Somatic CALR mutations in myeloproliferative neoplasms with nonmutated JAK2

Inhibition of glutamate regulated calcium entry into leukemic megakaryoblasts reduces cell proliferation and supports differentiation

Human megakaryocytes release glutamate and express glutamate-gated Ca(2+)-permeable N-methyl-D-aspartate receptors (NMDARs) that support megakaryocytic maturation. While deregulated glutamate pathways impact oncogenicity in some cancers, the role of glutamate and NMDARs in megakaryocytic malignancies remains unknown. The aim of this study was to determine if NMDARs participate in Ca(2+) responses in leukemic megakaryoblasts and if so, whether modulating NMDAR activity could influence cell growth. Three human cell lines, Meg-01, Set-2 and K-562 were used as models of leukemic megakaryoblasts. NMDAR components were examined in leukemic cells and human bone marrow, including in megakaryocytic disease. Well-established NMDAR modulators (agonists and antagonists) were employed to determine NMDAR effects on Ca(2+) flux, cell viability, proliferation and differentiation. Leukemic megakaryoblasts contained combinations of NMDAR subunits that differed from normal bone marrow and the brain. NMDAR agonists facilitated Ca(2+) entry into Meg-01 cells, amplified Ca(2+) responses to adenosine diphosphate (ADP) and promoted growth of Meg-01, Set-2 and K-562 cells. Low concentrations of NMDAR inhibitors (riluzole, memantine, MK-801 and AP5; 5-100μM) were weakly cytotoxic but mainly reduced cell numbers by suppressing proliferation. The use-dependent NMDAR inhibitor, memantine (100μM), reduced numbers and proliferation of Meg-01 cells to less than 20% of controls (IC50 20μM and 36μM, respectively). In the presence of NMDAR inhibitors cells acquired morphologic and immunophenotypic features of megakaryocytic differentiation. In conclusion, NMDARs provide a novel pathway for Ca(2+) entry into leukemic megakaryoblasts that supports cell proliferation but not differentiation. NMDAR inhibitors counteract these effects, suggesting a novel opportunity to modulate growth of leukemic megakaryoblasts.

Impact of bone marrow pathology on the clinical management of Philadelphia chromosome-negative myeloproliferative neoplasms

Philadelphia chromosome-negative myeloproliferative neoplasms include primary myelofibrosis (PMF), polycythemia vera (PV), and essential thrombocythemia (ET). Although these 3 entities share many pathogenic characteristics, such as dysregulated Janus kinase (JAK)/signal transducer and activator of transcription signaling, they differ substantially regarding prognosis, progression to myelofibrosis (MF), risk of leukemic transformation, and specific medical needs. Accurate diagnosis and classification of myeloproliferative neoplasms are prerequisites for appropriate risk-based therapy and should be based on an integrated approach following the World Health Organization guidelines that, in addition to clinical, molecular, and cytogenetic evaluation, includes the examination of bone marrow morphology. Reticulin fibrosis at presentation in ET and PV is associated with increased risk of myelofibrotic transformation, and higher fibrosis grade in patients with MF is associated with worse prognosis. Additional assessment of collagen deposition and osteosclerosis may further increase diagnostic and prognostic precision. Moreover, the evaluation of bone marrow pathology has become very important in the new era of disease-modifying agents. In randomized controlled phase 3 studies, the JAK1/JAK2 inhibitor ruxolitinib provided rapid and lasting improvement in MF-related splenomegaly and symptom burden as well as a survival advantage compared with placebo or best available therapy. Follow-up for up to 5 years of patients who participated in a phase 1/2 study of ruxolitinib, revealed stabilization or reversal of bone marrow fibrosis in a proportion of patients with MF. Combinations of JAK inhibitors with other therapies, including agents with antifibrotic and/or anti-inflammatory properties, may possibly decrease bone marrow fibrosis further and favorably influence clinical outcomes.

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

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

Impact of a prospective review program for reference laboratory testing requests

OBJECTIVES

To control the cost of reference laboratory testing, to ensure that its usage is medically appropriate, and to review the contribution of reference testing to patient care at our institution.

METHODS

A multidisciplinary institutional committee was convened to manage the utilization of reference testing. A subset of tests was designated to be reviewed in real time by a team of clinical pathologists in consultation with clinical subject matter experts.

RESULTS

Twelve percent of testing requests, accounting for approximately 18% of send-out costs, were determined to be clinically unnecessary or would not produce actionable results at that point during that patient's care and were therefore not performed. This intervention, combined with insourcing of frequently requested tests, resulted in a reduction in the costs of reference testing to less than half of that predicted by the rate of growth from 2005 to 2009. Molecular diagnostic tests displayed a higher cost per test than other forms of testing but had a similar degree of clinical impact.

CONCLUSIONS

Formal prospective review of reference laboratory testing requests resulted in substantial cost containment and improved the efficiency of patient care.

[CALR gene mutation detection and clinical observation of 150 essential thrombocythemia patients]

OBJECTIVE

To explore the prevalence of CARL gene mutations and the mutation types in patients with essential thrombocythemia (ET), and to compare the patients clinical characteristics of CALR mutation with JAK2 V617F, MPL W515K mutation patients and triple negative group.

METHODS

The mutations of CALR gene at extron 9 and MPL W515K in 150 ET patients were detected by PCR amplification followed by direct sequencing of genomic DNA, the JAK2 V617F mutation by using allele specific PCR.

