Long-term pharmacodynamic and clinical effects of twice- versus once-daily low-dose aspirin in essential thrombocythemia: The ARES trial.

Patients with essential thrombocythemia (ET) are treated with once-daily low-dose aspirin to prevent thrombosis, but their accelerated platelet turnover shortens the antiplatelet effect. The short-term Aspirin Regimens in EsSential Thrombocythemia trial showed that twice-daily aspirin dosing restores persistent platelet thromboxane (TX) inhibition. However, the long-term pharmacodynamic efficacy, safety and tolerability of twice-daily aspirin remain untested. We performed a multicenter, randomized, open-label, blinded-endpoint, phase-2 trial in which 242 patients with ET were randomized to 100 mg aspirin twice- or once-daily and followed for 20 months. The primary endpoint was the persistence of low serum TXB2, a surrogate biomarker of antithrombotic efficacy. Secondary endpoints were major and clinically relevant non-major bleedings, serious vascular events, symptom burden assessed by validated questionnaires, and in vivo platelet activation. Serum TXB2 was consistently lower in the twice-daily versus once-daily regimen on 10 study visits over 20 months: median 3.9 ng/mL versus 19.2 ng/mL, respectively; p < .001; 80% median reduction; 95% CI, 74%-85%. No major bleeding occurred. Clinically relevant non-major bleedings were non-significantly higher (6.6% vs. 1.7%), and major thromboses lower (0.8% vs. 2.5%) in the twice-daily versus once-daily group. Patients on the twice-daily regimen had significantly lower frequencies of disease-specific symptoms and severe hand and foot microvascular pain. Upper gastrointestinal pain was comparable in the two arms. In vivo platelet activation was significantly reduced by the twice-daily regimen. In patients with ET, twice-daily was persistently superior to once-daily low-dose aspirin in suppressing thromboxane biosynthesis and reducing symptom burden, with no detectable excess of bleeding and gastrointestinal discomfort.

Platelet thromboxane inhibition by low-dose aspirin in polycythemia vera: Ex vivo and in vivo measurements and in silico simulation.

Low-dose aspirin is currently recommended for patients with polycythemia vera (PV), a myeloproliferative neoplasm with increased risk of arterial and venous thromboses. Based on aspirin pharmacodynamics in essential thrombocythemia, a twice-daily regimen is recommended for patients with PV deemed at particularly high thrombotic risk. We investigated the effects of low-dose aspirin on platelet cyclooxygenase activity and in vivo platelet activation in 49 patients with PV, as assessed by serum thromboxane (TX) B2 and urinary TXA2 /TXB2 metabolite (TXM) measurements, respectively. A previously described pharmacokinetic-pharmacodynamic in silico model was used to simulate the degree of platelet TXA2 inhibition by once-daily (q.d.) and twice-daily (b.i.d.) aspirin, and to predict the effect of missing an aspirin dose during q.d. and b.i.d. regimens. Serum TXB2 averaged 8.2 (1.6-54.7) ng/ml and significantly correlated with the platelet count (γ = 0.39) and urinary TXM (γ = 0.52) in multivariable analysis. One-third of aspirin-treated patients with PV displayed less-than-maximal platelet TXB2 inhibition, and were characterized by significantly higher platelet counts and platelet-count corrected serum TXB2 than those with adequate inhibition. Eight patients with PV were sampled again after 12 ± 4 months, and had reproducible serum TXB2 and urinary TXM values. The in silico model predicted complete inhibition of platelet-derived TXB2 by b.i.d. aspirin, a prediction verified in a patient with PV with the highest TXB2 value while on aspirin q.d. and treated short-term with a b.i.d. regimen. In conclusion, one in three patients with PV on low-dose aspirin display less-than-maximal inhibition of platelet TXA2 production. Serum TXB2 measurement can be a valuable option to guide precision dosing of antiplatelet therapy in patients with PV.

