Myeloid/lymphoid neoplasms with eosinophilia and tyrosine kinase fusion genes: A workshop report with focus on novel entities and a literature review including paediatric cases.

Myeloid/lymphoid neoplasms with eosinophilia (M/LN-eo) and tyrosine kinase (TK) gene fusions are a rare group of haematopoietic neoplasms with a broad range of clinical and morphological presentations. Paediatric cases have increasingly been recognised. Importantly, not all appear as a chronic myeloid neoplasm and eosinophilia is not always present. In addition, standard cytogenetic and molecular methods may not be sufficient to diagnose M/LN-eo due to cytogenetically cryptic aberrations. Therefore, additional evaluation with fluorescence in-situ hybridisation and other molecular genetic techniques (array-based comparative genomic hybridisation, RNA sequencing) are recommended for the identification of specific TK gene fusions. M/LN-eo with JAK2 and FLT3-rearrangements and ETV6::ABL1 fusion were recently added as a formal member to this category in the International Consensus Classification (ICC) and the 5th edition of the WHO classification (WHO-HAEM5). In addition, other less common defined genetic alterations involving TK genes have been described. This study is an update on M/LN-eo with TK gene fusions with focus on novel entities, as illustrated by cases submitted to the Bone Marrow Workshop, organised by the European Bone Marrow Working Group (EBMWG) within the frame of the 21st European Association for Haematopathology congress (EAHP-SH) in Florence 2022. A literature review was performed including paediatric cases of M/LN-eo with TK gene fusions.

Targeting SAMHD1 with hydroxyurea in first-line cytarabine-based therapy of newly diagnosed acute myeloid leukaemia: Results from the HEAT-AML trial.

BACKGROUND: Treatment of newly diagnosed acute myeloid leukaemia (AML) is based on combination chemotherapy with cytarabine (ara-C) and anthracyclines. Five-year overall survival is below 30%, which has partly been attributed to cytarabine resistance. Preclinical data suggest that the addition of hydroxyurea potentiates cytarabine efficacy by increasing ara-C triphosphate (ara-CTP) levels through targeted inhibition of SAMHD1. OBJECTIVES: In this phase 1 trial, we evaluated the feasibility, safety and efficacy of the addition of hydroxyurea to standard chemotherapy with cytarabine/daunorubicin in newly diagnosed AML patients. METHODS: Nine patients were enrolled and received at least two courses of ara-C (1 g/m2 /2 h b.i.d. d1-5, i.e., a total of 10 g/m2 per course), hydroxyurea (1-2 g d1-5) and daunorubicin (60 mg/m2 d1-3). The primary endpoint was safety; secondary endpoints were complete remission rate and measurable residual disease (MRD). Additionally, pharmacokinetic studies of ara-CTP and ex vivo drug sensitivity assays were performed. RESULTS: The most common grade 3-4 toxicity was febrile neutropenia (100%). No unexpected toxicities were observed. Pharmacokinetic analyses showed a significant increase in median ara-CTP levels (1.5-fold; p = 0.04) in patients receiving doses of 1 g hydroxyurea. Ex vivo, diagnostic leukaemic bone marrow blasts from study patients were significantly sensitised to ara-C by a median factor of 2.1 (p = 0.0047). All nine patients (100%) achieved complete remission, and all eight (100%) with validated MRD measurements (flow cytometry or real-time quantitative polymerase chain reaction [RT-qPCR]) had an MRD level <0.1% after two cycles of chemotherapy. Treatment was well-tolerated, and median time to neutrophil recovery >1.0 × 109 /L and to platelet recovery >50 × 109 /L after the start of cycle 1 was 19 days and 22 days, respectively. Six of nine patients underwent allogeneic haematopoietic stem-cell transplantation (allo-HSCT). With a median follow-up of 18.0 (range 14.9-20.5) months, one patient with adverse risk not fit for HSCT experienced a relapse after 11.9 months but is now in second complete remission. CONCLUSION: Targeted inhibition of SAMHD1 by the addition of hydroxyurea to conventional AML therapy is safe and appears efficacious within the limitations of the small phase 1 patient cohort. These results need to be corroborated in a larger study.

