Diagnosis Of Systemic Mastocytosis Research Articles

Diagnosis of systemic mastocytosis with cryptic deletion of TET2 and DNMT3A resulting from unbalanced translocation.

Systemic mastocytosis (SM) is a rare haematological neoplasm associated with the gain of function mutation KIT D816V in 90% of adult patients. Classically, cytogenetic aberrations are not common except in cases of SM associated with another haematological neoplasm. We highlight here an unusual clinical presentation of SM and demonstrate the utility of advanced cytogenetic analysis (optical genome mapping, OGM) in detecting a novel cytogenetic abnormality resulting in an unusual mechanism of DNMT3A and TET2 loss of function.

How I diagnose systemic mastocytosis.

Systemic mastocytosis (SM) is a neoplasm of mast cells (MCs) characterized by their proliferation in extracutaneous organs. Systemic mastocytosis includes several entities with different clinical courses and prognoses. The rarity of this disease and the diversity of clinical and morphologic presentation make the diagnosis of SM very challenging. The aim of this review is to share our approach to the diagnosis of SM. We present 4 cases that highlight the spectrum of clinical and laboratory features of SM and outline the diagnostic process with an emphasis on morphology. Pathology and laboratory medicine play a key role in investigation of SM, as correct diagnosis requires integration of morphologic, molecular, and serologic findings. In addition to awareness of microscopic findings in SM, a pathologist must keep abreast with an expanding menu of ancillary studies, particularly molecular testing. Systemic mastocytosis is a challenging diagnosis that requires not only a demonstration of a clonal proliferation of MCs but also a correct subclassification based on the recently updated criteria.

Standardized indolent systemic mastocytosis evaluations across a health care system: implications for screening accuracy

AbstractTimely diagnosis of systemic mastocytosis (SM) remains challenging because of care heterogeneity. We implemented a standardized approach for SM screening and diagnosis using a novel health care system–wide international screening registry. A retrospective analysis assessed rates of SM, cutaneous mastocytosis (CM), and molecular diagnoses before and 2 years after care standardization. The accuracy of individual and combined SM screening tests, basal serum tryptase (BST) ≥11.5 and ≥20.0 ng/mL, REMA ≥2, monomorphic maculopapular CM (MPCM), and elevated BST based upon tryptase genotype, was analyzed. Tryptase genotyping and high-sensitivity KIT p.D816V testing increased substantially 2 years after care standardization. SM diagnoses doubled from 47 to 94, and KIT p.D816V molecular diagnoses increased from 24 to 79. Mean BST and KIT p.D816V variant allele frequency values were significantly lower in patients diagnosed after standardization. Hereditary-alpha tryptasemia prevalence was increased in SM before care standardization (4/30 [13.3%]) but reflected the general population prevalence 2 years later at (5/76 [6.6%]). Elevated BST based upon genotype and BST ≥11.5 ng/mL had the highest sensitivities at 84.2% and 88.3%, respectively. The presence of monomorphic MPCM, elevated BST based upon tryptase genotype, and the combination of REMA ≥2 with elevated BST based upon tryptase genotype had specificities >90%. BST >20.0 ng/mL had low sensitivity and specificity and was not required to establish any indolent SM (ISM) diagnosis. Care standardization increased SM diagnosis rates, particularly in patients with low BSTs. Stratifying BST based upon genotype had the best overall sensitivity and specificity of any ISM screening test and improved the REMA score specificity.

Serum chemistry profiling and prognostication in systemic mastocytosis: a registry-based study of the ECNM and GREM

AbstractCertain laboratory abnormalities correlate with subvariants of systemic mastocytosis (SM) and are often prognostically relevant. To assess the diagnostic and prognostic value of individual serum chemistry parameters in SM, 2607 patients enrolled within the European Competence Network on Mastocytosis and 575 patients enrolled within the German Registry on Eosinophils and Mast Cells were analyzed. For screening and diagnosis of SM, tryptase was identified as the most specific serum parameter. For differentiation between indolent and advanced SM (AdvSM), the following serum parameters were most relevant: tryptase, alkaline phosphatase, β2-microglobulin, lactate dehydrogenase (LDH), albumin, vitamin B12, and C-reactive protein (P < .001). With regard to subvariants of AdvSM, an elevated LDH of ≥260 U/L was associated with multilineage expansion (leukocytosis, r = 0.37, P < .001; monocytosis, r = 0.26, P < .001) and the presence of an associated myeloid neoplasm (P < .001), whereas tryptase levels were highest in mast cell leukemia (MCL) vs non-MCL (308μg/L vs 146μg/L, P = .003). Based on multivariable analysis, the hazard-risk weighted assignment of 1 point to LDH (hazard ratio [HR], 2.1; 95% confidence interval [CI], 1.1-4.0; P = .018) and 1.5 points each to β2-microglobulin (HR, 2.7; 95% CI, 1.4-5.4; P = .004) and albumin (HR, 3.3; 95% CI, 1.7-6.5; P = .001) delineated a highly predictive 3-tier risk classification system (0 points, 8.1 years vs 1 point, 2.5 years; ≥1.5 points, 1.7 years; P < .001). Moreover, serum chemistry parameters enabled further stratification of patients classified as having an International Prognostic Scoring System for Mastocytosis–AdvSM1/2 risk score (P = .027). In conclusion, serum chemistry profiling is a crucial tool in the clinical practice supporting diagnosis and prognostication of SM and its subvariants.

