Kurzfassung: We analyzed 597 patients with myeloproliferative neoplasms (MPN) who presented transient ischemic attacks (TIA, n  = 270) or ischemic stroke (IS, n  = 327). Treatment included aspirin, oral anticoagulants, and cytoreductive drugs. The composite incidence of recurrent TIA and IS, acute myocardial infarction (AMI), and cardiovascular (CV) death was 4.21 and 19.2%, respectively at one and five years after the index event, an estimate unexpectedly lower than reported in the general population. Patients tended to replicate the first clinical manifestation (hazard ratio, HR: 2.41 and 4.41 for recurrent TIA and IS, respectively); additional factors for recurrent TIA were previous TIA (HR: 3.40) and microvascular disturbances (HR: 2.30); for recurrent IS arterial hypertension (HR: 4.24) and IS occurrence after MPN diagnosis (HR: 4.47). CV mortality was predicted by age over 60 years (HR: 3.98), an index IS (HR: 3.61), and the occurrence of index events after MPN diagnosis (HR: 2.62). Cytoreductive therapy was a strong protective factor (HR: 0.24). The rate of major bleeding was similar to the general population (0.90 per 100 patient-years). In conclusion, the long-term clinical outcome after TIA and IS in MPN appears even more favorable than in the general population, suggesting an advantageous benefit-risk profile of antithrombotic and cytoreductive treatment.

Kurzfassung: Background: Philadelphia-negative Myeloproliferative Neoplasms (MPN) include Polycythemia Vera (PV), Essential Thrombocythemia (ET) and Myelofibrosis, both Primary (PMF) and secondary to PV or ET (PPV-MF and PET-MF). A MPN is frequently the underlying cause of splanchnic vein thrombosis (SVT). Ruxolitinib, a JAK1/2 inhibitor, efficiently reduced spleen volume and improved symptoms in patients (pts) with MF and PV in the COMFORT-I/II and RESPONSE phase III trials, and in ET pts in a phase II study. We reported (Blood 2014 124:3192) that ruxolitinib was safe in pts with MPN associated to SVT and effective in reducing spleen size at the planned primary endpoint analysis at 24 weeks (w) in a phase II clinical trial. Herein we present follow up data with cut off at 1 year after core period (a total of 72 w of treatment). Methods: Main enrolment criteria included diagnosis of PV, ET, PMF or PPV-/PET-MF associated with SVT, splenomegaly 〉 5 cm below costal margin (bcm), active anticoagulant or antiaggregant thrombosis prophylaxis, platelet count (plt) 〉 100 x109/L, neutrophils count 〉 1x109/L, normal hepatic and renal function, absence of esophageal varices 〉 grade 2. Pts who completed the 24 w of study treatment and tolerated well the drug and had evidence of clinically-significant improvement were allowed to enter an extension phase aimed at collecting and reviewing safety and efficacy data. The drug was provided free of charge by Novartis, that had no role in trial design nor in data analysis. Results: Diagnosis of MPN were: PMF 8 (38.1%), PV 5 (23.8%), ET 4 (19.1%), PPV-MF 3 (14.3%), PET-MF 1 (4.8%). Nineteen pts had spleno-porto-mesenteric thrombosis and 3 Budd-Chiari syndrome (BCS); one pt had both sites involved. Initial dose of ruxolitinib was 10 mg BID for PV, 25 mg BID for ET, 15 mg BID for MF pts with baseline (bl) platelet count of 100 to 200x109/L and 20 mg BID for platelet count 〉 200x109/L. Currently 17/21 pts are on active treatment, 14 completed w72; final data for all 17 pts will be available at meeting. One pt with MF discontinued from the study being shifted to commercial ruxolitinib at w60, one ET and one MF pt discontinued for inefficacy at w24 and one MF pt for an unrelated adverse event after w72. Efficacy: 13/21 (61.9%) pts obtained a ≥50% spleen length (sl) reduction by palpation at w24, that was maintained at w72 in 8/14 pts (57.1%). Median sl reduction at w72 was 63% (range 0-100). No significant differences in resistive or pulsatility index of splanchnic artery were noted, nor in esophageal varices status evaluated at w72. 