The international consensus classification of myeloid neoplasms and acute Leukemias: myeloproliferative neoplasms.

A group of international experts, including hematopathologists, oncologists, and geneticists were recently summoned (September 2021, Chicago, IL, USA) to update the 2016/17 World Health Organization classification system for hematopoietic tumors. After careful deliberation, the group introduced the new International Consensus Classification (ICC) for Myeloid Neoplasms and Acute Leukemias. This current in-depth review focuses on the ICC-2022 category of JAK2 mutation-prevalent myeloproliferative neoplasms (MPNs): essential thrombocythemia, polycythemia vera, primary myelofibrosis, and MPN, unclassifiable. The ICC MPN subcommittee chose to preserve the primary role of bone marrow morphology in disease classification and diagnostics, while also acknowledging the complementary role of genetic markers for establishing clonality, facilitating MPN subtype designation, and disease prognostication.

Impact of platelets on major thrombosis in patients with a normal white blood cell count in essential thrombocythemia.

OBJECTIVES: Cell counts have a significant impact on the complex mechanism of thrombosis in patients with essential thrombocythemia (ET). We recently demonstrated a considerable impact of white blood cell (WBC) counts on thrombotic risk in patients with optimized platelet counts by analysing a large anagrelide registry. In contrast, the current analysis of the registry aimed to estimate the influence of platelet counts on thrombotic risk in patients with optimized WBC counts. METHODS: Cox regression analysis and Kaplan-Meier plot were applied on all patients in the registry with optimized WBC counts. RESULTS: By using the calculated cut-off of 593 G/L for platelets, Cox regression analysis revealed a clear influence of elevated platelet counts on the occurrence of a major thrombotic event (P < .001). A Kaplan-Meier plot revealed a markedly shorter time to a major thrombotic event for patients with platelet counts above the cut-off (P < .001). CONCLUSIONS: The data show clear impact of platelet lowering on the thrombotic risk in ET patients with normal WBC counts. Therefore, selective platelet lowering with anagrelide appears sufficient for thrombotic risk reduction in WHO-diagnosed ET patients lacking leukocytosis.

The 2016 revision to the World Health Organization classification of myeloid neoplasms and acute leukemia.

The World Health Organization (WHO) classification of tumors of the hematopoietic and lymphoid tissues was last updated in 2008. Since then, there have been numerous advances in the identification of unique biomarkers associated with some myeloid neoplasms and acute leukemias, largely derived from gene expression analysis and next-generation sequencing that can significantly improve the diagnostic criteria as well as the prognostic relevance of entities currently included in the WHO classification and that also suggest new entities that should be added. Therefore, there is a clear need for a revision to the current classification. The revisions to the categories of myeloid neoplasms and acute leukemia will be published in a monograph in 2016 and reflect a consensus of opinion of hematopathologists, hematologists, oncologists, and geneticists. The 2016 edition represents a revision of the prior classification rather than an entirely new classification and attempts to incorporate new clinical, prognostic, morphologic, immunophenotypic, and genetic data that have emerged since the last edition. The major changes in the classification and their rationale are presented here.

The WHO diagnostic criteria for polycythemia vera-role of red cell mass versus hemoglobin/hematocrit level and morphology.

Regarding diagnosis of polycythemia vera (PV), discussion persists about hemoglobin (Hb) and/or hematocrit (Hct) threshold values as surrogate markers for red cell mass (RCM) and the diagnostic impact of bone marrow (BM) morphology. We performed a retrospective study on 290 patients with PV (151 males, 139 females; median age 65 years) presenting with characteristic BM features (initial biopsies, centralized evaluation) and endogenous erythroid colony (EEC) formations. This cohort included (1) a group of 229 patients when following the 2008 versus 256 patients diagnosed according to the 2016 World Health Organization (WHO) guidelines, all presented with increased RCM; (2) masked PV patients with low Hb (n = 143)/Hct (n = 45) recruited from the 2008 WHO cohort; (3) a cohort of 17 PV patients with elevated diagnostic Hb/Hct levels but low RCM; and (4) nine PV patients with increased RCM, opposing low Hb/Hct values. All patients were treated according to current PV guidelines (phlebotomies 87%, hydroxyurea 79%, and acetylsalicylic acid 87%). Applying the 2016 WHO criteria significantly increased concordance between RCM and Hb values compared with the 2008 WHO criteria (90 vs. 43% in males and 83 vs. 64% in females). Further analysis of the WHO 2016 PV cohort revealed that increased RCM is associated with increased Hb/Hct (93.8/94.6%). Our study supports and extends the diagnostic impact of the 2016 revised WHO classification for PV by highlighting the importance of characteristic BM findings and implies that Hb/Hct threshold values may be used as surrogate markers for RCM measurements.

