Molecular and clinical features of the myeloproliferative neoplasm associated with JAK2 exon 12 mutations

High frequency of JAK2 exon 12 mutations in Korean patients with polycythaemia vera: novel mutations and clinical significance

Gain-of-function mutations in JAK2 are the molecular hallmarks of polycythaemia vera (PV), one of the myeloproliferative neoplasms. Most (∼95%) patients harbour V617F mutation in exon 15, while the rest have small insertion/deletion mutations in exon 12. We investigated JAK2 mutations in 42 Korean patients with PV. V617F was detected by sequencing and allele-specific PCR. When V617F was negative, sequencing and fragment length analyses were performed to detect exon 12 mutations. As a result, all patients had JAK2 mutations: 37 (88%) harboured V617F, and 5 (12%) had exon 12 mutations. Two patients had novel exon 12 mutations (H538_R541delinsLII and F537_K539delinsVL). Genotype-phenotype correlations demonstrated lower white blood cell and platelet counts in exon 12 mutations than V617F. The frequency of JAK2 exon 12 mutations was higher than expected in Korean patients with PV. Molecular genetic testing for JAK2 exon 12 mutations is mandatory for diagnosis and genotype-phenotype correlations in patients with erythrocytosis and suspected PV.

Multicenter Retrospective Analysis of Turkish Patients with Chronic Myeloproliferative Neoplasms

Objective:

Chronic myeloproliferative neoplasms (CMPNs) that include polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF) are Philadelphia-negative malignancies characterized by a clonal proliferation of one or several lineages. The aim of this report was to determine the demographic features, disease characteristics, treatment strategies, and survival rates of patients with CMPNs in Turkey.

Materials and Methods:

Across all of Turkey, 9 centers were enrolled in the study. We retrospectively evaluated 708 CMPN patients’ results including 390 with ET, 213 with PV, and 105 with PMF.

Results:

The JAK2V617F mutation was found positive in 86% of patients with PV, in 51.5% of patients with ET, and in 50.4% of patients with PMF. Thrombosis and bleeding at diagnosis occurred in 20.6% and 7.5% of PV patients, 15.1% and 9% of ET patients, and 9.5% and 10.4% of PMF patients, respectively. Six hundred and eight patients (85.9%) received cytoreductive therapy. The most commonly used drug was hydroxyurea (89.6%). Leukemic and fibrotic transformations occurred at rates of 0.6% and 13.2%. The estimated overall survival in PV, ET, and PMF patients was 89.7%, 85%, and 82.5% at 10 years, respectively. There were no significant differences between survival in ET, PV, and PMF patients at 10 years.

Conclusion:

Our patients’ results are generally compatible with the literature findings, except for the relatively high survival rate in PMF patients. Hydroxyurea was the most commonly used cytoreductive therapy. Our study reflects the demographic features, patient characteristics, treatments, and survival rates of Turkish CMPN patients.

Where to Turn for Second-Line Cytoreduction After Hydroxyurea in Polycythemia Vera?

The goals of therapy in patients with polycythemia vera (PV) are to improve disease-related symptoms, prevent the incidence or recurrence of thrombosis, and possibly delay or prevent the transformation into myelofibrosis or acute myeloid leukemia (AML). Cytoreductive therapies have been used in older patients and those with a history of thrombosis to achieve these goals. Hydroxyurea (HU) remains the first-line cytoreductive choice; however, up to one in four patients treated with HU over time will develop resistance or intolerance to HU. More importantly, patients who fail HU have a 5.6-fold increase in mortality and a 6.8-fold increase risk of transformation to myelofibrosis or AML; therefore, alternative therapies are needed for these patients. Interferon-α has been used in PV and has shown significant activity in achieving hematologic responses and decreasing JAK2 V617F mutation allele burden. JAK inhibition has also been investigated and recently garnered regulatory approval for this indication. In this review, we will discuss the current treatment options that are available for patients after HU and the novel therapies that are currently under investigation.

IMPLICATIONS FOR PRACTICE

The outcomes of PV patients who fail or who are intolerant of hydroxyurea are poor. Although pegylated interferon can be considered in younger patients, currently, ruxolitinib is the only U.S. Food and Drug Administration-approved agent in this setting, representing a viable option, leading to hematocrit control and a reduction in spleen size and constitutional symptoms. Although a small number of patients will achieve a molecular response with continuous treatment, the implications of such response on the clinical outcomes are still unknown. Patients whose disease is not adequately controlled with ruxolitinib, or who lose their response, can be treated with low-dose busulfan or pipobroman; however, they should be encouraged to participate in trials with novel therapies.

New Strategies in Myeloproliferative Neoplasms: The Evolving Genetic and Therapeutic Landscape

The classical BCR-ABL1-negative myeloproliferative neoplasms (MPN) include essential thrombocythemia (ET), polycythemia vera (PV), and myelofibrosis (MF). Although these clonal disorders share certain clinical and genetic features, MF in particular is distinct for its complex mutational landscape, severe disease phenotype, and poor prognosis. The genetic complexity inherent to MF has made this disease extremely challenging to treat. Pharmacologic JAK inhibition has proven to be a transformative therapy in MPNs, alleviating symptom burden and improving survival, but has been hampered by off-target toxicities and, as monotherapy, has shown limited effects on mutant allele burden. In this review, we discuss the genetic heterogeneity contributing to the pathogenesis of MPNs, focusing on novel driver and epigenetic mutations and how they relate to combination therapeutic strategies. We discuss results from ongoing studies of new JAK inhibitors and report on new drugs and drug combinations that have demonstrated success in early preclinical and clinical trials, including type II JAK inhibitors, antifibrotic agents, and telomerase inhibitors.

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.

