Increased risk of recurrent thrombosis in patients with essential thrombocythemia carrying the homozygous JAK2 V617F mutation

Molecular Genetics of Thrombotic Myeloproliferative Neoplasms: Implications in Precision Oncology

Classical BCR-ABL-negative myeloproliferative neoplasms (MPN) include polycythaemia vera, essential thrombocythaemia, and primary myelofibrosis. Unlike monogenic disorders, a more complicated series of genetic mutations are believed to be responsible for MPN with various degrees of thromboembolic and bleeding complications. Thrombosis is one of the early manifestations in patients with MPN. To date, the driver genes responsible for MPN include JAK2, CALR, MPL, TET2, ASXL1, and MTHFR. Affords have been done to elucidate these mutations and the incidence of thromboembolic events. Several lines of evidence indicate that mutations in JAK2, MPL, TET2 and ASXL1 gene and polymorphisms in several clotting factors (GPIa, GPIIa, and GPIIIa) are associated with the occurrence and prevalence of thrombosis in MPN patients. Some polymorphisms within XRCC1, FBG, F2, F5, F7, F12, MMP9, HPA5, MTHFR, SDF-1, FAS, FASL, TERT, ACE, and TLR4 genes may also play a role in MPN manifestation. This review aims to provide an insightful overview on the genetic perspective of thrombotic complications in patients with MPN.

The role of driver mutations in myeloproliferative neoplasms: insights from mouse models

High frequency of JAK2V617F or CALR exon 9 mutations is a main molecular feature of myeloproliferative neoplasms (MPNs). Analysis of mouse models driven by these mutations suggests that they are a direct cause of MPNs and that the expression levels of the mutated genes define the disease phenotype. The function of MPN-initiating cells has also been elucidated by these mouse models. Such mouse models also play an important role in modeling disease to investigate the effects and action mechanisms of therapeutic drugs, such as JAK2 inhibitors and interferon α, against MPNs. The mutation landscape of hematological tumors has already been clarified by next-generation sequencing technology, and the importance of functional analysis of mutant genes in vivo should increase further in the future.

[Risk factors for recurrent thrombosis in patients with polycythemia vera and essential thrombocythemia]

目的

分析并探讨真性红细胞增多症（PV）和原发性血小板增多症（ET）患者发生再次血栓事件（再栓）的临床特点及危险因素。

方法

回顾性分析首都医科大学附属北京安贞医院2001年2月至2016年11月诊治的38例发生再栓事件的ET和PV患者的临床资料，采用Logistic回归分析再栓事件危险因素。

结果

共计104例首次血栓事件的ET和PV患者中，38例（36.5%）患者发生再栓，年发生率为9.8%/人，ET组、PV组再栓年发生率分别为12.3%/人、5.7%/人。再栓事件共56次，42.1%发生在首次血栓形成后1年内；动脉血栓症占97.4%（以急性冠脉综合征最为多见），静脉血栓症占2.6%。ET组再栓以急性冠脉综合征最多见（18例，64.3%），PV组以脑梗死最常见（7例，70.0%）。2次及以上再栓患者中，PV（9例，90.0%）明显多于ET（7例，25.0%）。再栓组初诊WBC>12.5×10⁹/L（52.6%对31.8%，P=0.036）、红细胞比容（Hct）>45%（50.0%对30.0%，P=0.046）、既往血栓史（86.8%对13.6%，P<0.001）、脾肿大（84.2%对33.3%，P<0.001）、治疗未缓解（52.6%对15.2%，P<0.001）、血栓事件分层高危患者占比（94.7%对53.0%，P<0.001）高于单次血栓组；Logistic回归分析显示，既往血栓史（OR=13.697，P=0.025）、脾肿大（OR=13.301，P=0.034）和血栓事件分层高危（OR=44.618，P=0.025）为ET/PV再栓的独立危险因素。

结论

ET和PV患者有较高的再栓发生率，ET患者再栓发生率高于PV患者，急性冠脉综合征多见；PV多次再栓发生率多于ET，脑梗死较多见。既往血栓史、脾肿大和血栓事件分层高危是再栓的独立危险预测因素。