RESULTS

(1)The CALR mutations were found in 38 patients (25.3%) of 150 ET patients. A total of 4 types of CALR mutations were identified (type Ic.1092_1143del52bp, n=17; type II c.1154_1155insTTGTC, n=16; type III c.1094_1139del46bp, n=4; type IV c.1103_1136del34bp, n=1). (2)The incidence of JAK2 V617F and MPL W515K was 61.3% (92/150) and 2.7% (4/150), respectively. The frequency of CALR mutation was 70.4% (38/54) in 54 ET patients without JAK2 V617F and MPL W515K mutations. The co-occurrence of any two kinds of gene mutations was not detected. (3)The hemoglobin level and leukocyte counts of patients with CARL mutations were significantly lower than that in patients with JAK2 V617F mutations (P<0.05). The median age of patients with CALR mutation was significantly higher than that of triple negative patients (59 years vs 29.5 years, P<0.01). Cytogenetic analysis was performed in 147 patients, and there were 4 abnormal karyotype cases. CALR mutation incidence was significantly higher in abnormal karyotype cases than that in normal ones (75% vs 24.5%, P=0.019).

CONCLUSION

The incidence of CALR mutations is high in ET patients without JAK2 V617F and MPL W515K mutations, and is associated with abnormal karyotype. CARL-mutated cases showed a significantly lower leucocyte and hemoglobin levels compared with JAK2 V617F mutated cases.

Allo-SCT for myelofibrosis: reversing the chronic phase in the JAK inhibitor era?

At present, allo-SCT is the only curative treatment for patients with myelofibrosis (MF). Unfortunately, a significant proportion of candidate patients are considered transplant ineligible due to their poor general condition and advanced age at the time of diagnosis. The approval of the first JAK inhibitor, ruxolitinib, for patients with advanced MF in 2011 has had a qualified impact on the treatment algorithm. The drug affords substantial improvement in MF-associated symptoms and splenomegaly but no major effect on the natural history. There has, therefore, been considerable support for assessing the drug's candidacy in the peritransplant period. The drug's precise impact on clinical outcome following allo-SCT is currently not known; nor are the drug's long-term efficacy and safety known. Considering the rarity of MF and the small proportion of patients who undergo allo-SCT, well designed collaborative efforts are required. In order to address some of the principal challenges, an expert panel of laboratory and clinical experts in this field was established, and an independent workshop held during the 54th American Society of Hematology Annual Meeting in New Orleans, USA on 6 December 2013, and the European Hematology Association's Annual Meeting in Milan, Italy on 13 June 2014. This document summarizes the results of these efforts.

CALR, JAK2, and MPL mutation profiles in patients with four different subtypes of myeloproliferative neoplasms: primary myelofibrosis, essential thrombocythemia, polycythemia vera, and myeloproliferative neoplasm, unclassifiable

OBJECTIVES

We investigated mutation profiles of CALR, JAK2, and MPL in 199 Korean patients with myeloproliferative neoplasms (MPNs).

METHODS

In total, 199 patients with MPN (54 primary myelofibrosis [PMF], 79 essential thrombocythemia [ET], 58 polycythemia vera [PV], and eight MPN-unclassifiable [MPN-U]) and 4 patients with acute panmyelosis with myelofibrosis (APMF) were retrospectively subjected to Sanger sequencing for CALR, JAK2, and MPL.

RESULTS

The overall frequency of CALR mutations was 12.6% (type 1 mutation, 16 patients; type 2 mutation, nine patients): most frequent in MPN-U (37.5%), followed by ET (17.7%) and PMF (14.8%). CALR mutations were not found in PV or APMF. CALR and JAK2 or MPL mutations were mutually exclusive. In PMF, the CALR mutations were associated with lower levels of leukocytes, lower bone marrow cellularity, and higher number of megakaryocytes. Patients with CALR-mutated ET more frequently progressed to the accelerated or blast phases compared with patients with JAK2 mutations. CALR mutations were frequently observed in the JAK2-negative MPNs, most frequently in MPN-U.

CONCLUSIONS

The prognostic significance of CALR mutations likely differs among the MPN subtypes.

Diagnosis, complications and management of chronic neutrophilic leukaemia: A case report

Chronic neutrophilic leukemia (CNL) is a rare myeloproliferative neoplasm characterized by sustained neutrophilia and the absence of the Philadelphia chromosome or the BCR-ABL1 fusion gene. The present study reports the case of a 59-year-old Caucasian female that was referred to The Francisco Gentil Portuguese Institute of Oncology (Porto, Portugal) with constitutional symptoms (mainly asthenia), marked leukocytosis (51.33×10⁹/l with 90% neutrophils), macrocytic anemia and splenomegaly. Bone marrow aspiration and biopsy revealed hypercellular marrow with clear predominance of segmented neutrophils. The karyotype was normal and the BCR-ABL1 fusion gene was not detected. After excluding a leukemoid reaction, a diagnosis of CNL was established. The clinical follow-up was complicated by hemorrhagic brain lesions and relapsing episodes of erythematous, well-demarcated and painful subcutaneous nodular lesions, consistent with Sweet's syndrome (SS). Multiple treatment strategies were administered, including use of hydroxyurea, imatinib and intensive chemotherapy. Nevertheless, progression was documented and the patient succumbed at 28 months post-diagnosis. The clinical course of CNL varies, and can be complicated by cerebral hemorrhage, blastic transformation or infection. Dermatological manifestations such as SS have seldom been reported in association. No evidence-based treatment currently exists and the majority of our knowledge is based on results from case reports and small series.