SF3B1-initiating mutations in MDS-RSs target lymphomyeloid hematopoietic stem cells.

Mutations in the RNA splicing gene SF3B1 are found in >80% of patients with myelodysplastic syndrome with ring sideroblasts (MDS-RS). We investigated the origin of SF3B1 mutations within the bone marrow hematopoietic stem and progenitor cell compartments in patients with MDS-RS. Screening for recurrently mutated genes in the mononuclear cell fraction revealed mutations in SF3B1 in 39 of 40 cases (97.5%), combined with TET2 and DNMT3A in 11 (28%) and 6 (15%) patients, respectively. All recurrent mutations identified in mononuclear cells could be tracked back to the phenotypically defined hematopoietic stem cell (HSC) compartment in all investigated patients and were also present in downstream myeloid and erythroid progenitor cells. While in agreement with previous studies, little or no evidence for clonal (SF3B1 mutation) involvement could be found in mature B cells, consistent involvement at the pro-B-cell progenitor stage was established, providing definitive evidence for SF3B1 mutations targeting lymphomyeloid HSCs and compatible with mutated SF3B1 negatively affecting lymphoid development. Assessment of stem cell function in vitro as well as in vivo established that only HSCs and not investigated progenitor populations could propagate the SF3B1 mutated clone. Upon transplantation into immune-deficient mice, SF3B1 mutated MDS-RS HSCs differentiated into characteristic ring sideroblasts, the hallmark of MDS-RS. Our findings provide evidence of a multipotent lymphomyeloid HSC origin of SF3B1 mutations in MDS-RS patients and provide a novel in vivo platform for mechanistically and therapeutically exploring SF3B1 mutated MDS-RS.

Challenges in Diagnosing Myelodysplastic Syndromes in the Era of Genetic Testing: Proceedings of the 13th Workshop of the European Bone Marrow Working Group.

The 13th workshop of the European Bone Marrow Working Group in Utrecht, The Netherlands, was devoted to studying myelodysplastic syndromes (MDS) and their boundaries. The panel received 44 cases submitted to the 3 invited categories, which included: reactive cytopenias with dysplasia, idiopathic cytopenia of undetermined significance, clonal haematopoiesis of indeterminate potential, idiopathic dysplasia of uncertain significance and overt MDS. For this summary, we have selected 17 cases that highlight difficulties in separating true MDS from other causes of cytopenia and the intricate relationship between clonal haematopoiesis and true MDS. In addition, cases of overt MDS with challenging features were also selected. All cases were stained for p53 expression. Using instructive submitted cases we discuss the following: (1) cytopenia with clonal haematopoiesis not fulfilling MDS criteria, (2) cytopenia and/or dysplasia with germline mutations and/or familial history suggesting an underlying gene defect, (3) MDS based on a recurrent chromosomal abnormality and (4) overt MDS with diagnostic difficulties due to concurrent treatment or disease. The lively discussion in the open forum of the workshop illustrated the need for better integrative understanding of the evolution of acquired genetic abnormalities in haematopoiesis, and the challenge of diagnosing true MDS in cytopenic patients with genetic abnormalities, either germline or acquired.

Megakaryocytes harbour the del(5q) abnormality despite complete clinical and cytogenetic remission induced by lenalidomide treatment.

