Distinct Myeloproliferative Neoplasms Research Articles

Clonal Megakaryocyte Dysplasia with Isolated Thrombocytosis Is a Distinct Myeloproliferative Neoplasm Phenotype

Introduction: About 15% of people with a myeloproliferative neoplasm (MPN) are identified as MPN, unclassifiable using the 2016 WHO classification. Methods: We tested whether persons with platelet concentration ≥450 × 10E+9/L, bone marrow megakaryocyte morphology typical of prefibrotic/early myelofibrosis (pre-MF), and no minor criteria of pre-MF should be classified as a distinct MPN subtype, clonal megakaryocyte dysplasia with isolated thrombocytosis (CMD-IT). Results: 139 subjects meet these criteria who we compared with primary myelofibrosis (PMF) including 402 with pre-MF and 521 with overt myelofibrosis. CMD-IT subjects were more likely female and younger. They had lower frequencies of JAK2^V617F compared with persons with PMF (55% vs. 70%; p < 0.001) and higher frequencies of CALR mutations (37% vs. 17%; p < 0.001). They also had lower frequency of variations associated with JAK2^V617F susceptibility, JAK2 46/1 (35% vs. 47%; p = 0.021), and VEGFA rs3025039 (12% vs. 17%; p = 0.030). Subjects with CMD-IT had lower incidences of thrombotic events compared with those with pre-MF (9.7% vs. 26%; p < 0.001) and longer survival (median, not reached vs. 23 years; HR = 0.34 (0.10, 0.30); p < 0.001). Conclusion: Our data indicate CMD-IT is a distinct MPN subtype and should be included in the classification of myeloid neoplasms.

Clonal Megakaryocyte Dysplasia with Normal Blood Values Is a Distinct Myeloproliferative Neoplasm

Introduction: In 1991, we reported 18 persons with a clinical-pathologic entity and termed atypical myeloproliferative disorder because they did not meet the contemporary diagnostic criteria for a myeloproliferative neoplasm. We sought to gain further knowledge on this disease entity. Methods: This retrospective cohort study included consecutive subjects registered in the database of the Center for the Study of Myelofibrosis in Pavia, Italy, from 1998 to 2020 (June), and diagnosed with atypical myeloproliferative disorder according to our adjudicated criteria. We studied clinical, histological, cytogenetic, and molecular covariates and risks of thrombosis, disease progression, and death. Data were compared with those of concurrent subjects with prefibrotic myelofibrosis. Results: Fifteen new subjects with atypical myeloproliferative disorder were identified. Seven were male. Median age was 50 years (IQR, 41–54 years). Thirteen were diagnosed with a synchronous symptomatic or incidentally detected thrombotic event. The bone marrow showed megakaryocyte hyperplasia with dysplasia. JAK2V617F was present in 10 subjects and CALR mutation in one. No other somatic mutations were identified in next generation sequencing. After a median follow-up of 101 months (IQR, 40–160 months), no subject had disease progression or blast transformation. Incidence of post-diagnosis or recurrent thrombosis was 3.9 events (95% confidence interval, 3.5–4.0) and 5.0 events (4.6–5.6) per 100 person-years. Features of subjects with atypical myeloproliferative disorder differed markedly from those of 546 subjects with prefibrotic myelofibrosis. Conclusion: Our data indicate that these 15 persons have a distinct myeloproliferative neoplasm. We propose naming this new disorder clonal megakaryocyte dysplasia with normal blood values.

Calreticulin del52 and ins5 knock-in mice recapitulate different myeloproliferative phenotypes observed in patients with MPN

Somatic mutations in the calreticulin (CALR) gene are associated with approximately 30% of essential thrombocythemia (ET) and primary myelofibrosis (PMF). CALR mutations, including the two most frequent 52 bp deletion (del52) and 5 bp insertion (ins5), induce a frameshift to the same alternative reading frame generating new C-terminal tails. In patients, del52 and ins5 induce two phenotypically distinct myeloproliferative neoplasms (MPNs). They are equally found in ET, but del52 is more frequent in PMF. We generated heterozygous and homozygous conditional inducible knock-in (KI) mice expressing a chimeric murine CALR del52 or ins5 with the human mutated C-terminal tail to investigate their pathogenic effects on hematopoiesis. Del52 induces greater phenotypic changes than ins5 including thrombocytosis, leukocytosis, splenomegaly, bone marrow hypocellularity, megakaryocytic lineage amplification, expansion and competitive advantage of the hematopoietic stem cell compartment. Homozygosity amplifies these features, suggesting a distinct contribution of homozygous clones to human MPNs. Moreover, homozygous del52 KI mice display features of a penetrant myelofibrosis-like disorder with extramedullary hematopoiesis linked to splenomegaly, megakaryocyte hyperplasia and the presence of reticulin fibers. Overall, modeling del52 and ins5 mutations in mice successfully recapitulates the differences in phenotypes observed in patients.