Implications of Janus Kinase 2 Mutation in Embolic Stroke of Unknown Source

The role of genetic mutations in cerebral ischemia is not completely understood. Among these genetic variations, Philadelphia-negative gain-of-function mutation in the janus kinase 2 (JAK2) protein leads to overexpression of the genes involved in cell growth and proliferation, and has been linked to development of hematological malignancies, specifically, myeloproliferative neoplasms (MPNs; essential thrombocythemia [ET], polycythemia vera [PV], and primary myelofibrosis). Overt ET and PV are known to induce a prothrombotic state that leads to development of vascular complications, including cerebral arterial or venous thrombosis. Thromboembolism can precede overt presentation of an MPN by 2-3 years. As such, for the selected cases of embolic stroke or cerebrovascular sinus thrombosis with otherwise undetermined source and persistent thrombocytosis or polycythemia, in the absence of a confirmed MPN diagnosis, screening for JAK2 mutation may be reasonable, as early diagnosis and appropriate treatment can influence outcome by preventing recurrent thrombotic events. In this article, we review the literature on the genetics, pathogenesis, clinical manifestations, and treatment of JAK2-associated thrombosis, and present 2 cases of JAK2-associated cerebral arterial infarction and cerebral and systemic venous thromboembolism with otherwise negative etiology workup for stroke.

The secondary prevention of venous thromboembolism: Towards an individual therapeutic strategy

After the anticoagulant withdrawal, a substantial proportion of patients with venous thromboembolism will develop recurrent events. Whether to consider an extended treatment depends on the risk of recurrence and bleeding risk. The assessment of the individual risk profile remains a difficult task. Several basal and post-basal factors modulate the risk of recurrence and may help clinicians to select patients who can benefit from the extended therapy. During the year 2017, new evidence regarding the post-basal factors was provided by the Morgagni and Scope studies. Another interesting novelty was the VTE-BLEED score, the first bleeding risk score that obtained the external validation in venous thromboembolism setting. In secondary prevention, the use of direct oral anticoagulants is growing instead of vitamin K antagonist. Even at lower doses, direct oral anticoagulants showed to be effective and safe, to reduce all-cause mortality and seemed to be superior to placebo for the composite outcome of fatal bleeding and fatal recurrence. After the recently published Einstein-Choice trial, the role of aspirin has become truly marginal as rivaroxaban 10 mg showed a bleeding risk similar to aspirin 100 mg but a greater effectiveness reducing the relative risk of recurrence by about 70%. Another option for secondary prevention could be sulodexide, with a lower protective effect than direct oral anticoagulants but an interesting safety profile. In conclusion, in our opinion, an individual strategy taking into account the risk of recurrence, bleeding risk, therapeutic options and patient preferences is the most appropriate approach to secondary prevention of venous thromboembolism.

Somatic Mutations in Philadelphia Chromosome-Negative Myeloproliferative Neoplasms

Myeloproliferative neoplasms (MPN) include polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF). MPN are characterized by clonal proliferation of myeloid progenitors leading to erythrocytosis, thrombocytosis, or leukocytosis, and risk of hemorrhagic and thrombotic events, as well as myelofibrosis and blast transformation. The discovery of somatic mutations in MPN, namely JAK2 V617F, JAK2 exon 12, MPL, and CALR mutations, has permitted a more specific approach to diagnosis and treatment. The prevalence of JAK2 V617F mutations is higher than 95% in PV, 50%-75% in ET and 40%-75% in PMF. JAK2 exon 12 mutations are specific of PV. A 20%-30% of patients with ET and PMF present a CALR mutation. The screening of mutations strengthens the diagnosis of MPN since 97% of MPN have at least 1 somatic mutation. Interestingly, different mutations grant different phenotype and prognosis. Of particular importance, CALR mutations grant a favorable prognosis in ET and PMF, while ASXL1 mutations confer a poorer outcome. In fact, the use of CALR/ASXL1 status for the prognostication of patients has increased clinical value and is now suggested for guidance of therapy in PMF. The increasing importance of mutations in the management of MPN warrants a more frequent revision of current diagnostic criteria and prognostic models and a better understanding of the mechanisms leading to MPN subset differentiation.

Assessing the thrombotic risk of patients with essential thrombocythemia in the genomic era

The molecular characterization of myeloproliferative neoplasms, including essential thrombocythemia (ET), has enabled deeper understanding of their pathogenesis. A driver lesion, namely, Janus kinase (JAK)2V617F, calreticulin (CALR) or myeloproliferative leukemia (MPL) gene mutation can be identified in the vast majority of patients. Each of these mutations is associated with distinct clinical features and may modulate the patients' clinical course, risk of complications, including vascular events, and survival. JAK2V617F appears to be a risk-modifying mutation and has been shown to increase the likelihood of thrombotic events in patients with ET across studies. As such, it has been included in prognostic models and its presence may influence treatment decisions. The association of CALR and MPL mutations with the incidence of vascular events has been less clear. Even more limited information is available on the contribution of additional non-driver lesions to the thrombotic risk. In this review we discuss the available evidence on the role of recurrent mutations in the risk of thrombotic complications in patients with ET and how these mutations weigh into modern prognostic scores.