Dissecting Genomic Aberrations in Myeloproliferative Neoplasms by Multiplex-PCR and Next Generation Sequencing

In order to assess the feasibility of amplicon-based parallel next generation sequencing (NGS) for the diagnosis of myeloproliferative neoplasms (MPN), we investigated multiplex-PCR of 212 amplicons covering genomic mutational hotspots in 48 cancer-related genes. Samples from 64 patients with MPN and five controls as well as seven (myeloid) cell lines were analyzed. Healthy donor and reactive erythrocytosis samples showed several frequent single-nucleotide polymorphisms (SNPs) but no known pathogenic mutation. Sequencing of the cell lines confirmed the presence of the known mutations. In the patient samples, JAK2 V617F was present in all PV, 4 of 10 ET, and 16 of 19 MF patients. The JAK2 V617F allele burden was different in the three groups (ET, 33+/-22%; PV 48+/-28% and MF 68+/- 29%). Further analysis detected both previously described and undescribed mutations (i.e., G12V NRAS, IDH1 R132H, E255G ABL, and V125G IDH1 mutations). One patient with lymphoid BC/Ph+ ALL who harbored a T315I ABL mutation and was treated with ponatinib was found to have developed a newly acquired V216M TP53 mutation (12% of transcripts) when becoming resistant to ponatinib. Ponatinib led to a decrease of ABL T315I positive transcripts from 47% before ponatinib treatment to 16% at the time of ponatinib resistance in this patient, suggesting that both TP53 and ABL mutations were present in the same clone and that the newly acquired TP53 mutation might have caused ponatinib resistance in this patient. In conclusion, amplicon-sequencing-based NGS allows simultaneous analysis of multiple MPN associated genes for diagnosis and during treatment and measurement of the mutant allele burden.

Primary thrombocytosis in children

Myeloproliferative neoplasms are uncommon disorders in children, for which we have limited understanding of the pathogenesis and optimal management. JAK2 and MPL mutations, while common drivers of myeloproliferative neoplasms in adult patients, are not clearly linked to pediatric disease. Management and clinical outcomes in adults have been well delineated with defined recommendations for risk stratification and treatment. This is not the case for pediatric patients, for whom there is neither a standard approach to workup nor any consensus regarding management. This review will discuss thrombocytosis in children, including causes of thrombocytosis in children, the limited knowledge we have regarding pediatric primary thrombocytosis, and our thoughts on potential risk stratification and management, and future questions to be answered by laboratory research and collaborative clinical study.

A rapid, highly accurate method for quantifying CALR mutant allele burden in persons with myeloproliferative neoplasms

BACKGROUND

Calreticulin (CALR) mutations were recently identified in a substantial proportion of persons with essential thrombocythemia (ET) and with primary myelofibrosis (PMF) without JAK2(V617F). Consequently rapid, sensitive, and specific methods to detect and quantify these mutations are needed.

METHODS

We studied samples from 1088 persons with myeloproliferative neoplasms (MPNs) including 421 JAK2(V617F) negative subjects with ET, PMF, polycythemia vera (PV), chronic myeloid leukemia (CML) and hyper-eosinophilic syndrome (HES). Detection of CALR exon 9 mutations was done by PCR amplification followed by fragment length analysis and direct sequencing. Dilution assays were used to determine CALR mutant allele burden.

RESULTS

We detected CALR mutations in blood and bone marrow samples from 152 subjects with ET and with PMF but not in samples from normal or persons with PV, CML, or HES. CALR mutant peaks were distinct from wild-type peaks and dilution experiments indicated a sensitivity level of 0.5-5% for a CALR mutant allele in a wild-type background. Diverse types of mutations were detected including deletions, insertions, and complex indels. All mutations were confirmed by direct sequencing. We also used dilution experiments to quantify mutant allele burden. We were able to reproducibly detect mutant allele levels as low 5% (0.5-5%) in a wild-type background.

CONCLUSIONS

PCR amplification followed by fragment length analysis is a rapid, sensitive, and specific method for screening persons with MPNs for CALR mutations, especially those with ET and PMF and for estimating mutant allele burden.

CSF3R and CALR mutations in paediatric myeloid disorders and the association of CSF3R mutations with translocations, including t(8; 21)

Mutations in the colony-stimulating factor 3 receptor (CSF3R) and calreticulin (CALR) genes have been reported in a proportion of adults with myeloproliferative disease. However, little is known about CSF3R or CALR mutations in paediatric myeloid disorders. We analysed CSF3R exons 14 and 17, and CALR exon 9, using direct sequencing in samples of paediatric acute myeloid leukaemia (AML; n = 521), juvenile myelomonocytic leukaemia (JMML; n = 40), myelodysplastic syndrome (MDS; n = 20) and essential thrombocythaemia (ET; n = 21). CSF3R mutations were found in 10 (1.2%) of 521 patients with AML; two in exon 14 (both missense mutations resulting in p.T618I) and eight in exon 17 (three frameshift mutations: p.S715X, p.Q774R, and p.S783Q; and five novel missense mutations: p.Q754K, p.R769H, p.L777F, p.T781I, and S795R). All of the patients with mutations in CSF3R exon 17 had chromosomal translocations, including four with t(8;21). At the time of reporting, seven of these ten patients are alive; three have died, due to side effects of chemotherapy. No CSF3R mutations were found in cases of MDS, JMML or ET. The only mutation found in the CALR gene was a frameshift (p.L367 fs) in one ET patient. We discuss the potential impact of these findings for the leukaemogenesis and clinical features of paediatric myeloid disorders.