Association of Platelet Thromboxane Inhibition by Low-Dose Aspirin With Platelet Count and Cytoreductive Therapy in Essential Thrombocythemia.

Essential thrombocythemia (ET) is a myeloproliferative neoplasm characterized by enhanced platelet production and thrombotic complications. The inhibition of platelet cyclooxygenase (COX) activity by the standard once-daily aspirin is mostly incomplete due to accelerated thrombopoiesis. The phase II Aspirin Regimens in EsSential thrombocythemia (ARES) trial has recently compared the efficacy of once- vs. twice- or three-times daily low-dose aspirin in inhibiting platelet thromboxane (TX) A2 production, as reflected by serum (s) TXB2 measurements. The present substudy characterized the determinants of the highly variable response to the standard aspirin 100 mg once-daily regimen in fully compliant patients with ET and the effects of the experimental dosing regimens on response variability. By multivariable analysis, the platelet count (directly) and cytoreductive treatment (inversely) were significantly associated with sTXB2 values in 218 patients with ET. However, the platelet count positively correlated with sTXB2 in patients not being treated with cytoreductive drugs (ρ = 0.51, P < 0.01, n = 84), but not in patients on cytoreduction. Patients in the lowest sTXB2 quartile were older, more often on cytoreductive drugs, had lower platelet count and Janus-Associated Kinase2 (JAK2)-V617F allele frequency as compared with patients in the upper sTXB2 quartiles. After 2 weeks of a twice- or 3-times daily aspirin regimen, the association between the platelet count and sTXB2 became similar in cytoreduced and non-cytoreduced patients. In conclusion, the platelet count appears the strongest determinant of TXA2 inhibition by once-daily low-dose aspirin in ET, with different patterns depending of cytoreductive treatment. More frequent aspirin dosing restores adequate platelet inhibition and reduces interindividual variability, independently of cytoreduction.

A randomized double-blind trial of 3 aspirin regimens to optimize antiplatelet therapy in essential thrombocythemia.

Essential thrombocythemia (ET) is characterized by abnormal megakaryopoiesis and enhanced thrombotic risk. Once-daily low-dose aspirin is the recommended antithrombotic regimen, but accelerated platelet generation may reduce the duration of platelet cyclooxygenase-1 (COX-1) inhibition. We performed a multicenter double-blind trial to investigate the efficacy of 3 aspirin regimens in optimizing platelet COX-1 inhibition while preserving COX-2-dependent vascular thromboresistance. Patients on chronic once-daily low-dose aspirin (n = 245) were randomized (1:1:1) to receive 100 mg of aspirin 1, 2, or 3 times daily for 2 weeks. Serum thromboxane B2 (sTXB2), a validated biomarker of platelet COX-1 activity, and urinary prostacyclin metabolite (PGIM) excretion were measured at randomization and after 2 weeks, as primary surrogate end points of efficacy and safety, respectively. Urinary TX metabolite (TXM) excretion, gastrointestinal tolerance, and ET-related symptoms were also investigated. Evaluable patients assigned to the twice-daily and thrice-daily regimens showed substantially reduced interindividual variability and lower median (interquartile range) values for sTXB2 (ng/mL) compared with the once-daily arm: 4 (2.1-6.7; n = 79), 2.5 (1.4-5.65, n = 79), and 19.3 (9.7-40; n = 85), respectively. Urinary PGIM was comparable in the 3 arms. Urinary TXM was reduced by 35% in both experimental arms. Patients in the thrice-daily arm reported a higher abdominal discomfort score. In conclusion, the currently recommended aspirin regimen of 75 to 100 once daily for cardiovascular prophylaxis appears to be largely inadequate in reducing platelet activation in the vast majority of patients with ET. The antiplatelet response to low-dose aspirin can be markedly improved by shortening the dosing interval to 12 hours, with no improvement with further reductions (EudraCT 2016-002885-30).

Increased von Willebrand factor levels in polycythemia vera and phenotypic differences with essential thrombocythemia.