[Ischemic heart failure making the diagnosis of a Vaquez disease: a rare event]

We present the case of a 46-year-old patient without any past medical history, admitted to our ICU for cardiogenic shock complicating acute coronary syndrome. The blood tests found polycethemia, a polycethemia vera was suspected and confirmed by genetic analysis. Ischemic heart failure as an initial symptom of polycethemia vera and its treatment by arterial bleeding is a rare event that we describe in this article.

Association between thromboembolic events and the JAK2 V617F mutation in myeloproliferative neoplasms

Thrombotic complications are a major cause of death in patients with Philadelphia chromosome-negative myeloproliferative neoplasms (MPNs), which are closely associated with the JAK2 V617F activating mutation. However, whether the presence of the JAK2 V617F mutation affects thrombotic risk is currently unknown, although some reports have suggested a variable association with thrombosis. Therefore, we investigated the association between JAK2 V617F and various complications, including thrombosis, in Japanese patients with MPNs. We assessed the JAK2 V617F status in 140 patients who were diagnosed or doubted as having some type of MPN by utilizing a JAK2 V617F-specific guanine-quenching probe. JAK2 V617F was detected in 31 of 51 patients (60.8%) with essential thrombocythemia, all 16 patients (100%) with polycythemia vera, 4 of 11 patients (36.4%) with primary myelofibrosis, 2 of 18 patients (11.1%) with other types of MPNs, and none of the 44 patients with doubted MPN. In the 78 patients with classical MPN, JAK2 V617F correlated with a leukocyte count ≥10,000/μl (p=0.046). Complications of thrombosis, hemorrhage, and leukemic transformation occurred in 21 (41.2%), 4 (25.0%), and 3 (27.3%) patients with classical MPN, respectively, and thrombotic events (TE) occurred more frequently in patients with JAK2 V617F than without (p=0.047). Based on these findings, initial screening for the JAK2 mutation and careful monitoring for thrombotic events should be performed in patients with MPN.

Assessing the risk and prognosis of thrombotic complications in cancer patients

CONTEXT

Cancer is characterized by the development of a prothrombotic state. Approximately 15% to 20% and 1.5% to 3.1% of cancer patients develop venous and arterial thrombosis, respectively, whereas 18% to 20% of idiopathic venous events are caused by an occult neoplasia. The highest risk is observed in hematologic, gastrointestinal, and lung malignancies, as well as in patients with active disease, especially in the first 3 months after cancer diagnosis. Hospitalization, surgical interventions, and implanted venous devices increase the thrombotic risk. Patients with metastatic disease, febrile neutropenia, infections, and severe comorbidities experience more frequently a thrombotic event. A contemporary prechemotherapy predictive model incorporates both clinical and biologic parameters, such as the primary cancer site, platelet count, white blood cell count, hemoglobin, use of erythropoietic agents, and body mass index. Several studies aim to clarify the prognostic value of tissue factor, P-selectin, thrombin generation, microparticles, and D-dimers.

OBJECTIVES

To summarize current views on epidemiology, risk factors, and predictive variables, discussing the future perspectives and existing limitations in clinical practice.

DATA SOURCES

Review of published literature, including review papers, epidemiologic studies, and clinical trials, in online medical databases.

CONCLUSIONS

The thrombogenic properties of tumor cells affect the prognosis and quality of life for the cancer population. Despite the improved awareness and prompt use of thromboprophylaxis, recent studies reported increased rates of thrombotic events, whereas the annual risks for thrombosis recurrence and bleeding are 21% and 12%, respectively. The clinical use of risk factors and prognostic parameters could allow for patient risk stratification and individualization of anticoagulant treatment.

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.

Pharmacological management of essential thrombocythemia

INTRODUCTION

Two factors have deeply influenced the area of essential thrombocythemia (ET). A gain-of-function mutation in the pseudokinase region of the JAK2 gene, which partly explains the pathophysiology of myeloproliferative neoplasms (MPNs), was discovered in 2005 and is present in 50 - 60% of ET patients. Furthermore, the 2008 WHO MPN classification outlined criteria for the separation of ET and early or prefibrotic primary myelofibrosis (PMF). However, these and other new findings have not yet changed the pharmacotherapy of ET, which is based on risk stratification for thrombohemorrhagic risk and aims to reduce thrombosis and bleeding.