Gene expression profiling of loss of TET2 and/or JAK2V617F mutant hematopoietic stem cells from mouse models of myeloproliferative neoplasms

Myeloproliferative neoplasms (MPNs) are clinically characterized by the chronic overproduction of differentiated peripheral blood cells and the gradual expansion of malignant intramedullary/extramedullary hematopoiesis. In MPNs mutations in JAK2 MPL or CALR are detected mutually exclusive in more than 90% of cases [1], [2]. Mutations in them lead to the abnormal activation of JAK/STAT signaling and the autonomous growth of differentiated cells therefore they are considered as “driver” gene mutations. In addition to the above driver gene mutations mutations in epigenetic regulators such as TET2 DNMT3A ASXL1 EZH2 or IDH1/2 are detected in about 5%–30% of cases respectively [3]. Mutations in TET2 DNMT3A EZH2 or IDH1/2 commonly confer the increased self-renewal capacity on normal hematopoietic stem cells (HSCs) but they do not lead to the autonomous growth of differentiated cells and only exhibit subtle clinical phenotypes [[4], [6], [7], [8],5]. It was unclear how mutations in such epigenetic regulators influenced abnormal HSCs with driver gene mutations how they influenced the disease phenotype or whether a single driver gene mutation was sufficient for the initiation of human MPNs. Therefore we focused on JAK2V617F and loss of TET2—the former as a representative of driver gene mutations and the latter as a representative of mutations in epigenetic regulators—and examined the influence of single or double mutations on HSCs (Lineage⁻Sca-1⁺c-Kit⁺ cells (LSKs)) by functional analyses and microarray whole-genome expression analyses [9]. Gene expression profiling showed that the HSC fingerprint genes [10] was statistically equally enriched in TET2-knockdown-LSKs but negatively enriched in JAK2V617F–LSKs compared to that in wild-type-LSKs. Double-mutant-LSKs showed the same tendency as JAK2V617F–LSKs in terms of their HSC fingerprint genes but the expression of individual genes differed between the two groups. Among 245 HSC fingerprint genes 100 were more highly expressed in double-mutant-LSKs than in JAK2V617F–LSKs. These altered gene expressions might partly explain the mechanisms of initiation and progression of MPNs which was observed in the functional analyses [9]. Here we describe gene expression profiles deposited at the Gene Expression Omnibus (GEO) under the accession number GSE62302 including experimental methods and quality control analyses.

BCR-ABL1- positive chronic myeloid leukemia with erythrocytosis presenting as polycythemia vera: a case report

Introduction

The World Health Organization classification of chronic myeloproliferative disease encompasses eight entities of bone marrow neoplasms, among them Breakpoint cluster region-Abelson murine leukemia viral oncogene homolog 1-positive chronic myeloid leukemia and polycythemia vera. Polycythemia vera requires, in the majority of cases (95%), the negativity of Breakpoint cluster region-Abelson murine leukemia viral oncogene homolog 1 rearrangement and the presence of the Janus kinase 2 mutation. We report a case of erythrocytosis as the primary manifestation of a chronic myeloid leukemia, with the presence of the Philadelphia chromosome and the Breakpoint cluster region-Abelson murine leukemia viral oncogene homolog 1 fusion gene, and in the absence of any Janus kinase 2 mutation.

Case presentation

A 68-year-old Caucasian woman, with a history of cigarette consumption and obstructive sleep apnoea syndrome (undergoing continuous positive airway pressure treatment) had presented to our institution with fatigue and a hemoglobin level of 18.6g/L, with slight leukocytosis at 16G/L, and no other anomalies on her complete blood cell count. Examination of her arterial blood gases found only a slight hypoxemia; erythropoietin and ferritin levels were very low and could not explain a secondary erythrocytosis.

Further analyses revealed the absence of any Janus kinase 2 mutation, thus excluding polycythemia vera. Taken together with a high vitamin B12 level, we conducted a Breakpoint cluster region-Abelson murine leukemia viral oncogene homolog 1 gene analysis and bone marrow cytogenetic analysis, both of which returned positive, leading to the diagnosis of chronic myeloid leukemia.

Conclusions

To date, this case is the first description of a Breakpoint cluster region-Abelson murine leukemia viral oncogene homolog 1-positive chronic myeloid leukemia, presenting with erythrocytosis as the initial manifestation, and mimicking a Janus kinase 2 V617F-negative polycythemia vera. Her impressive response to imatinib therapy underscores the importance of not missing this diagnosis.

