Polycythemia vera and essential thrombocythemia: 2017 update on diagnosis, risk-stratification, and management

DISEASE OVERVIEW

Polycythemia Vera (PV) and essential thrombocythemia (ET) are myeloproliferative neoplasms respectively characterized by erythrocytosis and thrombocytosis; other disease features include leukocytosis, splenomegaly, thrombosis, bleeding, microcirculatory symptoms, pruritus, and risk of leukemic or fibrotic transformation.

DIAGNOSIS

PV is defined by a JAK2 mutation, whose absence, combined with normal or increased serum erythropoietin level, makes the diagnosis unlikely. JAK2, CALR, and MPL mutations are the mutually exclusive "driver" mutations in ET with respective incidences of 55%, 25%, and 3%; approximately 17% are triple-negative. However, the same molecular markers might also be present in prefibrotic myelofibrosis, whose morphological distinction from ET is prognostically relevant.

SURVIVAL AND LEUKEMIC/FIBROTIC TRANSFORMATION

Median survivals are approximately 14 years for PV and 20 years for ET; the corresponding values for younger patients (age <60 years) are 24 and 33 years. Life-expectancy in ET is inferior to the control population. Driver mutational status has not been shown to affect survival in ET whereas the presence of JAK2/MPL mutations has been associated with higher risk of arterial thrombosis and that of MPL with higher risk of fibrotic progression. Risk factors for overall survival in both ET and PV include advanced age, leukocytosis and thrombosis. Leukemic transformation rates at 20 years are estimated at <10% for PV and 5% for ET; fibrotic transformation rates are slightly higher. Most recently, ASXL1, SRSF2, and IDH2 mutations have been associated with inferior overall, leukemia-free or fibrosis-free survival in PV; similarly adverse mutations in ET included SH2B3, SF3B1, U2AF1, TP53, IDH2, and EZH2.

THROMBOSIS RISK STRATIFICATION

Current risk stratification in PV and ET is designed to estimate the likelihood of recurrent thrombosis. Accordingly, PV includes two risk categories: high-risk (age >60 years or thrombosis history) and low-risk (absence of both risk factors). In ET, risk stratification includes four categories: very low risk (age ≤60 years, no thrombosis history, JAK2/MPL un-mutated), low risk (age ≤60 years, no thrombosis history, JAK2/MPL mutated), intermediate risk (age >60 years, no thrombosis history, JAK2/MPL un-mutated), and high risk (thrombosis history or age >60 years with JAK2/MPL mutation). In addition, presence of extreme thrombocytosis (platelets >1000 × 10(9)/L) might be associated with acquired von Willebrand syndrome (AvWS) and, therefore, risk of bleeding.

RISK-ADAPTED THERAPY

The main goal of therapy in PV and ET is to prevent thrombohemorrhagic complications. All patients with PV require phlebotomy to keep hematocrit below 45% and once-daily aspirin (81 mg). In addition, high-risk patients with PV require cytoreductive therapy. Very low risk ET patients might not require any form of therapy while low-risk patients require at least once-daily aspirin therapy. Cytoreductive therapy is also recommended for high-risk ET patients but it is not mandatory for intermediate-risk patients. First-line drug of choice for cytoreductive therapy, in both ET and PV, is hydroxyurea and second-line drugs of choice are interferon-α and busulfan. We currently do not recommend treatment with ruxolutinib or other JAK2 inhibitors in PV or ET, unless in the presence of severe and protracted pruritus or marked splenomegaly that is not responding to the aforementioned drugs. Screening for AvWS is recommended before administrating aspirin, in the presence of extreme thrombocytosis. Am. J. Hematol. 92:95-108, 2017. © 2016 Wiley Periodicals, Inc.

Laboratory Investigation of Myeloproliferative Neoplasms (MPNs): Recommendations of the Canadian Mpn Group

OBJECTIVES

To standardize diagnostic investigations for myeloproliferative neoplasms (MPNs) to increase homogeneity in patient care and to streamline diagnostic approaches in the most efficient and cost-effective manner.

METHODS

The development of Canadian expert consensus recommendations for the diagnosis of MPNs began with a review of the following: clinical evidence, daily practice, existing treatment guidelines, and availability of diagnostic tools. Each group member was assigned a specific topic, which they discussed with the entire group during several consensus meetings.

RESULTS

This document provides the Canadian MPN group's recommendations, proposed diagnostic algorithms, and background evidence upon which decisions were made.

