Essential thrombocythemia vs. early/prefibrotic myelofibrosis: Why does it matter

SOHO State of the Art Updates and Next Questions | Early Intervention in Myelofibrosis: Where Are We and Does It Matter?

Historically, therapeutic clinical trials in myelofibrosis have predominantly focused on targeting patients with higher-risk disease who are at risk of increased morbidity and mortality. The endpoints have been designed to target regularly measured disease parameters that are of immediate pertinence to patient's welfare including splenic volume reduction and symptom reduction. These efforts have resulted in meaningful and measurable improvements in disease parameters in these high-risk study populations and multiple FDA approved agents. However, they have not tackled specific interventions that may be applied to patients with earlier or less advanced disease state. In this review, we summarize evidence from completed and ongoing clinical trials investigating different aspects of intervention targeted at less advanced disease and advocate for the merit of this approach.

Easily Applicable Predictive Score for Differential Diagnosis of Prefibrotic Primary Myelofibrosis from Essential Thrombocythemia

Essential thrombocythemia (ET) and prefibrotic primary myelofibrosis (prePMF) initially have a similar phenotypic presentation with thrombocytosis. The aim of our study was to determine significant clinical-laboratory parameters at presentation to differentiate prePMF from ET as well as to develop and validate a predictive diagnostic prePMF model. This retrospective study included 464 patients divided into ET (289 pts) and prePMF (175 pts) groups. The model was built using data from a development cohort (229 pts; 143 ET, 86 prePMF), which was then tested in an internal validation cohort (235 pts; 146 ET, 89 prePMF). The most important prePMF predictors in the multivariate logistic model were age ≥ 60 years (RR = 2.2), splenomegaly (RR = 13.2), and increased lactat-dehidrogenase (RR = 2.8). Risk scores were assigned according to derived relative risk (RR) for age ≥ 60 years (1 point), splenomegaly (2 points), and increased lactat-dehidrogenase (1 point). Positive predictive value (PPV) for pre-PMF diagnosis with a score of ≥points was 69.8%, while for a score of ≥3 it was 88.2%. Diagnostic performance had similar values in the validation cohort. In MPN patients with thrombocytosis at presentation, the application of the new model enables differentiation of pre-PMF from ET, which is clinically relevant considering that these diseases have different prognoses and treatments.

Challenges of diagnosing and managing pre-fibrotic myelofibrosis: A case-based and practical approach

Pre-Fibrotic Myelofibrosis is a frequently under-recognised entity that has distinct features separate to those of both Essential Thrombocythaemia and overt Primary Myelofibrosis. Misdiagnosis is relatively common due to subtle differences in bone marrow trephine morphology and multidisciplinary approaches are required. The clinical phenotype and disease course is heterogeneous and hence management approaches tend to vary widely. Although patients may initially be asymptomatic, disease-related complications can include troublesome symptom burdens, increased incidence of both arterial and venous thromboses, haemorrhage, anaemia and an inherent risk of disease evolution to either overt myelofibrosis or blastic phase disease. Specific prognostic tools with high discriminatory power are lacking. Within this review we use case-based approaches to review the current literature, highlight challenges in both diagnostics and disease management and suggest contemporary approaches to improve patient outcomes.

Synoptic Diagnostics of Myeloproliferative Neoplasms: Morphology and Molecular Genetics

Simple Summary

The diagnosis of myeloproliferative neoplasms requires assessment of a combination of clinical, morphological, immunophenotypic and genetic features, and this integrated, multimodal approach forms the basis for precise classification. Evaluation includes cell counts and morphology in the peripheral blood, bone marrow aspiration and trephine biopsy, and may encompass flow cytometry for specific questions. Diagnosis nowadays is completed by targeted molecular analysis for the detection of recurrent driver and, optionally, disease-modifying mutations. According to the current World Health Organization classification, all myeloproliferative disorders require assessment of molecular features to support the diagnosis or confirm a molecularly defined entity. This requires a structured molecular analysis workflow tailored for a rapid and cost-effective diagnosis. The review focuses on the morphological and molecular features of Ph-negative myeloproliferative neoplasms and their differential diagnoses, addresses open questions of classification, and emphasizes the enduring role of histopathological assessment in the molecular era.