10/11 evaluated pts with echocardiography at w72 showed a median reduction of the cardiac output of 20.1% (range 2.3-42.2) mainly due to a reduction of heart rate and of cardiac index (-21.9%, range 8.8-44.3) due to increase in body surface area. The first effect could be attributed to decrease of proinflammatory cytokines, the second to weight gain associated with ruxolitinib. Symptomatology was evaluated by MPN-SAF up to w24, showing a median total symptom score reduction from 65 to 42. Safety: regardless of drug relationship, the most common adverse events (AE) (% any grade, % grade ≥3) were thrombocythopenia (57.1%; 14.3%) and anemia (33.3%, 19%) that were the main reasons for dose adjustments. Other AE included AST or ALT increase (42.9%, 0%), diarrhea (28.6%, 0%), abdominal pain (23.8%, 0%), ascites (19%, 0%), fever (23.8%, 0%), neutropenia, (9.5%, 9.5%), upper airways infection (19%, 0%), weight gain (14.3%, 4.8%), muscle cramps (14.3%, 0%). Three serious AE occurred: one case of hepatocarcinoma in a pts with BCS, one grade 2 pneumonia and one grade 2 haematemesis not related to esophageal varices. Median ruxolitinib total daily dose at w72, after dose adjustments, was 19.1 mg for MF, 16 mg for PV and 28.3 mg for ET. Median hemoglobin reduced from 12.9 gr/dL (range 9.4-16.7) at bl to 10.7 (8.4-14.4) at w16 and recovered at w72 (12.1, range 10.8-14.7). No pts received transfusions. Median platelet count was 212 x109/L (100-389) at bl, reached to the lowest level at w4 (139, range 48-252) and improved to 160 (69-285) at w72. Median leukocyte count decreased from 7.3 x109/L (1.8-16.4) at bl to 4.08 (1.2-21.7) at w 24, and remained substantially stable through w 72 (4.96; range 2.45-17.3). Median reduction of JAK2 allele burden at w72 was 9% (range 0-38). Conclusions: At w 72 follow up, ruxolitinib continues to be safe in pts with MPN associated to SVT and maintains efficacy against splenomegaly in 57% of the pts. Disclosures De Stefano: Roche: Research Funding; GlaxoSmithKline: Speakers Bureau; Bruno Farmaceutici: Research Funding; Novartis: Research Funding, Speakers Bureau; Janssen Cilag: Research Funding; Celgene: Speakers Bureau; Shire: Speakers Bureau; Amgen: Speakers Bureau. Barbui:Novartis: Speakers Bureau. Vannucchi:Novartis: Other: Research Funding paid to institution (University of Florence), Research Funding; Shire: Speakers Bureau; Baxalta: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau.

Kurzfassung: Splanchnic vein thrombosis (SVT) is one of the vascular complications of myeloproliferative neoplasms (MPN). We designed a phase 2 clinical trial to evaluate safety and efficacy of ruxolitinib in reducing splenomegaly and improving disease‐related symptoms in patients with MPN‐associated SVT. Patients diagnosed with myelofibrosis (12 cases), polycythemia vera (5 cases) and essential thrombocythemia (4 cases) received ruxolitinib for 24 weeks in the core study period. Spleen volume was assessed by magnetic resonance imaging (MRI) and splanchnic vein circulation by echo‐Doppler analysis. Nineteen patients carried JAK2 V617F, one had MPL W515L, and one CALR L367fs*46 mutation. Eighteen patients had spleno‐portal‐mesenteric thrombosis, two had Budd–Chiari syndrome, and one had both sites involved; 16 patients had esophageal varices. Ruxolitinib was well tolerated with hematological toxicities consistent with those of patients without SVT and no hemorrhagic adverse events were recorded. After 24 weeks of treatment, spleen volume reduction ≥35% by MRI was achieved by 6/21 (29%) patients, and a ≥50% spleen length reduction by palpation at any time up to week 24 was obtained by 13/21 (62%) patients. At week 72, 8 of the 13 (62%) patients maintained the spleen response by palpation. No significant effect of treatment on esophageal varices or in splanchnic circulation was observed. MPN‐related symptoms, evaluated by MPN‐symptom assessment form (SAF) TSS questionnaire, improved significantly during the first 4 weeks and remained stable up to week 24. In conclusion, this trial shows that ruxolitinib is safe in patients with MPN‐associated SVT, and effective in reducing spleen size and disease‐related symptoms.