CONCLUSIONS

Standardization of diagnostic investigations will increase homogeneity in patient care and provide a foundation for future clinical research in this rapidly evolving therapeutic area. Streamlining diagnostic approaches in the most efficient and cost-effective manner will also result in significant cost saving for the health care system.

Polycythemia vera and essential thrombocythemia: 2015 update on diagnosis, risk-stratification and management

DISEASE OVERVIEW

Polycythemia vera (PV) and essential thrombocythemia (ET) are myeloproliferative neoplasms, respectively characterized by erythrocytosis and thrombocytosis. Other disease features include leukocytosis, splenomegaly, thrombosis, bleeding, microcirculatory symptoms, pruritus, and risk of leukemic or fibrotic transformation.

DIAGNOSIS

PV is defined by a JAK2 mutation, whose absence, combined with normal or increased serum erythropoietin level, makes the diagnosis unlikely. Differential diagnosis in ET includes reactive thrombocytosis, chronic myeloid leukemia, and prefibrotic myelofibrosis. Janus kinase 2 (JAK2), calreticulin (CALR), or myeloproliferative leukemia virus oncogene (MPL) mutations occur in approximately 55%, 25%, and 3% of ET patients, respectively. The same molecular markers are also present in prefibrotic myelofibrosis, which needs to be morphologically distinguished from ET. Survival and leukemic/fibrotic transformation: Median survivals are ∼14 years for PV and 20 years for ET; the corresponding values for younger patients are 24 and 33 years. Life-expectancy in ET is inferior to the control population. JAK2/CALR mutational status does not affect survival in ET. Risk factors for survival in ET and PV include advanced age, leukocytosis, and thrombosis. Leukemic transformation rates at 20 years are estimated at <10% for PV and 5% for ET; fibrotic transformation rates are slightly higher. Thrombosis risk stratification: Current risk stratification in PV and ET is designed to estimate the likelihood of recurrent thrombosis: 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 consider JAK2V617F and cardiovascular risk factors as additional risk factors. Presence of extreme thrombocytosis might be associated with acquired von Willebrand syndrome (AvWS) and, therefore, risk of bleeding.

RISK-ADAPTED THERAPY

The main goal of therapy in PV and ET is to prevent thrombohemorrhagic complications. In low risk patients, this is accomplished by the use of low-dose aspirin and phlebotomy (hematocrit target <45%) in PV. In high risk (for thrombosis) patients, treatment with hydroxyurea is additionally recommended. Treatment with busulfan or interferon-α is usually effective in hydroxyurea failures and the additional value of JAK inhibitor therapy in such cases is limited. Screening for AvWS is recommended before administrating aspirin, in the presence of extreme thrombocytosis.

WHO classification of myeloproliferative neoplasms (MPN): A critical update

Although the revised World Health Organization (WHO) criteria for the diagnosis and classification of myeloproliferative neoplasms (MPN) were defined by a panel of expert hematopathologists and clinicians, controversy has been repeatedly expressed questioning the clinical usefulness and reproducibility of these diagnostic guidelines. In particular, the distinction between essential thrombocythemia (ET), early/prefibrotic primary myelofibrosis (PMF) and initial stages of polycythemia vera (PV) is still a matter of debate. In this context, it has been argued that clinical correlations with histological features were not firmly substantiated. On the other hand, recently published data from independently performed studies have repeatedly validated the reproducibility of the WHO criteria and provided persuasive evidence that discrimination of early/prefibrotic PMF has a significant impact on the risk of myelofibrotic and leukemic transformation. However, as has been explicitly required, the WHO concept is based on the recognition of characteristic bone marrow patterns and a consensus of clinical and molecular data.

Cooperation between pathologists and clinicians allows a better diagnosis of Philadelphia chromosome-negative myeloproliferative neoplasms

As no specific genetic lesions have yet been identified, the diagnosis of Philadelphia chromosome-negative myeloproliferative neoplasms is based on a simultaneous evaluation of the clinical, morphological and molecular features defined by the updated WHO classification, which allow most cases of full-blown disease to be classified. Nevertheless, about 10-15% of the patients have unclassifiable myeloproliferative neoplasms, most of whom are in the prodromal (early) phase of disease and identified by the presence of the JAK2 mutation, but lack the complete phenotype required by the WHO classification. The detection of these prodromal phases is extremely important in order to prevent dramatic thrombo-hemorrhagic complications and improve prognosis.