Genetic variation at MECOM, TERT, JAK2 and HBS1L-MYB predisposes to myeloproliferative neoplasms

Clonal proliferation in myeloproliferative neoplasms (MPN) is driven by somatic mutations in JAK2, CALR or MPL, but the contribution of inherited factors is poorly characterized. Using a three-stage genome-wide association study of 3,437 MPN cases and 10,083 controls, we identify two SNPs with genome-wide significance in JAK2(V617F)-negative MPN: rs12339666 (JAK2; meta-analysis P=1.27 × 10(-10)) and rs2201862 (MECOM; meta-analysis P=1.96 × 10(-9)). Two additional SNPs, rs2736100 (TERT) and rs9376092 (HBS1L/MYB), achieve genome-wide significance when including JAK2(V617F)-positive cases. rs9376092 has a stronger effect in JAK2(V617F)-negative cases with CALR and/or MPL mutations (Breslow-Day P=4.5 × 10(-7)), whereas in JAK2(V617F)-positive cases rs9376092 associates with essential thrombocythemia (ET) rather than polycythemia vera (allelic χ(2) P=7.3 × 10(-7)). Reduced MYB expression, previously linked to development of an ET-like disease in model systems, associates with rs9376092 in normal myeloid cells. These findings demonstrate that multiple germline variants predispose to MPN and link constitutional differences in MYB expression to disease phenotype.

Tetraspanin CD9 participates in dysmegakaryopoiesis and stromal interactions in primary myelofibrosis

Primary myelofibrosis is characterized by clonal myeloproliferation, dysmegakaryopoiesis, extramedullary hematopoiesis associated with myelofibrosis and altered stroma in the bone marrow and spleen. The expression of CD9, a tetraspanin known to participate in megakaryopoiesis, platelet formation, cell migration and interaction with stroma, is deregulated in patients with primary myelofibrosis and is correlated with stage of myelofibrosis. We investigated whether CD9 participates in the dysmegakaryopoiesis observed in patients and whether it is involved in the altered interplay between megakaryocytes and stromal cells. We found that CD9 expression was modulated during megakaryocyte differentiation in primary myelofibrosis and that cell surface CD9 engagement by antibody ligation improved the dysmegakaryopoiesis by restoring the balance of MAPK and PI3K signaling. When co-cultured on bone marrow mesenchymal stromal cells from patients, megakaryocytes from patients with primary myelofibrosis displayed modified behaviors in terms of adhesion, cell survival and proliferation as compared to megakaryocytes from healthy donors. These modifications were reversed after antibody ligation of cell surface CD9, suggesting the participation of CD9 in the abnormal interplay between primary myelofibrosis megakaryocytes and stroma. Furthermore, silencing of CD9 reduced CXCL12 and CXCR4 expression in primary myelofibrosis megakaryocytes as well as their CXCL12-dependent migration. Collectively, our results indicate that CD9 plays a role in the dysmegakaryopoiesis that occurs in primary myelofibrosis and affects interactions between megakaryocytes and bone marrow stromal cells. These results strengthen the "bad seed in bad soil" hypothesis that we have previously proposed, in which alterations of reciprocal interactions between hematopoietic and stromal cells participate in the pathogenesis of primary myelofibrosis.

Genomic diversity in myeloproliferative neoplasms: focus on myelofibrosis

The classical myeloproliferative neoplasms (MPNs) are a group of clonal diseases comprising essential thrombocythaemia (ET), polycythaemia vera (PV) and primary myelofibrosis (PMF). PMF is the rarest disease sub type and has been challenging to address due to the lack of a specific genetic marker, inadequate risk identification models and a highly variable clinical course. Continuous efforts have over time, seen the inclusion of cytogenetic information in prognostic scoring models that have resulted in improved risk stratification models providing further rationale for therapeutic management. Technological advances using single nucleotide polymorphism arrays increased the detection of known and novel MPN related changes and variant detection by massively parallel sequencing provided a large scale screening tool for the multitude of somatic gene mutations that have more recently been described in MPN. Some of these mutations show an association with specific cytogenetic changes or phenotypes. While PMF occurs mainly in adults, it has also been described in paediatric cases and shows distinct histopathological, genetic and clinical features in comparison. This review provides an overview of the genomics landscape of PMF and current developments in MPN therapy.

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

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

Clonal evolution revealed by whole genome sequencing in a case of primary myelofibrosis transformed to secondary acute myeloid leukemia

Clonal architecture in myeloproliferative neoplasms (MPNs) is poorly understood. Here we report genomic analyses of a patient with primary myelofibrosis (PMF) transformed to secondary acute myeloid leukemia (sAML). Whole genome sequencing (WGS) was performed on PMF and sAML diagnosis samples, with skin included as a germline surrogate. Deep sequencing validation was performed on the WGS samples and an additional sample obtained during sAML remission/relapsed PMF. Clustering analysis of 649 validated somatic single-nucleotide variants revealed four distinct clonal groups, each including putative driver mutations. The first group (including JAK2 and U2AF1), representing the founding clone, included mutations with high frequency at all three disease stages. The second clonal group (including MYB) was present only in PMF, suggesting the presence of a clone that was dispensable for transformation. The third group (including ASXL1) contained mutations with low frequency in PMF and high frequency in subsequent samples, indicating evolution of the dominant clone with disease progression. The fourth clonal group (including IDH1 and RUNX1) was acquired at sAML transformation and was predominantly absent at sAML remission/relapsed PMF. Taken together, these findings illustrate the complex clonal dynamics associated with disease evolution in MPNs and sAML.