Evaluation of the JAK2V617F Mutational Burden in Patients with Philadelphia Chromosome Negative Myeloproliferative Neoplasms: A Single-center Experience.

The identification of the JAK2V617F mutation in several distinct myeloproliferative neoplasms (MPNs) raised the question how one single mutation incites expression of at least three different clinical phenotypes, i.e., polycythemia vera (PV), essential thrombocythemia (ET) and primary myelofibrosis (PMF). In order to further evaluate already published data on the correlation between mutant JAK2V617F allele burden and specific hematological and clinical parameters, we tested the level of the JAK2 mutation in 134 JAK2+ patients with different MPNs. The patients were diagnosed according to the 2008 WHO criteria and followed for a median of 48 months. The JAK2 V617F quantification was done with a real time polymerase chain reaction (real time-PCR) method. The median allele burden was lowest in ET (25.8%), followed by 34.6% in PV and 51.8% in PMF patients (p<0.01). There was statistically significant association between the mutational load of 10.0-50.0% and blood count parameters in the PV patients (p<0.05). In PMF patients the mutational load was in correlation with older age and leukocyte count that were higher in patients with the mutational load of 10.0-50.0% and >50.0% compared to those with a mutational load of <10.0%. There were no statistically significant associations between the allele burden and blood counts in the ET cohort. Our study confirmed an association between the JAK2V617F allele burden and the distinct MPN phenotypes, indicating unfavorable prognosis in patients with a higher JAK2 allele burden. Our results suggest that JAK2 quantification should be incorporated in the diagnostic work-up of MPN patients as a useful tool for optimal treatment decision.

The 2006 → 2008 European Clinical, Molecular and Patholobiogical (2008 ECMP) Classification and the 2007 WHO Revised Criteria for Myeloproliferative Neoplasms

The classifications of Myeloproliferative Disorders (MPD) by the Polycythemia Vera Study Group (PVSG) and World Health Organization (WHO) used crude criteria for the diagnoses of Essential Thrombocythemia (ET), Polycythemia Vera (PV) and Primary Myelo Fibrosis (PMF). The PVSG and the 2007 WHO criteria for the diagnosis of ET and PVoverlook the very early prefibrotic stages of MPN. The 2008 European Clinical, Molecular and Pathological (2008 ECMP) criteria are sensitive for the detection of early stages of JAK2 V617F trilinear Myelo Proliferative Neoplasms (MPN) and could delineate three stages JAK2 V617F mutated ET: normocellular ET; ET with features of early PV (prodromal PV); and ET with Hypercellular Megakaryocytic Granulocytic Myeloproliferation (EMGM). The 2008 ECMP classification distinguishes six clinical PV stages that have important prognostic and therapeutic implications. Spontaneous EEC, low serum erythropoietin (EPO) levels and JAK2 mutations are highly specific for ET with PV features (prodromal PV), masked PV and classical PV. JAK2 wild type ET and MF have no blood and bone marrow features of PV. The detection and quantitation of JAK2 V617F mutation allele burden play a key-role in the diagnostic work-up and staging of ET, PV and MF patients. The JAK2 V617F mutation allele burden in heterozygous mutated ET and in combined heterozygous-homozygous or homozygous mutated PV and EMGM is of major clinical and prognostic significance. Pre-treatment bone marrow histopathology is of huge importance to document and stage the broad spectrum JAK2 mutated and JAK wild type MPN. JAK2 wild type ET carrying the MPL 515 mutation is a separate and distinct MPN entity of ET and MF without features of PV at diagnosis and during follow-up. JAK2 wild type hypercellular ET associated with Primary Megakaryocytic Granulocytic Myeloproliferation (PMGM) is the third MPN entity of elusive etiology. Myelofibrosis (MF) is not a primary MPN disease entity because Reticulin Fibrosis (RF) and Reticulin/Collagen Fibrosis (RCF) are a secondary response of polyclonal fibroblasts to cytokines released from the clonal granulocytic and megakaryocytic proliferative cells.