Abstract

The diagnosis of a myeloid neoplasm relies on a combination of clinical, morphological, immunophenotypic and genetic features, and an integrated, multimodality approach is needed for precise classification. The basic diagnostics of myeloid neoplasms still rely on cell counts and morphology of peripheral blood and bone marrow aspirate, flow cytometry, cytogenetics and bone marrow trephine biopsy, but particularly in the setting of Ph− myeloproliferative neoplasms (MPN), the trephine biopsy has a crucial role. Nowadays, molecular studies are of great importance in confirming or refining a diagnosis and providing prognostic information. All myeloid neoplasms of chronic evolution included in this review, nowadays feature the presence or absence of specific genetic markers in their diagnostic criteria according to the current WHO classification, underlining the importance of molecular studies. Crucial differential diagnoses of Ph− MPN are the category of myeloid/lymphoid neoplasms with eosinophilia and gene rearrangement of PDGFRA, PDGFRB or FGFR1, or with PCM1-JAK2, and myelodysplastic/myeloproliferative neoplasms (MDS/MPN). This review focuses on morphological, immunophenotypical and molecular features of BCR-ABL1-negative MPN and their differential diagnoses. Furthermore, areas of difficulties and open questions in their classification are addressed, and the persistent role of morphology in the area of molecular medicine is discussed.

Clinical and Molecular Attributes of Patients With BCR/ABL1-negative Myeloproliferative Neoplasms in India: Real-world Data and Challenges

INTRODUCTION

Classic BCR/ABL1-negative myeloproliferative neoplasms (MPNs) are characterized by clinical and genetic heterogeneity and include 4 distinct constituents. Very little data on clinical presentation and epidemiology of the same is available from the Indian setting.

PATIENTS AND METHODS

Patients referred to Hematology-Oncology from January 2018 to August 2020 with suspected MPNs were included in the analysis and prospectively followed-up. All patients were initially screened, and only those meeting the updated World Health Organization 2016 criteria were included in the analysis. Epidemiologic, clinical, and molecular characteristics were documented, and patients were followed-up prospectively.

RESULTS

A total of 233 patients were referred for evaluation of MPN, of which 63 were included in the analysis, including 39 males and 24 females. The median age at diagnosis was 57 years (range, 28-82 years), and 38% patients were younger than 50 years of age. The most common presentations were incidental detection in 35 (55.5%), abdominal symptoms in 13 (20%), fatiguability in 7 (11%), and recent vascular events in 6 (9.5%) patients. Final diagnosis was polycythemia vera in 27, essential thrombocytosis (ET) in 21, prefibrotic myelofibrosis in 9, and myelofibrosis in 6 patients. The frequency of driver mutations in polycythemia vera included JAK2 in 75%; in ET, JAK2 in 33%, CALR in 33%, and MPL in 4%; and in prefibrotic myelofibrosis, JAK2 in 66% and CALR in 33%. Aspirin was used for all patients along with risk-adapted cytoreduction with hydroxyurea. Ruxolitinib was reserved for symptoms refractory to hydroxyurea. After a median follow-up of 15 months (interquartile range, 10-28 months) from diagnosis, disease progression was noted in 4 patients. Two patients died at the end of the follow-up period, including 1 with secondary acute myeloid leukemia post myelofibrosis and one with ET and coexistent oral malignancy. The remaining 61 patients are alive and on regular treatment.

RESULTS

This is one of the first systematic descriptions and prospective follow-up of patients with BCR/ABL-negative MPNs from India. Our study indicates a younger median age of presentation and higher proportion of JAK2-unmutated disease across all subtypes. The primary role of bone marrow morphology and supportive role of somatic mutations in differentiating MPN subtypes is indicated.

CONCLUSIONS

This study sets the stage for a collaborative registry for defining epidemiologic data and long-term outcomes with MPN in India.

A provider's guide to primary myelofibrosis: pathophysiology, diagnosis, and management

Although understanding of the pathogenesis and molecular biology of primary myelofibrosis continues to improve, treatment options are limited, and several biological features remain unexplained. With an appropriate clinical history, exam, laboratory evaluation, and bone marrow biopsy, the diagnosis can often be established. Recent studies have better characterized prognostic factors and driver mutations in myelofibrosis, facilitated by use of next-generation sequencing. These advances have facilitated development of a management strategy that is based on both risk factors and clinical phenotype. For low-risk patients, treatment will depend on symptom severity. For patients with higher-risk disease, several treatments are available including JAK inhibitors, allogeneic hematopoietic stem cell transplant, and clinical trials using novel molecularly targeted therapies and rational drug combinations. In this review, we outline what is known about the disease pathogenesis, discuss an approach to reaching the diagnosis, review the prognosis of myelofibrosis, and detail current therapeutic strategies.

Clinical and molecular features of patients with prefibrotic primary myelofibrosis previously diagnosed as having essential thrombocythemia in Japan

OBJECTIVE

Prefibrotic/early primary myelofibrosis (pre-PMF) and essential thrombocythemia (ET) exhibited different features of bone marrow; however, this is not always easy to judge objectively, making pathologists' distinction often suboptimal. In the WHO 2008 criteria, pre-PMF was not defined as a subgroup of PMF; therefore, affected patients were at a higher risk of misdiagnosis with ET. In this study, we examined the prevalence of pre-PMF patients among those previously diagnosed with ET in Japan.