BACKGROUND: Acquired von Willebrand factor (VWF) deficiency was described in Philadelphia-negative myeloproliferative neoplasms, especially in essential thrombocythemia (ET). VWF phenotype in contemporary patients with polycythemia vera (PV) remains less explored. OBJECTIVES: To characterize the VWF phenotype in PV and to compare VWF phenotype in PV with matched healthy subjects and ET patients. PATIENTS/METHODS: We studied 48 PV patients, treated according to current recommendations (hematocrit ≤ 45%, on low-dose aspirin prophylaxis); 48 healthy and 41 subjects with ET, all sex, age, and blood group matched. We measured VWF antigen, activity, multimeric pattern, ADAMTS-13, and factor VIII (FVIII) antigen. RESULTS: In patients with PV, VWF antigen and activity were significantly higher than in healthy subjects (antigen: 119[96-137] vs 93[79-107] IU/dL; activity: 114[95-128] vs 90[79-107] IU/dL, respectively, medians and interquartile, P < 0.01), with normal multimeric distribution. ADAMTS-13 levels were similar between patients with PV and healthy subjects. FVIII levels were higher in PV than in healthy subjects (141[119-169] versus 98[88-123] IU/dL, respectively, P < 0.01). By multivariable analysis, JAK2-p.V617F allelic burden, erythrocyte count, and male sex significantly predicted VWF antigen and activity levels. As compared to patients with ET, patients with PV showed similar VWF antigen levels but approximately 40% higher activity (79[49-104] vs 112[93-125] IU/dL, respectively, P < 0.01). CONCLUSIONS: Patients with PV show increased VWF and FVIII levels, predicted by JAK2-p.V617F burden and erythrocyte count. At variance with ET, acquired VWF defect was not observed in PV. High VWF/FVIII levels may sustain the thrombotic diathesis of PV and may be investigated as biomarkers for risk stratification.

The Aspirin Regimens in Essential Thrombocythemia (ARES) phase II randomized trial design: Implementation of the serum thromboxane B2 assay as an evaluation tool of different aspirin dosing regimens in the clinical setting.

Once-daily (od), low-dose aspirin (75-100 mg) is recommended to reduce the thrombotic risk of patients with essential thrombocytemia (ET). This practice is based on data extrapolated from other high-risk patients and an aspirin trial in polycythemia vera, with the assumption of similar aspirin pharmacodynamics in the two settings. However, the pharmacodynamics of low-dose aspirin is impaired in ET, reflecting accelerated renewal of platelet cyclooxygenase (COX)-1. ARES is a parallel-arm, placebo-controlled, randomized, dose-finding, phase II trial enrolling 300 ET patients to address two main questions. First, whether twice or three times 100 mg aspirin daily dosing is superior to the standard od regimen in inhibiting platelet thromboxane (TX)A2 production, without inhibiting vascular prostacyclin biosynthesis. Second, whether long-term persistence of superior biochemical efficacy can be safely maintained with multiple vs. single dosing aspirin regimen. Considering that the primary study end point is serum TXB2, a surrogate biomarker of clinical efficacy, a preliminary exercise of reproducibility and validation of this biomarker across all the 11 participating centers was implemented. The results of this preliminary phase demonstrate the importance of controlling reproducibility of biomarkers in multicenter trials and the feasibility of using serum TXB2 as a reliable end point for dose-finding studies of novel aspirin regimens.

Unbiased pro-thrombotic features at diagnosis in 977 thrombocythemic patients with Philadelphia-negative chronic myeloproliferative neoplasms.