Differential clinical effects of different mutation subtypes in CALR-mutant myeloproliferative neoplasms

A quarter of patients with essential thrombocythemia or primary myelofibrosis carry a driver mutation of CALR, the calreticulin gene. A 52-bp deletion (type 1) and a 5-bp insertion (type 2 mutation) are the most frequent variants. These indels might differentially impair the calcium binding activity of mutant calreticulin. We studied the relationship between mutation subtype and biological/clinical features of the disease. Thirty-two different types of CALR variants were identified in 311 patients. Based on their predicted effect on calreticulin C-terminal, mutations were classified as: (i) type 1-like (65%); (ii) type 2-like (32%); and (iii) other types (3%). Corresponding CALR mutants had significantly different estimated isoelectric points. Patients with type 1 mutation, but not those with type 2, showed abnormal cytosolic calcium signals in cultured megakaryocytes. Type 1-like mutations were mainly associated with a myelofibrosis phenotype and a significantly higher risk of myelofibrotic transformation in essential thrombocythemia. Type 2-like CALR mutations were preferentially associated with an essential thrombocythemia phenotype, low risk of thrombosis despite very-high platelet counts and indolent clinical course. Thus, mutation subtype contributes to determining clinical phenotype and outcomes in CALR-mutant myeloproliferative neoplasms. CALR variants that markedly impair the calcium binding activity of mutant calreticulin are mainly associated with a myelofibrosis phenotype.

A Case of Recurrent Ischemic Stroke Involving Subacute, Progressive Intracranial Cerebral Arterial Sclerosis Prior to Diagnosis with JAK2-mutated Polycythemia Vera

CASE REPORT

A 58-year-old man presenting with no vascular risk factors visited our hospital with right hemiparesis and total aphasia. Diffusion-weighted magnetic resonance imaging of the brain showed multiple hyperintensities in watershed distributions in the left hemisphere. Magnetic resonance angiography (MRA) revealed stenosis of the middle cerebral artery, despite normal MRA findings 2 months prior. One year after the first stroke, the patient experienced a recurrent ischemic stroke involving the left anterior choroidal artery, pulmonary embolism, and deep venous thrombosis. After the recurrent stroke event, hemoglobin levels increased gradually. Two years after the first stroke, a JAK2V-617F mutation was detected.

CONCLUSION

Our report suggests that progressive intracranial arterial sclerosis and venous thrombosis of undetermined etiologies could be several initial symptoms of polycythemia vera.

Acquired familial Mediterranean fever associated with a somatic MEFV mutation in a patient with JAK2 associated post-polycythemia myelofibrosis

Background

A study was designed to identify the source of fever in a patient with post-polycythemia myelofibrosis, associated with clonal Janus Kinase 2 (JAK2) mutation involving duplication of exon 12. The patient presented with 1–2 day long self-limited periodic episodes of high fever that became more frequent as the hematologic disease progressed.

Methods

After ruling out other causes for recurrent fever, analysis of the pyrin encoding Mediterranean fever gene (MEFV) was carried out by Sanger sequencing in peripheral blood DNA samples obtained 4 years apart, in buccal cells, laser dissected kidney tubular cells, and FACS-sorted CD3-positive or depleted mononucleated blood cells. Hematopoeitc cells results were validated by targeted deep sequencing. A Sanger sequence based screen for pathogenic variants of the autoinflammatory genes NLRP3, TNFRSF1A and MVK was also performed.

Results

A rare, c.1955G>A, p.Arg652His MEFV gene variant was identified at negligible levels in an early peripheral blood DNA sample, but affected 46 % of the MEFV alleles and was restricted to JAK2-positive, polymorphonuclear and CD3-depleted mononunuclear DNA samples obtained 4 years later, when the patient experienced fever bouts. The patient was also heterozygous for the germ line, non-pathogenic NLRP3 gene variant, p.Q705K. Upon the administration of colchicine, the gold standard treatment for familial Mediterranean fever (FMF), the fever attacks subsided.

Conclusions

This is the first report of non-transmitted, acquired FMF, associated with a JAK2 driven clonal expansion of a somatic MEFV exon 10 mutation. The non-pathogenic germ line NLRP3 p.Q705K mutation possibly played a modifier role on the disease phenotype.

Molecular diagnostics of myeloproliferative neoplasms

Since the discovery of the JAK2 V617F mutation in the majority of the myeloproliferative neoplasms (MPN) of polycythemia vera, essential thrombocythemia and primary myelofibrosis ten years ago, further MPN-specific mutational events, notably in JAK2 exon 12, MPL exon 10 and CALR exon 9 have been identified. These discoveries have been rapidly incorporated into evolving molecular diagnostic algorithms. Whilst many of these mutations appear to have prognostic implications, establishing MPN diagnosis is of immediate clinical importance with selection, implementation and the continual evaluation of the appropriate laboratory methodology to achieve this diagnosis similarly vital. The advantages and limitations of these approaches in identifying and quantitating the common MPN-associated mutations are considered herein with particular regard to their clinical utility. The evolution of molecular diagnostic applications and platforms has occurred in parallel with the discovery of MPN-associated mutations, and it therefore appears likely that emerging technologies such as next-generation sequencing and digital PCR will in the future play an increasing role in the molecular diagnosis of MPN.

