Rumi, Elisa

Abstract Philadelphia-negative Myeloproliferative Neoplasms (MPN), including Polycythemia Vera (PV), Essential Thrombocythemia (ET), Myelofibrosis (Primary [PMF] and secondary to PV and ET [PPV-, PET-MF] and unclassified MPN (U-MPN), are associated with an increased risk of venous thrombosis in unusual sites, such as splanchnic vessels (SVT). SVT can lead to complications such as portal hypertension, esophageal and gastric varices, ascites,hepatic failure and biliopathy. According to a meta-analysis MPN is the underlying cause of portal vein thrombosis (PVT) in 31.5% and Budd Chiari syndrome (BCS) in 40.9% of cases (Smalberg, 2012); a more in-depth analysis of clinical characteristics and evolution of MPN-associated SVT has been hampered by heterogeneity of cohorts comprising small number of cases. We conducted a retrospective multicenter study in patients (pts) with SVT associated with WHO2008-diagnosed MPN, with the aim to describe patient characteristics, disease course and prognostic factors with potential implications for clinical practice. Data were collected from 16 international hematologic centers in the framework of the Italian AGIMM and the IWG-MRT groups. We collected 519 cases of pts with PVT, splenic or mesenteric vein thrombosis (75.1%) and BCS (24.9%) associated with MPN. We used as comparator a cohort of 1686 controls (Ctr) represented by MPN without (w/o) SVT: 741 ET (43.9%), 684 PV (39.7%), 261 PMF (15.5%). Frequency of MPN associated with SVT was 37.8% ET (n=196), 36.8% PV (n=191), 15.4% MF (n=80), 10% U-MPN (n=52). Median follow-up was 89.9 months (mo) (range 0.5-430). For SVT vs Ctr group females were 54.5% vs 44.4% in PV (P=0.001), 68.4 vs 63.5% (p=0.13) in ET, 63.7% vs 29.1% in PMF (p<0.0001); median age at MPN diagnosis (dg) was 43.5 yr (range 12-90) vs 60.6 yr (range 12-93) (p<0.0001). Age at SVT dg was 44 yr (range 15-85). In 240 cases (46.7%) MPN and SVT dg were coincident, in 121 (23.6%) SVT occurred before MPN dg (median 26 mo, range 4-307) and in 153 (29.8%) during MPN follow up (median 68 mo, range 4-362). JAK2V617F mutation was found in 94% PV vs 94% in Ctr, 84% vs 61% ET (p<0.0001), 88.1% vs 68% PMF (p=0.006) and in 93% U-MPN. Erythropoietin-independent colonies (EEC) were evaluated in 111 SVT pts and found in 80 (72%), accounting for 38/48 PV (79%), 31/44 ET (70.5%), 9/12 PMF (75%) and 2/7 U-MPN (28.6%). At dg, SVT PV pts had lower hemoglobin levels than Ctr: median was 17.4 g/dL vs 18.5 g/dL (p<0.0001) in male, 16.9 g/dL vs 17.7 g/dL (p=0.0006) in female. A co-existing thrombophilic status was found in 38.5% SVT vs 11.8% of Ctr (p<0.0001). Recurrent SVT occurred in 12.2% of pts with a rate of 1.6% person/year (CI 1.2-2.1); risk of venous thrombosis other than SVT was increased in SVT group vs Ctr (p=0.02), with no difference for arterial thrombosis. Hemorrhage was more frequent in SVT group (32%) vs Ctr (7.2%)(p<0.0001), mainly related to esophageal varices, which were present in 66.9% of SVT pts. There was no difference in evolution to MF and acute leukemia (AL) for PV and ET pts with and w/o SVT, while risk of AL was lower in MF with SVT (p<0.00001). Overall survival was shorter in ET pts with SVT vs Ctr (p<0.0001). In PMF survival was better in SVT group (p<0.00001) and was associated with a higher proportion of SVT pts in lowest risk categories: IPSS low 65%, intermediate-1 20%, intermediate-2 10% and high 5% compared with 15%, 34%, 25% and 26% in Ctr group. At last FU, 79/519 pts (15.2%) had died; causes of death were evolution to AL (15.4%), other cancers (13.8%), disease progression without AL (10.8%), SVT (10.8%), hepatic failure and venous thrombosis other than SVT (7.7% each), heart failure and arterial thrombosis (6.2% each), hemorrhage (5.5%), renal failure and infection (4.6% each). Therapy after SVT included anticoagulation in 77%, antiaggregant in 21.2% and combination in 1.8%; 70% received cytotoxic drugs; 12.4% were treated with transjugular porto-systemic shunt. Beta blocker therapy was used in 48.5% of pts and correlated with improved survival (p=0.041) MPN associated with SVT correlated with younger age and female sex and might antedate the clinical phenotype in a quarter of the patients. MPN-associated SVT equally affected PV and ET, was more likely to occur in the presence of JAK2V617F or underlying thrombophilia and predicted recurrent venous but not arterial thrombosis. The apparent association of SVT with better or worse prognosis in PMF and ET, respectively, requires further investigation. Disclosures No relevant conflicts of interest to declare.