In patients with Philadelphia-negative chronic myeloproliferative neoplasms (MPNs), the anti-thrombotic and/or cytoreductive treatment in the follow-up may affect the evaluation of the pro-thrombotic weight of the clinical and biological characteristics at diagnosis. In order to avoid this potential confounding effect, we investigated the relationship between prior thrombosis (PrTh: thrombosis occurred before diagnosis and before treatment) and the characteristics at diagnosis in 977 thrombocythemic patients with MPN, reclassified according to the WHO 2008 criteria. PrTh occurred in 194 (19.9%) patients, with similar rates in the different MPNs. In multivariate analysis, PrTh rate was significantly related to minor thrombocytosis (platelets ≤700×10(9)/L), leukocytosis (leukocytes >10×10(9)/L), higher hematocrit (HCT >45%), JAK2 V617F mutation, older age, and cardiovascular risk factors (CVRFs). The highest PrTh rate (33.9%) was associated with the coexistence of minor thrombocytosis and leukocytosis. Of note, the inverse relationship between PrTh rate and platelet count is consistent with the hemostatic paradox of thrombocytosis. In conclusion, this analysis in MPN patients disclosed the unbiased characteristics at diagnosis with a pro-thrombotic effect. Moreover, it suggests that the optimal control of blood cells counts, and CVRFs might be of utmost importance in the prevention of thrombosis during the follow-up.

A multicentre observational study for early diagnosis of Gaucher disease in patients with Splenomegaly and/or Thrombocytopenia.

Gaucher disease (GD) is the most common lysosomal disorder resulting from deficient activity of the ß-glucosidase enzyme that causes accumulation of glucosylceramide in the macrophage-monocyte system. Notably, because of non-specific symptoms and a lack of awareness, patients with GD experience long diagnostic delays. The aim of this study was to apply a diagnostic algorithm to identify GD type 1 among adults subjects referred to Italian haematology outpatient units because of splenomegaly and/or thrombocytopenia and, eventually, to estimate the prevalence of GD in this selected population. One hundred and ninety-six subjects (61 females, 135 males; mean age 47.8 ± 18.2 years) have been enrolled in the study and tested for ß-glucosidase enzyme activity on dried blood spot (DBS). Seven of 196 patients have been diagnosed with GD, (5 females and 2 males) with mean age 31.8 ± 8.2 years, with a prevalence of 3.6% (with a prevalence of 3.6% (I95% CI 1.4-7.2; 1/28 patients) in this population. These results show that the use of an appropriate diagnostic algorithm and a simple diagnostic method, such as DBS, are important tools to facilitate the diagnosis of a rare disease even for not disease-expert physicians.

Perceived challenges and attitudes to regimen and product selection from Italian haemophilia treaters: the 2013 AICE survey.

Despite great advances in haemophilia care in the last 20 years, a number of questions on haemophilia therapy remain unanswered. These debated issues primarily involve the choice of the product type (plasma-derived vs. recombinant) for patients with different characteristics: specifically, if they were infected by blood-borne virus infections, and if they bear high or low risk of inhibitor development. In addition, the most appropriate treatment regimen in non-inhibitor and inhibitor patients compel physicians operating at the haemophilia treatment centres (HTCs) to take important therapeutic decisions, which are often based on their personal clinical experience rather than on evidence-based recommendations from published literature data. To know the opinion on the most controversial aspects in haemophilia care of Italian expert physicians, who are responsible for common clinical practice and therapeutic decisions, we have conducted a survey among the Directors of HTCs affiliated to the Italian Association of Haemophilia Centres (AICE). A questionnaire, consisting of 19 questions covering the most important topics related to haemophilia treatment, was sent to the Directors of all 52 Italian HTCs. Forty Directors out of 52 (76.9%) responded, accounting for the large majority of HTCs affiliated to the AICE throughout Italy. The results of this survey provide for the first time a picture of the attitudes towards clotting factor concentrate use and product selection of clinicians working at Italian HTCs.

TET2 mutations in Ph-negative myeloproliferative neoplasms: identification of three novel mutations and relationship with clinical and laboratory findings.

