Somatic CALR mutations in myeloproliferative neoplasms with nonmutated JAK2

Current opinion and consensus statement regarding the diagnosis, prognosis, and treatment of patients with essential thrombocythemia: a survey of the Spanish Group of Ph-negative Myeloproliferative Neoplasms (GEMFIN) using the Delphi method

The current consensus on the diagnosis, prognosis, and treatment of essential thrombocythemia (ET) is based on experts' recommendations. However, several aspects of the diagnosis of, prognosis of, and therapy for ET are still controversial. The Delphi method was employed with an expert panel of members of the Spanish Group of Ph-negative Myeloproliferative Neoplasms in order to identify the degree of agreement on the diagnosis, prognosis, and treatment of ET. Nine leading experts selected a total of 41 clinical hematologists with well-known expertise in ET. An electronic questionnaire was used to collect the questions rated in a four-step scale. The questions were grouped into four blocks: diagnosis, risk stratification, goals of therapy, and treatment strategy. After the first round consisting of 80 questions, a second round including 14 additional questions focused on the recommendations advocated by experts of the European LeukemiaNet in 2011 was analyzed. The median and mean values for the first and second rounds were calculated. A summary of the conclusions considered as the most representative of each block of questions is presented. The Delphi method is a powerful instrument to address the current approaches and controversies surrounding ET.

Secondary acute myeloid leukemias arising from Philadelphia chromosome negative myeloproliferative neoplasms: pathogenesis, risk factors, and therapeutic strategies

The classic Philadelphia chromosome negative myeloproliferative neoplasms including primary myelofibrosis, polycythemia vera, and essential thrombocythemia are associated with a variable propensity for transformation into acute myeloid leukemia. Leukemic transformation in these disorders, so called MPN-blast phase, is uniformly associated with a poor prognosis. In recent years, there has been an increasing understanding of the molecular complexity underlying Philadelphia chromosome negative myeloproliferative neoplasms (Ph- MPNs), and this has spurred efforts to investigate the molecular risk factors associated with clinical outcome in these disorders, including the risk of leukemic transformation. At the same time, there is an ongoing and significant need for new approaches which have the potential to change the natural history of these disorders. This review will focus on the risk factors associated with the development of MPN in blast phase (MPN-BP) including clinical and molecular risk factors, current treatment strategies, and emerging investigational approaches.

Next-generation sequencing-based panel testing for myeloid neoplasms

Our ability to interrogate a broad array of genetic alterations in myeloid neoplasm has increased significantly with the advance in next-generation sequencing (NGS). In addition to morphologic examination, flow cytometry, and cytogenetics, NGS-based testing can add additional information to the diagnostic workup. More than a dozen myeloid-focused NGS-based panels are now available from commercial and academic laboratories. In this review, we examine the content of these panels in the context of our current understanding of driver alterations in myeloid neoplasms. With improved turnaround time, decreasing costs, and an expanding knowledge of the therapeutic and prognostic significance of the detected variants, NGS-based panel testing is likely to play a major role in the management of patients with myeloid neoplasm in the coming decade.

Determination of prognosis of Philadelphia chromosome-negative myeloproliferative neoplasms with a simple clinical examination: Retrospective analysis of 71 patients in a single institution

Philadelphia chromosome-negative myeloproliferative neoplasms (MPNs), including polycythemia vera (PV), essential thrombocytosis (ET) and primary myelofibrosis (PMF), are clonal hematopoietic diseases. A single-institution retrospective analysis was performed, including 71 MPN patients diagnosed at the Hakodate Municipal Hospital between April, 2001 and April, 2014, and certain clinical characteristics were identified as effective prognostic factors. The patients were categorized by risk factor scoring based on age, number of abnormal blood cell lineages and splenomegaly at diagnosis, and the association between this categorization and prognosis was analyzed using a statistical procedure. The effect of Janus kinase 2 (JAK2) V617F mutation on prognosis was also investigated. The MPN patients were consolidated into three risk groups based on the margin of intergroup survival differences: i) Score 1-2 (n=23), ii) score 3 (n=24) and iii) score 4-5 (n=24). MPN patients with scores of 4 or 5 exhibited poorer overall survival (OS) compared with those with lower scores (P<0.001). In addition, there were significant differences in event-free survival (EFS) among scoring groups (P=0.0059). PV and ET had a better prognosis compared with PMF, although this analysis suggested that PV and ET patients with scores of 4 or 5 may have a poorer prognosis in terms of OS (P=0.0052) and EFS (P=0.022) and should be closely followed up. We observed no significant prognostic effect of the JAK2V167F mutation for OS (P=0.28) or EFS (P=0.17). Our results suggested that a simple scoring system based on age, blood cell counts and presence of splenomegaly at diagnosis may be used for the long-term prognosis of MPN patients.