Histological characterization of liver involvement in systemic mastocytosis.

Systemic mastocytosis (SM) is characterized by the accumulation of atypical mast cells (MCs) in organs. Liver histology of SM has been marginally described and accurate histological classification is critical, given the consequences of aggressive SM diagnosis. We aimed to describe the histological features associated with liver SM using updated tools. Using the database of the French Reference Centre for Mastocytosis, we retrospectively identified patients with a liver biopsy (LB) and a diagnosis of SM. All LB procedures were performed according to the local physician in charge and centrally reviewed by an expert pathologist. A total of 28 patients were included: 6 had indolent SM, 9 had aggressive SM, and 13 had SM with an associated hematologic neoplasm. Twenty-five (89%) patients presented hepatomegaly, and 19 (68%) had portal hypertension. The LB frequently showed slight sinusoid dilatation (82%). Fibrosis was observed in 3/6 indolent SM and in almost all advanced SM cases (21/22), but none of them showed cirrhosis. A high MC burden (>50 MCs/high-power field) was correlated with elevated blood alkaline phosphatase levels (p = .030). The presence of portal hypertension was associated with a higher mean fibrosis grade (1.6 vs. 0.8 in its absence; p = .026). In advanced SM, the presence of nodular regenerative hyperplasia (NRH) was associated with decreased overall survival (9.5 vs. 46.3 months, p = .002). MC infiltration induced polymorphic hepatic lesions and the degree of fibrosis is associated with portal hypertension. NRH identifies a poor prognosis subgroup of patients with advanced SM. Assessing liver histology can aid in SM prognostic evaluation.

Multicolor flow cytometric immunophenotyping is highly sensitive and specific in identifying aberrant mast cells in the diagnostic workup of systemic mastocytosis.

Flow cytometric immunophenotyping (FCI) is a fast and sensitive method for characterizing hematolymphoid neoplasms. It is not widely used in the workup of systemic mastocytosis (SM), in part because of the technical challenges and in part because the utility of FCI in assessing mast cells is not well understood. The objectives of this study were to assess the diagnostic utility of FCI in establishing a diagnosis of SM and distinguishing SM from nonneoplastic mast cells and to examine the immunophenotypic findings among SM subtypes. We performed FCI on bone marrow samples suspicious for SM using a panel consisting of CD2, CD25, CD30, CD45, CD117, and HLA-DR. The cohort included 88 SM cases: 67 without an associated hematologic neoplasm (AHN) (PureSM) and 21 with an AHN (SM-AHN). We also assessed 40 normal/reactive controls. Overall, FCI was adequate for interpretation in 87 of 88 (99%) cases and detected at least 1 immunophenotypic aberrancy in 100% of SM cases. CD2, CD25, and CD30 were positive in 78%, 98%, and 90% of SM cases vs 0%, 13%, and 13% of cases with normal/reactive mast cells (P < .0001 for all). Two or 3 abnormalities were observed in 92% of SM cases but not in normal/reactive mast cells. Among SM cases, SM-AHN showed statistically significant less CD2 (38% vs 91%, P < .0001) and less co-expression of all 3 aberrant markers (CD2, CD25, and CD30 positive in 38% vs 86% of cases; P < .0001) than PureSM. Immunohistochemical analysis showed consistently weaker or focal expression of CD2, CD25, and CD30 than FCI, with CD2 and CD30 being falsely negative in 40% and 50% cases, respectively. A KIT D816V mutation was detected in 67% of PureSM cases and 76% of SM-AHN cases. Flow cytometric immunophenotyping is a quick, sensitive, high-yield tool for evaluating the immunophenotype of mast cells. An abnormal FCI finding should prompt careful histologic evaluation and sensitive KIT D816V mutation testing to address the possibility of SM. CD2, CD25, and CD30 are important markers for the detection of immunophenotypic aberrancy of mast cells, and their frequencies of aberrancy differ across SM subtypes.

Hereditary Alpha Tryptasemia: Validation of a Single-Well Multiplex Digital Droplet PCR Assay in a Cohort of Symptomatic Patients.