Molecular responses and chromosomal aberrations in patients with polycythemia vera treated with peg-proline-interferon alpha-2b

Fifty-one polycythemia vera (PV) patients were enrolled in the phase I/II clinical study PEGINVERA to receive a new formulation of pegylated interferon alpha (peg-proline-IFNα-2b, AOP2014/P1101). Peg-proline-IFNα-2b treatment led to high response rates on both hematologic and molecular levels. Hematologic and molecular responses were achieved for 46 and 18 patients (90 and 35% of the whole cohort), respectively. Although interferon alpha (IFNα) is known to be an effective antineoplastic therapy for a long time, it is currently not well understood which genetic alterations influence therapeutic outcomes. Apart from somatic changes in specific genes, large chromosomal aberrations could impact responses to IFNα. Therefore, we evaluated the interplay of cytogenetic changes and IFNα responses in the PEGINVERA cohort. We performed high-resolution SNP microarrays to analyze chromosomal aberrations prior and during peg-proline-IFNα-2b therapy. Similar numbers and types of chromosomal aberrations in responding and non-responding patients were observed, suggesting that peg-proline-IFNα-2b responses are achieved independently of chromosomal aberrations. Furthermore, complete cytogenetic remissions were accomplished in three patients, of which two showed more than one chromosomal aberration. These results imply that peg-proline-IFNα-2b therapy is an effective drug for PV patients, possibly including patients with complex cytogenetic changes. Am. J. Hematol. 90:288–294, 2015. © 2014 The Authors. American Journal of Hematology published by Wiley Periodicals, Inc.

Incidence, clinical features, and prognostic impact of CALR exon 9 mutations in essential thrombocythemia and primary myelofibrosis: an experience of a single tertiary hospital in Korea

We evaluated the incidence, clinical characteristics, and prognostic impact of calreticulin (CALR) mutations in essential thrombocythemia (ET) and primary myelofibrosis (PMF) patients. In all, 48 ET and 14 PMF patients were enrolled, and the presence of CALR mutations was analyzed by direct sequencing. Patients were classified into three subgroups according to Janus kinase 2 (JAK2) V617F and CALR mutation status, and their clinical features and prognosis were compared. CALR mutations were detected in 15 (24.2%) patients, and the incidence increased to 50.0% in 30 JAK2 V617F mutation-negative cases. These included 11 patients with three known mutations (c.1092_1143del [seven cases], c.1154_1155insTTGTC [three cases], and c.1102_1135del [one case]) and 4 patients with novel mutations. ET patients carrying CALR mutation were younger, had lower white blood cell counts, and experienced less thrombosis during follow-up than those carrying JAK2 V617F mutation, while both patient groups showed similar clinical features and prognosis. In ET patients without JAK2 V617F mutation, CALR mutation did not significantly affect clinical manifestation and prognosis. In conclusion, CALR mutation analysis could be a useful diagnostic tool for ET and PMF in 50% of the cases without JAK2 V617F mutations. The prognostic impact of CALR mutations needs further investigation.

[Complex molecular genetic algorithm in the diagnosis of myeloproliferative neoplasms]

INTRODUCTION

Mutations in Janus kinase 2, calreticulin and thrombopoietin receptor genes have been identified in the genetic background of Philadelphia chromosome negative, "classic" myeloproliferative neoplasms.

AIM

The aim of the authors was to identify driver mutations in a large myeloproliferative cohort of 949 patients.

METHOD

A complex array of molecular techniques (qualitative and quantitative allele-specific polymerase chain reactions, fragment analyzes, high resolution melting and Sanger sequencing) was applied.

RESULTS

All 354 patients with polycythemia vera carried Janus kinase 2 mutations (V617F 98.6%, exon 12: 1.4%). In essential thrombocythemia (n = 468), the frequency of V617F was 61.3% (n = 287), that of calreticulin 25.2% (n = 118), and that of thrombopoietin receptor mutations 2.1% (n = 10), while 11.3% (n = 53) were triple-negative. Similar distribution was observed in primary myelofibrosis (n = 127): 58.3% (n = 74) V617F, 23.6% (n = 30) calreticulin, 6.3% (n = 8) thrombopoietin receptor mutation positive and 11.8% (n = 15) triple-negative.

CONCLUSIONS

The recent discovery of calreticulin gene mutations led to definite molecular diagnostics in around 90% of clonal myeloproliferative cases.

How I treat polycythemia vera

Polycythemia vera (PV) is a chronic myeloproliferative neoplasm associated with JAK2 mutations (V617F or exon 12) in almost all cases. The World Health Organization has defined the criteria for diagnosis, but it is still unclear which parameter (hemoglobin or hematocrit) is the most reliable for demonstrating increased red cell volume and for monitoring response to therapy; also, the role of bone marrow biopsy is being revisited. PV is associated with reduced survival because of cardiovascular complications and progression to post-PV myelofibrosis or leukemia. Criteria for risk-adapted treatment rely on the likelihood of thrombosis. Controlled trials have demonstrated that incidence of cardiovascular events is reduced by sustained control of hematocrit with phlebotomies (low-risk patients) and/or cytotoxic agents (high-risk patients) and antiplatelet therapy with aspirin. Hydroxyurea and interferon may be used as first-line treatments, whereas busulfan is reserved for patients that are refractory or resistant to first-line agents. However, there is no evidence that therapy improves survival, and the significance of reduction of JAK2 mutated allele burden produced by interferon is unknown. PV is also associated with a plethora of symptoms that are poorly controlled by conventional therapy. This article summarizes my approach to the management of PV in daily clinical practice.

The molecular regulation of Janus kinase (JAK) activation

The JAK (Janus kinase) family members serve essential roles as the intracellular signalling effectors of cytokine receptors. This family, comprising JAK1, JAK2, JAK3 and TYK2 (tyrosine kinase 2), was first described more than 20 years ago, but the complexities underlying their activation, regulation and pleiotropic signalling functions are still being explored. Here, we review the current knowledge of their physiological functions and the causative role of activating and inactivating JAK mutations in human diseases, including haemopoietic malignancies, immunodeficiency and inflammatory diseases. At the molecular level, recent studies have greatly advanced our knowledge of the structures and organization of the component FERM (4.1/ezrin/radixin/moesin)-SH2 (Src homology 2), pseudokinase and kinase domains within the JAKs, the mechanism of JAK activation and, in particular, the role of the pseudokinase domain as a suppressor of the adjacent tyrosine kinase domain's catalytic activity. We also review recent advances in our understanding of the mechanisms of negative regulation exerted by the SH2 domain-containing proteins, SOCS (suppressors of cytokine signalling) proteins and LNK. These recent studies highlight the diversity of regulatory mechanisms utilized by the JAK family to maintain signalling fidelity, and suggest alternative therapeutic strategies to complement existing ATP-competitive kinase inhibitors.