Kurzfassung: Background In the recent International Prognostic Score for Thrombosis in essential thrombocythemia (IPSET-thrombosis), age and history of thrombosis were confirmed as independent risk factors for future thrombosis and the study also identified independent prothrombotic role for cardiovascular (CV) risk factors and JAK2 V617F mutation (Barbui et al. Blood 2012). Methods In the current study, we re-analyzed the original IPSET-thrombosis data in 1019 patients with WHO-defined ET in whom JAK2 mutational status was available, in order to quantify the individual contributions of JAK2 mutations and CV risk factors in conventionally-assigned low and high risk ET, as well as in age- versus thrombosis-defined high risk status. Results After a median follow-up of 6.8 and 5.0 years in conventionally-assigned low- and high-risk patients, respectively, the overall annual rate of total thrombosis (108 events) in conventionally-assigned low- and high-risk patients was 1.11%-pt/y (CI 0.81-1.52) and 2.46%-pt/y (CI 1.94-3.11) respectively (p=0.001), and the difference was mainly due to a higher frequency of arterial thrombosis in high-risk patients (p 〈 0.001).The influence of JAK2 mutational status and CV-risk factors on the rate of thrombosis in conventionally assigned low- and high-risk groups is presented in the table. Table 1. Additional risk factors N (%) Event Rate % pts/yr (95% CI) P-value P-value P-value trend Low risk 506 (50) 39 1.11 (0.81-1.52) None 200 (40) 7 0.44 (0.21-0.92) ref Cardiovascular risk factor 36 (7) 3 1.05 (0.34-3.25) 0.220 0.227 JAK2V617F 213 (43) 21 1.59 (1.04-2.44) 0.001 0.217 Both 52 (10) 8 2.57 (1.29-5.15) 〈 0.001 ref 〈 0.001 High risk 513 (50) 69 2.46 (1.94-3.11) None 111 (22) 10 1.44 (0.78-2.68) ref Cardiovascular risk factor 44 (9) 4 1.64 (0.62-4.37) 0.909 0.067 JAK2V617F 222 (43) 30 2.36 (1.65-3.38) 0.168 0.082 Both 136 (27) 25 4.17 (2.82-6.17) 0.011 ref 0.005 The number of major arterial and venous thrombosis was reported as rates per 100 patient-years and the difference among groups was assessed by Mantel Cox log-rank test i) Conventionally-assigned low-risk group. Amongst 506 patients, 200 (40%) displayed neither JAK2 mutation nor CV risk factors and their annual rate of thrombosis was 0.44%, as opposed to 1.05% in the presence of CV risk factors (P=NS), 1.59% in the presence of JAK2 mutation (p=0.001) and 2.57% in the presence of both CV risk factors and JAK2 mutation (P 〈 0.001). There was no significant difference when low-risk patients with both JAK2 mutation and CV risk factors were compared with either those with CV risk factors only (p=0.227) or those with JAK2 mutation only (p=0.217). ii) Conventionally assigned high-risk group: The absence or presence of one or both of the aforementioned additional risk factors for thrombosis were documented in 111 (22%), 44 (9%), 222 (43%) and 136 (27%) patients, respectively, with corresponding annual rates of thrombosis at 1.44%, 1.64%, 2.36% and 4.17% (Table). High-risk patients with both risk factors had a significantly higher risk of thrombosis compared to their counterparts with the absence of JAK2 mutations and CV risk factors (p=0.011). Additional analysis revealed limited enhancement of thrombosis risk by either JAK2 mutations or CV risk factors or both in patients whose high-risk status was defined by the presence of thrombosis history, regardless of age (P=NS). In contrast, the presence of JAK2 mutations, with or without CV risk factors, might have affected thrombosis risk in patients where high-risk status was defined by age alone (p=0.05). Conclusions The current study suggests the possibility of considering four risk categories in ET: "very low risk" group (age ≤60 years and without thrombosis history, JAK2 mutations or CV risk factors); "low risk" (age ≤60 years and without thrombosis history but with JAK2 mutations or CV risk factors); "intermediate risk" (age 〉 60 years but without thrombosis history or JAK2 mutations); and "high risk" (thrombosis history at any age or JAK2 -mutated patients who are older than 60 years of age). Treatment recommendations for each one of the above-mentioned new risk categories should be examined in the context of prospective controlled studies. Disclosures Barbui: Novartis: Speakers Bureau. Vannucchi:Novartis Pharmaceuticals Corporation: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Shire: Speakers Bureau; Baxalta: Membership on an entity's Board of Directors or advisory committees. Buxhofer-Ausch:AOP Orphan: Research Funding. De Stefano:Novartis: Research Funding, Speakers Bureau; Janssen Cilag: Research Funding; Shire: Speakers Bureau; GlaxoSmithKline: Speakers Bureau; Bruno Farmaceutici: Research Funding; Roche: Research Funding; Amgen: Speakers Bureau; Celgene: Speakers Bureau. Gisslinger:Janssen Cilag: Honoraria, Speakers Bureau; AOP ORPHAN: Consultancy, Honoraria, Research Funding, Speakers Bureau; Geron: Consultancy; Sanofi Aventis: Consultancy; Celgene: Consultancy, Honoraria, Research Funding, Speakers Bureau; Novartis: Honoraria, Research Funding, Speakers Bureau.

