Are MPNs vascular diseases?

Targeting PAR1 activation in JAK2V617F-driven philadelphia-negative myeloproliferative neoplasms: Unraveling its role in thrombosis and disease progression

Philadelphia chromosome-negative myeloproliferative neoplasms (Ph-MPNs) are clonal disorders marked by high morbidity and mortality, driven by uncontrolled myeloid proliferation from hematopoietic stem/progenitor cells (HSCs) and associated with a significant risk of thrombosis. This study explored the relationship between JAK2V617F and protease-activated receptor 1 (PAR1) by examining PAR1 expression and activation across various hematopoietic stem/progenitor cell (HSPC) subgroups, assessing their contribution to the hypercoagulable state in Ph-MPNs. We investigated the effects of thrombin, a PAR1 antagonist (vorapaxar), and a JAK2 inhibitor (ruxolitinib) on Ph-MPN cells. Mononuclear cells (MNCs) were isolated from Ph-MPN patients (n = 18), cord blood (CB) samples (n = 5) and healthy volunteers (n = 11). Specific subpopulations were sorted and analyzed for PAR1 expression and JAK2V617F status using qRT-PCR. PAR1 expression changes, along with other PAR pathway-related genes, were assessed post-treatment. Our results revealed that most PAR1+ cells (∼95 %) co-expressed CD34+, with a smaller JAK2V617F+ PAR1+ population lacking CD34. PAR1 expression was significantly higher in Ph-MPN MNCs compared to CB (p = 0.0005), particularly in EMP, HSC/EPC, and EPC subsets. Thrombin treatment reduced surface PAR1 expression, while PAR1 antagonist treatment further decrease the expression level. Combined PAR1 antagonist and ruxolitinib treatment significantly downregulated PAR1 expression (p < 0.0001), and several PAR-pathway-related genes were notably downregulated after treatment. This study highlights that elevated PAR1 expression in primitive hematopoietic subpopulations is linked to disease progression and thrombosis in Ph-MPNs, suggesting PAR1 as a potential therapeutic target. Combining PAR1 antagonists with JAK2 inhibitors shows promise in reducing PAR1 expression and mitigating thrombotic events in Ph-MPN patients.

Clinical Characteristics, Prognostic Factors, and Thrombotic and Bleeding Outcomes in Philadelphia Chromosome-Negative Myeloproliferative Neoplasms: A Single-Center Cohort Study in Thailand

Background Patients with Philadelphia chromosome-negative myeloproliferative neoplasms (Ph-neg MPNs), including polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF), face elevated risks of thrombosis and major bleeding. Because of these potentially severe complications, antiplatelet and anticoagulant therapies are often employed. This study aimed to evaluate thrombotic and bleeding events, identify associated risk factors, assess prognostic risk models, and investigate the effects of antithrombotic therapy in a Thai cohort of patients with Ph-neg MPNs. Methods This single-center cohort study in Thailand enrolled patients with Ph-neg MPNs from 2013 to 2023. Clinical characteristics, prognostic risk models (International Prognostic Scoring System (IPSS), International Prognostic Score for Essential Thrombocythemia (IPSET)-thrombosis, and Dynamic International Prognostic Scoring System (DIPSS)), and arterial and venous thrombotic events and bleeding complications were analyzed using descriptive statistics, logistic regression, and survival analysis. Results Among 173 patients, PV was the most common subtype (n = 111, 64.2%), with a male predominance and a median age of 57 years. Thrombotic events occurred in 36.9% (n = 41) of PV, 21.4% (n = 3) of PMF, and 18.8% (n = 9) of ET cases, with arterial thrombosis, particularly ischemic stroke, being the most frequent. The JAK2 V617F mutation was prevalent in 72.5% (n = 79) of PV, 70.8% (n = 34) of ET, and 50% (n = 5) of PMF patients. Notably, no major bleeding events were observed despite intensive antithrombotic therapy. Multivariable analysis revealed that prior ischemic stroke (OR 22.51, P = 0.007) and dizziness/headache (OR 7.26, P = 0.022) were significant risk factors for thrombosis. Overall survival (OS) varied by disease subtype. PV patients had a five-year OS of 94.9% and a 10-year OS of 87.2%. ET patients demonstrated a five-year OS of 77.4%. PMF patients had the lowest survival, with a five-year OS of 67.7%. Conclusions This cohort study offers important insights into the clinical characteristics and complication profiles of Ph-neg MPNs in a Thai population. Compared with Western cohorts, patients in this study exhibited a higher incidence of thrombotic events, particularly ischemic stroke. These findings emphasize the need to consider regional variations in disease presentation and underscore the value of individualized risk stratification to optimize patient management in diverse clinical settings.