AbstractMyeloproliferative Neoplasms (MPN) course can be complicated by thrombosis involving unusual sites as the splanchnic veins (SVT). Their management is challenging, given their composite vascular risk. We performed a retrospective, cohort study in the framework of the International Working Group for MPN Research and Treatment (IWG‐MRT), and AIRC‐Gruppo Italiano Malattie Mieloproliferative (AGIMM). A total of 518 MPN‐SVT cases were collected and compared with 1628 unselected, control MPN population, matched for disease subtype. Those with MPN‐SVT were younger (median 44 years) and enriched in females compared to controls; PV (37.1%) and ET (34.4%) were the most frequent diagnoses. JAK2V617F mutation was highly prevalent (90.2%), and 38.6% of cases had an additional hypercoagulable disorder. SVT recurrence rate was 1.6 per 100 patient‐years. Vitamin K‐antagonists (VKA) halved the incidence of recurrence (OR 0.48), unlike cytoreduction (OR 0.96), and were not associated with overall or gastrointestinal bleeding in multivariable analysis. Esophageal varices were the only independent predictor for major bleeding (OR 17.4). Among MPN‐SVT, risk of subsequent vascular events was skewed towards venous thromboses compared to controls. However, MPN‐SVT clinical course was overall benign: SVT were enriched in PMF with lower IPSS, resulting in significantly longer survival than controls; survival was not affected in PV and slightly reduced in ET. MPN‐U with SVT (n = 55) showed a particularly indolent phenotype, with no signs of disease evolution. In the to‐date largest, contemporary cohort of MPN‐SVT, VKA were confirmed effective in preventing recurrence, unlike cytoreduction, and safe; the major risk factor for bleeding was esophageal varices that therefore represent a major therapeutic target.

Abstract Abstract 277 Background: Current information on the natural history of polycythemia vera (PV) is mostly derived from early studies based on the PV Study Group diagnostic criteria. The World Health Organization (WHO) diagnostic approach to PV is currently the gold standard. The main objective of the current study was to describe survival, disease complication rates and risk factors in WHO-defined PV. Methods: Under the auspices of an International Working Group, seven international centers of excellence for myeloproliferative neoplasms submitted a total of 1,430 patients, locally diagnosed with “WHO-defined PV”. The two principle investigators (AT and TB) reviewed all the cases and selected 1,263 patients who were age 18 years or older, diagnosed after 1970, and whose submitted data included diagnostically essential information. Results I: Presenting Features: Median age was 60 years (range, 18–95; 51% females). The number of patients diagnosed between 1970–1990, 1991–2000, and 2001–2011 were 136 (11%), 337 (27%) and 790 (62%), respectively. Arterial/venous thrombosis history before or at diagnosis was documented in 142/73 and 80/42 patients, respectively. Other features at diagnosis included pruritus (37%), microvascular disturbances (29%), palpable splenomegaly (37%), abnormal karyotype (13%), and leukoerythroblastosis (6%). History of hypertension (45%), hyperlipidemia (17%), diabetes (9%), and tobacco use (15%) was also obtained. Results II: Clinical Course: To date, 228 (18%) deaths, 42 (3%) leukemic progressions, and 101 (8%) fibrotic transformations have been recorded. Post-diagnosis arterial or venous thrombosis occurred in 139 (11%) and 85 (7%) patients, respectively. Cytoreductive therapy had not been used in 342 (27%) patients whereas 154 (12%) patients were exposed to two or more cytoreductive drugs. Results III: Risk Factors: Multivariable analysis identified advanced age, leukocytosis, venous thrombosis history and abnormal karyotype as significant (p<0.01) risk factors for overall survival (OS). Receiver operating characteristic (ROC) plots delineated ages 69 (AUC 0.83) and 59 (AUC 0.61) years and leukocyte count 13 × 109/L (AUC=0.61) as the best discriminant levels in this regard; HR (95% CI) were 11.4 (7.7–16.9) for age ≥70 years, 3.8 (2.6–5.7) for age 60–69 years, and 2.0 (1.5–2.6) for leukocyte count ≥15 × 109/L. Results IV: Risk Stratification: HR-based risk scores were assigned