Historical views, conventional approaches, and evolving management strategies for myeloproliferative neoplasms

The classical Philadelphia chromosome-negative myeloproliferative neoplasms (MPN), which include essential thrombocythemia, polycythemia vera, and myelofibrosis (MF), are in a new era of molecular diagnosis, ushered in by the identification of the JAK2(V617F) and cMPL mutations in 2005 and 2006, respectively, and the CALR mutations in 2013. Coupled with increased knowledge of disease pathogenesis and refined diagnostic criteria and prognostic scoring systems, a more nuanced appreciation has emerged of the burden of MPN in the United States, including the prevalence, symptom burden, and impact on quality of life. Biological advances in MPN have translated into the rapid development of novel therapeutics, culminating in the approval of the first treatment for MF, the JAK1/JAK2 inhibitor ruxolitinib. However, certain practical aspects of care, such as those regarding diagnosis, prevention of vascular events, choice of cytoreductive agent, and planning for therapies, present challenges for hematologists/oncologists, and are discussed in this article.

Coexisting JAK2V617F and CALR Exon 9 Mutation in Essential Thrombocythemia

Classic "BCR-ABL1-negative" MPN is an operational sub-category of MPN that includes polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF) harboring JAK2V617F as the most common mutation. JAK2V617F can be detected in about 95 % of patients with PV while remaining 5 % of PV patients carry a somatic mutation of JAK2 exon 12. Approximately one-third of patients with ET or PMF do not carry any mutation in JAK2 or MPL. In December 2013, mutations were described in calreticulin (CALR) gene in 67-71 and 56-88 % of JAK2V617F and MPL negative patients with ET and PMF, respectively. Since this discovery CALR mutations have been reported to be mutually exclusive with JAK2V617F or MPL mutations. However recently few studies (eleven published reports) reported the coexistence of JAK2V617F and CALR in MPN. In the present study we are reporting JAK2V617F positive ET patient from our center with coexisting CALR exon 9 mutation type c.1214_1225del12 (p.E405_D408del) that was never reported before as a coexisting mutation and describing in detail the clinical outcomes.

From Philadelphia-Negative to JAK2-Positive: Effect of Genetic Discovery on Risk Stratification and Management

The 2005 discovery of the JAK2 mutation redefined the diagnosis and natural history of myeloproliferative neoplasms (MPNs). Most importantly, this improvement in the pathobiologic conceptualization has focused our evolution of this field from being defined as what it is not (e.g., Philadelphia [Ph]-negative) to what it is (e.g., JAK2-positive, CALR-positive) in the majority of MPN cases. In the ensuing 10 years, the field has experienced a paradigm shift in terms of understanding of the biologic basis of the development of MPNs, an explosion of knowledge of the genetics of MPNs, and has translated disease knowledge into effective targeted therapies. With greater uniformity and agreement on the diagnosis and differences among the individual MPNs, augmented by improved cytogenetic and molecular classification, attention has turned now to addressing the need for uniformity in risk stratification of patients in the clinic for both disease complications and disease transformation. This article will highlight the developments in the field with regard to risk stratification and prognostication in MPNs with focus on the clinical aspects of the patient who presents with either essential thrombocytosis (ET), polycythemia vera (PV), or myelofibrosis (MF).

Myeloproliferative neoplasms and inflammation: whether to target the malignant clone or the inflammatory process or both

The Philadelphia-negative myeloproliferative neoplasms (MPNs) are clonal disorders involving hematopoietic stem and progenitor cells and are associated with myeloproliferation, splenomegaly and constitutional symptoms. Similar signs and symptoms can also be found in patients with chronic inflammatory diseases, and inflammatory processes have been found to play an important role in the pathogenesis and progression of MPNs. Signal transduction pathways involving JAK1, JAK2, STAT3 and STAT5 are causally involved in driving both the malignant cells and the inflammatory process. Moreover, anti-inflammatory and immune-modulating drugs have been used successfully in the treatment of MPNs. However, to date, many unresoved issues remain. These include the role of somatic mutations that are present in addition to JAK2V617F, CALR and MPL W515 mutations, the interdependency of malignant and nonmalignant cells and the means to eradicate MPN-initiating and -maintaining cells. It is imperative for successful therapeutic approaches to define whether the malignant clone or the inflammatory cells or both should be targeted. The present review will cover three aspects of the role of inflammation in MPNs: inflammatory states as important differential diagnoses in cases of suspected MPN (that is, in the absence of a clonal marker), the role of inflammation in MPN pathogenesis and progression and the use of anti-inflammatory drugs for MPNs. The findings emphasize the need to separate the inflammatory processes from the malignancy in order to improve our understanding of the pathogenesis, diagnosis and treatment of patients with Philadelphia-negative MPNs.