The molecular landscape of myeloproliferative neoplasms associated with splanchnic vein thrombosis: Current perspective

BCR::ABL1-negative myeloproliferative neoplasms (MPNs) are classically represented by polycythemia vera, essential thrombocythemia, and primary myelofibrosis. BCR::ABL1-negative MPNs are significantly associated with morbidity and mortality related to an increased risk of thrombo-hemorrhagic events. They show a consistent association with splanchnic vein thrombosis (SVT), either represented by the portal, mesenteric or splenic vein thrombosis, or Budd-Chiari Syndrome. SVT is also a frequent presenting manifestation of MPN. MPNs associated with SVT show a predilection for younger women, high association with JAK2V617F mutation, low JAK2V617F variant allele frequency (generally <10 %), and low rates of CALR, MPL, or JAK2 exon 12 mutations. Next-Generation Sequencing techniques have contributed to deepening our knowledge of the molecular landscape of such cases, with potential diagnostic and prognostic implications. In this narrative review, we analyze the current perspective on the molecular background of MPN associated with SVT, pointing as well future directions in this field.

Pathological and genomic features of myeloproliferative neoplasms associated with splanchnic vein thrombosis in a single-center cohort

Here, we reviewed clinical-morphological data and investigated mutational profiles by NGS in a single-center series of 58 consecutive MPN-SVT patients admitted to our hospital between January 1979 and November 2021. We identified 15.5% of PV, 13.8% of ET, 34.5% of PMF, 8.6% of SMF and 27.6% of MPN-U. Most cases (84.5%) carried JAK2V617F mutation, while seven patients were characterized by other molecular markers, namely MPL in four and CALR mutations in three cases. NGS was performed in 54 (93.1%) cases: the most frequent additional mutations were found in TET2 (27.8%) and DNMT3A (16.7%) genes, whereas 25 (46.3%) patients had no additional mutation. Cases with JAK2V617F homozygosity had a higher median number of additional mutations than those with low allele burden. More importantly, all cases of leukemic evolution were characterized by a higher median number of co-mutations, and a co-mutational pattern of high-risk lesions, such as truncating mutations of ASXL1, bi-allelic TP53 loss, and CSMD1 mutations. Nevertheless, no difference was found between cases with and without additional somatic mutations regarding fibrotic progression, SVT recurrence, other thrombo-hemorrhagic complications, or death. After a median follow-up of 7.1 years, ten deaths were recorded; fibrotic progression/leukemic evolution was ascertained in one (1.7%) and six (10.3%) patients, respectively, while 22 (37.9%) patients suffered from recurrent thrombosis. In conclusion, our data underline the importance of using NGS analysis in the management of MPN-related SVT as it can support the MPN diagnosis, particularly in "triple-negative" cases, and provide additional information with potential consequences on prognosis and therapeutic strategies.

Circulating Endothelial Cell Levels Correlate with Treatment Outcomes of Splanchnic Vein Thrombosis in Patients with Chronic Myeloproliferative Neoplasms