to age ≥70 years (3 points), age 60–69 years (2 points) and leukocyte count ≥15 × 109/L (one point), in order to create four risk groups: low (zero points; n=492; median survival 322 months), intermediate-1 (one or 2 points; n=353; median survival 208 months; HR 3.8, 95% CI 2.5–5.8), intermediate-2 (3 points; n=286; median survival 132 months; HR 10.7, 95% CI 6.9–16.5), and high (4 points; n=56; median survival 90 months; HR 22.7, 95% CI 13.9–37.1) (Figure 1). Similar results were obtained when analysis was restricted to the 1,011 JAK2 mutation-positive patients (Figure 2). The particular risk model was equally robust in predicting leukemia-free survival (p=0.001). Conclusions: Age and leukocyte count matter the most in predicting survival in PV. The current study suggests additional prognostic value from karyotype and venous thrombosis history. Disclosures: Vannucchi: Novartis: Honoraria. Gisslinger:Novartis: Speakers Bureau; Celgene Austria: Speakers Bureau; AOP-Orphan: Speakers Bureau.

Abstract Abstract 5148 INTRODUCTION. Patients presenting with a clinical picture of essential thrombocythemia (ET) can actually have an early/prefibrotic myelofibrosis (PMF), according to current WHO criteria, in about 18% of cases. Laboratory tests which are significantly different in early/prefibrotic PMF as compared with histologically confirmed ET (WHO-ET) include decreased gender-matched hemoglobin (Hb), increased white blood cell (WBC), platelet (PLT) counts and lactate dehydrogenase (LDH) values. AIM. To evaluate sensitivity (SE) and specificity (SP) of blood cell counts and LDH, at presentation, for the diagnosis of early/prefibrotic PMF vs. WHO-ET. METHODS. Five hundred thirty-six cases (50%) who had complete laboratory data measured at diagnosis constituted the exploratory set of our study and were derived from an international ET database. The discriminatory ability of Hb, WBC, PLT and LDH in correctly classifying patients in the early/prefibrotic PMF or WHO-ET groups was initially tested by plotting their Receiving Operating Characteristic (ROC) curves and comparing the relative Areas Under the Curve (AUC) with the value of 0.50 (which stands for the completely useless of the test). Three parameters with statistically significant discriminatory power were chosen (Hb, WBC and LDH) and thresholds searched in order to guarantee at least 90% of SE or SP. Finally, a diagnostic algorithm was designed. The validation set of this analysis was constituted by 321 patients with WHO-ET (n=62) or early/prefibrotic PMF (n=259) diagnosed by the same pathologist who confirmed the training set cohort and collected in the Institute for Pathology, University of Cologne, Germany. SE and SP for the same parameters and thresholds as well as the final diagnostic algorithm were applied to this set of patients to demonstrate the results' reproducibility. RESULTS. Sensitivity and specificity to recognize early/prefibrotic PFM have been evaluated by ROC curves. The best performance was found for LDH (AUC = 0.7059). WBC and Hb had super imposable curves, with AUC of 0.6279 and 0.6257, respectively. The worst performance was registered for PLT count: its AUC was only 0.5628, not significantly different from the reference value of 0.50 (p=0.154). Thresholds of Hb, WBC and LDH were searched to achieve at least 90% of SE or SP. HB < 12 g/dL for women or <13 g/dL for men, and WBC >= 13 x109/L had higher SP (92% and 91%, respectively). High SP is highly related to the presence of early/prefibrotic PMF (true positives). On the contrary, LDH < 200 mU/mL and WBC < 7 x109/L had good sensitivity (91% and 94%, respectively). High SE is highly related to the absence of early/prefibrotic PMF (true negatives). By applying these SE and SP values in a step-by-step algorithm, nearly half of patients (48%) could be classified as WHO-ET or early/prefibrotic PMF, assuming at each step a margin of error of less than 10%. For the remaining 50% of patients, laboratory results didn't allow to suspect or exclude the presence of early/prefibrotic PMF. In the validation set of 321 patients classified by WHO 2008 as true ET or early/prefibrotic PMF (Cologne cohort) SP of anemia was 84%, WBC < 7 x109/L or >= 13 x109/L had 91% and 81% of SE and