Clonal heterogeneity as a driver of disease variability in the evolution of myeloproliferative neoplasms

Myeloproliferative neoplasms (MPNs) are clonal hematological diseases in which cells of the myelo-erythroid lineage are overproduced and patients are predisposed to leukemic transformation. Hematopoietic stem cells are the suspected disease-initiating cells, and these cells must acquire a clonal advantage relative to nonmutant hematopoietic stem cells to perpetuate disease. In 2005, several groups identified a single gain-of-function point mutation in JAK2 that associated with the majority of MPNs, and subsequent studies have led to a comprehensive understanding of the mutational landscape in MPNs. However, confusion still exists as to how a single genetic aberration can be associated with multiple distinct disease entities. Many explanations have been proposed, including JAK2V617F homozygosity, individual patient heterogeneity, and the differential regulation of downstream JAK2 signaling pathways. Several groups have made knock-in mouse models expressing JAK2V617F and have observed divergent phenotypes, each recapitulating some aspects of disease. Intriguingly, most of these models do not observe a strong hematopoietic stem cell self-renewal advantage compared with wild-type littermate controls, raising the question of how a clonal advantage is established in patients with MPNs. This review summarizes the current molecular understanding of MPNs and the diversity of disease phenotypes and proposes that the increased proliferation induced by JAK2V617F applies a selection pressure on the mutant clone that results in highly diverse clonal evolution in individuals.

The mutation profile of JAK2 and CALR in Chinese Han patients with Philadelphia chromosome-negative myeloproliferative neoplasms

Mutations in JAK2, MPL and CALR are highly relevant to the Philadelphia chromosome (Ph)-negative myeloproliferative neoplasms (MPNs). We performed high resolution melting analysis and Sanger sequencing together with T-A cloning to elucidate the unique mutation profile of these genes, in Chinese patients with MPNs. Peripheral blood DNA samples were obtained from 80 patients with polycythemia vera (PV), 80 patients with essential thrombocytosis (ET) and 50 patients with primary myelofibrosis (PMF). Ten PV patients were identified with diverse JAK2 exon 12 mutations. Five novel JAK2 Exon 12 mutation patterns (M532V/E543G, N533D, M535I/H538Y/K549I, E543G and D544N) were described. JAK2 V617F was detected in 140 samples (66 PV, 45 ET and 29 PMF). JAK2 Exon 12 mutations were prevalent (13%) and variable in the Chinese patients. Compared with PV patients with JAK2 V617F mutations, PV patients with JAK2 exon 12 mutations had an earlier median onset of disease (P = 0.0013). MPL W515L/K mutations were discerned in 4 ET and 3 PMF patients. Two kinds of CALR mutation, c. 1179_1230del and c. 1234_1235insTTGTC were detected in 20 ET and 16 PMF patients. A novel CALR mutation pattern (c. 1173_1223del/c. 1179_1230del) was identified in 2 PMF samples. In addition, 17 scattered point mutations in CALR c.1153 to c.1255 were also detected in 13 cases with CALR frame-shifting variations and 2 cases without CALR frame-shifting variations. Female patients showed a predisposition to CALR mutations (P = 0.0035). Chinese Ph-negative MPN patients have a unique mutation landscape in the common molecular markers of MPN diagnosis. Validation of the molecular diagnostic pipeline should be emphasized since there is a considerable ethnical diversity in the molecular profiles of Ph-negative MPNs.

Mutations and chromosomal rearrangements of JAK2: not only a myeloid issue

Until today, JAK2 alterations have been mainly associated with myeloid malignancies among which they play a key pathogenic role in chronic myeloproliferative neoplasms. More recently, aberrations involving the JAK2 gene have also been reported in lymphoid diseases, including acute leukemia and lymphomas. In addition, the constitutively activating JAK2V617F mutation has been identified in some patients affected by B-chronic lymphocytic leukemia with a concomitant myeloproliferative neoplasm. Interestingly, these cases could help us to better understand the pathogenesis of these myeloid and lymphoid diseases and reveal if they share a common ancestral progenitor or just coincide. The involvement of JAK2 in lymphoid neoplasms may suggest the possibility of new therapeutic approaches broadening the use of JAK1-2 inhibitors also to these malignancies.

JAK2V617F homozygosity drives a phenotypic switch in myeloproliferative neoplasms, but is insufficient to sustain disease

JAK2V617F homozygosity drives a phenotypic switch between myeloproliferative neoplasms. JAK2V617F homozygosity is insufficient to sustain clonal expansion.

From Janus kinase 2 to calreticulin: the clinically relevant genomic landscape of myeloproliferative neoplasms

Our understanding of the genetic basis of myeloproliferative neoplasms began in 2005, when the JAK2 (V617F) mutation was identified in polycythemia vera, essential thrombocythemia, and primary myelofibrosis. JAK2 exon 12 and MPL exon 10 mutations were then detected in subsets of patients, and subclonal driver mutations in other genes were found to be associated with disease progression. Recently, somatic mutations in the gene CALR, encoding calreticulin, have been found in most patients with essential thrombocythemia or primary myelofibrosis with nonmutated JAK2 and MPL. The JAK-STAT pathway appears to be activated in all myeloproliferative neoplasms, regardless of founding driver mutations. These latter, however, have different effects on clinical course and outcomes. Thus, evaluation of JAK2, MPL, and CALR mutation status is important not only for diagnosis but also for prognostication. These genetic data should now also be considered in designing clinical trials.