The mechanisms underlying lenalidomide-resistance of del(5q) MDS stem cells remain to be elucidated and may include cell-intrinsic as well as microenvironmental causes. Abnormal hypolobated megakaryocytes constitute one of the hallmarks of del(5q) MDS. We hypothesized that these cells have potential implications for the regulation of haematopoietic stem cells (HSC) similarly to what has recently been described for megakaryocytes in the murine system. Therefore, we conducted a study to determine the response of abnormal hypolobated megakaryocytes to lenalidomide therapy. We studied lenalidomide-treated patients in the MDS-004 trial as well as a cohort seen at our institution. Morphological evaluation at time of complete cytogenetic remission (CCyR) demonstrated the persistence of hypolobated megakaryocytes in all evaluable patients (n = 9). Furthermore, we provide evidence that the abnormal hypolobated morphology is restricted to del(5q) megakaryocytes, both at diagnosis and during CCyR. Using fluorescence in situ hybridisation analysis on flow-sorted stem- and progenitor populations, we observed a similar degree of clonal involvement in megakaryocyte-erythroid-progenitors as in HSC. Taken together, our findings suggest that megakaryocyte morphology might aid in the evaluation of patients where discontinuation of lenalidomide is considered and offers interesting hypotheses for further investigation of lenalidomide resistance.

Progression in patients with low- and intermediate-1-risk del(5q) myelodysplastic syndromes is predicted by a limited subset of mutations.

A high proportion of patients with lower-risk del(5q) myelodysplastic syndromes will respond to treatment with lenalidomide. The median duration of transfusion-independence is 2 years with some long-lasting responses, but almost 40% of patients progress to acute leukemia by 5 years after starting treatment. The mechanisms underlying disease progression other than the well-established finding of small TP53-mutated subclones at diagnosis remain unclear. We studied a longitudinal cohort of 35 low- and intermediate-1-risk del(5q) patients treated with lenalidomide (n=22) or not (n=13) by flow cytometric surveillance of hematopoietic stem and progenitor cell subsets, targeted sequencing of mutational patterns, and changes in the bone marrow microenvironment. All 13 patients with disease progression were identified by a limited number of mutations in TP53, RUNX1, and TET2, respectively, with PTPN11 and SF3B1 occurring in one patient each. TP53 mutations were found in seven of nine patients who developed acute leukemia, and were documented to be present in the earliest sample (n=1) and acquired during lenalidomide treatment (n=6). By contrast, analysis of the microenvironment, and of hematopoietic stem and progenitor cells by flow cytometry was of limited prognostic value. Based on our data, we advocate conducting a prospective study aimed at investigating, in a larger number of cases of del(5q) myelodysplastic syndromes, whether the detection of such mutations before and after lenalidomide treatment can guide clinical decision-making.

Immunophenotypic analysis of erythroid dysplasia in myelodysplastic syndromes. A report from the IMDSFlow working group.

Current recommendations for diagnosing myelodysplastic syndromes endorse flow cytometry as an informative tool. Most flow cytometry protocols focus on the analysis of progenitor cells and the evaluation of the maturing myelomonocytic lineage. However, one of the most frequently observed features of myelodysplastic syndromes is anemia, which may be associated with dyserythropoiesis. Therefore, analysis of changes in flow cytometry features of nucleated erythroid cells may complement current flow cytometry tools. The multicenter study within the IMDSFlow Working Group, reported herein, focused on defining flow cytometry parameters that enable discrimination of dyserythropoiesis associated with myelodysplastic syndromes from non-clonal cytopenias. Data from a learning cohort were compared between myelodysplasia and controls, and results were validated in a separate cohort. The learning cohort comprised 245 myelodysplasia cases, 290 pathological, and 142 normal controls; the validation cohort comprised 129 myelodysplasia cases, 153 pathological, and 49 normal controls. Multivariate logistic regression analysis performed in the learning cohort revealed that analysis of expression of CD36 and CD71 (expressed as coefficient of variation), in combination with CD71 fluorescence intensity and the percentage of CD117+ erythroid progenitors provided the best discrimination between myelodysplastic syndromes and non-clonal cytopenias (specificity 90%; 95% confidence interval: 84-94%). The high specificity of this marker set was confirmed in the validation cohort (92%; 95% confidence interval: 86-97%). This erythroid flow cytometry marker combination may improve the evaluation of cytopenic cases with suspected myelodysplasia, particularly when combined with flow cytometry assessment of the myelomonocytic lineage.