Improved Survival of Calreticulin-Mutated Patients Compared With Janus Kinase 2 in Primary Myelofibrosis: A Meta-Analysis

BACKGROUND

Next to janus kinase 2 (JAK2) and myeloproliferative leukemia protein, calreticulin (CALR) is a recently discovered mutation present in > 20% of patients diagnosed with primary myelofibrosis (PMF).

MATERIALS AND METHODS

Six studies published from December 2013 to December 2014 met the inclusion criteria for the present meta-analysis: 2 of an Asian and 4 of a non-Asian population. We assessed the biologic characteristics at diagnosis and investigated overall survival. The analyses were stratified by ethnic origin (Asian vs. non-Asian).

RESULTS

A total of 816 patients with the JAK2 mutation and 307 patients with the CALR mutation were included. The patients with the JAK2 mutation were older than those with the CALR mutation, and no statistically significant difference was noted in the gender distribution of the patients with PMF with the JAK2 versus CALR mutation. Patients with JAK2-mutated PMF had a higher white blood cell count, but no statistically significant evidence was found for a difference in the platelet count or hemoglobin level. No difference was found in thrombosis risk or acute leukemic transformation in those 2 populations. Major differences were found between the Asian and non-Asian populations. The difference in characteristics between JAK2 and CALR was larger in the Asian population than in the non-Asian population (P = .007). Also, in the non-Asian population, those with JAK2 mutation had lower platelet counts than the Asians (P = .06). In the non-Asian population, the patients diagnosed with JAK2-positive PMF had worse overall survival than the patients with CALR-positive PMF, with a combined hazard ratio of 2.43 (95% confidence interval, 1.83-3.22).

CONCLUSION

The results of the present meta-analysis have confirmed the role of the CALR mutation in the diagnosis of, and as a prognostic tool for, PMF. Our results suggest that patients with the CALR mutation will have better overall survival than patients with the JAK2 mutation in a non-Asian population.

Clinical prognostic factors and outcomes of essential thrombocythemia when transformed to myelodysplastic syndromes and acute myeloid leukemia

Transformation of essential thrombocythemia (ET) to myelodysplastic syndromes or acute myeloid leukemia is infrequent, comprising 1-5% of cases with dismal clinical outcome. Studies on prognosis in ET patients with leukemic transformation are limited. The large cohort included 40 patients (1990-2014) with ET transformation (median age of 59 years, M:F of 1:1). Median time from ET diagnosis to transformation was 76 months (26-481) with median follow-up time of 15 years. Advanced age, myelofibrosis (grade 2-3), and leukocytosis at the time of transformation were associated with inferior OS from transformation (p<0.05). Given rarity of the clinical scenario, multicenter efforts are encouraged.

Mutant calreticulin-expressing cells induce monocyte hyperreactivity through a paracrine mechanism

Mutations in the calreticulin gene (CALR) were recently identified in approximately 70-80% of patients with JAK2-V617F-negative essential thrombocytosis and primary myelofibrosis. All frameshift mutations generate a recurring novel C-terminus. Here we provide evidence that mutant calreticulin does not accumulate efficiently in cells and is abnormally enriched in the nucleus and extracellular space compared to wildtype calreticulin. The main determinant of these findings is the loss of the calcium-binding and KDEL domains. Expression of type I mutant CALR in Ba/F3 cells confers minimal IL-3-independent growth. Interestingly, expression of type I and type II mutant CALR in a nonhematopoietic cell line does not directly activate JAK/STAT signaling compared to wildtype CALR and JAK2-V617F expression. These results led us to investigate paracrine mechanisms of JAK/STAT activation. Here we show that conditioned media from cells expressing type I mutant CALR exaggerate cytokine production from normal monocytes with or without treatment with a toll-like receptor agonist. These effects are not dependent on the novel C-terminus. These studies offer novel insights into the mechanism of JAK/STAT activation in patients with JAK2-V617F-negative essential thrombocytosis and primary myelofibrosis.

The European Hematology Association Roadmap for European Hematology Research: a consensus document

The European Hematology Association (EHA) Roadmap for European Hematology Research highlights major achievements in diagnosis and treatment of blood disorders and identifies the greatest unmet clinical and scientific needs in those areas to enable better funded, more focused European hematology research. Initiated by the EHA, around 300 experts contributed to the consensus document, which will help European policy makers, research funders, research organizations, researchers, and patient groups make better informed decisions on hematology research. It also aims to raise public awareness of the burden of blood disorders on European society, which purely in economic terms is estimated at €23 billion per year, a level of cost that is not matched in current European hematology research funding. In recent decades, hematology research has improved our fundamental understanding of the biology of blood disorders, and has improved diagnostics and treatments, sometimes in revolutionary ways. This progress highlights the potential of focused basic research programs such as this EHA Roadmap.The EHA Roadmap identifies nine 'sections' in hematology: normal hematopoiesis, malignant lymphoid and myeloid diseases, anemias and related diseases, platelet disorders, blood coagulation and hemostatic disorders, transfusion medicine, infections in hematology, and hematopoietic stem cell transplantation. These sections span 60 smaller groups of diseases or disorders.The EHA Roadmap identifies priorities and needs across the field of hematology, including those to develop targeted therapies based on genomic profiling and chemical biology, to eradicate minimal residual malignant disease, and to develop cellular immunotherapies, combination treatments, gene therapies, hematopoietic stem cell treatments, and treatments that are better tolerated by elderly patients.