Circulating endothelial cells (CECs) are viable, apoptotic or necrotic cells, identified by CD 146 surface antigen expression, considered a biomarker of thrombotic risk, given their active role in inflammatory, procoagulant and immune processes of the vascular compartment. Growing evidence establishes that CECs are also involved in the pathogenesis of several hematological and solid malignancies. The primary aim of this study was to verify if CEC levels could predict both the course and treatment responses of splanchnic vein thrombosis (SVT), either in patients affected by myeloproliferative neoplasms (MPNs) or liver disease. Thus, a retrospective multicenter study was performed; fifteen patients receiving anticoagulant oral treatment with vitamin k antagonists (VKA) for SVT were evaluated. Nine patients were affected by MPN, and all of them received cytoreduction in addition to anticoagulant therapy; four of these patients had primary myelofibrosis (PMF) and were treated with ruxolitinib (RUX), and one patient with primary myelofibrosis, two patients with essential thrombocythemia (ET), and two patients with polycythemia vera (PV) were treated with hydroxyurea (HU). Six patients affected by liver diseases (three with liver cirrhosis and three with hepatocellular carcinoma) were included as the control group. CECs were assayed by flow cytometry on peripheral blood at specific time points, for up to six months after enrollment. The CEC levels were related to C-reactive protein (CRP) levels, splenic volume reduction, and thrombus recanalization, mainly in MPN patients. In patients with liver cirrhosis (LC) and hepatocellular carcinoma (HCC), for which the mechanism of SVT development is quite different, the relationship between CEC and SV reduction was absent. In conclusion, the CEC levels showed a significant correlation with the extent of venous thrombosis and endothelial cell damage in myeloproliferative neoplasm patients with splanchnic vein thrombosis. Although preliminary, these results show how monitoring CEC levels during cytoreductive and anticoagulant treatments may be useful to improve SVT outcome in MPN patients.

Platelet Heterogeneity in Myeloproliferative Neoplasms

Myeloproliferative neoplasms (MPNs) are a group of malignant disorders of the bone marrow where a dysregulated balance between proliferation and differentiation gives rise to abnormal numbers of mature blood cells. MPNs encompass a spectrum of disease entities with progressively more severe clinical features, including complications with thrombosis and hemostasis and an increased propensity for transformation to acute myeloid leukemia. There is an unmet clinical need for markers of disease progression. Our understanding of the precise mechanisms that influence pathogenesis and disease progression has been limited by access to disease-specific cells as biosources. Here, we review the landscape of MPN pathology and present blood platelets as potential candidates for disease-specific understanding. We conclude with our recent work discovering progressive platelet heterogeneity by subtype in a large clinical cohort of patients with MPN.

Platelet transcriptome identifies progressive markers and potential therapeutic targets in chronic myeloproliferative neoplasms

Predicting disease progression remains a particularly challenging endeavor in chronic degenerative disorders and cancer, thus limiting early detection, risk stratification, and preventive interventions. Here, profiling the three chronic subtypes of myeloproliferative neoplasms (MPNs), we identify the blood platelet transcriptome as a proxy strategy for highly sensitive progression biomarkers that also enables prediction of advanced disease via machine-learning algorithms. The MPN platelet transcriptome reveals an incremental molecular reprogramming that is independent of patient driver mutation status or therapy. Subtype-specific markers offer mechanistic and therapeutic insights, and highlight impaired proteostasis and a persistent integrated stress response. Using a LASSO model with validation in two independent cohorts, we identify the advanced subtype MF at high accuracy and offer a robust progression signature toward clinical translation. Our platelet transcriptome snapshot of chronic MPNs demonstrates a proof-of-principle for disease risk stratification and progression beyond genetic data alone, with potential utility in other progressive disorders.

Risk for Arterial and Venous Thrombosis in Patients With Myeloproliferative Neoplasms: A Population-Based Cohort Study

BACKGROUND

Patients with myeloproliferative neoplasms (MPNs) are reported to be at increased risk for thrombotic events. However, no population-based study has estimated this excess risk compared with matched control participants.

OBJECTIVE

To assess risk for arterial and venous thrombosis in patients with MPNs compared with matched control participants.

DESIGN

Matched cohort study.

SETTING

Population-based setting in Sweden from 1987 to 2009, with follow-up to 2010.

PATIENTS

9429 patients with MPNs and 35 820 matched control participants.

MEASUREMENTS

The primary outcomes were rates of arterial and venous thrombosis. Flexible parametric models were used to calculate hazard ratios (HRs) and cumulative incidence with 95% CIs.

RESULTS

The HRs for arterial thrombosis among patients with MPNs compared with control participants at 3 months, 1 year, and 5 years were 3.0 (95% CI, 2.7 to 3.4), 2.0 (CI, 1.8 to 2.2), and 1.5 (CI, 1.4 to 1.6), respectively. The corresponding HRs for venous thrombosis were 9.7 (CI, 7.8 to 12.0), 4.7 (CI, 4.0 to 5.4), and 3.2 (CI, 2.9 to 3.6). The rate was significantly elevated across all age groups and was similar among MPN subtypes. The 5-year cumulative incidence of thrombosis in patients with MPNs showed an initial rapid increase followed by gentler increases during follow-up. The HR for venous thrombosis decreased during more recent calendar periods.