Impact of white blood cells on thrombotic risk in patients with optimized platelet count in essential thrombocythemia.

OBJECTIVES: Risk of thrombosis is significantly enhanced by both elevated platelet (PLT) and white blood cell (WBC) counts according to a retrospective analysis of a large anagrelide registry in thrombocythemic MPN patients. We were interested in the impact of elevated WBC counts on thrombosis risk in patients where PLT counts were reduced below the calculated cutoff of 574.5 G/L by treatment with anagrelide. METHODS: Cox regression analysis and Kaplan-Meier plot were applied on all patients in the registry with optimized PLT counts. RESULTS: Using the calculated cutoff of 9.66 G/L for WBC, Cox regression analysis revealed a clear influence of elevated WBC counts on the occurrence of a major thrombotic event (P = .012). A Kaplan-Meier plot revealed a markedly shorter time to a major thrombotic event for patients with WBC counts above the cutoff (P = .001). CONCLUSIONS: These data suggest that additional correction of elevated WBC counts is mandatory in patients with optimally managed PLT counts to reduce thrombotic risk. This study is the first investigation in a prospectively observed large patient cohort which was treated homogenously allowing for evaluation of single parameters for an effect on thrombophilia.

Recommendations for the diagnosis and treatment of patients with polycythaemia vera.

OBJECTIVES: To present the Central European Myeloproliferative Neoplasm Organisation (CEMPO) treatment recommendations for polycythaemia vera (PV). METHODS: During meetings held from 2015 through 2017, CEMPO discussed PV and its treatment and recent data. RESULTS: PV is associated with increased risks of thrombosis/thrombo-haemorrhagic complications, fibrotic progression and leukaemic transformation. Presence of Janus kinase (JAK)-2 gene mutations is a diagnostic marker and standard diagnostic criterion. World Health Organization 2016 diagnostic criteria for PV, focusing on haemoglobin levels and bone marrow morphology, are mandatory. PV therapy aims at managing long-term risks of vascular complications and progression towards transformation to acute myeloid leukaemia and myelodysplastic syndrome. Risk stratification for thrombotic complications guides therapeutic decisions. Low-risk patients are treated first line with low-dose aspirin and phlebotomy. Cytoreduction is considered for low-risk (phlebotomy intolerance, severe/progressive symptoms, cardiovascular risk factors) and high-risk patients. Hydroxyurea is suspected of leukaemogenic potential. IFN-α has demonstrated efficacy in many clinical trials; its pegylated form is best tolerated, enabling less frequent administration than standard interferon. Ropeginterferon alfa-2b has been shown to be more efficacious than hydroxyurea. JAK1/JAK2 inhibitor ruxolitinib is approved for hydroxyurea resistant/intolerant patients. CONCLUSIONS: Greater understanding of PV is serving as a platform for new therapy development and treatment response predictors.

Pre-fibrotic/early primary myelofibrosis vs. WHO-defined essential thrombocythemia: The impact of minor clinical diagnostic criteria on the outcome of the disease.

The 2016 revised WHO criteria for the diagnosis of pre-fibrotic/early primary myelofibrosis (pre-PMF) require at least one of the following four borderline expressed minor clinical criteria: anemia, leukocytosis, elevated lactate dehydrogenase and splenomegaly. In this study, we evaluated the relative frequency of these four criteria in a group of 170 pre-PMF patients and compared them to 225 ET cases. More than 91% of pre-PMF cases showed one or more of these features required for diagnosis, by contrast with only 48% of ET patients. According to clinical data the cumulative risk of progression to advanced/overt PMF in pre-PMF was 36.9% after 15 years. After fitting cox regression models to analyze the impact of the minor criteria on overall survival, only leukocytosis remained as a significant predictor of survival in both pre-PMF and ET. Molecular characterization showed differences in survival in pre-PMF but not ET, with CALR being a more favorable mutation than JAK2. The different outcome of pre-PMF versus ET and associated molecular genetic data supports the concept of two different entities, rather than a continuum of the same disease. Although slightly less than 50% of ET patients also show one or more minor clinical criteria, accurate distinction between ET and pre-PMF is possible by following an integrated approach including histomorphological diagnosis and presence of minor clinical criteria.

Myeloproliferative neoplasms: Morphology and clinical practice.