Hereditary alpha tryptasemia (HαT) has significant prevalence and potential morbidity in the general population. However, it remains largely undiagnosed in routine clinical diagnostics due to low availability of efficient assessment methods. To address this issue, we developed a reliable and efficient single-well multiplex digital droplet PCR assay. The assay was based on the reconstruction of the TPSAB1 gene through quantification of the ratio of α- and β-tryptase copy number variants (CNV) in a single-well measurement. We performed analytical validation by determining CNV measurement clustering around the expected copy numbers in 281 cases and determined the diagnostic accuracy of basal serum tryptase (BST) to predict HαT and HαT subtypes in 141 symptomatic patients. The assay determined α- and β-tryptase CNVs with an overall accuracy, expressed as a 99% prediction interval, of 0.03 ± 0.27 copy numbers. The optimal BST cutoff level to predict HαT in symptomatic patients, who had no other explanation for relatively high tryptase levels (i.e., no diagnosis of systemic mastocytosis, myeloid neoplasm, or end-stage renal failure), was 9.2 ng/mL (sensitivity: 98.1%; specificity: 96.6%). HαT showed a linear gene-dose effect, with an average gene-dose increase of 7.5 ng/mL per extra α-tryptase gene. Our single-well multiplex digital droplet PCR assay accurately determined HαT and could be implemented as a state-of-the-art routine diagnostic test. The assay demonstrated a strong correlation with BST and the optimal threshold for identifying HαT in symptomatic patients with unexplained high tryptase concentrations was at a BST level of 9.2 ng/mL.

Predictive Value of Elevated Tryptase and Mediator Symptoms in Systemic Mastocytosis - a Single Center Experience

Background: Systemic mastocytosis (SM) is a rare clonal hematologic disorder primarily driven by the KIT D816V mutation in almost all (95%) patients. These patients most often have elevated serum tryptase levels and can present with a wide spectrum of symptoms caused by mediator release from clonal mast cell degranulation (e.g., skin rash, anaphylaxis, diarrhea, and neurocognitive symptoms). However, these symptoms are similar in other non-clonal mast cell disorders such as idiopathic mast cell activation syndrome (MCAS) and hereditary alpha-tryptasemia (HaT). As such, many patients are referred to hematology for SM work-up based on elevated serum tryptase and mediator release symptoms. We evaluated a real-world single-center experience determining whether elevated serum tryptase, mediator release symptoms, and/or a history of anaphylaxis correlated with a diagnosis of SM. Methods: We conducted a retrospective chart review of patients referred to the Mastocytosis Clinic at Huntsman Cancer Institute at the University of Utah for a year between August 2022 and July 2023. Data were collected by chart review and analyzed for disease characteristics, laboratory values, and diagnostic outcomes. Findings/Results: There were a total of 37 patients referred to us during the designated time period with either a tryptase value greater than 10.9 ug/L or abnormal mast cells found on tissue biopsy (e.g., skin, colon, etc) with or without systemic mediator release symptoms. Patients did not have to have a history of anaphylaxis to be seen. Of these, 7 patients already had a known diagnosis of SM and had bone marrow biopsy at an outside institution. Of the 30 remaining patients, 19 (63%) patients reported a history of at least one mediator release symptom, defined as pruritus, flushing, syncope, bloating, nausea, vomiting, or diarrhea. The median serum tryptase level was 17.4 ug/L. (Range 2 - 317 ug/L). KIT D816V mutation was detected in the peripheral blood by digital droplet PCR in 7 (23.3%) patients. Diagnostic bone marrow was done in 19 patients wherein 6 (31.5%) of them met the WHO diagnostic criteria for SM. Of these patients, 5 patients tested positive for KIT D816V mutation on peripheral blood and 1 patient had KIT wild type. Two patients with KIT D816V mutations did not receive bone marrow biopsy as they had no mediator release symptoms. The remaining 13 patients had a bone marrow biopsy but did not have a diagnosis consistent with SM, although some had rare scattered mast cells identified in the marrow. They were all KIT D816V mutation negative and serum tryptase ranged from 2.7 - 43 ug/L. As of the date of data analysis, 4 (30.7%) patients tested positive for HaT; serum tryptase ranged from 20 - 26 ug/L in this cohort. Conclusion: While SM can have a variety of clinical manifestations, including elevated tryptase level and mediator release symptoms, the presence of KIT D816V in the peripheral blood is a strong predictor of SM diagnosis. Persistently elevated serum tryptase without the KIT D816V mutation may suggest the likelihood of HaT, while only mediator release symptoms with normal serum tryptase and without the KIT mutation is a strong negative predictor of SM and HaT.

Development and Validation of a Diagnostic Tool for the Timely Diagnosis of Patients with Systemic Mastocytosis