Presence of atypical thrombopoietin receptor (MPL) mutations in triple-negative essential thrombocythemia patients

Enrichment of atypical MPL mutations in essential thrombocythemia. MPLS204P and MPLY591N mutants are weak gain-of-function mutants.

Rapid and robust reversion to essential thrombocythemia on treatment with Decitabine in a case of hydroxyurea-induced t-MDS/AML

Rapid remission of MDS/AML may be induced with Decitabine; however, significant megakaryocyte expansion and subsequent thrombocytosis may occur. Decitabine‐mediated reversion of the MDS to benign ET via hypomethylation of JAK/STAT pathway repressors is one potential mechanism to explain this observed phenomenon.

Genomic landscape of megakaryopoiesis and platelet function defects

Megakaryopoiesis is a complex, stepwise process that takes place largely in the bone marrow. At the apex of the hierarchy, hematopoietic stem cells undergo a number of lineage commitment decisions that ultimately lead to the production of polyploid megakaryocytes. On average, megakaryocytes release 10(11) platelets per day into the blood that repair vascular injuries and prevent excessive bleeding. This differentiation process is tightly controlled by exogenous and endogenous factors, which have been the topics of intense research in the hematopoietic field. Indeed, a skewing of megakaryocyte commitment and differentiation may entail the onset of myeloproliferative neoplasms and other preleukemic disorders together with acute megakaryoblastic leukemia, whereas quantitative or qualitative defects in platelet production can lead to inherited platelet disorders. The recent advent of next-generation sequencing has prompted mapping of the genomic landscape of these conditions to provide an accurate view of the underlying lesions. The aims of this review are to introduce the physiological pathways of megakaryopoiesis and to present landmark studies on acquired and inherited disorders that target them. These studies have not only introduced a new era in the fields of molecular medicine and targeted therapies but may also provide us with a better understanding of the mechanisms underlying normal megakaryopoiesis and thrombopoiesis that can inform efforts to create alternative sources of megakaryocytes and platelets.

Lysyl oxidase is associated with increased thrombosis and platelet reactivity

Lysyl oxidase (LOX) is overexpressed in various pathologies associated with thrombosis, such as arterial stenosis and myeloproliferative neoplasms (MPNs). LOX is elevated in the megakaryocytic lineage of mouse models of MPNs and in patients with MPNs. To gain insight into the role of LOX in thrombosis and platelet function without compounding the influences of other pathologies, transgenic mice expressing LOX in wild-type megakaryocytes and platelets (Pf4-Lox(tg/tg)) were generated. Pf4-Lox(tg/tg) mice had a normal number of platelets; however, time to vessel occlusion after endothelial injury was significantly shorter in Pf4-Lox(tg/tg) mice, indicating a higher propensity for thrombus formation in vivo. Exploring underlying mechanisms, we found that Pf4-Lox(tg/tg) platelets adhere better to collagen and have greater aggregation response to lower doses of collagen compared with controls. Platelet activation in response to the ligand for collagen receptor glycoprotein VI (cross-linked collagen-related peptide) was unaffected. However, the higher affinity of Pf4-Lox(tg/tg) platelets to the collagen sequence GFOGER implies that the collagen receptor integrin α2β1 is affected by LOX. Taken together, our findings demonstrate that LOX enhances platelet activation and thrombosis.

N-Glycan-based ER Molecular Chaperone and Protein Quality Control System: The Calnexin Binding Cycle

Helenius and colleagues proposed over 20-years ago a paradigm-shifting model for how chaperone binding in the endoplasmic reticulum was mediated and controlled for a new type of molecular chaperone- the carbohydrate-binding chaperones, calnexin and calreticulin. While the originally established basics for this lectin chaperone binding cycle holds true today, there has been a number of important advances that have expanded our understanding of its mechanisms of action, role in protein homeostasis, and its connection to disease states that are highlighted in this review.