SP, respectively. LDH values < 200 mU/mL had 85% of SE. By applying the same flow-chart, 46% of patients were classified as WHO-ET or early/prefibrotic PMF. CONCLUSIONS. The present study provides clinicians with laboratory parameters that should increase suspicion of early/prefibrotic PMF in a patient with a working clinical diagnosis of ET. In fact, while patients presenting clinically with ET can now be discriminated as true ET or early/prefibrotic PMF by adopting the WHO 2008 criteria that require bone marrow histology, an algorithm including baseline anemia, WBC count and LDH, allows this differentiation in about 50% of patients with a good approximation. However, for a definitive proof, bone marrow histology is still an integral part for final diagnosis. Disclosures: Vannucchi: Novartis: Honoraria.

Abstract Abstract 3891 Poster Board III-827 Age over 65 years, hemoglobin level lower than 10 g/dL, WBC count greater than 25 × 109/L, peripheral blood blasts equal to or greater than 1%, and presence of constitutional symptoms provide a reliable prediction of survival in patients with primary myelofibrosis (PMF) at diagnosis [Cervantes et al. Blood. 2009 Mar 26;113(13):2895-901]. In fact, based on the presence of 0 (low risk), 1 (intermediate risk-1), 2 (intermediate risk-2) or greater than or equal to 3 (high risk) of the above factors, 4 risk groups with no overlapping in their survival curves were defined. To investigate whether the acquisition of these prognostic factors during follow-up may predict survival anytime, we studied 525 PMF patients regularly followed at each participating Institution from 1980 to 2008. The study was carried out within the IWG-MRT, and an ad hoc database was developed for data collection. Patients with post-polycythemia vera and post-essential thrombocythemia myelofibrosis, and patients with pre-fibrotic myelofibrosis were excluded from this study. Overall, 68 patients (26% of subjects who were below the age of 65 at diagnosis) passed the 65-year age threshold during the study period, 158 (47% of patients without this risk factor at diagnosis) developed anemia, 72 (15% of patients without this risk factor at diagnosis) presented marked leukocytosis, 102 (27% of patients without this risk factor at diagnosis) had more than 1% peripheral blast cells, and 54 (14% of patients without these symptoms at diagnosis) had constitutional symptoms. All variables resulted significant when analyzed as time-dependent covariates in a multivariable Cox proportional hazard regression model, and all of them were therefore included in the subsequent models. Each variable was assigned an integer weight close to the corresponding hazard ratio (HR), and the sum of values obtained was used to allocate the patients into 4 risk categories (low, intermediate-1, intermediate-2, high). We developed 2 separate models, one for all patients (DIPSS) and the other one for patients below the age of 65 (age-adjusted DIPSS), both applicable during the course of the disease. Cumulative survival can be estimated with the Kaplan Meier method. The increased risk of death when changing risk category was estimated as HR. According to DIPSS, the HR was: 4.13 (95% CI: 1.73-9.82; P < .001) if the risk category shifted from low to intermediate-1, 4.61 (95% CI: 3.18-9.82; P < .001) from intermediate-1 to intermediate-2, and 2.54 (95% CI: 1.94-3.31; P < .001) from intermediate-2 to high. According to age-adjusted DIPSS, the HR was 3.97 (95% CI: 1.5-10.5, P = .005) if the risk category shifted from low to intermediate-1, 2.84 (95% CI: 1.46-5.54; P = .002) from intermediate-1 to intermediate-2, and 1.81 (95% CI: 1.08-3.04; P = .025) from intermediate-2 to high. In conclusion, this study shows that age over 65 years, hemoglobin level lower than 10 g/dL, WBC count greater than 25 × 109/L, peripheral blood blasts equal to or greater than 1%, and the presence of constitutional symptoms predict survival independently and in a time-dependent manner in patients with PMF. Both DIPSS and age-adjusted DIPSS allow a reliable prognostic assessment of PMF patients at any time during the clinical course of the disease, and are therefore useful for clinical decision making. Disclosures: No relevant conflicts of interest to declare.