High-throughput DNA sequence analysis was used to screen for TET2 mutations in peripheral blood derived DNA from 97 patients with BCR-ABL-negative myeloproliferative neoplasms (MPNs). Overall six mutations in the coding region of the gene were identified in 7 patients with an overall mutational frequency of 7.2%. In polycythemia vera patients (n = 25) 2 mutations were identified (8%), and in those with essential thrombocythemia (n = 55) 2 mutations (3.6%); in those with unclassifiable MPN (n = 8) 3 mutations (37.5%). No primary myelofibrosis patients (n = 6) harboured TET2 mutations. Three unreported mutations were identified (p.P177fs, p.C1298del, and p.P411del), the first two in patients with unclassifiable MPN, the last in a patient with essential thrombocythemia. On multivariate analysis the diagnosis of an unclassifiable MPN was significantly related to the presence of TET2 mutations (P = 0.02; OR: 2.81; 95% CI 1.11-7.06). We conclude that TET2 mutations occur in both JAK2 V617F-positive and -negative MPNs and are more frequent in MPN-U patients. This could represent the biological link between the different classes of myeloid malignancies.

Identifying determinants of variability to tailor aspirin therapy.

Once-daily, low-dose aspirin is a cornerstone in the prophylaxis and treatment of cardiovascular diseases. Aspirin 'resistance' still lacks definition, a standardized reference assay, underlying mechanisms, clinical impact or efficacy of alternative antiplatelet drugs. Aspirin response in several studies has been measured by different platelet function tests, not always reflecting aspirin pharmacodynamics, thus generating significantly heterogeneous results. The EMA indicated serum thromboxane B2 as the only valid surrogate assay to study different aspirin formulations. Rather than resistance, recent studies focused on sources of intra- and inter-individual variability in response to aspirin, based on pharmacokinetic and/or pharmacodynamic mechanisms. Drug interactions, diabetes, conditions of increased platelet output, obesity and aging can potentially increase the variability of aspirin response. Preliminary studies testing different aspirin regimens showed that twice-daily low doses were more effective than once-daily higher aspirin doses on surrogate end points of platelet inhibition. Large studies are needed to test new disease-tailored, low-dose aspirin regimens.

Oxidative stress and platelet activation in subjects with moderate hyperhomocysteinaemia due to MTHFR 677 C→T polymorphism.

The methylenetetrahydrofolate reductase (MTHFR) 677 C→T polymorphism may be associated with elevated total homocysteine (tHcy) levels, an independent risk factor for cardiovascular disease. It was the study objective to evaluate in vivo lipid peroxidation and platelet activation in carriers of the MTHFR 677 C→T polymorphism and in non-carriers, in relation to tHcy and folate levels. A cross-sectional comparison of urinary 8-iso-prostaglandin (PG)F(2α) and 11-dehydro-thromboxane (TX)B(2) (markers of in vivo lipid peroxidation and platelet activation, respectively) was performed in 100 carriers and 100 non-carriers of the polymorphism. A methionine-loading test and folic acid supplementation were performed to investigate the causal relationship of the observed associations. Urinary 8-iso-PGF(2α) and 11-dehydro-TXB(2) were higher in carriers with hyperhomocysteinaemia than in those without hyperhomocysteinaemia (p<0.0001). Hyperhomocysteinaemic carriers had lower folate levels (p=0.0006), higher urinary 8-iso-PGF(2α) (p<0.0001) and 11-dehydro-TXB(2) (p<0.0001) than hyperhomocysteinaemic non-carriers. On multiple regression analysis, high tHcy (p<0.0001), low folate (p<0.04) and MTHFR 677 C→T polymorphism (p<0.001) independently predicted high rates of 8-iso-PGF(2α) excretion. Methionine loading increased plasma tHcy (p=0.002), and both urinary prostanoid metabolites (p=0.002). Folic acid supplementation was associated with decreased urinary 8-iso-PGF(2α) and 11-dehydro-TXB2 excretion (p<0.0003) in the hyperhomocysteinaemic group, but not in the control group, with substantial inter-individual variability related to baseline tHcy level and the extent of its reduction. In conclusion, hyperhomocysteinaemia due to the MTHFR 677 C→T polymorphism is associated with enhanced in vivo lipid peroxidation and platelet activation that are reversible, at least in part, following folic acid supplementation. An integrated biomarker approach may help identifying appropriate candidates for effective folate supplementation.