In myeloproliferative neoplasms (MPNs), controversy persists regarding the usefulness and reproducibility of bone marrow (BM) features. Disagreements concerning the WHO classification are mainly focused on the discrimination between essential thrombocythemia (ET) and prefibrotic/early primary myelofibrosis (prePMF) and prodromal polycythemia vera (PV). Criticism mostly refers to lack of standardization of distinctive BM features precluding correct morphological pattern recognition. The distinction between WHO-defined ET and prePMF is not trivial because outcome is significantly worse in prePMF. Morphology was generally considered to be non-specific for the diagnosis of PV. Recent studies have revealed under-diagnosis of morphologically and biologically consistent PV.

Effect of treatment with a JAK2-selective inhibitor, fedratinib, on bone marrow fibrosis in patients with myelofibrosis.

BACKGROUND: Progressive bone marrow fibrosis (BMF) is a cardinal feature of many myeloproliferative neoplasms (MPNs) and there is a documented association between the severity of BMF and overall prognosis. We conducted an exploratory analysis of sequential BMF data from two phase I studies of long-term treatment with the Janus kinase 2 (JAK2) inhibitor fedratinib in patients with myelofibrosis. METHODS: Bone marrow samples were obtained at baseline and after every six cycles (24 weeks) of daily fedratinib treatment. Fibrosis was centrally assessed by three independent haematopathologists, who were blinded to the patients' data, and graded according to European Consensus Myelofibrosis Grading Criteria. The analysis population comprised patients with a baseline BMF grade ≥1, and at least one post-baseline BMF grade assessment. Changes in BMF grade compared with baseline were classified as improvement (≥1 grade reduction), stabilisation (no change in any baseline BMF grade <3) or worsening (≥1 grade increase). RESULTS: Twenty-one patients were included in the analysis. A total of 153 bone marrow samples were analysed. Improvement or stabilisation of BMF from baseline was recorded in 15 of 18 (83%) evaluable patients at cycle 6 and in four of nine (44%) evaluable patients at cycle 30. Two patients achieved resolution of their BMF (grade = 0) by cycle 12. CONCLUSIONS: This exploratory analysis indicates that improvement or even resolution of BMF may be achievable with JAK2 inhibitor therapy in some patients with MPNs and myelofibrosis.

Patterns of presentation and thrombosis outcome in patients with polycythemia vera strictly defined by WHO-criteria and stratified by calendar period of diagnosis.

Most studies in polycythemia vera (PV) include patients with both remote and most recent diagnostic periods and are therefore vulnerable to inaccurate interpretation of time-dependent data. We addressed the particular issue by analyzing presenting characteristics and outcome data among 1,545 patients with WHO-defined PV stratified by a diagnosis period of before or after 2005, which coincides with the first description of JAK2V617F as the molecular marker of PV. Patients diagnosed after 2005 displayed lower hemoglobin values (P < 0.0001) and older age (P = 0.007) at diagnosis; we suggest ease of diagnosis offered by a molecular marker enabled earlier diagnosis and broader application across older age groups that is further enhanced by recent trends in increased attention and health monitoring for the elderly. Post-2005 diagnosed patients were also more or less likely to receive aspirin and cytoreductive therapy, respectively, and, despite their older age distribution, displayed significantly lower risk of thrombosis in high risk disease. Regardless of the contributing factors to the latter phenomenon, our observations underscore the need to reassess current demographics and frequencies of thrombosis in clinical trial designs including thrombosis prevention in PV.

Dynamic of bone marrow fibrosis regression predicts survival after allogeneic stem cell transplantation for myelofibrosis.

We correlate regression of bone marrow fibrosis (BMF) on day 30 and 100 after dose- reduced allogeneic stem cell transplantation (allo-SCT) in 57 patients with primary or post-essential thrombocythemia/polycythemia vera myelofibrosis with graft function and survival. The distribution of International Prognostic Scoring System (IPSS) risk score categories was 1 patient with low risk, 5 patients with intermediate-1 risk, 18 patients with intermediate-2 risk, and 33 patients with high risk. Before allo-SCT, 41 patients (72%) were classified as XXX [myclofibrosis (MF)]-3 and 16 (28%) were classified as MF-2 according to the World Health Organization criteria. At postengraftment day +30 (±10 days), 21% of the patients had near-complete or complete regression of BMF (MF-0/-1), and on day +100 (±20 days), 54% were MF-0/-1. The 5-year overall survival rate at day +100 was 96% in patients with MF-0/-1 and 57% for those with MF-2/-3 (P = .04). There was no difference in BMF regression at day +100 between IPSS high-risk and low/intermediate-risk patients. Complete donor cell chimerism at day +100 was seen in 81% of patients with MF-0/-1 and in 31% of those with MF-2/-3. Patients with MF-2/-3 at day +100 were more likely to be transfusion-dependent for either RBCs (P = .014) or platelets (P = .018). Rapid BMF regression after reduced-intensity conditioning allo-SCT resulted in a favorable survival independent of IPSS risk score at transplantation.