Integrated genomic analysis illustrates the central role of JAK-STAT pathway activation in myeloproliferative neoplasm pathogenesis

Genomic studies have identified somatic alterations in the majority of myeloproliferative neoplasms (MPN) patients, including JAK2 mutations in the majority of MPN patients and CALR mutations in JAK2-negative MPN patients. However, the role of JAK-STAT pathway activation in different MPNs, and in patients without JAK2 mutations, has not been definitively delineated. We used expression profiling, single nucleotide polymorphism arrays, and mutational profiling to investigate a well-characterized cohort of MPN patients. MPN patients with homozygous JAK2V617F mutations were characterized by a distinctive transcriptional profile. Notably, a transcriptional signature consistent with activated JAK2 signaling is seen in all MPN patients regardless of clinical phenotype or mutational status. In addition, the activated JAK2 signature was present in patients with somatic CALR mutations. Conversely, we identified a gene expression signature of CALR mutations; this signature was significantly enriched in JAK2-mutant MPN patients consistent with a shared mechanism of transformation by JAK2 and CALR mutations. We also identified a transcriptional signature of TET2 mutations in MPN patent samples. Our data indicate that MPN patients, regardless of diagnosis or JAK2 mutational status, are characterized by a distinct gene expression signature with upregulation of JAK-STAT target genes, demonstrating the central importance of the JAK-STAT pathway in MPN pathogenesis.

Myelofibrosis-associated complications: pathogenesis, clinical manifestations, and effects on outcomes

Myelofibrosis (MF) is a rare chronic BCR-ABL1 (breakpoint cluster region-Abelson murine leukemia viral oncogene homologue 1)-negative myeloproliferative neoplasm characterized by progressive bone marrow fibrosis, inefficient hematopoiesis, and shortened survival. The clinical manifestations of MF include splenomegaly, consequent to extramedullary hematopoiesis, cytopenias, and an array of potentially debilitating abdominal and constitutional symptoms. Dysregulated Janus kinase (JAK)-signal transducer and activator of transcription signaling underlies secondary disease-associated effects in MF, such as myeloproliferation, bone marrow fibrosis, constitutional symptoms, and cachexia. Common fatal complications of MF include transformation to acute leukemia, thrombohemorrhagic events, organ failure, and infections. Potential complications from hepatosplenomegaly include portal hypertension and variceal bleeding, whereas extramedullary hematopoiesis outside the spleen and liver - depending on the affected organ - may result in intracranial hypertension, spinal cord compression, pulmonary hypertension, pleural effusions, lymphadenopathy, skin lesions, and/or exacerbation of abdominal symptoms. Although allogeneic stem cell transplantation is the only potentially curative therapy, it is suitable for few patients. The JAK1/JAK2 inhibitor ruxolitinib is effective in improving splenomegaly, MF-related symptoms, and quality-of-life measures. Emerging evidence that ruxolitinib may be associated with a survival benefit in intermediate- or high-risk MF suggests the possibility of a disease-modifying effect. Consequently, ruxolitinib could provide a treatment backbone to which other (conventional and novel) therapies may be added for the prevention and effective management of specific MF-associated complications.

Myelofibrosis-associated complications: pathogenesis, clinical manifestations, and effects on outcomes

Myelofibrosis (MF) is a rare chronic BCR-ABL1 (breakpoint cluster region-Abelson murine leukemia viral oncogene homologue 1)-negative myeloproliferative neoplasm characterized by progressive bone marrow fibrosis, inefficient hematopoiesis, and shortened survival. The clinical manifestations of MF include splenomegaly, consequent to extramedullary hematopoiesis, cytopenias, and an array of potentially debilitating abdominal and constitutional symptoms. Dysregulated Janus kinase (JAK)-signal transducer and activator of transcription signaling underlies secondary disease-associated effects in MF, such as myeloproliferation, bone marrow fibrosis, constitutional symptoms, and cachexia. Common fatal complications of MF include transformation to acute leukemia, thrombohemorrhagic events, organ failure, and infections. Potential complications from hepatosplenomegaly include portal hypertension and variceal bleeding, whereas extramedullary hematopoiesis outside the spleen and liver - depending on the affected organ - may result in intracranial hypertension, spinal cord compression, pulmonary hypertension, pleural effusions, lymphadenopathy, skin lesions, and/or exacerbation of abdominal symptoms. Although allogeneic stem cell transplantation is the only potentially curative therapy, it is suitable for few patients. The JAK1/JAK2 inhibitor ruxolitinib is effective in improving splenomegaly, MF-related symptoms, and quality-of-life measures. Emerging evidence that ruxolitinib may be associated with a survival benefit in intermediate- or high-risk MF suggests the possibility of a disease-modifying effect. Consequently, ruxolitinib could provide a treatment backbone to which other (conventional and novel) therapies may be added for the prevention and effective management of specific MF-associated complications.