Aspirin-insensitive thromboxane biosynthesis in essential thrombocythemia is explained by accelerated renewal of the drug target.

Essential thrombocythemia (ET) is characterized by enhanced platelet generation and thrombotic complications. Once-daily low-dose aspirin incompletely inhibits platelet thromboxane A(2) (TXA(2)) in the majority of ET patients. In the present study, we investigated the determinants of aspirin-insensitive platelet TXA(2) biosynthesis and whether it could be further suppressed by changing the aspirin dose, formulation, or dosing interval. In 41 aspirin-treated ET patients, the immature platelet count predicted serum TXB(2) independently of platelet count, age, JAK-2 V617F mutation, or cytoreduction (ß = 3.53, P = .001). Twenty-one aspirin-treated patients with serum TXB(2) ≥ 4 ng/mL at 24 hours after dosing were randomized to the following 7-day regimens in a crossover design: enteric-coated aspirin 100 mg twice daily, enteric-coated aspirin 200 mg once daily, or plain aspirin 100 mg once daily. A twice-daily regimen caused a further 88% median (IQR, 78%-92%, P < .001) TXB(2) reduction and normalized the functional platelet response to aspirin, as assessed by urinary 11-dehydro-TXB(2) excretion and the VerifyNow Aspirin assay. Doubling the aspirin dose reduced serum TXB(2) only partially by 39% median (IQR, 29%-54%, P < .05). We conclude that the abnormal megakaryopoiesis characterizing ET accounts for a shorter-lasting antiplatelet effect of low-dose aspirin through faster renewal of platelet cyclooxygenase-1, and impaired platelet inhibition can be rescued by modulating the aspirin dosing interval rather than the dose.

Intracranial haemorrhage in the Italian population of haemophilia patients with and without inhibitors.

Intracranial haemorrhage (ICH) is the most serious bleeding symptom in haemophiliacs, resulting in high rates of mortality and disabling sequelae. The Association of Italian Haemophilia Centres carried out a retrospective survey (1987-2008) of ICH occurring in haemophiliacs with the goals to establish: (i) incidence, location of bleeding, death rate and disabling sequels; (ii) risk factors for ICH; and (iii) treatment used during the acute phase of ICH and for recurrence prevention. A total of 112 ICH episodes had occurred in 88 patients (78 haemophilia A, 10 haemophilia B), 24 of whom experienced recurrences. The cumulative hazard of ICH for the whole cohort over the entire follow-up period was 26.7 per 1000 patients, and the annualized rate of ICH was 2.50 events per 1000 patients (95% CI 1.90-3.31). The risk of ICH was higher in the youngest children (24.4 per 1000, 95% CI 12.7-47.0 in the first year of age and 14.9, 95% CI 7.1-31.4 in the second year of age) and then progressively rose again after the age of 40. Univariate, bivariate (age-adjusted) and multivariate analysis investigating the effects of patient characteristics on ICH occurrence showed that haemophilia severity and inhibitor status were strongly associated with ICH [severe vs. mild, HR 3.96 (2.39-6.57); inhibitor vs. non-inhibitor 2.52 (1.46-4.35)]. HCV infection was also associated with the risk of ICH [HR 1.83 (1.25-2.69)]. Therapeutic suggestions based upon our experience to control ICH recurrence are provided.

Clinical and laboratory features of 103 patients from 42 Italian families with inherited thrombocytopenia derived from the monoallelic Ala156Val mutation of GPIbα (Bolzano mutation).