LIMITATION

No information on individual laboratory results or treatment.

CONCLUSION

Patients with MPNs across all age groups have a significantly increased rate of arterial and venous thrombosis compared with matched control participants, with the highest rates at and shortly after diagnosis. Decreases in the rate of venous thrombosis over time likely reflect advances in clinical management.

PRIMARY FUNDING SOURCE

The Cancer Research Foundations of Radiumhemmet, Blodcancerfonden, the Swedish Research Council, the regional agreement on medical training and clinical research between Stockholm County Council and Karolinska Institutet, the Adolf H. Lundin Charitable Foundation, and Memorial Sloan Kettering Cancer Center.

Do we need antiplatelet therapy in thrombocytosis? Pro

Thrombocytosis (defined as platelets >450 × 109/l) has several aetiologies. After having excluded spurious thrombocytosis (e. g., due to microspherocytes, schistocytes, cryoglobulins, or bacteria), the differential diagnosis of true thrombocytosis encompasses secondary causes (as diverse as inflammation, infection, malignancy, iron deficiency, or asplenia), primary hereditary (rare forms of familial thrombocytosis) and primary acquired entities (either in the context of a myelodys-plastic syndrome or more frequently a myeloproliferative neoplasia). This manuscript addresses the following aspects: 1) diagnostic approach to thrombocytosis; 2) various mechanisms leading to a high platelet count; 3) potential of some of these mechanisms to modulate platelet function, producing hyper-reactive platelets and thus exerting a direct impact on the thrombotic risk; 4) indication of anti-thrombotic treatment in patients with thrombocytosis. There is a single prospective randomized clinical trial showing the benefit of acetyl-salicylic acid in polycythaemia vera. For other types of primary thrombocytosis and for secondary forms, treatment decisions have to be individualized according to the patient thrombotic and bleeding risks, taking into account the mechanism causing thrombocytosis. This manuscript discusses experimental and clinical data suggesting that besides patients with essential thrombocythaemia and other forms of primary thrombocytosis also those with thrombocytosis in the context of chronic inflammation, malignancy, or exposure to high altitude might benefit from anti-platelet treatment.

A rare vascular complication in a patient with essential thrombocythaemia: spontaneous abdominal aortic dissection

A 27-year-old woman complained of waist and back pain. Abdominal computed tomography angiography showed abdominal aortic dissection, the blood count revealed a high platelet count of 1655 × 10⁹ /L. Negative for JAK2V617F, CALR and MPL mutations (i.e. triple-negative), the patient was diagnosed as essential thrombocythaemia (ET) with abdominal aortic dissection and was treated with cytoreduction and antiplatelet drugs. Cases of abdominal aortic dissection in ET have not been previously reported. As such, we proposed a mechanism of abdominal aortic dissection caused by endothelial dysfunction and further emphasised appropriate management in ET with abdominal aortic dissection.

Bone mineral density and microarchitecture in patients with essential thrombocythemia and polycythemia vera

In this cross-sectional study of 45 patients with myeloproliferative neoplasms, we found no evidence of secondary osteoporosis.

INTRODUCTION

Patients with essential thrombocythemia (ET) and polycythaemia vera (PV) are at increased risk of fractures but the underlying mechanisms have not been settled. We conducted a study to assess bone mineral density, microarchitecture, estimated bone strength and global bone turnover in 45 patients with ET or PV.

METHODS

Patients were evaluated in a cross-sectional study with dual energy X-ray absorptiometry (DXA) at the hip and spine; high-resolution peripheral quantitative computed tomography (HR-pQCT) at the distal radius and distal tibia; and biochemical markers of bone turnover including pro-collagen type 1 N-terminal pro-peptide, osteocalcin, C-terminal cross-linking telopeptide of type 1 collagen and bone-specific alkaline phosphatase. Also, 45 healthy comparisons, matched on age, height and weight with each patient were included as control subjects.