Functional roles of calreticulin in cancer biology

Calreticulin is a highly conserved endoplasmic reticulum chaperone protein which participates in various cellular processes. It was first identified as a Ca²⁺-binding protein in 1974. Accumulated evidences indicate that calreticulin has great impacts for the development of different cancers and the effect of calreticulin on tumor formation and progression may depend on cell types and clinical stages. Cell surface calreticulin is considered as an “eat-me” signal and promotes phagocytic uptake of cancer cells by immune system. Moreover, several reports reveal that manipulation of calreticulin levels profoundly affects cancer cell proliferation and angiogenesis as well as differentiation. In addition to immunogenicity and tumorigenesis, interactions between calreticulin and integrins have been described during cell adhesion, which is an essential process for cancer metastasis. Integrins are heterodimeric transmembrane receptors which connect extracellular matrix and intracellular cytoskeleton and trigger inside-out or outside-in signaling transduction. More and more evidences reveal that proteins binding to integrins might affect integrin-cytoskeleton interaction and therefore influence ability of cell adhesion. Here, we reviewed the biological roles of calreticulin and summarized the potential mechanisms of calreticulin in regulating mRNA stability and therefore contributed to cancer metastasis.

Response to ruxolitinib in patients with intermediate-1-, intermediate-2-, and high-risk myelofibrosis: results of the UK ROBUST Trial

Myelofibrosis is characterized by splenomegaly and debilitating constitutional symptoms that negatively impact patients' quality of life. ROBUST, a UK, open-label, phase II study, evaluated the safety and efficacy of ruxolitinib in patients with myelofibrosis (N = 48), including intermediate-1 risk patients. The primary composite endpoint was the proportion of patients achieving treatment success [≥ 50% reduction in palpable spleen length and/or a ≥ 50% decrease in Myelofibrosis Symptom Assessment Form Total Symptom Score (MF-SAF TSS)] at 48 weeks. This was the first time that efficacy of ruxolitinib in myelofibrosis has been evaluated based on these criteria and the first time the MF-SAF was used in a population of patients solely from the United Kingdom. Overall, 50% of patients and 57% of intermediate-1 risk patients, achieved treatment success; reductions in spleen length and symptoms were observed in all risk groups. The majority of patients (66.7%) experienced ≥ 50% reductions from baseline in spleen length at any time. Improvements in MF-SAF TSS were seen in 80.0%, 72.7%, and 72.2% of intermediate-1, intermediate-2, and high-risk patients, respectively. Consistent with other studies of ruxolitinib, the most common haematological adverse events were anaemia and thrombocytopenia. Results indicate that most patients with myelofibrosis, including intermediate-1 risk patients, may benefit from ruxolitinib treatment.

Molecular insights into regulation of JAK2 in myeloproliferative neoplasms

The critical role of Janus kinase-2 (JAK2) in regulation of myelopoiesis was established 2 decades ago, but identification of mutations in the pseudokinase domain of JAK2 in myeloproliferative neoplasms (MPNs) and in other hematologic malignancies highlighted the role of JAK2 in human disease. These findings have revolutionized the diagnostics of MPNs and led to development of novel JAK2 therapeutics. However, the molecular mechanisms by which mutations in the pseudokinase domain lead to hyperactivation of JAK2 and clinical disease have been unclear. Here, we describe recent advances in the molecular characterization of the JAK2 pseudokinase domain and how pathogenic mutations lead to constitutive activation of JAK2.

Mutations and long-term outcome of 217 young patients with essential thrombocythemia or early primary myelofibrosis

We investigated the influence of molecular status on disease characteristics and clinical outcome in young patients (⩽ 40 years) with World Health Organization (WHO)-defined essential thrombocythemia (ET) or early/prefibrotic primary myelofibrosis (early-PMF). Overall, 217 patients with ET (number 197) and early-PMF (number 20) were included in the analysis. Median follow-up time was 10.2 years. The cumulative incidence of thrombosis, hemorrhages and disease evolution into myelofibrosis/acute leukemia were 16.6%, 8.6% and 3% at 15 years, respectively. No differences were detectable between ET and early-PMF patients, although the latter cohort showed a trend for worse combined-event free survival (EFS). Mutation frequency were 61% for JAK2V617F, 25% for CALR and 1% for MPLW515K, and were comparable across WHO diagnosis; however, JAK2V617F allele burden was higher in the early-PMF group. Compared with JAK2V617F-positive patients, CALR-mutated patients displayed higher platelet count and lower hemoglobin level. CALR mutations significantly correlated with lower thrombotic risk (9.1% versus 21.7%, P = 0.04), longer survival (100% versus 96%, P = 0.05) and better combined-EFS (86% versus 71%, P = 0.02). However, non-type 1/type 2 CALR mutations ('minor' mutations) and abnormal karyotype were found to correlate with increased risk of disease evolution. At last contact, six patients had died; in five cases, the causes of death were related to the hematological disease and occurred at a median age of 64 years (range: 53-68 years). Twenty-eight patients (13%) were unmutated for JAK2, CALR and MPL: no event was registered in these 'triple-negative' patients.