AREAS COVERED

Studies on the basis for and the validation of the WHO classification as well as studies on possible new risk factors are covered. The most important drugs for ET treatment and consensus recommendations for management of ET are also presented.

EXPERT OPINION

The new WHO classification should be used for both ET studies and clinical practice, since true ET has a different prognosis than early PMF. The management of patients should be based on risk stratification. Age > 60 years or previous throbosis (high risk) and platelet counts > 1500 × 10(9)/l warrant cytoreductive treatment, and high risk patients and selected low risk patients should be given anti-aggregation therapy.

Correlations between Janus kinase 2 V617F allele burdens and clinicohematologic parameters in myeloproliferative neoplasms

BACKGROUND

This study evaluated potential correlations between the allele burden of the Janus kinase 2 (JAK2) V617F mutation and clinicohematologic characteristics in patients with myeloproliferative neoplasms (MPN).

METHODS

Clinical and hematologic features were reviewed for 103 MPN patients, including patients with polycythemia vera (PV, 22 patients), essential thrombocythemia (ET, 64 patients), and primary myelofibrosis (PMF, 17 patients). JAK2 V617F allele status and allele burdens were measured by allele-specific PCR and pyrosequencing, respectively.

RESULTS

The JAK2 V617F mutation was detected in 95.5%, 68.8%, and 52.9% of PV, ET, and PMF patients, respectively. JAK2 V617F-positive ET patients were significantly older and exhibited higher neutrophil fractions, a higher frequency of thrombotic events, and a higher myelofibrosis rate than JAK2 V617F-negative patients (P <0.05). PV patients carried the highest mean T allele burden (66.0%±24.9%) compared with ET (40.5%±25.2%) and PMF patients (31.5%±37.0%) (P =0.00). No significant correlations were detected between V617F allele burden and patient age, white blood cell count, Hb, Hct, or the platelet count for PV, ET, or PMF patients. ET patients with organomegaly had a higher JAK2 V617F allele burden (53.4%±23.7%) than patients without organomegaly (35.6%±24.3%) (P =0.03).

CONCLUSIONS

The JAK2 V617F mutational status and its allele burden correlate with the clinicohematologic phenotypes of ET patients, including older age, higher neutrophil count, and greater rates of organomegaly, thrombotic events, and myelofibrosis. For PV and PMF patients, larger-scale studies involving more MPN patients are needed.

A novel, highly sensitive and rapid allele-specific loop-mediated amplification assay for the detection of the JAK2V617F mutation in chronic myeloproliferative neoplasms

BACKGROUND

The identification of the JAK2V617F mutation is mandatory in the diagnostic work-up of Philadelphia chromosome-negative myeloproliferative neoplasms. Several molecular techniques to detect this mutation are currently available, but each of them has some limits.

DESIGN AND METHODS

We set up a novel molecular method for the identification of the JAK2V617F mutation based on an allele-specific loop-mediated amplification, not polymerase chain reaction analysis. This innovative technique amplifies DNA targets under isothermal conditions with high specificity, efficiency and rapidity. The method does not require either a thermal cycler or gel separation and the DNA amplification reaction is visible to the naked eye and can be monitored by turbidimetry. This method was validated on DNA from cell lines as well as from patients with myeloproliferative neoplasms. The results were compared with those obtained by conventional polymerase chain reaction methods.

RESULTS

This assay detects, within 1 hour, the JAK2V617F mutation down to an allele burden of 0.1-0.01%. All samples positive by polymerase chain reaction (n=146) proved positive when tested by allele-specific loop-mediated amplification and none of the 80 negative controls gave false positive results. In addition, six patients with essential thrombocythemia previously diagnosed as being JAK2V617F negative by polymerase chain reaction analysis were found to be positive (at a low level) by allele-specific loop-mediated amplification. Furthermore, this assay discriminated the amount of JAK2V617F tumor allele within intervals of positivity, above 50%, between 50% and 10% and below 10%.

CONCLUSIONS

Allele-specific loop-mediated amplification is a simple, robust and easily applicable method for the molecular diagnosis and monitoring of JAK2V617F mutation in patients with chronic myeloproliferative neoplasms.