Kurzfassung: Introduction Malignancy can be heralded by unprovoked venous thromboembolism (VTE) but also by arterial thrombosis. To date it is unknown whether this association is present also in myeloproliferative neoplasms (MPN), in which arterial thrombosis is more frequent that venous thrombosis and solid tumors are reported with an increased frequency. The MPN-K nested case-control study addressed the impact of cytoreductive drugs on the risk of developing second cancer in MPN patients (Barbui T et al, Leukemia 2019); here we re-examined the study database to evaluate the frequency and type of vascular complications in MPN patients with second cancer excluding leukemia and to establish whether arterial and venous thrombosis during follow-up after diagnosis of MPN could predict the occurrence of a second cancer. Patients and methods Cases were patients with second cancer diagnosed concurrently or subsequent to the diagnosis of MPN. Controls were MPN patients without second cancer. For each case with second cancer, up to 3 cancer-free controls were matched by each center for sex, age at MPN diagnosis, date of MPN diagnosis, and MPN disease duration. Each set consisting of one case and their matched-controls had a similar observational period (from MPN diagnosis until the index date of diagnosis for the second cancer). The study included 647 cases with second cancer (carcinoma, non-melanoma-skin cancers, hematological secondary cancer and melanoma). The most frequent category was carcinoma (n=426, 65.8%). Cases were comparable with the 1,234 matched controls for demographics, type of MPN, and exposure to potential confounders such as mutational profile, abnormal karyotype and cardiovascular risk factors. The thrombotic events of interest were ischemic stroke, transient ischemic attacks, acute coronary syndromes, peripheral arterial thrombosis, deep venous thrombosis (including thrombosis of cerebral and splanchnic veins) and pulmonary embolism. Thrombosis had to be concurrent with or in the 2 years before MPN diagnosis or occurring after MPN diagnosis. The cumulative incidence of either arterial or venous thrombosis from MPN diagnosis was estimated by the Kaplan-Meier method and was compared between cases and controls using the log-rank test. A conditional logistic regression model estimated the Odds Ratio (OR) with 95% Confidence Interval (CI) of second cancer associated with the occurrence of thrombosis before/at diagnosis of MPN and during follow-up. Other covariates were patient age, cardiovascular risk factors, the JAK2V617F mutation, and treatment during follow-up. Results Approximately 20% of either MPN cases or controls had thrombosis before MPN or at diagnosis (19.8% vs. 21.1%, respectively, p=0.462). After a median observation time from diagnosis of MPN to an index date of 4.5 years (interquartile range 1.5-8.2) in cases and 3.7 years (interquartile range 1.5-7.5) in controls, cases showed a percentage of thrombosis higher than in controls (75/647, 11.6% vs. 100/1234, 8.1%, respectively, p=0.013). Approximately one-third of thrombosis preceding cancer occurred in the 12 months before the diagnosis of second cancer (22/75, 29.3%). The excess of thrombosis in cases was due to a higher frequency of arterial thrombosis (6.2% vs. 3.7%, p=0.015), whereas no significant difference was found for venous thrombosis (5.4% vs. 4.3%, p=0.277). While the cumulative incidence of venous thrombosis over time was similar among cases and controls (p=0.864), the cumulative incidence of arterial thrombosis was higher in cases with second cancer (p=0.006) (Figure 1). The excess of arterial thrombosis after MPN diagnosis was limited to cases with carcinoma (6.8% vs 3.9%, p=0.027). In a multivariable model, arterial thrombosis during the follow-up was confirmed to be an independent predictor factor for carcinoma, with an odds ratio of 1.97 (95%CI 1.14-3.41, p=0.015). Conclusions. These findings reveal an association of arterial thrombosis with subsequent second cancer (namely carcinoma) in MPN patients. A possible biological plausibility for this link may be related to an underlying common pathogenic mechanism such as an aberrant