METHOD

We reviewed bone marrow specimens and clinical and molecular parameters of patients who were previously diagnosed with ET by the WHO 2008 criteria.

RESULTS

Among 107 ET patients, 13 patients were redefined as having pre-PMF. Pre-PMF patients exhibited a higher frequency of MPL mutation and increased platelet counts compared to true ET patients. Molecular analysis revealed the frequencies of high-risk molecular mutations, such as ASXL1, EZH2, and SRSF2, were significantly increased in pre-PMF patients than those in true ET patients.

CONCLUSION

These results demonstrated the value of reexamining clinical records for patients diagnosed with ET by the WHO 2008 criteria and emphasized that adequate examinations of patients' bone marrow are crucial for an accurate diagnosis of pre-PMF and ET.

The epidemiology and clinical characteristics of myeloproliferative neoplasms in Malaysia

Background

The evolution of molecular studies in myeloproliferative neoplasms (MPN) has enlightened us the understanding of this complex disease consisting of polycythaemia vera (PV), essential thrombocythemia (ET) and primary myelofibrosis (PMF). The epidemiology is well described in the western world but not in Asian countries like Malaysia.

Materials and methods

This retrospective national registry of MPN was conducted from year 2009 to 2015 in Malaysia.

Results

A total of 1010 patients were registered over a period of 5 years. The mean age was 54 years with male predominance. The ethnic distribution revealed that Chinese had a relatively high weighted incidence proportion (43.2%), followed by Indian (23.8%), Malay (15.8%) and other ethnic groups (17.2%). The types of MPN reported were 40.4% of ET (n = 408), 38.1% of PV (n = 385), 9.2% of PMF (n = 93), 3.1% of hypereosinophilic syndrome (HES) (n = 31) and 7.9% of unclassifiable MPN (MPN-U) (n = 80). Splenomegaly was only palpable clinically in 32.2% of patients. The positive JAK2 V617F mutation was present in 644 patients with 46.6% in PV, 36.0% in ET, 9.0% in PMF, and 7.4% in MPN-U, and had significantly lower haemoglobin (p < 0.001), haematocrit (p < 0.001) and white blood cells (WBC) (p < 0.001) than those with negative mutation. Significant differences in platelet and WBC count were detected in ethnic groups and MPN sub-types. There were more arterial thrombosis events seen in those with JAK2 V617F mutation as compared to venous thrombosis events (23.1% vs 4.4%). The bleeding rate was only 6.6%. Among the risk factors, previous thrombosis, old age (≥ 60 years) and hypertension were significantly correlated to positive JAK2 V617F mutation. The arterial thrombosis event is associated with higher presenting HB, HCT and PLT while the bleeding event is associated with lower presenting HB, HCT but higher PLT. The presence of JAK2 V617F mutation is associated with higher risk of arterial thrombosis.

Conclusion

Chinese ethnicity is associated with higher rates of MPN. The history of thrombosis, age ≥ 60 years and hypertension are risk factors that can be correlated to JAK2 V617F mutation. This study is instrumental for policy makers to ensure preventive strategies can be implemented in future.

GATA1 Expression in BCR/ABL1-negative Myeloproliferative Neoplasms

Background

This study aimed to determine GATA1 expression levels to better characterize subgroups in BCR/ABL1-negative myeloproliferative neoplasms (MPNs).

Methods

This study enrolled 49 patients diagnosed as having BCR/ABL1-negative MPN on the basis of the 2016 World Health Organization classification : nine polycythemia vera (PV), 17 essential thrombocythemia (ET), 12 prefibrotic primary myelofibrosis (prePMF), and 11 overt primary myelofibrosis (PMF). Relevant clinical and laboratory data were retrieved from the medical records. The molecular analysis of CALR and MPL mutations and quantification of JAK2 V617F allele burden were performed. GATA1 expression was assessed by an immunohistochemical assay on bone marrow biopsy. GATA1 expression was analyzed serially in 18 patients.

Results

GATA1 expression decreased significantly in PMF compared with that in other subtypes, while no statistical difference was identified between ET and prePMF. GATA1 expression did not differ according to the mutation profiles or the allele burden of JAK2 V617F, but it decreased significantly in patients with overt fibrosis or leukemic transformation.

Conclusions

Our results suggest that GATA1 expression is significantly low in PMF and decreases with progressive fibrosis and possibly with leukemic transformation, although our attempt to accurately distinguish between subgroups using GATA1 immunohistochemical approach did not achieve statistical significance. A large patient cohort with long term follow-up is required to evaluate the prognostic value of GATA1 expression.