JAK2 or CALR mutation status defines subtypes of essential thrombocythemia with substantially different clinical course and outcomes

Patients with essential thrombocythemia may carry JAK2 (V617F), an MPL substitution, or a calreticulin gene (CALR) mutation. We studied biologic and clinical features of essential thrombocythemia according to JAK2 or CALR mutation status and in relation to those of polycythemia vera. The mutant allele burden was lower in JAK2-mutated than in CALR-mutated essential thrombocythemia. Patients with JAK2 (V617F) were older, had a higher hemoglobin level and white blood cell count, and lower platelet count and serum erythropoietin than those with CALR mutation. Hematologic parameters of patients with JAK2-mutated essential thrombocythemia or polycythemia vera were related to the mutant allele burden. While no polycythemic transformation was observed in CALR-mutated patients, the cumulative risk was 29% at 15 years in those with JAK2-mutated essential thrombocythemia. There was no significant difference in myelofibrotic transformation between the 2 subtypes of essential thrombocythemia. Patients with JAK2-mutated essential thrombocythemia and those with polycythemia vera had a similar risk of thrombosis, which was twice that of patients with the CALR mutation. These observations are consistent with the notion that JAK2-mutated essential thrombocythemia and polycythemia vera represent different phenotypes of a single myeloproliferative neoplasm, whereas CALR-mutated essential thrombocythemia is a distinct disease entity.

Somatic mutations of calreticulin in myeloproliferative neoplasms

BACKGROUND

Approximately 50 to 60% of patients with essential thrombocythemia or primary myelofibrosis carry a mutation in the Janus kinase 2 gene (JAK2), and an additional 5 to 10% have activating mutations in the thrombopoietin receptor gene (MPL). So far, no specific molecular marker has been identified in the remaining 30 to 45% of patients.

METHODS

We performed whole-exome sequencing to identify somatically acquired mutations in six patients who had primary myelofibrosis without mutations in JAK2 or MPL. Resequencing of CALR, encoding calreticulin, was then performed in cohorts of patients with myeloid neoplasms.

RESULTS

Somatic insertions or deletions in exon 9 of CALR were detected in all patients who underwent whole-exome sequencing. Resequencing in 1107 samples from patients with myeloproliferative neoplasms showed that CALR mutations were absent in polycythemia vera. In essential thrombocythemia and primary myelofibrosis, CALR mutations and JAK2 and MPL mutations were mutually exclusive. Among patients with essential thrombocythemia or primary myelofibrosis with nonmutated JAK2 or MPL, CALR mutations were detected in 67% of those with essential thrombocythemia and 88% of those with primary myelofibrosis. A total of 36 types of insertions or deletions were identified that all cause a frameshift to the same alternative reading frame and generate a novel C-terminal peptide in the mutant calreticulin. Overexpression of the most frequent CALR deletion caused cytokine-independent growth in vitro owing to the activation of signal transducer and activator of transcription 5 (STAT5) by means of an unknown mechanism. Patients with mutated CALR had a lower risk of thrombosis and longer overall survival than patients with mutated JAK2.

CONCLUSIONS

Most patients with essential thrombocythemia or primary myelofibrosis that was not associated with a JAK2 or MPL alteration carried a somatic mutation in CALR. The clinical course in these patients was more indolent than that in patients with the JAK2 V617F mutation. (Funded by the MPN Research Foundation and Associazione Italiana per la Ricerca sul Cancro.).

Polycythemia vera: current pharmacotherapy and future directions

INTRODUCTION

In the past, management of polycythemia vera (PV) was built upon a cornerstone of control over erythrocytosis, through therapeutic phlebotomy, as well as the use of low-dose aspirin. Historically, selected patients were managed with additional cytoreductive therapies to decrease the risk of vascular events, with the recognition that these therapies likely did not impede progression.

AREAS COVERED

Recent clinical trials have demonstrated, in a randomized fashion, that optimal control of the hematocrit to target levels < 45% are important for decreasing the risk of vascular events. We are identifying that our historical set of cytoreductive agents, such as hydroxyurea, may be replaced in the future. The first candidate is pegylated interferon alpha-2a, which is demonstrating the ability to control vascular events and control extended hematopoiesis, while potentially having impact on fibrotic progression and Janus kinase 2 (JAK2) V1617F mutant allele burden. Ruxolitinib, as well as other JAK2 inhibitors in development, are demonstrating that this class of agents is making a very meaningful impact on the risk of vascular events in PV, controlling expanded hematopoiesis, as well as helping with symptomatic burden.

EXPERT OPINION

Future goals include attaining a better understanding of the specific roles of JAK inhibitor therapy and whether their use in combination with standard therapies offers greater efficacy than single agents alone.

Thrombotic complications of myeloproliferative neoplasms: risk assessment and risk-guided management

Philadelphia-negative myeloproliferative neoplasms are considered to be acquired thrombophilic states. Thromboses, both arterial and venous (not rarely in unusual sites), are often the initial events leading to the diagnosis. After diagnosis, the yearly incidence of thrombotic events is highly variable, and ranges from approximately 1% to 10%. The identification of patients at risk who may benefit from antithrombotic therapy remains a challenge, and it is currently based on age and history of thrombotic events. However, the predictive value of these clinical characteristics is rather limited. Few prospective studies and even fewer interventional randomized studies are available, and there are no studies designed to formally validate the use of risk stratification. The implementation of laboratory parameters such as leukocytosis and/or the JAK2 V617F mutation into a scoring system may be of interest. The mechanisms at work leading to thrombosis remain largely speculative, but are likely to be complex and multifactorial, with a prominent role of cell-cell interactions, mostly owing to qualitative changes. The long-term treatment options to prevent thrombosis are, schematically, aspirin alone as primary prevention for the low-risk patients, and cytoreduction combined with aspirin for the other patients. In very low-risk young essential thrombocythemia patients, abstention can even be considered. The optimal duration of anticoagulation after a thrombotic event is not established. All antithrombotic therapies should be balanced with the hemorrhagic risk, which can also be increased in these patients.

Polycythemia vera and essential thrombocythemia: 2013 update on diagnosis, risk-stratification, and management

DISEASE OVERVIEW

Polycythemia Vera (PV) and essential thrombocythemia (ET) are myeloproliferative neoplasms (MPN) primarily characterized by erythrocytosis and thrombocytosis, respectively. Other disease features include leukocytosis, splenomegaly, thrombohemorrhagic complications, vasomotor disturbances, pruritus and a small risk of disease progression into acute myeloid leukemia or myelofibrosis.