Discrepancies between bone marrow histopathology and clinical phenotype in BCR-ABL1-negative myeloproliferative neoplasms associated with splanchnic vein thrombosis

We examined a consecutive series of 29 patients with myeloproliferative neoplasms (MPNs) associated with splanchnic vein thrombosis (SVT) in order to evaluate their bone marrow morphology and identify possible associations between histological findings and clinical features. Eleven patients showed the morphological features of polycythemia vera (PV), 11 of primary myelofibrosis (PMF) and six of essential thrombocythemia (ET). Molecular analyses identified the JAK2 V617F mutation in 27 patients; one of the JAK2-negative patients carried the MPL W515K mutation, the other was "triple-negative" (no JAK2, MPL or CALR mutation). On the basis of the WHO classification, three patients were classified as having PV, 11 as having PMF, and two as having ET; the remaining 13 cases fell into the MPN-unclassifiable category as there were discrepancies between their morphological and clinical features. In conclusion, our findings suggest that bone marrow histology should always be considered a key component of the diagnostic algorithm in patients with SVT, but that it is not enough to distinguish the different entities. This is particularly important because diagnoses of PV, PMF or ET have very different prognoses and obviously imply different therapies. It is therefore necessary to adopt a comprehensive approach that considers morphological, clinical and molecular data.

A novel mutation in EED associated with overgrowth

In a patient suspected clinically to have Weaver syndrome, we ruled out mutations in EZH2 and NSD1, then identified a previously undescribed de novo mutation in EZH2's partner protein EED. Both proteins are members of the Polycomb Repressive Complex 2 that maintains gene silencing. On the basis of the similarities of the patient's phenotype to Weaver syndrome, which is caused by de novo mutations in EZH2, and on other lines of evidence including mouse Eed hypomorphs, we characterize this mutation as probably pathogenic for a Weaver-like overgrowth syndrome. This is the first report of overgrowth and related phenotypes associated with a constitutional mutation in human EED.

Reducing symptom burden in patients with myeloproliferative neoplasms in the era of Janus kinase inhibitors

Philadelphia chromosome-negative myeloproliferative neoplasms (MPNs) are clonal stem cell-derived malignancies that include primary myelofibrosis, polycythemia vera and essential thrombocythemia and are characterized by dysregulated Janus kinase-signal transducers and activators of transcription (JAK-STAT) signaling. Clinical manifestations include splenomegaly, cytopenias and/or systemic inflammation. Patients have a heterogeneous symptom profile that includes fatigue, loss of appetite, pruritus and night sweats, which significantly impact quality of life (QoL) and lead to poor survival outcomes. With the introduction of JAK inhibitors, improvement in disease-related symptoms has emerged as a realistic expectation of therapy and an integral measure of clinical efficacy. The JAK1/JAK2 inhibitor ruxolitinib is approved for the treatment of myelofibrosis and is currently under clinical development for polycythemia vera. Ruxolitinib has demonstrated significant reductions in symptom burden, with consequent improvements in QoL measures. With the potential to improve QoL, recognition of the impact and burden of symptoms on patients with MPNs is critical.

CD133 marks a stem cell population that drives human primary myelofibrosis

Primary myelofibrosis is a myeloproliferative neoplasm characterized by bone marrow fibrosis, megakaryocyte atypia, extramedullary hematopoiesis, and transformation to acute myeloid leukemia. To date the stem cell that undergoes the spatial and temporal chain of events during the development of this disease has not been identified. Here we describe a CD133(+) stem cell population that drives the pathogenesis of primary myelofibrosis. Patient-derived circulating CD133(+) but not CD34(+)CD133(-) cells, with a variable burden for JAK2 (V617F) mutation, had multipotent cloning capacity in vitro. CD133(+) cells engrafted for up to 10 months in immunocompromised mice and differentiated into JAK2-V617F(+) myeloid but not lymphoid progenitors. We observed the persistence of human, atypical JAK2-V617F(+) megakaryocytes, the initiation of a prefibrotic state, bone marrow/splenic fibrosis and transition to acute myeloid leukemia. Leukemic cells arose from a subset of CD133(+) cells harboring EZH2 (D265H) but lacking a secondary JAK2 (V617F) mutation, consistent with the hypothesis that deregulation of EZH2 activity drives clonal growth and increases the risk of acute myeloid leukemia. This is the first characterization of a patient-derived stem cell population that drives disease resembling both chronic and acute phases of primary myelofibrosis in mice. These results reveal the importance of the CD133 antigen in deciphering the neoplastic clone in primary myelofibrosis and indicate a new therapeutic target for myeloproliferative neoplasms.

Are all cases of paediatric essential thrombocythaemia really myeloproliferative neoplasms? Analysis of a large cohort

Sporadic essential thrombocythaemia (ET) is rare in paediatrics, and the diagnostic and clinical approach to paediatric cases cannot be simply copied from experience with adults. Here, we assessed 89 children with a clinical diagnosis of ET and found that 23 patients (25·8%) had a clonal disease. The JAK2 V617F mutation was identified in 14 children, 1 child had the MPL W515L mutation, and 6 had CALR mutations. The monoclonal X-chromosome inactivation pattern was seen in six patients (two with JAK2 V617F and two with CALR mutations). The other 66 patients (74·2%) had persistent thrombocytosis with no clonality. There were no clinical or haematological differences between the clonal and non-clonal patients. The relative proportion of ET-specific mutations in the clonal children was much the same as in adults. The higher prevalence of non-clonal cases suggests that some patients may not have myeloproliferative neoplasms, with significant implications for their treatment.