The 2016 WHO classification and diagnostic criteria for myeloproliferative neoplasms: document summary and in-depth discussion

The new edition of the 2016 World Health Organization (WHO) classification system for tumors of the hematopoietic and lymphoid tissues was published in September 2017. Under the category of myeloproliferative neoplasms (MPNs), the revised document includes seven subcategories: chronic myeloid leukemia, chronic neutrophilic leukemia, polycythemia vera (PV), primary myelofibrosis (PMF), essential thrombocythemia (ET), chronic eosinophilic leukemia-not otherwise specified and MPN, unclassifiable (MPN-U); of note, mastocytosis is no longer classified under the MPN category. In the current review, we focus on the diagnostic criteria for JAK2/CALR/MPL mutation-related MPNs: PV, ET, and PMF. In this regard, the 2016 changes were aimed at facilitating the distinction between masked PV and JAK2-mutated ET and between prefibrotic/early and overtly fibrotic PMF. In the current communication, we (i) provide practically useful resource tables and graphs on the new diagnostic criteria including outcome, (ii) elaborate on the rationale for the 2016 changes, (iii) discuss the complementary role of mutation screening, (iv) address ongoing controversies and propose solutions, (v) attend to the challenges of applying WHO criteria in routine clinical practice, and (vi) outline future directions from the perspectives of the clinical pathologist.

The 2016 WHO classification and diagnostic criteria for myeloproliferative neoplasms: document summary and in-depth discussion

The new edition of the 2016 World Health Organization (WHO) classification system for tumors of the hematopoietic and lymphoid tissues was published in September 2017. Under the category of myeloproliferative neoplasms (MPNs), the revised document includes seven subcategories: chronic myeloid leukemia, chronic neutrophilic leukemia, polycythemia vera (PV), primary myelofibrosis (PMF), essential thrombocythemia (ET), chronic eosinophilic leukemia-not otherwise specified and MPN, unclassifiable (MPN-U); of note, mastocytosis is no longer classified under the MPN category. In the current review, we focus on the diagnostic criteria for JAK2/CALR/MPL mutation-related MPNs: PV, ET, and PMF. In this regard, the 2016 changes were aimed at facilitating the distinction between masked PV and JAK2-mutated ET and between prefibrotic/early and overtly fibrotic PMF. In the current communication, we (i) provide practically useful resource tables and graphs on the new diagnostic criteria including outcome, (ii) elaborate on the rationale for the 2016 changes, (iii) discuss the complementary role of mutation screening, (iv) address ongoing controversies and propose solutions, (v) attend to the challenges of applying WHO criteria in routine clinical practice, and (vi) outline future directions from the perspectives of the clinical pathologist.

Prognosis of Primary Myelofibrosis in the Genomic Era

Currently, prognostication in primary myelofibrosis (PMF) relies on the International Prognostic Scoring System (IPSS), dynamic IPSS (DIPSS), and DIPSS-plus, which incorporate age, blood counts, constitutional symptoms, circulating blasts, red cell transfusion need, and karyotype. Although the JAK2 V617F mutation was discovered a decade ago and MPL mutations shortly thereafter, it was the recent discovery of CALR mutations in the vast majority of JAK2/MPL-unmutated patients and recognition of the powerful impact of CALR mutations and triple-negative (JAK2/MPL/CALR-negative) status on outcome that set the stage for revision of traditional prognostic models to include molecular information. Additionally, the advent of next-generation sequencing has identified a host of previously unrecognized somatic mutations across hematologic malignancies. As in the myelodysplastic syndromes, the majority of common and prognostically informative mutations in PMF affect epigenetic regulation and mRNA splicing. Thus, a need has arisen to incorporate mutational information on genes such as ASXL1 and SRSF2 into risk stratification systems. Mutations in yet other genes appear to be important players in leukemic transformation, and new insights into disease pathogenesis are emerging. Finally, the number of prognostically detrimental mutations may affect both survival and response to ruxolitinib, which has significant implications for clinical decision making. In this review, we briefly summarize the prognostic models in use today and discuss in detail the somatic mutations commonly encountered in patients with PMF, along with their prognostic implications and role in leukemic transformation. Emerging prognostic models that incorporate new molecular information into existing systems or exclude clinical variables are also presented.

Clinical course and outcome of essential thrombocythemia and prefibrotic myelofibrosis according to the revised WHO 2016 diagnostic criteria