inflammatory response consistently found in MPN. This observation may have practical implications and suggests careful clinical surveillance for early diagnosis of second cancer in MPN patients with arterial thrombosis during the follow-up. Disclosures Palandri: Novartis: Consultancy, Honoraria. Iurlo:Novartis: Other: Speaker Honoraria; Incyte: Other: Speaker Honoraria; Pfizer: Other: Speaker Honoraria. Bonifacio:Incyte: Honoraria; Novartis: Honoraria; Amgen: Honoraria; Pfizer: Honoraria; BMS: Honoraria. Rumi:novartis: Honoraria, Research Funding. Elli:Novartis: Membership on an entity's Board of Directors or advisory committees. Lunghi:Pfizer: Honoraria; Novartis: Honoraria; Incyte: Honoraria. Benevolo:Novartis Pharmaceuticals: Consultancy. McMullin:Italopharma: Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Speakers Bureau; Daiko Sanyo: Membership on an entity's Board of Directors or advisory committees. Griesshammer:Novartis: Consultancy, Honoraria, Speakers Bureau. Vannucchi:CTI: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Incyte: Membership on an entity's Board of Directors or advisory committees; Italfarmaco: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene Corporation: Membership on an entity's Board of Directors or advisory committees. Rambaldi:Pfizer: Consultancy, Speakers Bureau; Novartis: Consultancy, Speakers Bureau; Celgene: Consultancy, Speakers Bureau; Amgen: Consultancy, Speakers Bureau.

Kurzfassung: INTRODUCTION The incidence of secondary cancer (SC) in patients with myeloproliferative neoplasms (MPN) is high and comparable to that of thrombosis. However, the identification of patient subgroups that might be at increased susceptibility of developing SC has not been systematically addressed. We report here the results of an international case-control study (MPN-K) aimed at comparing the frequency of exposure to possible causes of SC in patients with classical MPN, polycythemia vera (PV), essential thrombocythemia (ET) and myelofibrosis (MF). METHODS This European Leukaemia Network (ELN) study reports MPN patients from 28 sites of 5 European countries and Israel, diagnosed in the period from 2000 to 2016. Cases were MPN patients with concomitant diagnosis of a non-myeloid SC (n=15) or its presentation during the course of the disease (n=412). Controls were MPN patients cancer-free, matched to the paired case for sex, age (±5 years), date of MPN diagnosis (±5 years), and MPN disease duration (±6 years). A multivariable conditional logistic regression model was used to estimate the effect of selected variables on total SC risk and in different types of SC. RESULTS Among 1,259 MPN patients, there were 427 cases and 832 matched controls. Cases presented melanoma (n=20; 4.7%), non-melanoma skin cancer (n=69; 16.2% - basal/squamous cell carcinoma), non-skin solid cancer (n=290; 67.9%) including breast, ovary/uterus, colorectal, upper gastrointestinal, liver/pancreas, lung, prostate/urinary, other and lymphoproliferative diseases (n=48; 11.2%) including multiple myeloma, chronic lymphocytic leukemia, low and high grade B- and T-lymphoma. At diagnosis, there were slightly more patients with PV among SC cases (n= 152; 35.6%) than controls (n=256; 30.8%), while conversely there were slightly less ET patients among cases (n=196; 45.9%) than controls (n=426; 51.2%). Cases and controls presented similar proportion of MF diagnosis (n=79 cases, 18.5% and 150 controls, 18.0%). Driver mutations (JAK2 V617, EXON-12, CALR, MPL), non-driver mutations and abnormal karyotype were equally represented in cases and controls. Other variables such as cardiovascular risk factors, exposure to cancerogens, family history of cancer and chronic inflammatory diseases were reported with similar frequency in cases and controls. After MPN diagnosis, exposure to first and other lines of treatments until the index event, with Phlebotomy (n=193; 15.3%), Hydroxyurea (n=814; 64.7%), Anagrelide (n=14; 1.1%), Interferon (n=30; 2.4%), Pipobroman (n=8; 0.6%), Busulphan (n=13; 1.0%), Ruxolitinib (n=11; 0.9%), was similar in the two groups except for aspirin that was used less frequently (p=0.043) in cases (n=320; 74.9%) compared to controls (n=664; 79.9%). In particular, the lower use of aspirin was circumscribed to non-skin solid tumors. A multivariable analysis was carried out in all patients and stratified by different type of tumors (Table). In non-skin solid cancers, the time to exposure of the MPN disease 〉 5 years (OR=2.95; 95% CI 1.54-5.66, p=0.001) and the PV phenotype (OR=2.40, 95% CI 1.15-5.01, p=0.020) were more burdened by the incidence of events than the reference ET group. No difference in SC risk was found for MF patients compared to patients with ET. Interestingly, the independent protective role of aspirin retained its statistical significance only in non-skin SC. In non-melanoma skin cancer, multivariable analysis revealed that the presence of JAK2 mutation was less associated with SC (OR=0.32, 95% CI 0.13-0.81, p=0.016) and confirmed that exposure to HU and other cytotoxic agents was associated with a significantly higher risk of SC (OR=6.00, 95% CI 1.23-29.28, p=0.027 and OR=9.80, 95% CI 1.24-77.78, p=0.031, respectively). This finding was not seen in non-skin SC and in lymphoma. CONCLUSION The considered clinical and biological features, at MPN diagnosis, were not different in cases with SC and controls. During the course of the disease, three factors significantly and independently affected the risk of SC in these MPN patients: 1) patients with PV had a 77% higher risk than those with ET, 2) patients with MPN duration of more than 5 years had a twice higher risk than those with lower duration, 3) for the first time, we documented that in non-skin solid cancers, aspirin treatment reduced SC risk of 38%. Exposure to HU and other cytoreductive drugs was confirmed as a risk factor for non-melanoma skin cancer. Disclosures Palandri: Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Marchetti:Gilead: Consultancy; takeda: Speakers Bureau; amgen: Speakers Bureau; janssen: Speakers Bureau. Griesshammer:Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau.

Kurzfassung: Introduction. Prefibrotic myelofibrosis (pre-PMF) is a unique entity in the 2016 WHO classification of myeloproliferative neoplasms with distinct clinical phenotype and outcome [Guglielmelli P, Blood 2017]. Compared to essential thrombocythemia (ET), pre-PMF is characterized by more pronounced disease manifestations, adverse mutation profile and worse outcome. Previous studies [Rumi E, Oncotarget 2017] showed that patients (pts) with pre-PMF present a risk of vascular events similar to ET. However, no studies performed a comprehensive assessment of risk factors for thrombosis in pre-PMF. The current study aimed to identify risk factors for thrombosis and bleeding in a large series of pre-PMF pts and explore the effectiveness of contemporary prognostic models developed specifically for ET. Patients and Methods. The study included 382 pre-PMF pts, diagnosed by 2016 WHO criteria, referred by 4 Italian Centers. Previously published methods were used to genotype JAK2, MPL, CALR, EZH2, ASXL1, IDH1/2 and SRSF2; a high molecular risk (HMR) category was defined according to Vannucchi A, [Leukemia 2013]. Thrombosis‐free survival (TFS) was determined from diagnosis to the first thrombotic event. Pts were grouped according to the conventional risk stratification system [Barbui T, JCO 2011] , IPSET‐thrombosis [Barbui T, Blood 2012] and revised IPSET‐thrombosis [Barbui T, BCJ 2015] . Cox-regression model was used for univariate analysis. Harrell's concordance (C) statistic was calculated to measure the incremental accuracy of multivariable models sequentially adjusted for new predictors of thrombotic risk. A P 〈 0.05 was considered statistically significant. Results. At diagnosis, 65 pts (17%) experienced major thrombotic events which included 35 (9%) arterial and 31 (8%) venous thromboses. With a median follow-up of 6.9 y (range 0.08-32.6), 56 (15%) pts developed an arterial or venous thrombotic event, with a total incidence rate of 1.99% pts/year (pt-y); 30 (8%) were arterial and 28 (7%) venous events with incidence rate of 1.00% pt-y and 0.95% pt-y, respectively. Splanchnic vein thrombosis (SVT) represented the most frequent venous events before/at diagnosis (26%). During the follow-up, 