Background: Systemic mastocytosis (SM), a rare, clonal mast cell disease associated with heterogenous clinical presentation, is characterized by severe, debilitating and often unpredictable skin, gastrointestinal, neurocognitive, and systemic symptoms (including life-threatening anaphylaxis), long-term co-morbidities, and in Advanced SM (AdvSM), organ damage due to mast cell infiltration. SM consists of 2 distinct groups of variants, advanced and non-advanced: AdvSM includes aggressive SM (ASM), SM with an associated hematologic neoplasm (SM-AHN), and mast cell leukemia (MCL); non-AdvSM includes indolent SM (ISM) and smoldering SM (SSM). Arriving at a definitive diagnosis may take years and is one of the challenges of SM management. To aid clinicians in the identification of SM, we developed and validated a diagnostic algorithm using data from select community hematology practices in the United States. Methods: A sample of 209 patients (SM and control) was obtained from the Quality Cancer Care Alliance (QCCA), a network of 19 community oncology and hematology practices. Data collection consisted of patient characteristics, laboratory parameters, and signs and symptoms at presentation. General linear models (GLM) with a logit link function were used in a backwards elimination process with the p value set at &amp;lt; 0.05 to identify patient factors at presentation that were associated with a diagnosis of SM. A Dx scoring algorithm (range: 0-26) was then derived from the final model coefficients, with the intent of correctly differentiating between SM and non-SM patients. A receiver operating characteristic (ROC) curve analysis was then done to measure the Dx accuracy of the algorithm. Results: Data from 105 SM and 104 non-SM control (diagnosed with hematological cancers) patients were collected from QCCA. The SM cohort included patients with different SM subtypes, including: ISM (47.6%); ASM (9.5%); SM-AHN (19.0%); MCL (1.9%); and subtype not documented (21.9%). The factors identified as being predictive ofa correct diagnosis of SM were 1) patient age, 2) lymph node status, 3) absolute neutrophil count, and 4-7) the following symptoms within 30 days of presentation: diarrhea, rash, skin lesions, and unintended weight loss. In the algorithm, patients were assigned scores for each diagnostic factor they possessed [Figure 1]. The final score was then associated with an overall percent likelihood of a positive SM diagnosis. The area under the ROC curve was 0.89 (95%CI 0.84-0.93), indicating good predictive accuracy. Patients with a total score of ≥ 9 units were found to be at highest risk for a positive SM diagnosis with the associated sensitivity, specificity, and positive predictive values of 84.8%, 76.0%, and 82.7%, respectively. Conclusions: This model indicates that the presence or absence of 7 characteristics may help determine whether patients are at increased risk of having SM. Use of this diagnostic algorithm may help facilitate earlier detection of SM by raising clinical suspicion to facilitate appropriate clinical workup, which would allow the timely initiation of effective targeted therapies for this rare disease. Additional application and external validation of the algorithm in a new sample of 162 patients managed through another community oncology network is ongoing.

Performance and Interlaboratory Reproducibility of Droplet Digital Polymerase Chain Reaction (ddPCR) and Real Time PCR for KIT D816V Mutation Detection: A Nationwide Pilot Study By the RIMA (Rete Italiana Mastocitosi) Association

Systemic Mastocytosis (SM) is a rare hematological neoplasm, but its incidence is probably underestimated because of the heterogeneity of clinical symptoms and presentation that may cause diagnostic difficulties especially outside reference centers. Detection of the activating D816V KIT mutation in the bone marrow or peripheral blood is one of the minor criteria for the diagnosis of SM, but it poses some challenges since in the indolent forms (the most frequent) the mast cell burden is very low. For this reason, the National Comprehensive Cancer Network and the European Competence Network on Mastocytosis (ECNM) recommend a high-sensitivity PCR-based assay, such as Allele-Specific Oligonucleotide-Real Time Quantitative PCR (ASO-qPCR) or ddPCR, while Sanger and Next Generation Sequencing are considered not adequate. Accurate quantitation of allele burden (AB) is also desirable since it offers diagnostic (an AB³10% qualifies as a B-finding according to the latest WHO classification) and prognostic information and might be used to monitor response to tyrosine kinase inhibitors. Despite the widespread routine availability of real time and digital PCR technologies, a map of labs across Italy offering KIT D816V testing with adequate sensitivity is lacking, nor have cooperative efforts aimed to check lab performance and reproducibility of diagnostic results ever been performed. Based on these premises, RIMA undertook, with the sponsorship of the GIMEMA Working Party on Chronic Myeloproliferative Neoplasms, a project aimed to: i) build a nationwide network of competent reference laboratories performing KIT D816V mutation testing; ii) promote harmonization of local procedures and ensure adequate proficiency and cross-comparability of results. The pilot phase of this project involved 7 labs (L) spread across the country (Milan, Bologna, Verona, Florence, Rome, Naples, Pavia) serving one or more reference clinical centers for the diagnosis and management of SM. First, a survey aimed to assess the techniques and procedures in use in each participating lab was conducted. Five labs (L2-L6) used a commercial ddPCR assay (KIT p.D816V c.2447A&amp;gt;T, Assay ID dHsaCP2000023; Bio-Rad); one lab (L7) used a home brew ASO-qPCR assay; one lab (L1) used a commercial semi-quantitative real time PCR-based assay (PlentiPlex Mastocytosis D816V kit; Pentabase). All labs performed analyses in duplicate or triplicate using DNA as input material, with amounts variable from 50 to 250ng/replicate. Reported limit of detection (LoD) was 0.0003% for the home brew method and 0.01% for the commercial methods. Subsequently, a round robin test to evaluate and compare performance in terms of sensitivity and inter-lab reproducibility was carried out. Mutated and wild-type DNA isolated from HMC-1.2 and HL-60 cells, respectively, was mixed and diluted to mimic different D816V ABs, from 10% down to 0.01%. Dilutions were externally assessed by the UK Wessex Genomics Laboratory Service, using an accredited ddPCR assay with a limit of detection (LoD) of 0.01%. Of note, the sixth dilution (D6) was scored as slightly below their LoD (0.008%; 3 positive droplets only). Identical batches of blinded vials were then distributed and analyzed in parallel by the 7 participating labs according to their own routine protocols. Positivity/negativity as scored by L1-7 and AB values as scored by L2-7 are detailed in Table 1. All the evaluated methods proved highly accurate in the detection and, for ddPCR and ASO-qPCR, in the quantitation of the KIT D816V (R 2 between 0.988 and 0.998). A very high degree of concordance was achieved, for all dilutions, across different labs and methods (CV between 0.07 and 0.8). D6 was scored borderline by L1 and positive by all other labs. This pilot experience demonstrates that the evaluated PCR-based methods may reliably identify and quantitate the KIT D816V mutation down to an AB of 0.01% with a high degree of cross-comparability of results, thus assisting clinicians in the diagnosis and monitoring of SM patients. To the best of our knowledge, this is the first cooperative effort aimed to assess the performance and reproducibility of KIT D816V mutation testing in SM. Involvement of additional Italian labs is already planned, and further implementation within the ECNM will be proposed. Definition of common SOPs, uniform sample requirements and web-based reporting following the GIMEMA LabNet model will be pursued.