Risk of Wernicke's encephalopathy and cardiac disorders in patients with myeloproliferative neoplasm

The objectives of the study were to estimate the incidence of Wernicke's encephalopathy (WE) and cardiac disorders among patients with myeloproliferative neoplasms (MPN), and compare it with those without MPN. A total of 39,761 MPN patients were identified from the US Marketscan database. Approximately 27% of them were 65+ years of age, and 51% were male. Patients with MPN had higher rates of WE, compared to those without MPN (MPN vs. non-MPN: 1.09 vs. 0.39/1000 person-year, adjusted HR=2.19, 95%CI 1.43-3.34). Patients with MPN also had higher rates of cardiac events (congestive heart failure: MPN vs. non-MPN: 9.27 vs. 3.70/1000 person-year, adjusted HR=1.64, 95%CI 1.42-1.88; acute myocardial infarction: MPN vs. non-MPN: 10.45 vs. 5.02/1000 person-year, adjusted HR=1.44, 95%CI 1.27, 1.63; cardiac arrhythmia: MPN vs. non-MPN: 106.5 vs. 53.9/1000 person-year, adjusted HR=1.42, 95%CI 1.36-1.48). Physicians who care for patients with MPN should be aware of increased risk of WE and cardiac disorders in this population.

Frequency and allele burden of CALR mutations in Chinese with essential thrombocythemia and primary myelofibrosis without JAK2(V617F) or MPL mutations

CALR mutations are detected in about 50% of persons of predominately European descent with essential thrombocythemia (ET) or primary myelofibrosis (PMF) with wild-type alleles of JAK2 and MPL. We studied 1088 Chinese with diverse myeloproliferative neoplasms including ET (N=234) and PMF (N=50) without JAK2(V617F) or MPL exon 10 mutations. CALR mutation was detected in 53% (95% CI, 46-60%) of subjects with ET and 56% (95% CI, 41-70%) of subjects with PMF. 152 CALR mutations were identified clustering into 15 types including deletions (N=8), insertions (N=3) and complex indels (N=4). We also identified 9 new mutations. Mean (±SD) mutant allele burden was 31±12% (range, 0.5-69%). Persons with PMF had higher CALR mutant allele burdens than those with ET (38±8% vs. 29±12%; P<0.001). Amongst persons with CALR mutations, those with PMF had different clinical features from those with ET. These data may be useful for diagnosing ET and PMF in Chinese who are about 40% of all persons with ET and PMF and for monitoring therapy-response. They also highlight similarities and differences in CALR mutations between Chinese and persons of predominately European descent with these diseases.

Effect of mutation order on myeloproliferative neoplasms

BACKGROUND

Cancers result from the accumulation of somatic mutations, and their properties are thought to reflect the sum of these mutations. However, little is known about the effect of the order in which mutations are acquired.

METHODS

We determined mutation order in patients with myeloproliferative neoplasms by genotyping hematopoietic colonies or by means of next-generation sequencing. Stem cells and progenitor cells were isolated to study the effect of mutation order on mature and immature hematopoietic cells.

RESULTS

The age at which a patient presented with a myeloproliferative neoplasm, acquisition of JAK2 V617F homozygosity, and the balance of immature progenitors were all influenced by mutation order. As compared with patients in whom the TET2 mutation was acquired first (hereafter referred to as "TET2-first patients"), patients in whom the Janus kinase 2 (JAK2) mutation was acquired first ("JAK2-first patients") had a greater likelihood of presenting with polycythemia vera than with essential thrombocythemia, an increased risk of thrombosis, and an increased sensitivity of JAK2-mutant progenitors to ruxolitinib in vitro. Mutation order influenced the proliferative response to JAK2 V617F and the capacity of double-mutant hematopoietic cells and progenitor cells to generate colony-forming cells. Moreover, the hematopoietic stem-and-progenitor-cell compartment was dominated by TET2 single-mutant cells in TET2-first patients but by JAK2-TET2 double-mutant cells in JAK2-first patients. Prior mutation of TET2 altered the transcriptional consequences of JAK2 V617F in a cell-intrinsic manner and prevented JAK2 V617F from up-regulating genes associated with proliferation.

CONCLUSIONS

The order in which JAK2 and TET2 mutations were acquired influenced clinical features, the response to targeted therapy, the biology of stem and progenitor cells, and clonal evolution in patients with myeloproliferative neoplasms. (Funded by Leukemia and Lymphoma Research and others.).

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.

Therapy for myeloproliferative neoplasms: when, which agent, and how?

Myeloproliferative neoplasms, including polycythemia vera (PV), essential thrombocythemia, and myelofibrosis (MF) (both primary and secondary), are recognized for their burdensome symptom profiles, life-threatening complications, and risk of progression to acute leukemia. Recent advancements in our ability to diagnose and prognosticate these clonal malignancies have paralleled the development of MPN-targeted therapies that have had a significant impact on disease burden and quality of life. Ruxolitinib has shown success in alleviating the symptomatic burden, reducing splenomegaly and improving quality of life in patients with MF. The role and clinical expectations of JAK2 inhibition continues to expand to a variety of investigational arenas. Clinical trials for patients with MF focus on new JAK inhibitors with potentially less myelosuppression( pacritinib) or even activity for anemia (momelotinib). Further efforts focus on combination trials (including a JAK inhibitor base) or targeting new pathways (ie, telomerase). Similarly, therapy for PV continues to evolve with phase 3 trials investigating optimal frontline therapy (hydroxyurea or IFN) and second-line therapy for hydroxyurea-refractory or intolerant PV with JAK inhibitors. In this chapter, we review the evolving data and role of JAK inhibition (alone or in combination) in the management of patients with MPNs.