Cytomorphology review of 100 newly diagnosed lower-risk MDS patients in the European LeukemiaNet MDS (EUMDS) registry reveals a high inter-observer concordance.

The European LeukemiaNet MDS (EUMDS) registry is collecting data of myelodysplastic syndrome (MDS) patients belonging to the IPSS low or intermediate-1 category, newly diagnosed by local cytologists. The diagnosis of MDS can be challenging, and some data report inter-observer variability with regard to the assessment of the MDS subtype. In order to ensure that correct diagnoses were made by the participating centres, blood and bone marrow slides of 10% of the first 1000 patients were reviewed by an 11-person panel of cytomorphologists. All slides were rated by at least 3 panel members (median 8 panel members; range 3-9). Marrow slides from 98 out of 105 patients were of good quality and therefore could be rated properly according to the WHO 2001 classification, including assessment of dysplastic lineages. The agreement between the reviewers whether the diagnosis was MDS or non-MDS was strong with an intra-class correlation coefficient (ICC) of 0.85. Six cases were detected not to fit the entry criteria of the registry, because they were diagnosed uniformly as CMML or AML by the panel members. The agreement by WHO 2001 classification was strong as well (ICC = 0.83). The concordance of the assessment of dysplastic lineages was substantial for megakaryopoiesis and myelopoiesis and moderate for erythropoiesis. Our data show that in general, the inter-observer agreement was high and a very low percentage of misdiagnosed cases had been entered into the EUMDS registry. Further studies including histomorphology are warranted.

TERT rs2736100 genotypes are associated with differential risk of myeloproliferative neoplasms in Swedish and Chinese male patient populations.

The telomerase reverse transcriptase (TERT) gene rs2736100_C allele has recently been shown to be associated with an increased risk for myeloproliferative neoplasms (MPNs) among Caucasians. However, it is unknown if this association is present in other ethnical populations and whether rs2736100 allele frequencies mirror the incidence of MPNs in a population. Here we genotyped TERT rs2736100 variants in 126 Swedish and 101 Chinese MPN patients and their age-, sex-, and ethnically-matched healthy controls. Healthy Chinese adults had a higher frequency of the A allele and lower frequencies of the C allele compared to Swedish counterparts (57.4 vs 47.0 % for A, 42.6 vs 53.0 % for C, P = 0.006). Both Swedish and Chinese patients harbored significantly higher C allele frequency than their controls (62.7 vs 53.0 % and 57.4 vs 42.6 % for Swedish and Chinese, respectively, P = 0.004). Swedes and Chinese bearing the CC genotype had a significantly increased risk of MPN compared to AA carriers (OR = 2.47; 95 % CI: 1.33-4.57, P = 0.003, for Swedes, and OR = 3.45; 95 % CI: 1.52-7.85, P = 0.005, for Chinese). Further analyses showed that rs2736100_CC was associated with robustly enhanced risk in males only (CC vs AA, OR = 5.11; 95 % CI: 2.19-11.92, P < 0.0001). The CC-carrying MPN patients exhibited significantly higher TERT expression than patients with the AC genotype. Collectively, the rs2736100_C is a risk allele for MPNs in Swedish and Chinese males, and the lower incidence of MPNs in the Chinese population is correlated with a lower rs2736100_C risk allele frequency.

Mutations in idiopathic cytopenia of undetermined significance assist diagnostics and correlate to dysplastic changes.