Concurrent detection of targeted copy number variants and mutations using a myeloid malignancy next generation sequencing panel allows comprehensive genetic analysis using a single testing strategy

Currently, comprehensive genetic testing of myeloid malignancies requires multiple testing strategies with high costs. Somatic mutations can be detected by next generation sequencing (NGS) but copy number variants (CNVs) require cytogenetic methods including karyotyping, fluorescence in situ hybidization and microarray. Here, we evaluated a new method for CNV detection using read depth data derived from a targeted NGS mutation panel. In a cohort of 270 samples, we detected pathogenic mutations in 208 samples and targeted CNVs in 68 cases. The most frequent CNVs were 7q deletion including LUC7L2 and EZH2, TP53 deletion, ETV6 deletion, gain of RAD21 on 8q, and 5q deletion, including NSD1 and NPM1. We were also able to detect exon-level duplications, including so-called KMT2A (MLL) partial tandem duplication, in 9 cases. In the 63 cases that were negative for mutations, targeted CNVs were observed in 4 cases. Targeted CNV detection by NGS had very high concordance with single nucleotide polymorphism microarray, the current gold standard. We found that ETV6 deletion was strongly associated with TP53 alterations and 7q deletion was associated with mutations in TP53, KRAS and IDH1. This proof-of-concept study demonstrates the feasibility of using the same NGS data to simultaneously detect both somatic mutations and targeted CNVs.

Loss of the proteostasis factor AIRAPL causes myeloid transformation by deregulating IGF-1 signaling

AIRAPL (arsenite-inducible RNA-associated protein-like) is an evolutionarily conserved regulator of cellular proteostasis linked to longevity in nematodes, but its biological function in mammals is unknown. We show herein that AIRAPL-deficient mice develop a fully-penetrant myeloproliferative neoplastic process. Proteomic analysis of AIRAPL-deficient mice revealed that this protein exerts its antineoplastic function through the regulation of the insulin/insulin-like growth factor 1 (IGF-1) signaling pathway. We demonstrate that AIRAPL interacts with newly synthesized insulin-related growth factor-1 receptor (IGF1R) polypeptides, promoting their ubiquitination and proteasome-mediated degradation. Accordingly, genetic and pharmacological IGF1R inhibitory strategies prevent the hematological disease found in AIRAPL-deficient mice as well as that in mice carrying the Jak2(V617F) mutation, thereby demonstrating the causal involvement of this pathway in the pathogenesis of myeloproliferative neoplasms. Consistent with its proposed role as a tumor suppressor of myeloid transformation, AIRAPL expression is widely abrogated in human myeloproliferative disorders. Collectively, these findings support the oncogenic relevance of proteostasis deregulation in hematopoietic cells, and they unveil novel therapeutic targets for these frequent hematological neoplasias.

Myeloproliferative neoplasms: A decade of discoveries and treatment advances

Myeloproliferative neoplasms (MPN) are clonal stem cell diseases, first conceptualized in 1951 by William Dameshek, and historically included chronic myeloid leukemia (CML), polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF). In 1960, Nowell and Hungerford discovered an invariable association between the Philadelphia chromosome (subsequently shown to harbor the causal BCR-ABL1 mutation) and CML; accordingly, the term MPN is primarily reserved for PV, ET, and PMF, although it includes other related clinicopathologic entities, according to the World Health Organization (WHO) classification system. In 2005, William Vainchenker and others described a Janus kinase 2 mutation (JAK2V617F) in MPN and this was followed by a series of additional descriptions of mutations that directly or indirectly activate JAK-STAT: JAK2 exon 12, myeloproliferative leukemia virus oncogene (MPL) and calreticulin (CALR) mutations. The discovery of these, mostly mutually exclusive, "driver" mutations has contributed to revisions of the WHO diagnostic criteria and risk stratification in MPN. Mutations other than JAK2, CALR and MPL have also been described in MPN and shown to provide additional prognostic information. From the standpoint of treatment, over the last 50 years, Louis Wasserman from the Unites States and Tiziano Barbui from Italy had skillfully organized and led a number of important clinical trials, whose results form the basis for current treatment strategies in MPN. More recently, allogeneic stem cell transplant, as a potentially curative treatment modality, and JAK inhibitors, as palliative drugs, have been added to the overall therapeutic armamentarium in myelofibrosis. In the current review, I will summarize the important advances made in the last 10 years regarding the science and practice of MPN.

Frequency of Calreticulin (CALR) Mutation and Its Clinical Prognostic Significance in Essential Thrombocythemia and Primary Myelofibrosis: A Meta-analysis

Objective As the calreticulin (CALR) mutation frequency is significantly associated with essential thrombocythemia (ET) and primary myelofibrosis (PMF), this mutation may be an important biomarker in patients with ET and PMF. Methods We performed a literature search until April 2015 and obtained 21 relevant studies. The outcome was pooled as the effect size by using the Stata software program. Results The CALR mutation frequencies in patients with ET and PMF were 19% and 22%, respectively. The CALR mutation ratio in Asian patients with ET was 23% and higher than that in European-American patients (16%). Moreover, the mutation ratio in Asian patients with PMF was lower (21%) than that in European-American patients (23%). A slight trend toward fibrotic transformation was found in ET with CALR mutations, whereas leukemic transformation was not significant in patients with ET or PMF with CALR mutations. Conclusion CALR mutations significantly influence the incident of ET as demonstrated by the meta-analysis.