RESULTS

Patients and comparisons had almost identical BMDs: 0.96 (IQR: 0.85-1.07) g/cm² and 0.96 g/cm² (IQR: 0.86-1.05 g/cm²), respectively. As well all microarchitecture and estimated bone strength measures were highly similar in the two groups. Levels of bone turnover markers were within reference values in patients.

CONCLUSION

These results reveal no evidence of secondary osteoporosis among patients with ET or PV. The mechanism behind the increased fracture risk in ET or PV patients remains unknown.

The myeloproliferative neoplasms, unclassifiable: clinical and pathological considerations

In this study, we investigate in detail the morphological, clinical and molecular features of 71 consecutive patients with a diagnosis of myeloproliferative neoplasms, unclassifiable. We performed a meticulous morphological analysis and found that most of the cases displayed a hypercellular bone marrow (70%) with normal erythropoiesis without left-shifting (59%), increased granulopoiesis with left-shifting (73%) and increased megakaryocytes with loose clustering (96%). Megakaryocytes displayed frequent giant forms with hyperlobulated or bulbous nuclei and/or other maturation defects. Interestingly, more than half of the cases displayed severe bone marrow fibrosis (59%). Median values of hemoglobin level and white blood cells count were all within the normal range; in contrast, median platelets count and lactate dehydrogenase were increased. Little less than half of the patients (44%) showed splenomegaly. JAK2V617F mutation was detected in 72% of all patients. Among the JAK2-negative cases, MPLW515L mutation was found in 17% and CALR mutations in 67% of the investigated cases, respectively. Finally, by multiple correspondence analysis of the morphological profiles, we found that all but four of the cases could be grouped in three morphological clusters with some features similar to those of the classic BCR-ABL1-negative myeloproliferative neoplasms. Analysis of the clinical parameters in these three clusters revealed discrepancies with the morphological profile in about 55% of the patients. In conclusion, we found that the category of myeloproliferative neoplasm, unclassifiable is heterogeneous but identification of different subgroups is possible and should be recommended for a better management of these patients.

CD18 promoter methylation is associated with a higher risk of thrombotic complications in primary myelofibrosis

Morbidity and mortality of BCR-ABL1-negative myeloproliferative neoplasm (MPN) patients are influenced by disease-related hemostatic complications, mostly of thrombotic nature. The pathogenesis of thrombosis is multifactorial: in particular, it has been demonstrated that a deregulated expression of Mac1 (also known as surface receptor integrin CD18/CD11b) by leukocytes has a role in favoring platelets' activation in MPN patients. Based on these data, we investigated the epigenetic status of CD18/CD11b in 78 primary myelofibrosis (PMF) patients to explore any possible association between the epigenetic profiles of these two genes and thrombotic risk. The percentage of CD18 methylation in the PMF samples ranged from hypomethylated to hypermethylated (range: 11-90 %, mean: 64 %), whereas in controls CD18 methylation status clustered in a more restricted interval (range: 24-68 %, mean: 45 %; cases vs.

CONTROLS

p = 0.006). Furthermore, the results showed that CD18 hypermethylation (>76 % methylation) was correlated with thrombotic complications. On the contrary, CD11b promoter resulted unmethylated (1-5 %) in both cases and controls. Previous studies showed that older age, JAK2V617F mutation, and thrombophilia might play a role in MPN patients' thrombotic risk. In our cases, the prognostic value of these variables was coherent, being thrombotic events significantly associated with age >65 years (p = 0.001), JAK2 mutation (p = 0.01), and positive thrombophilia tests (p = 0.04). However, multivariate analysis showed that only CD18 methylation and age >65 years were independent prognostic factors of thrombosis (p = 0.02 and p = 0.04, respectively). Taken together, our findings suggest a possible role of CD18 epigenetic regulation in the pathogenesis of the thrombotic complications in PMF patients.