Review and Updates on Systemic Mastocytosis and Related Entities

Mast cell disorders range from benign proliferations to systemic diseases that cause anaphylaxis and other diverse symptoms to mast cell neoplasms with varied clinical outcomes. Mastocytosis is the pathologic process of the accumulation of abnormal mast cells in different organs, mostly driven by KIT mutations, and can present as cutaneous mastocytosis, systemic mastocytosis (SM), and mast cell sarcoma. The WHO 5th edition classification divides systemic mastocytosis into bone marrow mastocytosis, indolent systemic mastocytosis, smoldering systemic mastocytosis, aggressive systemic mastocytosis, systemic mastocytosis with an associated hematologic neoplasm, and mast cell leukemia. The new ICC classifies SM slightly differently. The diagnosis of SM requires the integration of bone marrow morphologic, immunophenotypic, and molecular findings, as well as clinical signs and symptoms. Moreover, understanding the wide range of clinical presentations for patients with mast cell disorders is necessary for accurate and timely diagnosis. This review provides an updated overview of mast cell disorders, with a special emphasis on SM, including the latest approaches to diagnosis, prognostic stratification, and management of this rare disease.

The international consensus classification of eosinophilic disorders and systemic mastocytosis.

Based on new data and increased understanding of disease molecular genetics, the international consensus classification (ICC) has made several changes in the diagnosis and classification of eosinophilic disorders and systemic mastocytosis. Myeloid/lymphoid neoplasms with eosinophilia (M/LN-eo) and gene rearrangements have been renamed as M/LN-eo with tyrosine kinase gene fusions (M/LN-eo-TK). The category has been expanded to include ETV6::ABL1 and FLT3 fusions, and to accept PCM1::JAK2 and its genetic variants as formal members. The overlaps and differences between M/LN-eo-TK and BCR::ABL1-like B-lymphoblastic leukemia (ALL)/de novo T-ALL sharing the same genetic lesions are addressed. Besides genetics, ICC for the first time has introduced bone marrow morphologic criteria in distinguishing idiopathic hypereosinophilia/hypereosinophilic syndrome from chronic eosinophilic leukemia, not otherwise specified. The major diagnostic criteria for systemic mastocytosis (SM) in the ICC remain largely based on morphology, but several minor modifications/refinements have been made in criteria related to diagnosis, subclassification, and assessment of disease burden (B- and C-findings). This review is to focus on the ICC updates related to these disease entities, illustrated through changes related to morphology, molecular genetics, clinical features, prognosis, and treatment. Two practical algorithms are provided in navigating through the diagnosis and classification systems of hypereosinophilia and SM.

Recent advances in diagnosis and therapy in systemic mastocytosis.

Mastocytosis is a heterogeneous neoplasm characterized by accumulation of neoplastic mast cells in various organs. There are three main types: cutaneous mastocytosis (CM), systemic mastocytosis (SM), and mast cell sarcoma. CM mainly affects children and is confined to the skin, whereas SM affects adults and is characterized by extracutaneous involvement, with or without cutaneous involvement. Most cases of SM have an indolent clinical course; however, some types of SM have aggressive behavior and a poor prognosis. Recent advances in the understanding of the molecular changes in SM have changed the diagnosis and treatment of aggressive and advanced SM subtypes. The International Consensus Classification and World Health Organization refined the diagnostic criteria and classification of SM as a result of accumulation of clinical experience and advances in molecular diagnostics. Somatic mutations in the KIT gene, most frequently KIT D816V, are detected in 90% of patients with SM. Expression of CD30 and any KIT mutation were introduced as minor diagnostic criteria after the introduction of highly sensitive screening methods. SM has a wide spectrum of clinical features, and only a few drugs are effective at treating advanced SM. Currently, the mainstay of SM treatment is limited to the management of chronic symptoms related to release of mast cell mediators. Small-molecule kinase inhibitors targeting the KIT-downstream and KIT-independent pathways were recently approved for treating advanced SM. I describe recent advances in diagnosis of SM, and review the currently available and emerging therapeutic options for SM management.