BACKGROUND: Bernard-Soulier syndrome is a very rare form of inherited thrombocytopenia that derives from mutations in GPIbα, GPIbß, or GPIX and is typically inherited as a recessive disease. However, some years ago it was shown that the monoallelic c.515C>T transition in the GPIBA gene (Bolzano mutation) was responsible for macrothrombocytopenia in a few Italian patients. DESIGN AND METHODS: Over the past 10 years, we have searched for the Bolzano mutation in all subjects referred to our institutions because of an autosomal, dominant form of thrombocytopenia of unknown origin. RESULTS: We identified 42 new Italian families (103 cases) with a thrombocytopenia induced by monoallelic Bolzano mutation. Analyses of the geographic origin of affected pedigrees and haplotypes indicated that this mutation originated in southern Italy. Although the clinical expression was variable, patients with this mutation typically had a mild form of Bernard-Soulier syndrome with mild thrombocytopenia and bleeding tendency. The most indicative laboratory findings were enlarged platelets and reduced GPIb/IX/V platelet expression; in vitro platelet aggregation was normal in nearly all of the cases. CONCLUSIONS: Our study indicates that monoallelic Bolzano mutation is the most frequent cause of inherited thrombocytopenia in Italy, affecting 20% of patients recruited at our institutions during the last 10 years. Because many people from southern Italy have emigrated during the last century, this mutation may have spread to other countries.

Is the absence of JAK2 mutation a risk factor for bleeding in essential thrombocythemia? An analysis of 106 patients.

BACKGROUND: JAK2(V617F) mutation has been recognized as a possible thrombotic risk factor in essential thrombocythaemia (ET). It's role is probably due to an increased myeloid proliferation and white blood cells (WBC) activation. Only few data are available about the effect of JAK2(V617F) on hemorrhagic risk. The aim of our study was to evaluate the influence of the mutational status on hemorrhagic complication. METHODS: We retrospectively analysed laboratory and clinical findings of 106 consecutive patients with ET to evaluate possible relationships between thrombosis, abnormal bleeding, peripheral blood count, overexpression of PRV1 and JAK2(V617F) mutational status. RESULTS: ON UNIVARIATE ANALYSIS WE FOUND: an association between JAK2(V617F) mutation and thrombotic events before or at diagnosis (p<0.003, OR=4.44, 95% CI=1.74-12.4); no statistical correlation between the median value of JAK2(V617F) burden and an increased risk of thrombosis (p=0.4, 95% CI= -22.8-10.4); significant relationships between mutated status and higher haematocrit, high WBC count and low platelet count; and a strong correlation between JAK2(V617F) and PRV1 overexpression (p<0.0001). Moreover, the presence of the JAK2(V617F) mutation and a WBC count greater than 8.4 x 10(9)/L were found to be independent factors related to thrombotic complications in multivariable analysis (p<0.006, OR=3.85, 95% CI=1.3-11.9; and p<0.002, OR=2.8, 95% CI=1.08-7.03, respectively). The prognostic impact of JAK2 mutation status and WBC count on thrombosis was evaluated in the whole cohort. Only new cases occurring in patients without previous thrombotic events were recorded for the analysis. The multivariable analysis showed a statistical correlation between the presence of the mutation and a WBC count greater than 8.12 x 10(6)/L and an increased risk of thrombosis if no cytoreductive treatment was started at diagnosis (JAK2(V617F) p=0.02; WBC p=0.02; OR=4.97; 95% CI=1.04-23.8). Finally, wild-type JAK2 was associated with a higher haemorrhagic risk (p=0.02) in univariate analysis but only a platelet count greater than 1,022 x 10(9)/L was associated with an increased risk of bleeding in the multivariable analysis. CONCLUSION: Our data confirm the role of both JAK2(V617F) as factor associated with an increased risk of thrombosis at the diagnosis and during follow-up in no treated patients. Moreover a WBC count over 8.4 x 10(9)/L1 was also strictly associated to an increased risk of thrombosis. Regarding bleedings, our statistical analysis allows to exclude the mutation protective role on haemorrhage.