Cytopenia is common in the elderly population and etiology may be difficult to assess. Here, we investigated the occurrence of mutations in patients with idiopathic cytopenia of undetermined significance and the usefulness in improving diagnostics. We included 60 patients with persistent cytopenia > 6 months without definite diagnosis of hematological neoplasm after routine assessment. Bone marrow material underwent a blinded morphology review and DNA was sequenced with a targeted 20 gene panel representing the most commonly mutated genes in myelodysplastic syndrome. Thirty seven (62%) patients carried at least one mutation at inclusion, and of these 95% carried a mutation in TET2, ASXL1, SRSF2, or DNMT3A. The most commonly mutated gene was TET2 observed in 43% of all patients. During one to eight years follow-up seven patients progressed to a myeloid neoplasm and six of these had a detectable mutation at study entry. Median time to progression was 53 months (range 10-78), and at time of progression each patient had at least two mutations detected. Mutations in TP53 and NRAS were not present in patients at inclusion, but identified as secondary hits triggering progression. The morphology review was concordant in 68% of all cases, and 93% of the cases reclassified into the group "highly suspicious for MDS" had a mutation. All patients who had a concordant review "highly suspicious for MDS" had at least two mutations detected. Overall, we show that morphology examination is challenging in this heterogeneous group and targeted sequencing helps identify patients at risk of progression. Am. J. Hematol. 91:1234-1238, 2016. © 2016 Wiley Periodicals, Inc.

Detection of central nervous system involvement in childhood acute lymphoblastic leukemia by cytomorphology and flow cytometry of the cerebrospinal fluid.

BACKGROUND: Therapy directed at the central nervous system (CNS) is an essential part of the treatment for childhood acute lymphoblastic leukemia (ALL). The current evaluation of CNS involvement based on cytomorphological examination of the cerebrospinal fluid (CSF) alone is not as sensitive with low cell counts as flow cytometric immunophenotyping (FCI) of the CSF. However, the importance of low CSF blasts counts at diagnosis is uncertain. We sought to determine the significance of FCI in relation to conventional morphological examination. PROCEDURE: We retrospectively compared FCI of the CSF with cytomorphology at diagnosis or relapse of childhood ALL. All patients were diagnosed 2000-2012 in Stockholm or Umeå, Sweden. Clinical data were collected from medical records and the Nordic leukemia registry. Treatment assignment was based on morphological examination only. RESULTS: The cohort was comprised of 214 patients with ALL. CSF involvement was detected by both methods in 20 patients, in 17 by FCI alone, and in one patient by cytomorphology alone. The relapse rate was higher for patients with negative cytology but positive FCI compared to those without CNS involvement using both methods. The difference was especially marked in the current protocol. However, none of the patients with negative CSF cytology but positive FCI had a CNS relapse. CONCLUSIONS: FCI of the CSF increased the detection rate of CNS involvement of ALL approximately two times compared to cytomorphology. Patients with low-level CNS involvement may benefit from additional intensified systemic or CNS-directed therapy, but larger studies are needed.

p53 protein expression independently predicts outcome in patients with lower-risk myelodysplastic syndromes with del(5q).

Del(5q) myelodysplastic syndromes defined by the International Prognostic Scoring System as low- or intermediate-1-risk (lower-risk) are considered to have an indolent course; however, recent data have identified a subgroup of these patients with more aggressive disease and poorer outcomes. Using deep sequencing technology, we previously demonstrated that 18% of patients with lower-risk del(5q) myelodysplastic syndromes carry TP53 mutated subclones rendering them at higher risk of progression. In this study, bone marrow biopsies from 85 patients treated with lenalidomide in the MDS-004 clinical trial were retrospectively assessed for p53 expression by immunohistochemistry in association with outcome. Strong p53 expression in ≥ 1% of bone marrow progenitor cells, observed in 35% (30 of 85) of patients, was significantly associated with higher acute myeloid leukemia risk (P=0.0006), shorter overall survival (P=0.0175), and a lower cytogenetic response rate (P=0.009), but not with achievement or duration of 26-week transfusion independence response. In a multivariate analysis, p53-positive immunohistochemistry was the strongest independent predictor of transformation to acute myeloid leukemia (P=0.0035). Pyrosequencing analysis of laser-microdissected cells with strong p53 expression confirmed the TP53 mutation, whereas cells with moderate expression predominantly had wild-type p53. This study validates p53 immunohistochemistry as a strong and clinically useful predictive tool in patients with lower-risk del(5q) myelodysplastic syndromes. This study was based on data from the MDS 004 trial (clinicaltrials.gov identifier: NCT00179621).