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

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

Patterns of Disease Progression in Patients with Systemic Mastocytosis: A US Population-Level Analysis Using Health Claims-Based Dataset

Background Systemic mastocytosis (SM) is a rare clonal mast cell neoplasm driven by the KIT D816V mutation in ~95% of patients (pts). SM includes AdvSM (aggressive SM, SM with associated hematological neoplasm, and mast cell leukemia) and non-advanced SM (indolent & smoldering SM), which accounts for ~95% of cases. The uncontrolled proliferation and activation of mast cells can cause severe & unpredictable symptoms resulting in debilitation, reduced QOL, and organ infiltration and damage with reduced survival in AdvSM. While WHO criteria differentiate between subtypes of mastocytosis, there remains a lack of understanding of patterns of disease progression between SM subtypes. In this analysis we developed a novel claims-based algorithm to identify SM cases and assess disease progression. Methods Using a large, nationally representative claims database, we identified a cohort of SM pts with observed claims activity in each of the year 2019-2022. We developed a novel claims-based algorithm based on WHO diagnostic criteria (2016), including codes for laboratory tests, procedures, and treatments typically used for management of SM. Pts were included if they fulfilled 1 of the following criteria: had ≥2 diagnoses with an SM-specific ICD-10 code (D47.02, C96.21, C94.3X) at least 30 days apart in any setting of care; bone marrow biopsy followed by 1 SM diagnosis (dx) claim code in any setting of care; or 1 SM dx code in any setting of care & at least 1 prescription claim for an SM-specific treatment (avapritinib, midostaurin, imatinib, cladribine, interferons, brentuximab, omalizumab, montelukast, or cromolyn sodium). Pts were then categorized as either AdvSM, higher symptom ISM (ISM-higher), or lower symptom ISM (ISM-lower) based on additional disease-specific codes (Table 1) accumulated over the pt's total observable claims history, from 2015 to the date of evaluation. For pts who met these criteria, SM subtyping was evaluated as of Dec 31, 2019, Dec 31, 2020, and Dec 31, 2021. Treatment rates of select SM-directed therapies were also evaluated over the 12- month period from Jan-Dec, 2021. Results Of 10,939 pts with SM, 80% (8,707 pts) with claims in each of the years 2019, 2020, 2021 and 2022 were included. The first analysis looked at pts’ disease category as of Dec 2021 and assessed utilization of several SM-directed Rx therapies. This included 1,587 AdvSM, 2,705 ISM-higher, and 4,415 ISM-lower pts. Among pts across all cohorts, the most frequently observed therapies were anti-mediator therapies (AdvSM 20%, ISM-higher 37%, ISM-lower 20%) and cromolyn sodium (AdvSM 10%, ISM-higher 19%, ISM-lower 12%). When evaluating disease category evolution, 11.3% and 18.8% of pts with ISM-low migrated to ISM-higher or AdvSM over a 12-month (Dec 2020 - Dec 2021), or 24-month (Dec 2019 - Dec 2021) interval respectively. Across all ISM types, 2.2% of pts progressed to AdvSM in a 12-month interval, and 3.9% progressed to AdvSM over a 24-month interval. Among those pts who emerged with AdvSM in a 12-month interval ending Dec 2021 (N=392), 33% progressed from ISM-Lower or ISM-higher while 67% appeared as de novo diagnoses. Conclusions This study used a large claims dataset to identify pts with SM, classified them with a novel algorithm, and describe patterns of disease progression over a 12-month or 24-month interval. Of note, while this algorithm has been developed with expert clinical input, inherent limitations of claims and a single ICD-10 code for SM leave some ambiguity around the true clinical dx of these pts. Despite this, these analyses reflect the accumulation of severe symptoms over time by a meaningful subset of pts. Approximately 35% of pts with an SM dx did not have a SM dx 2 years prior, possibly due in part to the recency of the SM ICD-10 codes and also raising concerns regarding timely dx. Further, not all ISM pts demonstrated truly indolent disease behavior, illustrated by the 30% of ISM pts categorized as ISM-high requiring greater use of symptom-directed and disease-specific therapies. Finally, the proportion of AdvSM pts on FDA-approved TKI-directed therapies remain low, highlighting large unmet treatment need. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