The recently revised World Health Organization (WHO) classification of myeloid neoplasms recognizes prefibrotic myelofibrosis (prePMF) as a distinct entity, characterized by well-defined histopathologic features together with minor clinical criteria (leukocytes, anemia, increased LDH, splenomegaly). The aim of the study was to examine the clinical relevance of distinguishing prePMF from essential thrombocythemia (ET). We identified in our database all patients affected with ET, prePMF and primary myelofibrosis (PMF) diagnosed according to 2008 WHO criteria with a bone marrow fibrosis grade 0-1 at diagnosis and one DNA sample to define the mutational status. The bone marrow morphology of all 404 identified patients was reviewed by an expert pathologist and patients were reclassified according to the 2016 WHO criteria. After reclassification, our cohort included 269 ET, 109 prePMF, and 26 myeloproliferative neoplasm unclassificable. In comparison with ET, patients with prePMF had higher leukocyte count, lower hemoglobin level, higher platelet count, higher LDH values, and higher number of circulating CD34-positive cells; they showed more frequently splenomegaly (all P values < ·001). CALR mutations were more frequent in prePMF than in ET (35·8% vs 17·8%, P < ·001). PrePMF patients had shorter overall survival (P < ·001) and a trend to a higher incidence of leukemic evolution (P ·067) compared to ET patients, while they did not differ in terms of thrombotic and bleeding complications. In conclusion, ET and prePMF diagnosed according to 2016 WHO criteria are two entities with a different clinical phenotype at diagnosis and a different clinical outcome.

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.

Polycythemia and Thrombocytosis

Myeloproliferative neoplasms (MPNs) are diseases of excess cell proliferation from bone marrow precursors. Two classic MPNs, polycythemia vera (PV) and essential thrombocytosis (ET), are conditions of excess proliferation of red blood cells and platelets, respectively. Although PV and ET involve different cells in the myeloid lineage, their clinical presentations have shared features, consistent with overlapping mutations in growth factor signaling. The management of both diseases involves minimizing the risk of thrombotic and hemorrhagic complications. Both PV and ET can progress to myelofibrosis or acute myeloid leukemia, portending a poor prognosis. MPNs can also present as primary myelofibrosis.

The role of the extracellular matrix in primary myelofibrosis

Primary myelofibrosis (PMF) is a myeloproliferative neoplasm that arises from clonal proliferation of hematopoietic stem cells and leads to progressive bone marrow (BM) fibrosis. While cellular mutations involved in the development of PMF have been heavily investigated, noteworthy is the important role the extracellular matrix (ECM) plays in the progression of BM fibrosis. This review surveys ECM proteins contributors of PMF, and highlights how better understanding of the control of the ECM within the BM niche may lead to combined therapeutic options in PMF.

Austrian recommendations for the management of primary myelofibrosis, post-polycythemia vera myelofibrosis and post-essential thrombocythemia myelofibrosis: an expert statement

The entity "myelofibrosis" represents a subgroup of the Philadelphia chromosome-negative myeloproliferative neoplasms. It comprises primary myelofibrosis, post-polycythemia vera myelofibrosis and post-essential thrombocythemia myelofibrosis. This heterogeneous disease is characterized by clonal myeloproliferation, dysregulated kinase signalling and the abnormal expression of several proinflammatory cytokines. Clinically, patients present with symptoms related to thrombocytosis/leukocytosis, anemia and/or progressive splenomegaly. Mutations in Janus kinase 2, an enzyme that is essential for the normal development of erythrocytes, granulocytes, and platelets, notably the V617F mutation, have been identified in approximately 60% of patients with primary myelofibrosis. Recent molecular advances have not only elucidated critical pathways in the pathogenesis of the disease, but also contributed to a more precise assessment of a patient's individual risk. While allogeneic stem cell transplantation remains the only curative treatment, the natural course of the disease and the patient's survival and quality of life may be improved by new treatments, notably ruxolitinib, the first Janus kinase 1/2 inhibitor approved for the management of myelofibrosis. Additional treatment options are being explored.

Primary myelofibrosis and its targeted therapy

Primary myelofibrosis is a unique entity among BCR-ABL-negative myeloproliferative diseases, manifesting as bone marrow fibrosis and pancytopenia. Considerable evidence indicates that genetic and epigenetic abnormalities can result in defective clonal hematopoietic stem cell proliferation in addition to bone marrow microenvironment alteration. The "bad seeds in bad soil" theory illustrates the orchestrating efforts of hematopoietic stem cells, stromal cells, and their surrounding signaling molecules in myelofibrosis progression and malignancy transformation, though the exact mechanism of myelofibrosis is still not clear. This study reviews current concepts and questions regarding the pathogenesis of primary myelofibrosis and discusses the emerging targeted therapy aimed at restoring normal bone marrow environment and halting bone marrow fibrotic deterioration.

The 2016 revision of WHO classification of myeloproliferative neoplasms: Clinical and molecular advances

Clinical evidence supports the need of changing the diagnostic criteria of the 2008 updated WHO classification for polycythemia vera (PV), essential thrombocythemia (ET) and primary myelofibrosis (PMF). In JAK2-mutated patients who show characteristic bone marrow (BM) morphology, clinical studies demonstrated that a hemoglobin level of 16.5g/dL in men and 16.0g/dl for women or a hematocrit value of 49% in men and 48% in women are the optimal cut off levels for distinguishing JAK2-mutated ET from "masked/prodromal" PV. Therefore BM morphology was upgraded to a major diagnostic criterion. Regarding ET the key issue was to improve standardization of prominent BM features enhancing differentiation between "true" ET and prefibrotic/early primary myelofibrosis (prePMF). These two entities have shown a different epidemiology and clinical outcomes. Concerning prePMF a more explicit clinical characterization of minor criteria is mandated for an improved distinction from ET and overt PMF and accurate diagnosis and outcome prediction.

