrow mast cell immunophenotyping in adults with mast cell disease: a prospective study of 33 patients

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.

Hematologic manifestations of systemic mast cell disease: A prospective study of laboratory and morphologic features and their relation to prognosis

purpose: Systemic mast cell disease (SMCD) follows an indolent course in most patients, but a significant number of patients die of neoplastic hematologic disorders. Reviews of the literature and retrospective studies in a single institution have defined features that may be associated with a poor prognosis, but prospective studies have been lacking. Therefore, we prospectively analyzed the relationship between clinical, laboratory, and hematopathologic findings and clinical outcome in a series of 46 patients with mast cell disease. This analysis was employed to both define clinically useful prognostic variables and describe the histologic evolution of bone marrow mast cell infiltration and its relationship to hematologic neoplasia. patients and methods: Forty-six adult patients were referred to the National Institutes of Health (NIH) with clinical and/or pathologic evidence of mast cell proliferation. All patients had bone marrow examinations, and 10 patients underwent serial bone marrow biopsies. The diagnosis of SMCD required pathologic documentation of bone marrow mast cell infiltrates. The patients were followed for up to 13 years at the NIH (up to 30 years after the initial pathologic diagnosis of mast cell disease). Statistical analysis defined the correlation between variables and the presence of diagnostic bone marrow lesions. The Kaplan-Meier method was used to construct survival curves, and the effects of various variables on the survival time were examined. results: Thirty-two of 46 patients (74%) had a bone marrow biopsy diagnostic for SMCD. The remaining 14 patients were considered to have cutaneous mast cell disease (CMCD). Univariate analysis showed that hepatosplenomegaly, alkaline phosphatase level, absolute lymphocyte count, and age at onset of symptoms were positively correlated with SMCD, whereas hemoglobin level was negatively associated with diagnostic bone marrow lesions. With multivariate analysis, only hemoglobin and absolute lymphocyte count remained as significant independent predictors of bone marrow findings. No CMCD patient died or had significant clinical deterioration in the 1- to 30-year period of follow-up (median = 8.5 years), whereas 10 of 32 SMCD patients (31%) died from 1 to 22 years after diagnosis (median = 2.5 years) (p <0.0001). Univariate analysis revealed the following variables as significantly increasing the risk of death in patients with SMCD: later onset of symptoms, absence of cutaneous mastocytosis, thrombocytopenia, elevated lactate dehydrogenase (LDH) level, anemia, bone marrow hypercellularity, qualitative peripheral blood smear abnormalities, elevated alkaline phosphatase level, and hepatosplenomegaly. Multivariate analysis showed that only the age at onset of symptoms and LDH levels were significant independent predictors of survival. Eight of the 10 SMCD patients who died had myeloproliferative or myelodysplastic syndromes or acute nonlymphocytic leukemia. conclusion: Our prospective study has defined a number of important variables in patients with clinical evidence of mast cell proliferation that can predict both the presence of SMCD and the likelihood of fatal disease. Since recent evidence suggests that mast cells derive from a bone marrow hematopoietic progenitor, SMCD may represent a myeloproliferative condition with the propensity to evolve into a neoplastic granulocytic disorder in a significant minority of patients.