[Differential diagnosis of myeloproliferative neoplasms. Quantitative NF-E2 immunohistochemistry for differentiating between essential thrombocythemia and primary myelofibrosis]

BACKGROUND

Besides essential thrombocythemia (ET), polycythemia vera (PV) and primary myelofibrosis (PMF) the myeloproliferative neoplasms (MPN) defined by the World Health Organization (WHO) comprise the entity of unclassifiable MPNs (MPN, U). The exact differential diagnosis of the specific MPN entities can be challenging particularly at early stages of the diseases. So far, pathologists have had to rely only on histomorphological evaluation of bone marrow biopsies in combination with laboratory data because helpful ancillary tests are not yet available. Even molecular tests, such as JAK2 mutation analysis are not helpful particularly in the differential diagnosis of ET and PMF because both entities are associated with the V617F mutation in 50 % of the cases. Recently overexpression of the transcription factor NF-E2 in MPN was described.

MATERIALS AND METHODS

A collective of samples consisting of 163 bone marrow biopsies including 139 MPN cases was stained immunohistochemically for NF-E2 and analyzed regarding the subcellular localization of NF-E2 in erythroid progenitor cells. The results were compared between the MPN entities as well as the controls and statistical analyses were conducted.

RESULTS AND DISCUSSION

This study showed that NF-E2 immunohistochemistry and analysis of the proportion of nuclear positive erythroblasts of all erythroid precursor cells can help to distinguish between ET and PMF even in early stages of the diseases. An MPN, U case showing a proportion of more than 20 % nuclear positive erythroblasts can be classified as a PMF with 92 % accuracy.

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.

Subcellular mislocalization of the transcription factor NF-E2 in erythroid cells discriminates prefibrotic primary myelofibrosis from essential thrombocythemia

The World Health Organization (WHO) classification of myeloproliferative neoplasms (MPNs) comprises several entities including essential thrombocythemia (ET); primary myelofibrosis (PMF); and MPN, unclassifiable (MPN,U). Differential diagnosis between ET and early, prefibrotic PMF can be challenging but is critical because clinical course and outcome vary considerably between these entities. We have previously shown that the transcription factor nuclear factor erythroid 2 (NF-E2) is aberrantly expressed in MPN patients. Here we demonstrate that NF-E2 is mislocalized in PMF cells and that aberrant NF-E2 localization discriminates statistically highly significantly between ET and PMF. A threshold of 20% nuclear NF-E2 staining was cross-validated by ".682+ bootstrapping." Moreover, this cutoff correctly classifies diagnostic bone marrow biopsies of MPN,U patients specified upon follow-up as ET or PMF with 92% accuracy. Because interobserver concordance between independent pathologists was high (Spearman's rank correlation coefficient, 0.727), we propose that quantitative NF-E2 immunohistochemistry represents a diagnostic tool that can reliably support a differential diagnosis between ET and PMF.

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.

Polycythemia vera and essential thrombocythemia: 2012 update on diagnosis, risk stratification, and management

DISEASE OVERVIEW

Polycythemia vera (PV) and essential thrombocythemia (ET) are myeloproliferative neoplasms 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 confirms the diagnosis and its absence, combined with normal or increased serum erythropoietin level, excludes the diagnosis. Differential diagnosis of ET had to include chronic myelogenous leukemia and prefibrotic myelofibrosis. A JAK2 mutation is found in approximately 60% of patients with ET.

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. 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 and this is effectively and safely accomplished by the use of low-dose aspirin (PV and ET), phlebotomy (PV) and hydroxyurea (high risk PV and ET). 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.

How to manage children and young adults with myeloproliferative neoplasms

On the basis of my personal clinical and research experience and validated by the current literature, my approach to the management of pediatric (age <18 years) and young patients (age <40 years) with classic myeloproliferative neoplasms is presented by focusing on diagnosis, patient communication, risk stratification and therapy. The WHO-2008 diagnostic criteria are recommended, even though in children suspected with essential thrombocythemia (ET), a specific set of diagnostic features may be required. Patient communication includes information on natural history, genetic abnormalities and counseling in all women of child-bearing age. The main challenge in children and young adults with ET and polycythemia vera (PV) is to avoid recurrence of major thrombosis by selecting those patients who ultimately can benefit from cytotoxic and antithrombotic therapy without increasing the incidence of drug-induced side effects. In asymptomatic low-risk patients no therapy is prescribed while in high-risk low-dose aspirin, hydroxyurea and interferon-alpha are my first line drugs. My first decision when considering treatment of a young patient with primary myelofibrosis (PMF) or post-PV or post ET-myelofibrosis, is whether he/she qualifies for bone marrow allotransplantation. In the remaining young PMF patients palliative therapy or experimental drugs are considered.