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.

Recent advances in understanding myelofibrosis and essential thrombocythemia

The classic BCR-ABL-negative myeloproliferative neoplasms (MPNs), a form of chronic malignant hemopathies, have been classified into polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF). ET and PMF are two similar disorders in their pathogenesis, which is marked by a key role of the megakaryocyte (MK) lineage. Whereas ET is characterized by MK proliferation, PMF is also associated with aberrant MK differentiation (myelodysplasia), leading to the release of cytokines in the marrow environment, which causes the development of myelofibrosis. Thus, PMF is associated with both myeloproliferation and different levels of myelodysplastic features. MPNs are mostly driven by mutated genes called MPN drivers, which abnormally activate the cytokine receptor/JAK2 pathway and their downstream effectors. The recent discovery of CALR mutations has closed a gap in our knowledge and has shown that this mutated endoplasmic reticulum chaperone activates the thrombopoietin receptor MPL and JAK2. These genetic studies have shown that there are two main types of MPNs: JAK2V617F-MPNs, including ET, PV, and PMF, and the MPL-/CALR-MPNs, which include only ET and PMF. These MPN driver mutations are associated with additional mutations in genes involved in epigenetics, splicing, and signaling, which can precede or follow the acquisition of MPN driver mutations. They are involved in clonal expansion or phenotypic changes or both, leading to myelofibrosis or leukemic transformation or both. Only a few patients with ET exhibit mutations in non-MPN drivers, whereas the great majority of patients with PMF harbor one or several mutations in these genes. However, the entire pathogenesis of ET and PMF may also depend on other factors, such as the patient’s constitutional genetics, the bone marrow microenvironment, the inflammatory response, and age. Recent advances allowed a better stratification of these diseases and new therapeutic approaches with the development of JAK2 inhibitors.

The evolution and clinical relevance of prognostic classification systems in myelofibrosis

Primary myelofibrosis, the most aggressive of the classic Philadelphia chromosome-negative myeloproliferative neoplasms (MPNs), is a clonal disorder characterized by often debilitating constitutional symptoms and splenomegaly, bone marrow fibrosis and resultant cytopenias, extramedullary hematopoiesis, risk of leukemic transformation, and shortened survival. Post-polycythemia vera and post-essential thrombocythemia myelofibrosis represent similar entities, although some differences are being recognized. Attempts to classify patients with myelofibrosis into prognostic categories have been made since the late 1980s, and these scoring systems continue to evolve as new information becomes available. Over the last decade, the molecular pathogenesis of MPNs has been elucidated considerably, and the Janus kinase (JAK) 1/2 inhibitor ruxolitinib is the first drug specifically approved by the US Food and Drug Administration to treat patients with intermediate-risk and high-risk myelofibrosis. This article reviews the evolution of prognostic criteria in myelofibrosis, emphasizing the major systems widely in use today, as well as recently described, novel systems that incorporate emerging data regarding somatic mutations. Risk factors for thrombosis and conversion to MPN blast phase also are discussed. Finally, the practical usefulness of the current prognostic classification systems in terms of clinical decision making is discussed, particularly within the context of some of their inherent weaknesses. Cancer 2016;122:681-692. © 2015 American Cancer Society.

Clinical impact of bone marrow morphology for the diagnosis of essential thrombocythemia: comparison between the BCSH and the WHO criteria

Essential thrombocythemia (ET) is currently diagnosed either by the British Committee of Standards in Haematology (BCSH) criteria that are predominantly based on exclusion and not necessarily on bone marrow (BM) morphology, or the World Health Organization (WHO) criteria that require BM examination as essential criterion. We studied the morphological and clinical features in patients diagnosed according either to the BCSH (n=238) or the WHO guidelines (n=232). The BCSH-defined ET cohort was re-evaluated by applying the WHO classification. At presentation, patients of the BCSH group showed significantly higher values of serum lactate dehydrogenase and had palpable splenomegaly more frequently. Following the WHO criteria, the re-evaluation of the BCSH-diagnosed ET cohort displayed a heterogeneous population with 141 (59.2%) ET, 77 (32.4%) prefibrotic primary myelofibrosis (prePMF), 16 (6.7%) polycythemia vera and 4 (1.7%) primary myelofibrosis. Contrasting WHO-confirmed ET, the BCSH cohort revealed a significant worsening of fibrosis-free survival and prognosis. As demonstrated by the clinical data and different outcomes between WHO-diagnosed ET and prePMF, these adverse features were generated by the inadvertent inclusion of prePMF to the BCSH group. Taken together, the diagnosis of ET without a scrutinized examination of BM biopsy specimens will generate a heterogeneous cohort of patients impairing an appropriate clinical management.