Evolving Therapeutic Strategies for the Classic Philadelphia-Negative Myeloproliferative Neoplasms

Despite the emergence of JAK inhibitors, there is a need for disease-modifying treatments for Philadelphia-negative myeloproliferative neoplasms (MPNs). JAK inhibitors ameliorate symptoms and address splenomegaly, but because of the heterogeneous contributors to the disease process, JAK inhibitor monotherapy incompletely addresses the burden of disease. The ever-growing understanding of MPN pathogenesis has provided the rationale for testing novel and targeted therapeutic agents, as monotherapies or in combination, in preclinical and clinical settings. A number of intriguing options have emerged, and it is hoped that further progress will lead to significant changes in the natural history of MPNs.

Coexistence of p190 BCR/ABL Transcript and CALR 52-bp Deletion in Chronic Myeloid Leukemia Blast Crisis: A Case Report

We introduce a 78-year-old woman presented with thrombocytosis and high blast count who had a history of splenectomy. Her cytogenetic analysis revealed aberrant chromosomal rearrangements in different clonal populations harboring 46XX karyotype with t(9;22) (q34;q11). RT-PCR assay detected the e1a2 BCR-ABL translocation resulting from rearrangement of the minor breakpoint cluster region (m-bcr) in BCR gene. Subsequent evaluation of the disease showed calreticulin (CALR) 52-bp deletion as well as the absence of JAK2^V617F heterozygous mutation in granulocyte population of peripheral blood using allele-specific PCR and bi-directional DNA sequencing. To our knowledge, this is the first case of a patient initially diagnosed as p190 BCR-ABL transcript positive CML in blast crisis characterized by a 52-bp deletion in CALR gene.

Molecular Pathogenesis and Clinical Significance of Driver Mutations in Primary Myelofibrosis: A Review

Primary myelofibrosis (PMF) is a rare chronic BCR-ABL1-negative myeloproliferative neoplasm characterized by progressive bone marrow fibrosis, inefficient hematopoiesis, and shortened survival. The clinical manifestations of PMF include splenomegaly, consequent to extramedullary hematopoiesis, pancytopenias, and an array of potentially debilitating constitutional symptoms. The diagnosis is based on bone marrow morphology and clinical criteria. Mutations in the JAK2 (V617F), MPL (W515), and CALR (exon 9 indel) genes are found in approximately 90% of patients whereas the remaining 10% are so-called triple negatives. Activation of the JAK/STAT pathway results in overproduction of abnormal megakaryocytes leading to bone marrow fibrosis. These mutations might be accompanied by other mutations, such as ASXL1. The commonly used prognostication scoring for PMF is based on the International Prognostic Scoring System. The subsequently developed Dynamic International Prognostic Scoring System-plus employs clinical as well as cytogenetic variables. In PMF, CALR mutation is associated with superior survival and ASXL1 with inferior outcome. Patients with triple-negative PMF have a higher incidence of leukemic transformation and lower overall survival compared with CALR- or JAK2-mutant patients. The impact of genetic lesions on survival is independent of current prognostic scoring systems. These observations indicate that driver and passenger mutations define distinct disease entities within PMF. Accounting for them is not only relevant to clinical decision-making, but should also be considered in designing clinical trials.

A link between the driver mutations and dysregulated apoptosis in BCR-ABL1 negative myeloproliferative neoplasms

The current understanding of BCR-ABL1 negative myeloproliferative neoplasms pathogenesis is centred on the phenotypic driver mutations in JAK2, MPL, or CALR genes, and the constitutive activation of JAK-STAT pathway. Nonetheless, there is still a need to better characterize the cellular processes that are triggered by these genetic alterations, such as apoptosis that might play a role in the pathological expansion of the myeloid lineages and, especially, in the morphological anomalies of the bone marrow megakaryocytes. In this article we will explore the connection between the driver mutations in MPN and the abnormal apoptosis that might be translated in new therapeutic strategies.

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.

RECQL5 Suppresses Oncogenic JAK2-Induced Replication Stress and Genomic Instability

JAK2V617F is the most common oncogenic lesion in patients with myeloproliferative neoplasms (MPNs). Despite the ability of JAK2V617F to instigate DNA damage in vitro, MPNs are nevertheless characterized by genomic stability. In this study, we address this paradox by identifying the DNA helicase RECQL5 as a suppressor of genomic instability in MPNs. We report increased RECQL5 expression in JAK2V617F-expressing cells and demonstrate that RECQL5 is required to counteract JAK2V617F-induced replication stress. Moreover, RECQL5 depletion sensitizes JAK2V617F mutant cells to hydroxyurea (HU), a pharmacological inducer of replication stress and the most common treatment for MPNs. Using single-fiber chromosome combing, we show that RECQL5 depletion in JAK2V617F mutant cells impairs replication dynamics following HU treatment, resulting in increased double-stranded breaks and apoptosis. Cumulatively, these findings identify RECQL5 as a critical regulator of genome stability in MPNs and demonstrate that replication stress-associated cytotoxicity can be amplified specifically in JAK2V617F mutant cells through RECQL5-targeted synthetic lethality.