Abstract Survival of patients with primary myelofibrosis (PMF) is highly variable, ranging from months to even decades. Although treatment of PMF remains mostly palliative, the increasing use of allogeneic hemopoietic stem cell transplantation and introduction of newer therapies has raised the need for a better prognostic stratification of these patients. The initial features of 1,054 patients (638M/416F; median age 64 years, range 10–90) consecutively diagnosed with PMF in seven institutions from Europe and USA between 1980 and 2007 were evaluated for prognostic significance. Patients with the so-called “pre-fibrotic” form of PMF were not considered. The variables assessed were those previously shown to be of prognostic value in PMF, those clinically meaningful, and possible confounders (namely, diagnostic period and series of origin). The effect of the potential prognostic factors on survival was evaluated by the Cox proportional hazards regression and the proportional hazards assumption checked in every model by graphical methods and the Grambsch-Therneau test. A prognostic model was identified through a stepwise selection process, based on a z-test of the regression coefficients, and evaluated by calculating its discriminating power (measured by Harrell’s C concordance index), as compared to that of current PMF prognostic systems, and its positive predictive accuracy for actual survival longer (or shorter) than definite periods of time from diagnosis. The replicability of both the prognostic variables and the new prognostic score was tested by bootstrap re-sampling, in which 1,000 samples of the same size than the original series were built by random extraction with reposition. Median survival of the overall series was 69 months (95% CI: 61–76), with 49% of patients having died at the time of study. At multivariate analysis, five initial variables were associated with shorter survival: age > 65 years, constitutional symptoms (weight loss, fever, sweats), Hb < 10 g/dL, leukocyte count > 25×109/L, and blood blasts 1%. The hazard ratios of these variables did not differ substantially, ranging from 2.89 (95% CI: 2.46–3.61) for Hb < 10 g/dL to 1.80 (95% CI: 1.50–2.17) for blood blasts 1% and, therefore, one point was assigned to each one. Based on this, among the 1,001 patients of the series with all the necessary data available, four risk groups were identified with no overlapping in the 95% CI of their survival curves (figure): low risk (no factor, 22% of patients; median survival 135 months); intermediate risk-1 (one factor, 29% of patients; median survival 95 months); intermediate risk-2 (two factors; 28% of patients; median survival 48 months); and high risk (three factors, 21% of patients; median survival 27 months). The new prognostic score showed high predictive accuracy and replicability and had higher discriminating power than current risk-based PMF classifications. In the 409 patients with assessable metaphases, presence of cytogenetic abnormalities (observed in 30% of cases) was associated with shorter survival and contributed to prognosis, but only in patients in the intermediate-risk groups. No prognostic influence for either JAK2 V617F mutational status (n= 345) or blood CD34+ cell count (n= 150) was noted. This new prognostic scoring system substantially improves existing risk-based classifications of PMF and may help in treatment-decision making and in the design and analysis of newer therapies for the disease. Figure Figure