A pilot phase I dose finding safety study of the thrombopoietin-receptor agonist, eltrombopag, in patients with myelodysplastic syndrome treated with azacitidine.

OBJECTIVES: Thrombocytopenia is an independent adverse prognostic factor in patients with Myelodysplastic syndromes (MDS). Azacitidine, first-line treatment for the majority of patients with higher-risk MDS, is associated with aggravated thrombocytopenia during the first cycles. Eltrombopag is a novel thrombopoietin receptor agonist, which also has been shown to inhibit proliferation of leukaemia cell lines in vitro. This phase I clinical trial was designed to explore the safety and tolerability of combining eltrombopag with azacitidine in patients with MDS. In addition, we assessed the potential effects of eltrombopag on hematopoietic stem and progenitor cells (HSPCs) from included patients. PATIENTS AND METHODS: Previously untreated patients with MDS eligible for treatment with azacitidine and with a platelet count <75 × 10(9) /L were included. Patients received eltrombopag in dose escalation cohorts during three cycles of azacitidine. RESULTS: Twelve patients, with a median age of 74 yr, were included. Severe adverse events included infectious complications, deep vein thrombosis and transient ischaemic attack. The maximal tolerated eltrombopag dose was 200 mg qd. Complete remission or bone marrow remission was achieved in 4 of 12 patients. Platelet counts improved or remained stable in 9 of 12 patients despite azacitidine treatment. No increase in blast count, disease progression, or bone marrow fibrosis related to study medication was reported. Eltrombopag did not induce cycling of HSPCs. CONCLUSION: The combination of eltrombopag with azacitidine in high-risk MDS patients is feasible and well tolerated. Improvements in platelet counts and the potential antileukaemic effect of eltrombopag should be explored in a randomised study.

The role of flow cytometry in the classification of myeloid disorders.

The World Health Organization classification (WHO-HAEM5) and the International Consensus Classification (ICC 2022) of myeloid neoplasms are based on the integration of clinical, morphologic, immunophenotypic, and genomic data. Flow cytometric immunophenotyping (FCIP) allows the identification, enumeration, and characterization of hematopoietic cells, and is therefore a powerful tool in the diagnosis, classification, and monitoring of hematological neoplasms. The vast majority of flow cytometry (FCM) studies in chronic myeloid neoplasms focus on its role in myelodysplastic neoplasms (MDS). FCM can also be helpful for the assessment of myeloproliferative neoplasms (MPN) and MDS/MPN, including the early detection of evolving myeloid or lymphoid blast crisis and the characterization of monocytic subsets. The classification of acute myeloid leukemia (AML) is primarily based on cytogenetic and molecular findings; however, FCIP is needed for subclassification of AML, not otherwise specified (NOS; ICC)/AML defined by differentiation (WHO-HAEM5). The main role of FCM in AML remains in making a rapid diagnosis and as a tool for measurable residual disease monitoring. Machine learning and artificial intelligence approaches can be used to analyze and classify FCM data. This article, based on an invited lecture at the 106th Annual Meeting of the German Society of Pathology in 2023, reviews the role of FCM in the classification of myeloid neoplasms, including recent publications on the application of artificial intelligence.

A series of case studies illustrating the role of flow cytometry in the diagnostic work-up of myelodysplastic syndromes.

Current guidelines recommend flow cytometric analysis as part of the diagnostic assessment of patients with cytopenia suspected for myelodysplastic syndrome. Herein we describe the complete work-up of six cases using multimodal integrated diagnostics. Flow cytometry assessments are illustrated by plots from conventional and more recent analysis tools. The cases demonstrate the added value of flow cytometry in case of hypocellular, poor quality, or ambiguous bone marrow cytomorphology. Moreover, they demonstrate how immunophenotyping results support clinical decision-making in inconclusive and clinically 'difficult' cases.

Multicenter prospective evaluation of diagnostic potential of flow cytometric aberrancies in myelodysplastic syndromes by the ELN iMDS flow working group.