Disease characteristics and clinical outcome in young adults with essential thrombocythemia versus early/prefibrotic primary myelofibrosis.

In the present study, we investigated disease characteristics and clinical outcome in young patients (< 40 years) with World Health Organization (WHO)-defined essential thrombocythemia (ET) compared with early/prefibrotic primary myelofibrosis (PMF) with presenting thrombocythemia. We recruited 213 young patients (median age, 33.6 years), including 178 patients (84%) with WHO-defined ET and 35 patients (16%) showing early PMF. Median follow-up time was 7.5 years. A trend for more overall thrombotic complications, particularly arterial, was seen in early PMF compared with ET. Progression to overt myelofibrosis was 3% in ET and 9% in early PMF, but no transformation into acute leukemia was observed. Combining all adverse events (thrombosis, bleeding, and myelofibrosis), the rate was significantly different (1.29% vs 3.43% of patients/year, P = .01) in WHO-ET and early PMF, respectively. In multivariate analysis, early PMF and the JAK2V617F mutation emerged as independent factors predicting cumulative adverse events.

Initial bone marrow reticulin fibrosis in polycythemia vera exerts an impact on clinical outcome.

We examined the prevalence and prognostic relevance of bone marrow reticulin fibrosis in 526 patients with World Health Organization-defined polycythemia vera evaluated at the time of initial diagnosis. Seventy-four patients (14%) displayed mostly grade 1 reticulin fibrosis, with only 2 cases showing higher-grade fibrosis. Presenting clinical and laboratory characteristics, including JAK2V617F allele burden, between patients with and without fibrosis were similar for the most part, with the exception of a higher prevalence of palpable splenomegaly in patients with fibrosis (P < .01). Patients with fibrosis were less prone to experience thrombosis during their clinical course (1.1 vs 2.7 per 100 patient-years; P = .03) and more prone to develop post-polycythemia vera myelofibrosis (2.2 vs 0.8 per 100 patient-years; P = .01). There was no significant difference between the 2 groups in terms of overall or leukemia-free survival. The present study clarifies the incidence, degree, and prognostic relevance of bone marrow fibrosis obtained at time of initial diagnosis of polycythemia vera.

A prognostic model to predict survival in 867 World Health Organization-defined essential thrombocythemia at diagnosis: a study by the International Working Group on Myelofibrosis Research and Treatment.

Diagnosis of essential thrombocythemia (ET) has been updated in the last World Health Organization (WHO) classification. We developed a prognostic model to predict survival at diagnosis, named IPSET (International Prognostic Score for ET), studying patients with WHO-defined ET. Age 60 years or older, leukocyte count ≥ 11 × 10(9)/L, and prior thrombosis significantly affected survival, by multivariable Cox regression. On the basis of the hazard ratio, we assigned 2 points to age and 1 each to leukocyte count and thrombosis. So, the IPSET model allocated 867 patients into 3 risk categories with significantly different survival: low (sum of points = 0; median survival not reached), intermediate (sum = 1-2; median survival 24.5 years), and high (sum = 3-4, median survival 13.8 years). The IPSET model was further validated in 2 independent cohorts including 132 WHO-defined ET and 234 Polycythemia Vera Study Group-defined ET patients. The IPSET model was able to predict the occurrence of thrombosis, and not to predict post-ET myelofibrosis. In conclusion, IPSET, based on age ≥ 60 years, leukocyte count ≥ 11 × 10(9)/L, and history of thrombosis allows prognostic assessment of WHO-defined ET and the validation process makes IPSET applicable in all patients phenotypically appearing as ET.

Decanucleotide insertion polymorphism of F7 significantly influences the risk of thrombosis in patients with essential thrombocythemia.