SYSTEMIC MASTOCYTOSIS WITH CONCURRENT ALPHA-GAL ASSOCIATED ANAPHYLAXIS

<h3>Introduction</h3> We present a case of a patient, diagnosed with systemic mastocytosis (SM), who was also found to have anaphylaxis to galactose-α-1,3-galactose (alpha-gal) several years after his initial SM diagnosis. <h3>Case Description</h3> The patient initially presented in his 20s with recurrent episodes of hypotension, pre-syncope, and syncope. An extensive cardiac and neurologic workup did not elucidate an etiology. He moved to Mississippi and had a six-year period with no episodes. In 2015, he was admitted to the intensive care unit due to presumed septic shock secondary to an infected pilonidal cyst. A tryptase level during hospitalization was elevated at >30, and a bone marrow biopsy confirmed the diagnosis of indolent SM. After starting antihistamines, the patient was initially free of anaphylaxis episodes. The patient then began experiencing weekly anaphylactic episodes, often with severe hypotension, sometimes requiring multiple doses of epinephrine. Episodes persisted despite increased antihistamine regimen. After extensive testing, he was found to have elevated alpha-gal specific IgE and was diagnosed with alpha-gal-associated anaphylaxis. With mammalian meat avoidance, he had no further anaphylactic episodes. <h3>Discussion</h3> Our reports highlight the importance of considering food allergens, particularly alpha-gal, in locations with a high incidence of lone star tick bites, as possible triggers for recurrent anaphylaxis in patients with SM. Given the delayed presentation of alpha-gal reactions and the inherent propensity for patients with SM to experience anaphylaxis, this diagnosis can easily be overlooked. The case also suggests the possibility that underlying SM may be associated with more severe manifestations of alpha-gal reaction.

MPN-182 Droplet Digital PCR for Non-Invasive Detection of the KIT D816V Mutation in the Peripheral Blood of Patients With Suspected Systemic Mastocytosis.

Systemic mastocytosis (SM) is a rare and underdiagnosed hematologic neoplasm. Detection of the D816V KIT mutation in the bone marrow (BM) is one of the minor criteria for the diagnosis of SM and requires sensitive methods like ASO-qPCR. In patients with suspected SM, non-invasive pre-screening of peripheral blood (PB) by ASO-qPCR has been shown to detect the D816V mutation with a concordance with BM results of 92% in indolent SM (ISM) patients with skin lesions and of 66% in those without skin lesions. However, ASO-qPCR is not standardized, and commercial kits are not available. Droplet digital PCR (ddPCR) might be a valuable alternative to ASO-qPCR. To validate a commercially available ddPCR assay for the detection and quantitation of the KIT D816V mutation and to evaluate its potential as a non-invasive screening tool in patients with suspected SM. To assess specificity and calculate the limit of blank, PB samples from 30 healthy donors (HDs) were used. The limit of detection was determined by mixing KIT D816V-mutated (HMC-1.2) and unmutated (HMC-1.1) cell lines in order to mimic different allele burdens, from 50% down to 0.01%. Accuracy was investigated by analyzing, in parallel, 35 samples from patients with confirmed or suspected ISM by ASO-qPCR and ddPCR. Concordance between ddPCR results in BM and PB was assessed in 60 matched PB/BM samples. ddPCR was performed using 50 ng/µL of genomic DNA with the KIT p.D816V human mutation assay on a QX200 instrument (Bio-Rad). No KIT D816V-positive events were detected in any of the HD samples. In HMC 1.2 cell dilutions, KIT D816V mutation could be detected down to 0.01% allele burden. Comparison of ddPCR and ASO-qPCR revealed very high concordance in mutation detection and quantitation. All patients positive for KIT D816V in the BM also tested positive in the PB by ddPCR. Moreover, ddPCR revealed high concordance in mutation quantitation between BM and PB, even at very low variant allele frequencies. ddPCR is an attractive alternative to ASO-qPCR for KIT D816V mutation detection and quantification in SM and may reliably detect the D816V mutation non-invasively in PB in patients with suspected SM.

Patient-reported outcomes among patients with systemic mastocytosis in routine clinical practice: Results of the TouchStone SM Patient Survey.