Systematic discovery of complex insertions and deletions in human cancers

Complex insertions and deletions (indels) are formed by simultaneously deleting and inserting DNA fragments of different sizes at a common genomic location. Here we present a systematic analysis of somatic complex indels in the coding sequences of samples from over 8,000 cancer cases using Pindel-C. We discovered 285 complex indels in cancer-associated genes (such as PIK3R1, TP53, ARID1A, GATA3 and KMT2D) in approximately 3.5% of cases analyzed; nearly all instances of complex indels were overlooked (81.1%) or misannotated (17.6%) in previous reports of 2,199 samples. In-frame complex indels are enriched in PIK3R1 and EGFR, whereas frameshifts are prevalent in VHL, GATA3, TP53, ARID1A, PTEN and ATRX. Furthermore, complex indels display strong tissue specificity (such as VHL in kidney cancer samples and GATA3 in breast cancer samples). Finally, structural analyses support findings of previously missed, but potentially druggable, mutations in the EGFR, MET and KIT oncogenes. This study indicates the critical importance of improving complex indel discovery and interpretation in medical research.

Clinical and molecular response to interferon-α therapy in essential thrombocythemia patients with CALR mutations

Pegylated IFNα induces hematologic and molecular remission in CALR-mutated ET patients. The analysis of additional mutations highlights the presence of subclones with variable evolutions during IFNα therapy.

Postpartum haemorrhage in a woman with essential thrombocythemia carrying calreticulin mutation: a case report

Coagulation disorder associated with essential thrombocythemia may exacerbate the prothrombotic state physiologically occurring during pregnancy. We report a case of a severe postpartum haemorrhage in a 35-year-old woman previously diagnosed with essential thrombocythemia and carrying the somatic calreticulin mutation. She was referred to our Thrombosis and Haemostasis Unit for pregnancy management. A treatment with low-dose aspirin was prescribed until the labour started, as the platelets count raised above 1000 × 10/l. At the time of bleeding, no residual placenta was detected at the revision of the uterine cavity.Although the postpartum is a high-risk period for thrombotic events, we have to carefully evaluate in women with essential thrombocythemia the likelihood of developing a hemorrhagic complication.

The Role of PTEN in Myeloid Malignancies

PTEN deletion in the mouse and in the zebrafish highlights the essential role of this tumor suppressor in the development of myeloid malignancies, in particular acute myeloid leukemia and myeloproliferative disorders. In humans, extensive genetic sequences of myeloid malignancies did not reveal recurrent PTEN mutations and deletions. However, PTEN was shown to be functionally inactivated in several acute myeloid leukemia and chronic myeloid leukemia samples, through both post-trasductional modifications, changes in protein levels and cellular compartmentalization. Notably, non genomic inactivation of PTEN in myeloid malignancies could represent a challenging therapeutic opportunity for these diseases. Targeting those mechanisms that affect PTEN function could indeed promote PTEN reactivation with consequent cancer selective apoptosis induction. In this review we will describe the role of PTEN in the development of myeloid malignancies.

Management of symptoms in polycythemia vera and essential thrombocythemia patients

The BCR-ABL-negative myeloproliferative neoplasms (MPNs) are clonal stem cell derived malignancies, which include polycythemia vera (PV), essential thrombocythemia (ET), and myelofibrosis (MF). The MPNs are characterized by dysregulated JAK-STAT signaling pathways. PV and ET are associated with an increased risk of thrombo-hemorrhagic complications, risk of progression to MF and leukemia. Presentation of patients with PV and ET is variable and usually as a result of abnormal full blood count indices (raised hemoglobin and hematocrit, leukocytosis, and thrombocytosis). Presentation with thrombosis or splenomegaly occurs in ∼30% of patients. Historically thought of as indolent compared with MF, patients with PV and ET have significant disease symptom burden which does not directly correlate to the current clinical prognostic classifications. The mainstay of therapy is reserved for patients with high-risk disease and thus excludes a population of patients with significant symptom related morbidity impacting their quality-of-life and survival. Recent treatment strategies have aimed to incorporate disease burden assessment into the selection of therapeutic interventions such as JAK2 inhibitors and HDAC inhibitors. We will review the advances in the field of MPN symptom assessment and symptom burden experienced by ET and PV patients. We will also discuss the risk-stratified management of ET and PV patients alongside symptom assessment and the impact of potential novel therapies, for patients who fail to respond to conventional treatment.