Myeloproliferative neoplasms: Current molecular biology and genetics

Myeloproliferative neoplasms (MPNs) are clonal disorders characterized by increased production of mature blood cells. Philadelphia chromosome-negative MPNs (Ph-MPNs) consist of polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF). A number of stem cell derived mutations have been identified in the past 10 years. These findings showed that JAK2V617F, as a diagnostic marker involving JAK2 exon 14 with a high frequency, is the best molecular characterization of Ph-MPNs. Somatic mutations in an endoplasmic reticulum chaperone, named calreticulin (CALR), is the second most common mutation in patients with ET and PMF after JAK2 V617F mutation. Discovery of CALR mutations led to the increased molecular diagnostic of ET and PMF up to 90%. It has been shown that JAK2V617F is not the unique event in disease pathogenesis. Some other genes' location such as TET oncogene family member 2 (TET2), additional sex combs-like 1 (ASXL1), casitas B-lineage lymphoma proto-oncogene (CBL), isocitrate dehydrogenase 1/2 (IDH1/IDH2), IKAROS family zinc finger 1 (IKZF1), DNA methyltransferase 3A (DNMT3A), suppressor of cytokine signaling (SOCS), enhancer of zeste homolog 2 (EZH2), tumor protein p53 (TP53), runt-related transcription factor 1 (RUNX1) and high mobility group AT-hook 2 (HMGA2) have also identified to be involved in MPNs phenotypes. Here, current molecular biology and genetic mechanisms involved in MNPs with a focus on the aforementioned factors is presented.

Rationale for revision and proposed changes of the WHO diagnostic criteria for polycythemia vera, essential thrombocythemia and primary myelofibrosis

The 2001/2008 World Health Organization (WHO)-based diagnostic criteria for polycythemia vera (PV), essential thrombocythemia (ET) and primary myelofibrosis (PMF) were recently revised to accomodate new information on disease-specific mutations and underscore distinguishing morphologic features. In this context, it seems to be reasonable to compare first major diagnostic criteria of the former WHO classifications for myeloproliferative neoplasm (MPN) and then to focus on details that have been discussed and will be proposed for the upcoming revision of diagnostic guidelines. In PV, a characteristic bone marrow (BM) morphology was added as one of three major diagnostic criteria, which allowed lowering of the hemoglobin/hematocrit threshold for diagnosis, which is another major criterion, to 16.5 g/dl/49% in men and 16 g/dl/48% in women. The presence of a JAK2 mutation remains the third major diagnostic criterion in PV. Subnormal serum erythropoietin level is now the only minor criterion in PV and is used to capture JAK2-unmutated cases. In ET and PMF, mutations that are considered to confirm clonality and specific diagnosis now include CALR, in addition to JAK2 and MPL. Also in the 2015 discussed revision, overtly fibrotic PMF is clearly distinguished from early/prefibrotic PMF and each PMF variant now includes a separate list of diagnostic criteria. The main rationale for these changes was to enhance the distinction between so-called masked PV and JAK2-mutated ET and between ET and prefibrotic early PMF. The proposed changes also underscore the complementary role, as well as limitations of mutation analysis in morphologic diagnosis. On the other hand, discovery of new biological markers may probably be expected in the future to enhance discrimination of the different MPN subtypes in accordance with the histological BM patterns and corresponding clinical features.

Analysis of phenotype and outcome in essential thrombocythemia with CALR or JAK2 mutations

The JAK2 V617F mutation, the thrombopoietin receptor MPL W515K/L mutation and calreticulin (CALR) mutations are mutually exclusive in essential thrombocythemia and support a novel molecular categorization of essential thrombocythemia. CALR mutations account for approximately 30% of cases of essential thrombocythemia. In a retrospective study, we examined the frequency of MPL and CALR mutations in JAK2 V617F-negative cases of essential thrombocythemia (n=103). In addition, we compared the clinical phenotype and outcome of CALR mutant cases of essential thrombocythemia with a cohort of JAK2 V617F-positive essential thrombocythemia (n=57). CALR-positive cases represented 63.7% of double-negative cases of essential thrombocythemia, and most carried CALR type 1 or type 2 indels. However, we also identified one patient who was positive for both the JAK2 V617F and the CALR mutations. This study revealed that CALR mutant essential thrombocythemia is associated with younger age, higher platelet counts, lower erythrocyte counts, leukocyte counts, hemoglobin, and hematocrit, and increased risk of progression to myelofibrosis in comparison with JAK2 V617F-positive essential thrombocythemia. Analysis of the CALR mutant group according to indel type showed that CALR type 1 deletion is strongly associated with male gender. CALR mutant patients had a better overall survival than JAK2 V617F-positive patients, in particular patients of age 60 years or younger. In conclusion, this study in a Belgian cohort of patients supports and extends the growing body of evidence that CALR mutant cases of essential thrombocythemia are phenotypically distinct from JAK2 V617F-positive cases, with regards to clinical and hematologic presentation as well as overall survival.