Systemic mastocytosis (SM) is a rare clonal neoplasm driven by KIT D816V and other mutations. Data were collected from the patient perspective on disease burden and included an SM-specific symptom assessment tool. US adults aged 18 years and older with a self-reported SM diagnosis completed an online TouchStone SM Patient Survey of 100 items, including the 12-item Short-Form Health Survey, the Indolent Systemic Mastocytosis Symptom Assessment Form, and the Work Productivity and Activity Impairment Questionnaire, as well as questions about SM diagnosis, the impact of SM on daily activities, work impairment, and health care use. The results were analyzed using descriptive statistics. Fifty-six individuals completed the survey (89% women; median age, 48 years; mean time since diagnosis, 6.7 years), reporting indolent SM (66%), aggressive SM (9%), smoldering SM (5%), and unknown SM subtype (18%). Over a 1-year recall, respondents reported seeking emergency care for anaphylaxis (30%) and taking three or more prescription medications (52%) for SM. Over one half of patients (54%) reduced their work hours because of SM, and 64% avoided leaving home because of symptoms. A majority of respondents (93%) had experienced ≥10 SM-related symptoms, noting that the most bothersome were anaphylactic episodes (18%), abdominal/stomach pain (16%), diarrhea/loose stools (13%), and fatigue (11%). Whereas an Indolent Systemic Mastocytosis Symptom Assessment Form-derived total symptom score of 28 is used to indicate moderate-to-severe symptoms, the mean total symptom score was 52.7. Mental and physical component summary scores from the 12-item Short-Form Health Survey were below population norms. Patients who were surveyed reported substantial symptom burden and unmet needs because of SM, as evidenced by seeking emergency care and reporting bothersome symptoms, poor quality of life, and reduced work hours and productivity. The objective of this research was to understand the burden and unmet needs in the rare disease of systemic mastocytosis (SM) to guide future care. Fifty-six patients completed an online survey containing questions about their diagnosis, medications, health care use, quality of life, and SM symptoms. The results demonstrated that SM is associated with severe and burdensome symptoms, anaphylactic events, emergency department visits, use of multiple medications, reduced ability to work, and poor physical and psychological quality of life. These findings suggest the need for future advances to address unmet needs in patients affected by SM.

Perceptions of patient disease burden and management approaches in systemic mastocytosis: Results of the TouchStone Healthcare Provider Survey.

Systemic mastocytosis (SM) is a rare clonal neoplasm driven by the KIT D816V mutation and has a broad range of debilitating symptoms. In this study, the authors evaluated SM disease perceptions and management strategies among US health care providers (HCPs). Hematologist/oncologist (H/O) HCPs and allergist/immunologist (A/I) HCPs who were treating four or more patients with SM completed an online, 51-item TouchStone HCP Survey, which queried provider characteristics, perceptions of disease burden, and current management. Descriptive analyses by specialty and SM subtype were performed. Of 304 HCPs contacted, 111 (37%) met eligibility criteria, including 51% A/I specialists and 49% H/O specialists. On average, the HCPs had 14 years of practice experience and cared for 20 patients with SM. A/I HCPs saw more patients with nonadvanced SM (78%) compared with H/O HCPs, who saw similar proportions of patients with nonadvanced SM (54%) and advanced SM (46%). HCPs reported testing 75% of patients for the KIT D816V mutation and found an estimated prevalence of 47%. On average, HCPs estimated 8 months between symptom onset and SM diagnosis. HCPs reported that 62% of patients with indolent SM felt depressed or discouraged because of symptoms. In terms of treatment goals for SM, both types of specialists prioritized symptom improvement for nonadvanced SM and improved survival for advanced SM while also prioritizing improving patient quality of life. Both A/I and H/O specialists highlighted unmet needs for patients with SM. The HCPs surveyed reported a lower rate of KIT D816V mutations and a perceived shorter time between symptom onset and SM diagnosis compared with published estimates. Specialists treating systemic mastocytosis (SM) completed a 51-item questionnaire about their clinical practices and perceptions of disease impact. The study included 111 hematology, oncology, allergy, and immunology physicians. Physicians reported that most patients had nonadvanced disease, yet SM symptoms significantly disrupted their patients' lives. Physicians estimated that SM is diagnosed within months of symptom onset, in contrast with published reports of years' long delays reported by patients with SM. This study identified unmet needs that can inform educational and patient management priorities in this rare disease.

Functional imaging with dual-energy computed tomography for supplementary non-invasive assessment of mast cell burden in systemic mastocytosis

Systemic mastocytosis (SM) is characterized by multifocal accumulation of neoplastic mast cells (MCs), predominately affecting the bone marrow (BM). Imaging with computed tomography (CT) is used for assessment of bone mineral density and structure. However, the value of functional imaging with dual-energy CT (DECT) and the assessment of virtual-non-calcium attenuation values (VNCa-AV) for visualization of BM disease burden in SM has not yet been assessed. DECT of the axial skeleton was performed in 18 patients with SM (indolent SM [ISM], n = 6; smoldering SM [SSM]/advanced SM [AdvSM], n = 12) and 18 control subjects. VNCa-AV were obtained in 5 representative vertebraes per patient and correlated with laboratory, morphologic and molecular parameters. VNCa-AV strongly correlated with quantitative BM MC infiltration (r = 0.7, R2 = 0.49, P = 0.001) and serum tryptase levels (r = 0.7, R2 = 0.54, P < 0.001). Mean VNCa-AV were significantly higher in SSM/AdvSM as compared to ISM (− 9HU vs. − 54HU, P < 0.005) and controls (− 38HU, P < 0.005). Nine of 10 (90%) patients with a VNCa-AV > − 30HU and 7/7 (100%) patients with a VNCa-AV > − 10HU had SSM or AdVSM. BM VNCa-AV provide information about the MC burden of SM patients and correlate with SM subtypes. DECT may therefore serve as a supplementary tool for SM diagnosis, subclassification and monitoring in a one-stop-shop session.