Incidence and risk factors for bleeding in 1104 patients with essential thrombocythemia or prefibrotic myelofibrosis diagnosed according to the 2008 WHO criteria

In an international study of 1104 patients with essential thrombocythemia (ET), a histological review according to the 2008 World Health Organization (WHO) criteria confirmed ET in 891 patients (WHO-ET, 81%), and revised the diagnosis to prefibrotic primary myelofibrosis (PMF) in 180 patients (PMF, 16%). Major bleeding during follow-up occurred in 55 (6%) WHO-ET and 21 (12%) PMF patients (P = 0.009), at a rate of 0.79 and 1.39% patients per year, respectively, (P = 0.039). In a multivariable analysis, predictors of bleeding included diagnosis of PMF (P = 0.05; hazard ratio (HR) 1.74), leukocytosis (P = 0.04; HR 1.74), previous hemorrhage (P = 0.025; HR 2.35) and aspirin therapy (P=0.001; HR 3.16). The analysis restricted to patients with WHO-ET confirmed previous hemorrhage (P = 0.043; HR 1.92) and aspirin (P=0.027; HR 2.24) as independent risk factors. The current study reveals that major bleeding associated with thrombocytosis might be relatively specific to PMF, as opposed to WHO-defined ET. Furthermore, it shows that low-dose aspirin exacerbates these hemorrhagic events of PMF. In contrast, thrombocytosis per se was not a risk factor for bleeding; however, low-dose aspirin had a synergistic hemorrhagic effect unmasking the bleeding tendency of patients with extreme thrombocytosis. These observations carry significant therapeutic implications in these two WHO entities.

Survival and disease progression in essential thrombocythemia are significantly influenced by accurate morphologic diagnosis: an international study

PURPOSE

The WHO diagnostic criteria underscore the role of bone marrow (BM) morphology in distinguishing essential thrombocythemia (ET) from early/prefibrotic primary myelofibrosis (PMF). This study examined the clinical relevance of such a distinction.

METHODS

Representatives from seven international centers of excellence for myeloproliferative neoplasms convened to create a clinicopathologic database of patients previously diagnosed as having ET (N = 1,104). Study eligibility criteria included availability of treatment-naive BM specimens obtained within 1 year of diagnosis. All bone marrows subsequently underwent a central re-review.

RESULTS

Diagnosis was confirmed as ET in 891 patients (81%) and was revised to early/prefibrotic PMF in 180 (16%); 33 patients were not evaluable. In early/prefibrotic PMF compared with ET, the 10-year survival rates (76% and 89%, respectively) and 15-year survival rates (59% and 80%, respectively), leukemic transformation rates at 10 years (5.8% and 0.7%, respectively) and 15 years (11.7% and 2.1%, respectively), and rates of progression to overt myelofibrosis at 10 years (12.3% and 0.8%, respectively) and 15 years (16.9% and 9.3%) were significantly worse. The respective death, leukemia, and overt myelofibrosis incidence rates per 100 patient-years for early/prefibrotic PMF compared with ET were 2.7% and 1.3% (relative risk [RR], 2.1; P < .001), 0.6% and 0.1% (RR, 5.2; P = .001), and 1% and 0.5% (RR, 2.0; P = .04). Multivariable analysis confirmed these findings and also identified age older than 60 years (hazard ratio [HR], 6.7), leukocyte count greater than 11 × 10(9)/L (HR, 2.01), anemia (HR, 2.95), and thrombosis history (HR, 2.81) as additional risk factors for survival. Thrombosis and JAK2V617F incidence rates were similar between the two groups. Survival in ET was similar to the sex- and age-standardized European population.

CONCLUSION

This study validates the clinical relevance of strict adherence to WHO criteria in the diagnosis of ET and provides important information on survival, disease complication rates, and prognostic factors in strictly WHO-defined ET and early/prefibrotic PMF.

Uses and abuses of JAK2 and MPL mutation tests in myeloproliferative neoplasms a paper from the 2010 William Beaumont hospital symposium on molecular pathology

JAK2V617F is sufficiently prevalent in BCR-ABL1-negative myeloproliferative neoplasms (MPNs) to be useful as a clonal marker. JAK2V617F mutation screening is indicated for the evaluation of erythrocytosis, thrombocytosis, splanchnic vein thrombosis, and otherwise unexplained BCR-ABL1-negative granulocytosis. However, the mutation does not provide additional value in the presence of unequivocal morphologic diagnosis, and its presence does not necessarily distinguish one MPN from another or provide useful prognostic information. In general, quantitative cell-based JAK2V617F mutation assays are preferred because the additional information obtained on mutant allele burden enhances diagnostic certainty and facilitates monitoring of response to treatment. JAK2 exon 12 mutation screening is indicated only in the presence of JAK2V617F-negative erythrocytosis that is associated with a subnormal serum erythropoietin level. MPL mutations are neither frequent nor specific enough to warrant their routine use for MPN diagnosis, but they may be useful in resolving specific diagnostic problems. The practice of en bloc screening for JAK2V617F, JAK2 exon 12, and MPL mutations is scientifically irrational and economically irresponsible.