The Bone Marrow-Mediated Protection of Myeloproliferative Neoplastic Cells to Vorinostat and Ruxolitinib Relies on the Activation of JNK and PI3K Signalling Pathways

The classical BCR-ABL-negative Myeloproliferative Neoplasms (MPN) are a group of heterogeneous haematological diseases characterized by constitutive JAK-STAT pathway activation. Targeted therapy with Ruxolitinib, a JAK1/2-specific inhibitor, achieves symptomatic improvement but does not eliminate the neoplastic clone. Similar effects are seen with histone deacetylase inhibitors (HDACi), albeit with poorer tolerance. Here, we show that bone marrow (BM) stromal cells (HS-5) protected MPN-derived cell lines (SET-2; HEL and UKE-1) and MPN patient-derived BM cells from the cytotoxic effects of Ruxolitinib and the HDACi Vorinostat. This protective effect was mediated, at least in part, by the secretion of soluble factors from the BM stroma. In addition, it correlated with the activation of signalling pathways important for cellular homeostasis, such as JAK-STAT, PI3K, JNK, MEK-ERK and NF-κB. Importantly, the pharmacological inhibition of JNK and PI3K pathways completely abrogated the BM protective effect on MPN cell lines and MPN patient samples. Our findings shed light on mechanisms of tumour survival and may indicate novel therapeutic approaches for the treatment of MPN.

BMSCs and hematopoiesis

Recent discoveries have significantly expanded our previous knowledge about the role of bone marrow mesenchymal stem cells (BMSCs) in hematopoiesis. BMSCs and their derivatives modulate blood production and immunity at different levels but a prominent role has emerged for BMSCs in the regulation of hematopoietic stem and progenitor cells (HSPCs). Additionally, BMSC-like cells regulate B and T cell lymphopoiesis and also probably myelopoiesis. Furthermore, BMSCs might also exhibit key regulatory properties in non-physiological conditions. BMSCs in extramedullary sites might provide a permissive microenvironment to allow for transient hematopoiesis. BMSCs might be also involved in the manifestation and/or the development of hematopoietic diseases, as stemming from their emerging roles in the progression of hematological malignancies. Here we review some key molecular pathways, adhesion molecules and ligand/receptor interactions that mediate the crosstalk between BMSCs and hematopoietic stem cells (HSCs) in health and disease. The development of novel markers to visualize and isolate individual cells will help to dissect the stromal-hematopoietic interplay.

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.

Novel working hypothesis for pathogenesis of hematological malignancies: combination of mutations-induced cellular phenotypes determines the disease (cMIP-DD)

Recent progress in high-speed sequencing technology has revealed that tumors harbor novel mutations in a variety of genes including those for molecules involved in epigenetics and splicing, some of which were not categorized to previously thought malignancy-related genes. However, despite thorough identification of mutations in solid tumors and hematological malignancies, how these mutations induce cell transformation still remains elusive. In addition, each tumor usually contains multiple mutations or sometimes consists of multiple clones, which makes functional analysis difficult. Fifteen years ago, it was proposed that combination of two types of mutations induce acute leukemia; Class I mutations induce cell growth or inhibit apoptosis while class II mutations block differentiation, co-operating in inducing acute leukemia. This notion has been proven using a variety of mouse models, however most of recently found mutations are not typical class I/II mutations. Although some novel mutations have been found to functionally work as class I or II mutation in leukemogenesis, the classical class I/II theory seems to be too simple to explain the whole story. We here overview the molecular basis of hematological malignancies based on clinical and experimental results, and propose a new working hypothesis for leukemogenesis.

Targeting megakaryocytic-induced fibrosis in myeloproliferative neoplasms by AURKA inhibition

Primary myelofibrosis (PMF) is characterized by bone marrow fibrosis, myeloproliferation, extramedullary hematopoiesis, splenomegaly and leukemic progression. Moreover, the bone marrow and spleens of individuals with PMF contain large numbers of atypical megakaryocytes that are postulated to contribute to fibrosis through the release of cytokines, including transforming growth factor (TGF)-β. Although the Janus kinase inhibitor ruxolitinib provides symptomatic relief, it does not reduce the mutant allele burden or substantially reverse fibrosis. Here we show through pharmacologic and genetic studies that aurora kinase A (AURKA) represents a new therapeutic target in PMF. Treatment with MLN8237, a selective AURKA inhibitor, promoted polyploidization and differentiation of megakaryocytes with PMF-associated mutations and had potent antifibrotic and antitumor activity in vivo in mouse models of PMF. Moreover, heterozygous deletion of Aurka was sufficient to ameliorate fibrosis and other PMF features in vivo. Our data suggest that megakaryocytes drive fibrosis in PMF and that targeting them with AURKA inhibitors has the potential to provide therapeutic benefit.