16% and 8% of pts experienced myelofibrotic or leukemic progression, and 105 (27%) died, with incidence rate of 2.05% pt-y, 0.95% pt-y and 3.41% pt-y, respectively. In univariate analysis, factors significant for arterial thrombosis after diagnosis were age 〉 65y (HR 2.88; P=0.005), WBC 〉 10x109/L (HR 2.43; P=0.026), presence of 〉 1 generic CV risk factor (HR 2.16; P=0.047), JAK2V617F (HR 3.35; P=0.027) and HMR status (HR 13.1; P=0.027). Conversely, only history of previous thrombosis (HR 3.06; P=0.005) and previous venous event (HR 5.53; P 〈 0.0001) retained significance for predicting venous thrombosis. Pts were effectively stratified according to IPSET and conventional risk model. The risk of thrombosis in IPSET low-, intermediate-, and high-risk categories was 0.67%, 2.05% and 2.95% pt-y, and 1.47% pt-y and 2.71% pt-y in 2-tiered thrombotic risk model. (Figure 1); in revised-IPSET, 0.54%, 2.23%, 2.44% and 2.69 %pt-y in the very low, low, intermediate- and high-risk category. When WBC 〉 10x109/L or HMR variables were incorporated into IPSET model, the C-statistic increased significantly for the prediction of arterial events: from baseline value of 0.68 to 0.74 adding WBC and 0.91 HMR status. The proportion of pts who experienced major bleeding was 3% prior/at diagnosis,and 7% during follow-up, with total incidence rate of 0.94% pt-y. In univariate analysis, predictors for major bleeding during follow-up were age 〉 75y (HR 3.34; P=0.011), WBC 〉 13x109/L (HR 2.33; P=0.035), presence of 〉 1 generic CV risk factor (HR 2.41; P=0.035), particularly hypertension (HR 2.63; P=0.016) and grade-1 fibrosis (HR 2.28; P=0.05). High platelet count and treatment, including antiplatelet and anticoagulant drugs, did not reach statistical significance. Conclusions. Overall, this study identified independent risk factors for major thrombosis and bleeding in pre-PMF. Of interest, we report that HMR status predicted for arterial thrombosis during the follow-up. Pre-PMF pts showed remarkably high rate of venous thrombosis, mostly represented by SVT. The 3-tiered IPSET prognostic model for thrombosis reliably predicted occurrence of thrombotic events in pre-PMF and should be considered as standard reference. Figure 1 Disclosures Rumi: novartis: Honoraria, Research Funding. Thiele:Shire: Research Funding; Incyte: Consultancy, Honoraria, Other: Remuneration, Research Funding; Sanofi: Consultancy, Honoraria, Other: Remuneration; Novartis: Consultancy, Honoraria, Other: Remuneration, Research Funding; AOP Orphan Pharmaceuticals: Consultancy, Research Funding. Vannucchi:Incyte: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Italfarmaco: Membership on an entity's Board of Directors or advisory committees; CTI BioPharma: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau.

Kurzfassung: We collected 1500 patients with myeloproliferative neoplasms (MPN) and arterial or venous thrombosis (935/565), pooling three independent cohorts previously reported. Long-term treatment with antiplatelet drugs or vitamin K-antagonists (VKA) was given to 1391 (92.7%) patients; 975 (65%) patients received hydroxyurea (HU). We recorded 348 recurrences (venous in 142 cases) over 6075 patient-years, with an incidence rate of 5.7 per 100 pt-years (95% CI 5.1–6.4). The site of the first thrombosis predicted the site of recurrence. Independent factors influencing the rate of novel arterial thrombosis were HU (HR 0.67, 95% CI 0.46–0.98), antiplatelet treatment (HR 0.54, 95% CI 0.35–0.82), and VKA (HR 0.58, 95% CI 0.35–0.96). On the contrary, the recurrence of venous thromboses was significantly diminished only by VKA (HR 0.60, 95% CI 0.37–0.95), while HU prevented late but not early recurrences after venous thrombosis at common sites. Of note, we failed to demonstrate a positive effect of HU in the prevention of recurrent splanchnic vein thrombosis. In conclusion, in MPN patients, HU plays a role in the prevention of arterial thrombosis, together with aspirin and VKA, whereas its action in the prevention of recurrent venous thrombosis is uncertain. Such findings call for future studies to optimize and personalize secondary prophylaxis after MPN-related thrombosis.