DIAGNOSIS

Almost all patients with PV harbor a JAK2 mutation. When PV is suspected, the presence of a JAK2 mutation highly suggests the diagnosis and its absence, combined with normal or increased serum erythropoietin level, excludes the diagnosis. Differential diagnosis of ET should include reactive thrombocytosis, chronic myeloid leukemia, prefibrotic myelofibrosis and RARS-T (refractory anemia with ring sideroblasts associated with marked thrombocytosis). A JAK2 mutation is found in 50-70% of patients with ET, myelofibrosis or RARS-T and is capable of distinguishing reactive from clonal thrombocytosis.

RISK STRATIFICATION

Current risk stratification in PV and ET is designed to estimate the likelihood of thrombotic complications: high-risk is defined by the presence of age >60 years or presence of thrombosis history; low-risk is defined by the absence of both of these two risk factors. Recent data considers JAK2V617F and cardiovascular (CV) risk factors as additional risk factors for thrombosis. Presence of extreme thrombocytosis (platelet count >1,000 × 10(9) /L) might be associated with acquired von Willebrand syndrome (AvWS) and, therefore, risk of bleeding. Risk factors for shortened survival in both PV and ET include advanced age, leukocytosis, and history of thrombosis.

RISK-ADAPTED THERAPY

Survival is near-normal in ET and reasonably long in PV. The 10-year risk of leukemic/fibrotic transformation is <1%/1% in ET and <3%/10% in PV. In contrast, the risk of thrombosis exceeds 20%. The main goal of therapy is therefore to prevent thrombohemorrhagic complications. In low risk patients, this is effectively and safely accomplished by the use of low-dose aspirin in both PV and ET and phlebotomy (hematocrit target of <45%) in PV. In high risk patients, treatment with hydroxyurea is additionally recommended, although not mandated in older patients without JAK2V617F or CV risk factors. Treatment with busulfan or interferon-α is usually effective in hydroxyurea failures. Screening for clinically significant AvWS is recommended before administrating aspirin in the presence of extreme thrombocytosis.

Comprehensive review of JAK inhibitors in myeloproliferative neoplasms

Myeloproliferative neoplasms (MPNs) are clonal hematopoietic stem-cell disorders, characterized phenotypically by the abnormal accumulation of mature-appearing myeloid cells. Polycythemia vera, essential thrombocythemia, primary myelofibrosis (also known as 'BCR-ABL1-negative' MPNs), and chronic myeloid leukemia (CML) are the primary types of MPNs. After the discovery of the BCR-ABL1 fusion protein in CML, several oncogenic tyrosine kinases have been identified in 'BCR-ABL1-negative' MPNs, most importantly, JAK2V617F mutation. The similarity in the clinical characteristics of the BCR-ABL1-negative MPN patients along with the prevalence of the Janus kinase mutation in this patient population provided a strong rationale for the development of a new class of pharmacologic inhibitors that target this pathway. The first of its class, ruxolitinib, has now been approved by the food and drug administration (FDA) for the management of patients with intermediate- to high-risk myelofibrosis. Ruxolitinib provides significant and sustained improvements in spleen related and constitutional symptoms secondary to the disease. Although noncurative, ruxolitinib represents a milestone in the treatment of myelofibrosis patients. Other types of JAK2 inhibitors are being tested in various clinical trials at this point and may provide better efficacy data and safety profile than its predecessor. In this article, we comprehensively reviewed and summarized the available preclinical and clinical trials pertaining to JAK inhibitors.

Methods for detecting mutations in the human JAK2 gene

Mutations in the JAK2 gene are prevalent in the human myeloid malignancies, being present in virtually all cases of polycythemia vera, and a significant proportion of patients with other myeloproliferative disorders. Various methods for the detection of acquired mutations in this gene are available depending on the need for sensitivity, quantification, or the ability to detect many different mutations. We summarize the various methods published and discuss their relative merits for each application. Two commonly used methods, quantitative real-time PCR (QPCR) for the detection of the JAK2 V617F mutation and high resolution melt-curve analysis (HRM) for the detection of multiple mutations within JAK2 exon 12, demonstrate the utility of each method and their limitations. The choice of methodology is dependent on the application; therefore there is no gold standard for detecting mutations in this gene.

Ruxolitinib: a potent and selective Janus kinase 1 and 2 inhibitor in patients with myelofibrosis. An update for clinicians

Ruxolitinib became the first US Food and Drug Administration approved therapy for myelofibrosis in 2011 and EU approval is anticipated in summer 2012. Two large phase III trials (known as the COMFORT studies) were the basis for this approval and were published recently. In this review article we discuss the challenges in managing myelofibrosis, the information to date about ruxolitinib and speculate as to the future direction with this and similar agents.

Molecular biology of Philadelphia-negative myeloproliferative neoplasms

Myeloproliferative neoplasms are clonal diseases of hematopoietic stem cells characterized by myeloid hyperplasia and increased risk of developing acute myeloid leukemia. Myeloproliferative neoplasms are caused, as any other malignancy, by genetic defects that culminate in the neoplastic phenotype. In the past six years, since the identification of JAK2V617F, we have experienced a substantial increase in our knowledge about the genetic mechanisms involved in the genesis of myeloproliferative neoplasms. Mutations described in several genes have revealed a considerable degree of molecular homogeneity between different subtypes of myeloproliferative neoplasms. At the same time, the molecular differences between each subtype have become clearer. While mutations in several genes, such as JAK2, myeloproliferative leukemia (MPL) and LNK have been validated in functional assays or animal models as causative mutations, the roles of other recurring mutations in the development of disease, such as TET2 and ASXL1 remain to be elucidated. In this review we will examine the most prevalent recurring gene mutations found in myeloproliferative neoplasms and their molecular consequences.