Abstract BACKGROUND. In primary myelofibrosis (PMF), survival from time of diagnosis is predicted by the international prognostic scoring system (IPSS), and from time of referral, by the dynamic IPSS (DIPSS) or DIPSS-plus. JAK2/CALR/MPL mutational status and presence and number of other prognostically-relevant mutations (ASXL1, SRSF2, EZH2, IDH1/2) provide IPSS/DIPSS-plus independent prognostic information. The objective in the current study was to revise IPSS, by including mutation-relevant prognostic information. METHODS. The study included 986 PMF patients divided into learning (n=588) and validation (n=398) cohorts. Previously published methods were used to screen for mutations involving JAK2,MPL, CALR, EZH2, ASXL1, IDH1/2 and SRSF2. The clinical variables assessed were those previously identified as being prognostically-relevant by IPSS or DIPSS-plus. The prognostic model (MIPSS) was developed through a stepwise selection process, based on a z-test of the regression coefficients, and its relative quality was measured by means of the Akaike information criterion. RESULTS. In the Italian learning cohort (n=588),median follow-up was 3.6years (95% CI, 0.03-30.8) for alive patients and 196 (33.3%) deaths and 67 leukemic transformations were documented. IPSS risk distribution was low in 26%, intermediate-1 in 30%, intermediate-2 in 24% and high in 20%. Mutational frequencies were approximately 63% for JAK2, 20% CALR, 6% MPL, 7% EZH2, 22% ASXL1, 2.5% IDH1/2 and 9% SRSF2. Constitutional symptoms were recorded in 28.6% of patients, splenomegaly 75% (18% >10cm from LCM) and grade 3 fibrosis 21%. Overall 252 patients were evaluable for karyotype and abnormalities were detected in 35%, including 9.5% unfavorable. Univariate analysis identified the following risk factors for inferior survival: age >60 years, constitutional symptoms, hemoglobin <100g/L, leukocytes >25x109/L, platelets <200x109/L, circulating blasts 1% or greater, splenomegaly >10cm, grade 3 fibrosis, unfavorable karyotype, triple-negativity for JAK2, MPL and CALR (TN), JAK2 or MPL mutation, and mutations in ASXL1, SRSF2, EZH2 or IDH1/2. In multivariable analysis, age >60 years, constitutional symptoms, hemoglobin <100g/L, platelets <200x109/L, TN, JAK2 or MPL mutation, ASXL1 and SRSF2 mutation remained significant; these variables were subsequently assigned the following HR-weighted adverse points: 1.5, 0.5, 0.5, 1.0, 1.5, 0.5, 0.5 and 0.5, respectively. Subsequently, four risk groups with no overlap in the 95% CI of their survival curves were delineated (Figure 1A): low (score 0-0.5); Intermediate-1 (score 1-1.5); Intermediate-2 (score 2-3.5); and high (score 4 or greater). The number of patients in each risk category, median survivals and HR and 95% CI values are included in figure 1A. Akaike information criterion indicated that MIPSS performed better than IPSS in predicting survival (1611.6 vs 1649.0). Leukemia-free survival was also predicted by high (p<0.01) and intermediate 1/2 (p<0.01) risk MIPSS. In the Mayo Clinic validation cohort (n=398), median age 63 years; males 64%,median follow-up for alive patients was 7.5 years and 271 (68%) deaths and 51 (13%) leukemic transformations were documented. DIPSS-plus risk distribution was low in 13%, intermediate-1 18%, intermediate-2 37% and high 32%. Mutational frequencies were approximately 51% for JAK2, 30% CALR, 7.5% MPL, 5% EZH2, 36% ASXL1, 5.6% IDH1/2 and 13% SRSF2. MIPSS performed equally well in this cohort, as illustrated in figure 1B, which includes number of patients in each risk category with their median survival and HR and 95% CI values. Leukemia-free survival in the Mayo cohort was also predicted by high (p<0.01) and intermediate-2 (p=0.04) risk MIPSS. Patients in the Mayo cohort were fully annotated for karyotype, which was MIPSS-independent in its prognostic value for both overall (p<0.01) and leukemia-free (p<0.01) survival. CONCLUSIONS. MIPSS addresses the mutation-relevant prognostic information gap in IPSS and performs equally well in the setting of patients seen at time of diagnosis or referral. Karyotype carries MIPSS-independent prognostic value that is recognized in an alternative GIPSS prognostic model (see accompanying ASH 2014 abstract), which complements MIPSS. Figure 1 Figure 1. Disclosures No relevant conflicts of interest to declare.