Differential biological activity of disease-associated JAK2 mutants

The JAK2V617F mutation has been identified in most patients with myeloproliferative neoplasms (MPNs), including polycythemia vera, essential thrombocythemia and primary myelofibrosis. Although JAK2V617F is the predominant allele associated with MPNs, other activating Janus kinase 2 (JAK2) alleles (such as K539L, T875N) also have been identified in distinct MPNs. The basis for the differences in the in vivo effects of different JAK2 alleles remains unclear. We have characterized three different classes of disease-associated JAK2 mutants (JAK2V617F, JAK2K539L and JAK2T875N) and found significant differences in biochemical, signaling and transforming properties among these different classes of JAK2 mutants. Structured summary of protein interactionsEpoRphysically interactswithJak2 by anti bait coimmunoprecipitation(View Interaction1,2,3)

JAK2 V617F Positive Essential Thrombocythemia Complicated by B-cell Chronic Lymphocytic Leukemia: An Uncommon Association and Diagnostic Pitfall

The development of a chronic lymphoproliferative disorder in a patient with a clonally distinct myeloproliferative neoplasm (MPN) is a rare phenomenon. Here we report a case of essential thrombocythemia (ET) who, 15 years later, developed B-cell chronic lymphocytic leukemia (B-CLL). Molecular studies showed the myeloid cells were positive for the JAK2 V617F mutation, while the CLL cells were negative, emphasizing that these are 2 distinct, unrelated clonal hematologic malignancies in the same individual.

Distinct Clinical Phenotypes Associated with JAK2V617F Reflect Differential STAT1 Signaling

The JAK2V617F mutation is associated with distinct myeloproliferative neoplasms, including polycythemia vera (PV) and essential thrombocythemia (ET), but it remains unclear how it generates disparate disorders. By comparing clonally-derived mutant and wild-type cells from individual patients, we demonstrate that the transcriptional consequences of JAK2V617F are subtle, and that JAK2V617F-heterozygous erythroid cells from ET and PV patients exhibit differential interferon signaling and STAT1 phosphorylation. Increased STAT1 activity in normal CD34-positive progenitors produces an ET-like phenotype, whereas downregulation of STAT1 activity in JAK2V617F-heterozygous ET progenitors produces a PV-like phenotype. Our results illustrate the power of clonal analysis, indicate that the consequences of JAK2V617F reflect a balance between STAT5 and STAT1 activation and are relevant for other neoplasms associated with signaling pathway mutations.

Conditional expression of heterozygous or homozygous Jak2V617F from its endogenous promoter induces a polycythemia vera–like disease

AbstractA somatic point mutation (V617F) in the JAK2 tyrosine kinase was found in a majority of patients with polycythemia vera (PV), essential thrombocythemia, and primary myelofibrosis. However, contribution of the JAK2V617F mutation in these 3 clinically distinct myeloproliferative neoplasms (MPNs) remained unclear. To investigate the role of JAK2V617F in the pathogenesis of these MPNs, we generated an inducible Jak2V617F knock-in mouse, in which the expression of Jak2V617F is under control of the endogenous Jak2 promoter. Expression of heterozygous mouse Jak2V617F evoked all major features of human polycythemia vera (PV), which included marked increase in hemoglobin and hematocrit, increased red blood cells, leukocytosis, thrombocytosis, splenomegaly, reduced serum erythropoietin (Epo) levels and Epo-independent erythroid colonies. Homozygous Jak2V617F expression also resulted in a PV-like disease associated with significantly greater reticulocytosis, leukocytosis, neutrophilia and thrombocytosis, marked expansion of erythroid progenitors and Epo-independent erythroid colonies, larger spleen size, and accelerated bone marrow fibrosis compared with heterozygous Jak2V617F expression. Biochemical analyses revealed Jak2V617F gene dosage-dependent activation of Stat5, Akt, and Erk signaling pathways. Our conditional Jak2V617F knock-in mice provide an excellent model that can be used to further understand the molecular pathogenesis of MPNs and to identify additional genetic events that cooperate with Jak2V617F in different MPNs.