BCR-ABL1-negative chronic myeloid neoplasms: an update on management techniques

Recent discoveries concerning mutations associated with chronic myeloproliferative neoplasms have modified our understanding of the biology of these incurable diseases and guided us to the development of inhibitors active on the constitutively activated JAK-STAT pathway. Concurrently, numerous studies dealt with clinical issues; it led to a revised WHO classification; clarified the role of mutated JAK2 and leukocytosis in the pathogenesis of cardiovascular events; allowed the development of risk prognostic scores and tools for monitoring response to therapy; and resulted in completion of Phase III trials with JAK2 inhibitor in myelofibrosis. All these results hold the promise of improving patient prognostication and therapeutic approach, with the aim of efficiently preventing disease-associated complications and, hopefully, to improve the dismal survival associated with myelofibrosis. This review discusses how to manage, according to current clinical practice, the steps of diagnosis, prognostication and therapeutic choices in myeloproliferative neoplasm patients.

Genotype-phenotype interactions in the myeloproliferative neoplasms

The chronic myeloproliferative neoplasms (MPNs) are clonal disorders characterized by overproduction of mature myeloid cells. They share associations with molecular abnormalities such as the JAK2V617F mutation but are distinguished by important phenotypic differences. This review first considers the factors that may influence phenotype in JAK2-mutated MPNs, especially polycythemia vera (PV) and essential thrombocythemia (ET), and then discusses the mutations implicated in JAK2-negative MPNs such as in MPL and epigenetic regulators. Current evidence supports a model where ET and PV are disorders of relatively low genetic complexity, whereas evolution to myelofibrosis or blast-phase disease reflects accumulation of a higher mutation burden.

Pathology consultation on myeloproliferative neoplasms

In 2008, the World Health Organization (WHO) revised the classification system for myeloproliferative neoplasms (MPNs). MPNs include chronic myelogenous leukemia, essential thrombocythemia, polycythemia vera, primary myelofibrosis, and several other disorders. The newer classification system incorporates mutations discovered in the JAK2 and MPL genes. The importance of understanding the role of mutations in JAK2, MPL, and other genes that have been discovered in MPNs is highlighted by the change in the 2008 WHO MPN classification system. Moreover, the development of highly specific inhibitors of JAK2 further stresses the importance of molecular testing in MPN diagnosis and prognosis.

[Clinical significance of the quantification of JAK2V617F allele burden in classical Ph-negative myeloproliferative neoplasms]

BACKGROUND AND OBJECTIVES

Our study has investigated the presence of the mutation V617F in the JAK2 gene in patients diagnosed with chronic myeloproliferative neoplasms (MPNs). Furthermore, we determined if JAK2 (V617F) allelic burden associates with a specific clinical phenotype and if its quantification can be used as a marker to predict outcome and complications in patients with MPNs.

PATIENTS AND METHODS

A retrospective observational study was conducted from 1987 to 2011 in the Haematology Department of La Paz University Hospital. The allelic burden was measured in 114 patients diagnosed with MPNs: 39 polycythemia vera (PV) patients, 71 essential thrombocythaemia patients and 6 primary myelofibrosis patients. The quantitative real-time polymerase chain reaction (qRT-PCR) technology was used to determinate the percentage of mutated alleles in peripheral blood neutrophils. Patients were divided in 2 groups: heterozygous if the result was≤50% of the tested cells, and homozygous if it was positive in>50% of the cells.

RESULTS

Sixty-nine patients were positive for the JAK2 mutation and 45 were negative. Among those positive, the mutation was associated with arterial thrombosis. In addition, we demonstrate in the homozygous group that the V617F mutation is associated to PV, advanced age, leukocytosis, marked haematopoiesis and splenomegaly.

CONCLUSIONS

The presence of V617F mutation is associated with a higher incidence of thrombosis, leukocytosis and splenomegaly. The identification of mutation on the JAK2 gene could help in a better definition of evolution and prognostic stratification of the myeloproliferative disorders.

The JAK2 V617F mutation in patients with cerebral venous thrombosis

BACKGROUND

It is currently unclear whether or not cerebral venous thrombosis, such as splanchnic venous thrombosis, can be the first manifestation of an underlying myeloproliferative neoplasm.

OBJECTIVE

To determine the prevalence of the JAK2 V617F mutation in patients with a first episode of cerebral venous thrombosis.

PATIENTS

In this retrospective cohort study, patients with cerebral venous thrombosis were tested for the JAK2 V617F mutation and were followed until the development of a myeloproliferative neoplasm or censored at the end of follow-up.

RESULTS

Ten of 152 patients (6.6%) carried the JAK2 V617F mutation. Three of them had known acquired risk factors for thrombosis, and five had thrombophilia. Six patients met the diagnostic criteria for myeloproliferative neoplasm at the time of cerebral venous thrombosis, and three additional patients developed the disease during the follow-up (median duration 7.8 years, range 6 months to 21.3 years), giving an annual incidence of 0.26% patient-years (95% confidence interval 0.05-0.64). The last patient has no evidence of disease after 3 years of follow-up. Patients without the JAK2 V617F mutation at the time of cerebral venous thrombosis were retested at the end of the follow-up and remained negative, with normal blood counts (log-rank test χ(2) : 159 [P<0.0001]).

CONCLUSIONS

Cerebral venous thrombosis can be the first symptom of a myeloproliferative neoplasm. Patients with cerebral venous thrombosis can carry the JAK2 V617F mutation, irrespective of blood count.