BACKGROUND: Myelodysplastic syndromes (MDS) represent a diagnostic challenge. This prospective multicenter study was conducted to evaluate pre-defined flow cytometric markers in the diagnostic work-up of MDS and chronic myelomonocytic leukemia (CMML). METHODS: Thousand six hundred and eighty-two patients with suspected MDS/CMML were analyzed by both cytomorphology according to WHO 2016 criteria and flow cytometry according to ELN recommendations. Flow cytometric readout was categorized 'non-MDS' (i.e. no signs of MDS/CMML and limited signs of MDS/CMML) and 'in agreement with MDS' (i.e., in agreement with MDS/CMML). RESULTS: Flow cytometric readout categorized 60% of patients in agreement with MDS, 28% showed limited signs of MDS and 12% had no signs of MDS. In 81% of cases flow cytometric readouts and cytomorphologic diagnosis correlated. For high-risk MDS, the level of concordance was 92%. A total of 17 immunophenotypic aberrancies were found independently related to MDS/CMML in ≥1 of the subgroups of low-risk MDS, high-risk MDS, CMML. A cut-off of ≥3 of these aberrancies resulted in 80% agreement with cytomorphology (20% cases concordantly negative, 60% positive). Moreover, >3% myeloid progenitor cells were significantly associated with MDS (286/293 such cases, 98%). CONCLUSION: Data from this prospective multicenter study led to recognition of 17 immunophenotypic markers allowing to identify cases 'in agreement with MDS'. Moreover, data emphasizes the clinical utility of immunophenotyping in MDS diagnostics, given the high concordance between cytomorphology and the flow cytometric readout. Results from the current study challenge the application of the cytomorphologically defined cut-off of 5% blasts for flow cytometry and rather suggest a 3% cut-off for the latter.

Clinical application of flow cytometry in patients with unexplained cytopenia and suspected myelodysplastic syndrome: A report of the European LeukemiaNet International MDS-Flow Cytometry Working Group.

This article discusses the rationale for inclusion of flow cytometry (FCM) in the diagnostic investigation and evaluation of cytopenias of uncertain origin and suspected myelodysplastic syndromes (MDS) by the European LeukemiaNet international MDS Flow Working Group (ELN iMDS Flow WG). The WHO 2016 classification recognizes that FCM contributes to the diagnosis of MDS and may be useful for prognostication, prediction, and evaluation of response to therapy and follow-up of MDS patients.

Multiparameter flow cytometry in the evaluation of myelodysplasia: Analytical issues: Recommendations from the European LeukemiaNet/International Myelodysplastic Syndrome Flow Cytometry Working Group.

Multiparameter flow cytometry (MFC) is one of the essential ancillary methods in bone marrow (BM) investigation of patients with cytopenia and suspected myelodysplastic syndrome (MDS). MFC can also be applied in the follow-up of MDS patients undergoing treatment. This document summarizes recommendations from the International/European Leukemia Net Working Group for Flow Cytometry in Myelodysplastic Syndromes (ELN iMDS Flow) on the analytical issues in MFC for the diagnostic work-up of MDS. Recommendations for the analysis of several BM cell subsets such as myeloid precursors, maturing granulocytic and monocytic components and erythropoiesis are given. A core set of 17 markers identified as independently related to a cytomorphologic diagnosis of myelodysplasia is suggested as mandatory for MFC evaluation of BM in a patient with cytopenia. A myeloid precursor cell (CD34+ CD19- ) count >3% should be considered immunophenotypically indicative of myelodysplasia. However, MFC results should always be evaluated as part of an integrated hematopathology work-up. Looking forward, several machine-learning-based analytical tools of interest should be applied in parallel to conventional analytical methods to investigate their usefulness in integrated diagnostics, risk stratification, and potentially even in the evaluation of response to therapy, based on MFC data. In addition, compiling large uniform datasets is desirable, as most of the machine-learning-based methods tend to perform better with larger numbers of investigated samples, especially in such a heterogeneous disease as MDS.