Essential thrombocythemia versus early primary myelofibrosis: a multicenter study to validate the WHO classification

Controversy persists regarding the role of histopathology in the distinction between essential thrombocythemia (ET) and early-prefibrotic primary myelofi-brosis (PMF) presenting with thrombocythemia. To investigate the impact and reproducibility of bone marrow (BM) morphology according to the World Health Organization classification, 295 patients with the presumptive clinical diagnosis of either ET or early PMF were studied. Data of this cohort (Vienna group) were compared with 732 corresponding patients (Cologne group). Evaluating blindly (only age and gender known) BM specimens, the 2 groups of pathologists achieved an overall consensus of 78% regarding the total series and 88% concerning the discrimination between ET versus PMF. In 126 ET and 81 early PMF patients without pretreatment and complete documentation, a 90% concordance with the independently established clinical diagnosis was found. In 12 patients, overlapping of histopathology and some clinical findings between ET and polycythemia vera occurred. Contrasting ET, early PMF showed significant differences of presenting hematologic data and an unfavorable prognosis (estimated mean survival, 14 vs 21 years). Comparison of clinical and survival data of the Vienna cohort with the historical Cologne series revealed an overall congruence. This study highlights the impact of BM morphology for the differentiation between true vs false ET.

Mutations with epigenetic effects in myeloproliferative neoplasms and recent progress in treatment: Proceedings from the 5th International Post-ASH Symposium

Immediately following the 2010 annual American Society of Hematology (ASH) meeting, the 5th International Post-ASH Symposium on Chronic Myelogenous Leukemia and BCR-ABL1-Negative Myeloproliferative Neoplasms (MPNs) took place on 7–8 December 2010 in Orlando, Florida, USA. During this meeting, the most recent advances in laboratory research and clinical practice, including those that were presented at the 2010 ASH meeting, were discussed among recognized authorities in the field. The current paper summarizes the proceedings of this meeting in BCR-ABL1-negative MPN. We provide a detailed overview of new mutations with putative epigenetic effects (TET oncogene family member 2 (TET2), additional sex comb-like 1 (ASXL1), isocitrate dehydrogenase (IDH) and enhancer of zeste homolog 2 (EZH2)) and an update on treatment with Janus kinase (JAK) inhibitors, pomalidomide, everolimus, interferon-α, midostaurin and cladribine. In addition, the new ‘Dynamic International Prognostic Scoring System (DIPSS)-plus' prognostic model for primary myelofibrosis (PMF) and the clinical relevance of distinguishing essential thrombocythemia from prefibrotic PMF are discussed.

Annual Clinical Updates in Hematological Malignancies: a continuing medical education series: polycythemia vera and essential thrombocythemia: 2011 update on diagnosis, risk-stratification, and management

DISEASE OVERVIEW

Polycythemia vera (PV) and essential thrombocythemia (ET) are myeloproliferative neoplasms 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 leukemia or myelofibrosis.

DIAGNOSIS

Diagnosis is based on JAK2 mutation status (PV and ET), serum erythropoietin (Epo) level (PV), and bone marrow histopathology (ET). The presence of a JAK2 mutation and subnormal serum Epo level confirm a diagnosis of PV. Differential diagnosis in ET should include chronic myelogenous leukemia and prefibrotic myelofibrosis.

RISK STRATIFICATION

Current risk stratification in PV and ET is designed to estimate the likelihood of thrombotic complications: high-risk-age > 60 years or presence of thrombosis history; low-risk-absence of both of these two risk factors. Presence of extreme thrombocytosis (platelet count > 1,000 x 10⁹/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 age > 60 years, leukocytosis, history of thrombosis, and anemia.

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 < 5%/10% in PV. In contrast, the risk of thrombosis exceeds 20%. The main goal of therapy is therefore to prevent thrombohemorrhagic complications and this is effectively and safely accomplished by the use of low-dose aspirin (PV and ET), phlebotomy (PV), and hydroxyurea (high risk PV and ET). Treatment with busulfan or interferon-a is usually effective in hydroxyurea failures.