Abstract Abstract 1746 Diagnosis of essential thrombocythemia (ET) has been updated in the last World Health Organization (WHO) classification, that provides a guideline to distinguish ET from early/prefibrotic primary myelofibrosis. These two conditions differ in term of disease evolution and survival (Barbui et al, J. Clin. Oncol. 2011). To design a prognostic model for survival in WHO-defined ET (International Prognostic Score for Essential Thrombocythemia, IPSET), we studied 891 patients with strict WHO diagnostic criteria. Demographics have been presented elsewhere (Barbui et al, J. Clin. Oncol. 2011). We tested the prognostic impact on survival of age, prior thrombosis, leukocyte count, platelet count, hemoglobin level, JAK mutational status, splenomegaly. Harrell's C concordance statistics were used to set the best cutoff levels of continuous variables in order to predict survival. Univariate Cox proportional hazard regression showed that age over 60 years (P<.0001), leukocyte count greater than 11 x109/L (P<.0001), anemia (P=.04), platelet count greater than 1000 x109/L (P<.004) and prior history of thrombosis (P< 0001) were significant risk factors for survival. Age over 60 years (hazard ratio-HR- 6.5, 95% CI: 3.9–10.7; P<.0001), leukocyte count greater than 11 × 109/L (HR: 3.1, 95% CI: 2–4.7; P<.0001) and prior history of thrombosis (HR: 2.9, 95% CI: 1.9–4.5; P< 0001) retained statistical significance on survival by multivariable analysis and were included in the new prognostic model. We assigned each factor an integer weight close to the corresponding HR in the multivariable Cox regression: weight 2 for age over 60 years; weight 1 for leukocyte count greater than 11 x109/L and for prior thrombosis. Finally, we defined the IPSET score by allocating patients into three risk categories with significantly different survival according to the sum of weights: low risk (sum of weights=0; n= 342; median survival not reached), intermediate risk (sum=1-2; N=374; median survival 24.5 years), and high risk (sum=3-4, n=158; median survival 13.8 years). Fisher exact test did not reveal a difference in the distribution of the causes of death among IPSET categories. We validated the model in two independent cohorts: one from Germany (132 WHO-defined ET) and another from France (234 ET patients not strictly diagnosed according to WHO). Log rank test and Cox regression showed significant differences in term of survival among IPSET categories in both series. Finally, we designed an age-specific IPSET model for patients younger than 60 years (IPSET-y). Using the same methodology, we found that age over 45 years (weight 2), leukocyte count greater than 11 × 109/L (weight 1) and prior history of thrombosis (weight 1) were independent risk factors for survival. IPSET-y defined three risk categories (LR, sum=0; IR, sum=1-2; HR, sum=3–4) with a median survival not reached in LR and IR, and of 22.3 years in HR. In conclusion, IPSET, based on age over 60 years, leukocyte count greater than 11 x109/L and history of thrombosis allows prognostic assessment of WHO-defined ET. The validation process makes IPSET applicable in all patients phenotypically appearing as ET. IPSET models may be useful for treatment decision-making. Disclosures: Vannucchi: Italfarmaco: Consultancy; Novartis: Honoraria. Gisslinger:AOP Orphan Pharmaceuticals AG: Research Funding.