Recurrent venous thromboembolism: what is the risk and how to prevent it

Venous thromboembolism (VTE) that includes deep vein thrombosis and/or pulmonary embolism is a frequent, severe, and potentially lethal disease. After a first episode, VTE has a strong tendency to recur. While VTE is an acute disease, it may have variable outcomes in early and late phases after initial presentation. Furthermore, the incidence of late, clinically important consequences (postthrombotic syndrome and/or chronic thromboembolic pulmonary hypertension) increases in case of recurrent events. The aims of the present review are (i) to analyze the incidence and risk factors for recurrence of VTE (either those related to the type of first thrombotic event or to the patients), the risks associated with occurrence of recurrent events, and the problems linked to the diagnosis, not always easy, of recurrent events; (ii) to discuss whether or not it is possible to predict the individual risk of recurrence after a first event, by stratifying patients at high or low risk of recurrence, and how this can influence their treatment; (iii) to comment what the current guidelines and guidance suggest/recommend about anticoagulant treatment after a first VTE event and, finally, to propose practical indications on how to manage individual patients affected by VTE.

Venous thromboembolism in patients with essential thrombocythemia and polycythemia vera

Polycythemia vera (PV) and essential thrombocythemia (ET) are myeloproliferative neoplasms (MPNs), which generally follow a benign and indolent clinical course. However, venous thromboses are common and constitute the main cause of morbidity and mortality. The discovery of the JAK2V617F mutation and other biomarkers has advanced our understanding of these diseases. There is a strong association between the presence of the JAK2V617F mutation and the development of thrombosis in ET. If venous thrombosis presents with unusual manifestations, the diagnosis of a MPN, such as PV or ET, should be part of the differentials. Treatment of venous thrombosis in MPN follows the same principle as in other patients with venous thrombosis, but careful attention to primary and secondary prophylaxis in addition to heparin-induced thrombocytopenia should be given. Cytoreductive therapy is indicated in high-risk subgroups of PV and ET patients, and alternative therapeutic agents have different effects on risk of venous thrombosis. New therapeutic approaches are emerging, and JAK2 inhibitors, histone deacetylase inhibitors and next-generation anticoagulants are in various stages of clinical development for the treatment of MPN, but their exact role in thrombosis prevention and treatment remains unclear.

Neurological disorders in essential thrombocythemia

Patients with essential thrombocythemia often complain of various subjective neurological symptoms. This prospective study aims to assess their incidence and response to therapy. Among 37 consecutive patients with essential thrombocythemia, 11 presented with neurological symptoms. Among them 4 had thrombotic events, 7 complained of transient or fluctuating subjective symptoms, and one had both. Brain magnetic resonance imagery failed to detect any substratum in patients with subjective symptoms. JAK2V617F mutation was found in 9 of 11 patients with neurological symptoms versus 14 of 26 patients without symptoms. Ten patients received low-dose aspirin for these symptoms: complete resolution was observed in 3, improvement with persisting episodes in 2, and resistance to aspirin in 2 patients, in whom addition of cytoreductive therapy became necessary to resolve those disabling symptoms. In this prospective cohort, 30% of patients with essential thrombocythemia presented neurological symptoms. Aspirin was fully efficient in only 30% of cases. JAK2V617F mutation could be a risk factor for such symptoms.

Mouse models of myeloproliferative neoplasms: JAK of all grades

In 2005, several groups identified a single gain-of-function point mutation in the JAK2 kinase that was present in the majority of patients with myeloproliferative neoplasms (MPNs). Since this discovery, much effort has been dedicated to understanding the molecular consequences of the JAK2V617F mutation in the haematopoietic system. Three waves of mouse models have been produced recently (bone marrow transplantation, transgenic and targeted knock-in), which have facilitated the understanding of the molecular pathogenesis of JAK2V617F-positive MPNs, providing potential platforms for designing and validating novel therapies in humans. This Commentary briefly summarises the first two types of mouse models and then focuses on the more recently generated knock-in models.

JAK2 mutation and thrombosis in the myeloproliferative neoplasms

The clinical course of the classic myeloproliferative neoplasms (MPNs) is burdened by an increased rate of cardiovascular events, which are the major cause of mortality. Age and history of thrombosis are the criteria used to stratify patients to the most appropriate therapeutic options. However, the mechanisms ultimately responsible for the increased thrombotic tendency have not yet been elucidated; abnormalities of blood cell count, neutrophil and platelet activation, and a state of hypercoagulability can all occur. Recurrent mutations in JAK2 or MPL have been described in MPNs and serve as disease markers. There is also evidence that a JAK2V617F mutant state represents an independent factor associated with thrombosis, and abnormalities of cell function attributable to JAK2V617F have been characterized. It is hoped that elucidation of the role mutant JAK2 plays in MPNs will improve our understanding of the pathophysiology of thrombosis and eventually result in improved patient treatment using molecularly targeted drugs.