Limitations of fibrosis grade as diagnostic criteria for post polycythemia vera and essential thrombocytosis myelofibrosis

BACKGROUND

The clinical phenotype of patients with myeloproliferative neoplasms (MPNs) including primary myelofibrosis (PMF), polycythemia vera (PV), and essential thrombocytosis (ET) whom manifest WHO grade 1 marrow fibrosis is poorly defined. Current IWG-MRT criteria require 2+ marrow fibrosis for diagnosis of post PV/ET myelofibrosis (MF). In contrast, the 2008 WHO definition of PMF does not require a minimum fibrosis threshold.

METHODS

We retrospectively analyzed the clinical characteristics of 91 MPN patients with 1+ marrow fibrosis. We compared the clinical phenotype of sub threshold fibrosis PV/ET with that manifested by PMF. We applied the IWG-MRT criteria for post-PV/ET MF with the fibrosis component omitted and evaluated for percentage of criteria fulfillment.

RESULTS

When IWG-MRT criteria were applied to the PV/ET group, 38/58 (66%) of patients fulfilled criteria for diagnosis of post-PV/ET myelofibrosis except for the 2+ fibrosis requirement. Comparison of sub threshold fibrotic PV/ET clinical phenotype to PMF revealed similar characteristics including heavy symptomatic burden (57% and 52%), presence of splenomegaly (43% and 55%), leukoerythroblastic blood smear (38% and 45%), and median hemoglobin (12.8g/dL and 11.1g/dL).

CONCLUSION

MPN progression represents a biological spectrum and definitions of progression in ET/PV may benefit from criteria not restricted by degree of fibrosis.

Thrombosis in essential thrombocytemia and early/prefibrotic primary myelofibrosis: the role of the WHO histological diagnosis

BACKGROUND

Vascular events represent the most frequent complications of thrombocytemias. We aimed to evaluate their risk in the WHO histologic categories of Essential Thrombocytemia (ET) and early Primary Myelofibrosis (PMF).

METHODS

From our clinical database of 283 thrombocytemic patients, we selected those with available bone marrow histology performed before any treatment, at or within 1 year from diagnosis, and reclassified the 131 cases as true ET or early PMF, with or without fibrosis, according to the WHO histological criteria. Vaso-occlusive events at diagnosis and in the follow-up were compared in the WHO-groups.

RESULTS

Histologic review reclassified 61 cases as ET and 72 cases as early PMF (26 prefibrotic and 42 with grade 1 or 2 fibrosis). Compared to ET, early PMF showed a significant higher rate of thrombosis both in the past history (22% vs 8%) and at diagnosis (15.2% vs 1.6%), and an increased leukocyte count (8389 vs 7500/mmc). Venous thromboses (mainly atypical) were relatively more common in PMF than in ET. Patients with prefibrotic PMF, although younger, showed a significant higher 15-year risk of developing thrombosis (48% vs 16% in fibrotic PMF and 17% in ET). At multivariate analysis, age and WHO histology were both independent risk-factors for thrombosis during follow-up; patients >60 yr-old or with prefibrotic PMF showed a significantly higher risk at 20 years than patients <60 yr-old with ET or fibrotic PMF (47% vs 4%, p = 0.005).

CONCLUSIONS

Our study support the importance of WHO histologic categories in the thrombotic risk stratification of patients with thrombocytemias.

VIRTUAL SLIDES

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/2020211863144412 .

The secret life of a megakaryocyte: emerging roles in bone marrow homeostasis control

Megakaryocytes are rare cells found in the bone marrow, responsible for the everyday production and release of millions of platelets into the bloodstream. Since the discovery and cloning, in 1994, of their principal humoral factor, thrombopoietin, and its receptor c-Mpl, many efforts have been directed to define the mechanisms underlying an efficient platelet production. However, more recently different studies have pointed out new roles for megakaryocytes as regulators of bone marrow homeostasis and physiology. In this review we discuss the interaction and the reciprocal regulation of megakaryocytes with the different cellular and extracellular components of the bone marrow environment. Finally, we provide evidence that these processes may concur to the reconstitution of the bone marrow environment after injury and their deregulation may lead to the development of a series of inherited or acquired pathologies.