OBJECTIVE: There is strong evidence that certain thrombophilic single nucleotide polymorphisms (SNPs) account for an increased risk of thrombosis. The additive impact of inherited thrombotic risk factors to a certain disease- immanent thrombotic risk is vastly unknown. Therefore, we aimed to investigate the influence of three novel, preselected SNPs on the risk of thrombosis in patients diagnosed with myeloproliferative neoplasm (MPN). METHOD: In 167 patients with a diagnosis of essential thrombocythemia (ET) or prefibrotic primary myelofibrosis (PMF) thrombophilic SNPs in the genes of factor VII (F7), nitric oxide synthase 3 (NOS3) and FcɣRIIa (FCGR2A) were determined. Subsequently, the polymorphic variants were correlated with the incidence of major thrombosis after diagnosis. RESULTS: Decanucleotide insertion polymorphism of F7 emerged as an independent, significant risk factor for total thrombosis and arterial thrombosis in particular in the whole group of patients (P = 0.0007) as well as in the separate analysis of patients with ET (P = 0.0002). CONCLUSION: Our results illustrate that the risk of thrombosis in MPN is significantly multiplied by inherited thrombophilic SNPs. This result points to the importance of a combined consideration of the inherited and the acquired hypercoagulable state in patients with MPN. Larger studies are needed to confirm and extend these important findings.

Discriminating between essential thrombocythemia and masked polycythemia vera in JAK2 mutated patients.

In patients not meeting the required hematocrit (HCT) or hemoglobin (Hb) thresholds according to BCSH and the WHO diagnostic criteria, the diagnosis of masked polycythemia vera (mPV) has been proposed. A comparison of HCT or Hb values with the expression of JAK2V617F, JAK2 exon 12, and CALR mutations in strictly WHO-defined 257 overt PV and 140 mPV (59 mPV according to BCSH) and 397 patients with essential thrombocythemia (ET) was performed. Hb and HCT thresholds of mPV patients were significantly higher than JAK2V617F ET (P < 0.0001). The best cut-off for Hb to discriminate JAK2-mutated ET from PV was 16.5 g/dL for males and 16.0 g/dL for females. For HCT, this was 49% in males and 48% in females. The proportion of patients correctly classified as ET or PV when regarding Hb or HCT levels was 95% in males and 93% in females and 94% in both males and females, respectively.

Masked polycythemia vera (mPV): results of an international study.

We examined the baseline features and clinical outcomes of 140 patients presenting with JAK2V617F positivity and a bone marrow morphology conforming with WHO criteria of polycythemia vera (PV), but a hemoglobin level of <18.5 g/dL in males (range 16.0-18.4) and <16.5 g/dL in females (range 15.0-16.4). This cohort operationally referred to as masked PV (mPV) was compared with 257 patients with overt PV and displayed male predominance, a more frequent history of arterial thrombosis and thrombocytosis. Incidence of thrombosis was similar between the two groups but mPV displayed significantly higher rates of progression to myelofibrosis and acute leukemia and inferior survival. In multivariable analysis mPV diagnosis was an independent predictor of poor survival along with age >65 years and leukocyte count >10 × 10(9) /L. Our data suggest that mPV is a heterogeneous myeloproliferative neoplasia and not necessarily an early/ pre-polycythemic form of classical PV that at onset in a small fraction of patients clinically may mimic essential thrombocythemia. On the other hand, the majority mPV may have a longer prodrome of undiagnosed PV or a disease biology akin to primary myelofibrosis-post PV myelofibrosis that could explain the worsening of outcome in comparison to overt/classical manifestations.

Masked polycythemia vera diagnosed according to WHO and BCSH classification.

Polycythemia vera (PV) is currently diagnosed by the World Health Organization (WHO) criteria regarding hemoglobin (HB) levels and JAK2V617F and related mutations or by the British Committee for Standards in Haematology (BCSH) guidelines predominantly based on hematocrit (HCT) values (>52% in men and >48% in women) in JAK2 mutated patients. We examined clinical features at diagnosis and outcome in 397 mutated PV patients showing a bone marrow (BM) morphology conforming with the WHO descriptions but including also cases with a HB level <18.5 g/dL in males (range 16.0-18.4) and <16.5 g/dL in females (range 15.0-16.4). These patients were regarded as masked PV (mPV) comprising 140 (35%) cases of our cohort. A comparison with the BCSH criteria based on HCT levels revealed a decrease of mPV patients to 59 (15%). In both classification systems, mPV patients were more males, presented more frequently with higher platelet counts, and increased BM reticulin fibrosis. A worsening of overall survival was documented in mPV patients in comparison with overt PV following the WHO (P = 0.011) as well as the BCSH (P = 0.0019) criteria. Risk factors for inferior survival in mPV were age >65 years and white blood cell count >15 × 10(9) /L. Without these risk factors mPV patients had the same survival as overt PV suggesting that a fraction of patients with HB lower than that required for WHO diagnosis should still be considered as overt PV. This study has established the existence of mPV by two different classification systems based on either HB or HCT threshold values.