Health care setting and severity, symptom burden, and complications in patients with Philadelphia-negative myeloproliferative neoplasms (MPN): a comparison between university hospitals, community hospitals, and office-based physicians

Philadelphia-negative myeloproliferative neoplasms (MPN) comprise a heterogeneous group of chronic hematological malignancies with significant variations in clinical characteristics. Due to the long survival and the feasibility of oral or subcutaneous therapy, these patients are frequently treated outside of larger academic centers. This analysis was performed to elucidate differences in MPN patients in three different health care settings: university hospitals (UH), community hospitals (CH), and office-based physicians (OBP). The MPN registry of the Study Alliance Leukemia is a non-interventional prospective study including adult patients with an MPN according to WHO criteria (2008). For statistical analysis, descriptive methods and tests for significant differences were used. Besides a different distribution of MPN subtypes between the settings, patients contributed by UH showed an impaired medical condition, a higher comorbidity burden, and more vascular complications. In the risk group analyses, the majority of polycythemia vera (PV) and essential thrombocythemia (ET) patients from UH were classified into the high-risk category due to previous vascular events, while for PV and ET patients in the CH and OBP settings, age was the major parameter for a high-risk categorization. Regarding MPN-directed therapy, PV patients from the UH setting were more likely to receive ruxolitinib within the framework of a clinical trial. In summary, the characteristics and management of patients differed significantly between the three health care settings with a higher burden of vascular events and comorbidities in patients contributed by UH. These differences need to be taken into account for further analyses and design of clinical trials.

Bleeding, thrombosis, and anticoagulation in myeloproliferative neoplasms (MPN): analysis from the German SAL-MPN-registry

BACKGROUND

Patients with Ph-negative myeloproliferative neoplasms (MPN), such as polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF), are at increased risk for thrombosis/thromboembolism and major bleeding. Due to the morbidity and mortality of these events, antiplatelet and/or anticoagulant agents are commonly employed as primary and/or secondary prophylaxis. On the other hand, disease-related bleeding complications (i.e., from esophageal varices) are common in patients with MPN. This analysis was performed to define the frequency of such events, identify risk factors, and assess antiplatelet/anticoagulant therapy in a cohort of patients with MPN.

METHODS

The MPN registry of the Study Alliance Leukemia is a non-interventional prospective study including adult patients with an MPN according to WHO criteria (2008). For statistical analysis, descriptive methods and tests for significant differences as well as contingency tables were used to identify the odds of potential risk factors for vascular events.

RESULTS

MPN subgroups significantly differed in sex distribution, age at diagnosis, blood counts, LDH levels, JAK2V617F positivity, and spleen size (length). While most thromboembolic events occurred around the time of MPN diagnosis, one third of these events occurred after that date. Splanchnic vein thrombosis was most frequent in post-PV-MF and MPN-U patients. The chance of developing a thromboembolic event was significantly elevated if patients suffered from post-PV-MF (OR 3.43; 95% CI = 1.39-8.48) and splenomegaly (OR 1.76; 95% CI = 1.15-2.71). Significant odds for major bleeding were previous thromboembolic events (OR = 2.71; 95% CI = 1.36-5.40), splenomegaly (OR = 2.22; 95% CI 1.01-4.89), and the administration of heparin (OR = 5.64; 95% CI = 1.84-17.34). Major bleeding episodes were significantly less frequent in ET patients compared to other MPN subgroups.

CONCLUSIONS

Together, this report on an unselected "real-world" cohort of German MPN patients reveals important data on the prevalence, diagnosis, and treatment of thromboembolic and major bleeding complications of MPN.

[Thrombotic events and significance of the IPSET thrombosis risk evaluation score in essential thrombocythaemia]

INTRODUCTION

Thrombo-haemorrhagic complications contribute to both morbidity and mortality in patients with essential thrombocythaemia.

AIM

The aim of the authors was to estimate the incidence of thrombotic events and to examine the clinical utility of IPSET thrombosis risk evaluation score against conventional two-categorical (low and high) risk assessment.

METHOD

A retrospective analysis was carried out on 155 patients with essential thrombocythaemia (106 females; median age, 61 years) in a period between 1999 and 2014.

RESULTS

The analysis revealed 55 (35.5%) major thrombotic events before and 25 (16.1%) major thrombotic complications after establishment of the haematologic diagnosis. Significant differences were observed in thrombosis-free survival between the different IPSET groups (p = 0.002).

CONCLUSIONS

The IPSET model was first examined in this cohort of patients with essential thrombocythaemia diagnosed in a single Hungarian haematologic centre. The results suggest that this score may provide more information than the conventional thrombosis risk assessment.

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.

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.