Abstract Abstract 3846 INTRODUCTION There is strong evidence indicating that the clear-cut separation of prefibrotic primary myelofibrosis (PMF) from essential thrombocythemia (ET) by consequent application of the World Health Organization (WHO) 2008 criteria is reflected in different, well defined clinical pictures and divergent prognoses (Barbui et al, JCO 2011,Thiele et al, Blood 2011). Very recently the specific risk profile for arterial and venous thrombosis in WHO- diagnosed ET was published (Carobbio et al, Blood 2011). In PMF so far all published data on vascular events were exclusively based on overt disease manifestations until now there are no data available regarding prefibrotic stages. Consequently, we aimed to evaluate the corresponding risk profile of patients with WHO-diagnosed prefibrotic PMF. METHODS A total number of 264 patients with WHO-defined prefibrotic PMF derived from either the Medical University of Vienna or an International Database (Barbui et al, JCO 2011) were studied. Nonfatal thrombotic events considered in this study were reported as rates per 100 patient-years and included transient ischemic attacks, thrombotic cerebrovascular accidents, coronary artery disease, myocardial infarction, peripheral arterial disease, deep vein thrombosis of peripheral vasculature, pulmonary embolism, and abdominal large vein thrombosis. Cardiovascular risks factors considered, comprised of arterial hypertension, diabetes mellitus and tobacco use. To evaluate risk factors for total thrombosis and for arterial and venous events in particular multivariate Cox- regression analysis including the co-variables sex, age, previous thrombotic event, laboratory parameters measured at diagnosis and need for cytoreductive and/or antiplatelet therapy during follow-up was calculated. P values less than 0.05 were considered as statistically significant. RESULTS After a median follow- up of 5.8 years (range0.0 – 27.2), the total rate of non fatal thrombotic events was 2.1% patient-years (95% CI, 1.5–2.8); the incidence of arterial events was higher (1.7% patient- years) than of venous events (0.6% patient-years).Considering thrombosis in general a higher white blood cell (WBC) count enhances the risk significantly (p=0.005; HR 1.15). This is also true in arterial events in particular (p=0.047; HR 1.12). A lower platelet count is associated with a higher risk for thrombotic events; for thrombosis in general this association is of borderline significance (p=0.056; HR 0.99), for arterial thrombosis in particular of significance (p= 0.042; HR 0.99). A lower hemoglobin level is associated with a higher risk for venous thrombosis (p=0.007; HR 0.59). CONCLUSION Leukocytosis appears as a risk factor for thrombosis in general and also for arterial thrombosis in particular in WHO-diagnosed prefibrotic PMF. Moreover, higher platelet counts seem to decrease significantly the risk for thrombotic events in general and arterial thrombosis in particular. Anemia is associated with a higher risk for venous thrombosis. These observations are partly in line with recently published findings in WHO-diagnosed ET (Carobbio et al,2011) and might indicate the existence of a specific risk profile for thrombotic events in prefibrotic PMF. This is the first study reporting data on the risk profile for thrombosis in WHO-diagnosed prefibrotic PMF. Certainly these findings ask for validation in a larger patient population. Disclosures: Gisslinger: Novartis: Speakers Bureau; Celgene Austria: Research Funding, Speakers Bureau; AOP-Orphan Pharmaceuticals AG: Speakers Bureau. Vannucchi:Novartis: Honoraria.

Abstract Abstract 457 Introduction- The 2008 World Health Organization (WHO) diagnostic criteria for myeloproliferative neoplasms (MPN) underscore the role of bone marrow (BM) morphology in distinguishing essential thrombocythemia (ET) from early, and at times prefibrotic, primary myelofibrosis (PMF) that clinically presents like ET. The value of such a distinction in predicting clinical outcome has been questioned by some investigators. Study Design- Clinician scientists and hematopathologists from seven international centers of excellence for ET convened to design a clinicopathologic database of patients locally diagnosed and treated as ET. Study eligibility criteria included availability of treatment-naïve BM specimens obtained within one year of diagnosis. All bone marrows subsequently underwent a central blinded re-review by the author of the pertinent WHO chapter (JT) who applied strict WHO guidelines to identify cases of early PMF that were spuriously diagnosed as ET. Results- Revision of the BM biopsies according to the WHO morphological criteria confirmed ET in 891 patients (81%). Diagnosis was revised to early, prefibrotic PMF in 180 patients (16%). The remaining 33 (3%) BM specimens were qualitatively inadequate for accurate classification or represented unclassified cases. i) At presentation, early PMF, as opposed to true ET, was characterized by higher leukocyte (p<0.0001) and platelet (p=0.002) counts, lower hemoglobin (p=0.01) and hematocrit (p=0.001) levels, higher serum lactate dehydrogenase level (p<0.0001), higher circulating CD34+ cell count (p=0.03) and higher rate of palpable splenomegaly. JAK2V617F mutational frequency was 60% in each of the two groups. ii) Median follow-up was 6.2 years for ET and 7.0 years for early PMF. During this period, the rates of arterial (1.2-1.4% patients/year) and venous (0.6 patients/year) thrombotic complications were similar in the two groups. However, patients with early PMF, as compared to those with ET, were more likely to develop overt myelofibrosis (1% vs. 0.5% patients/year; RR=2.0, p=0.04) or acute leukemia (0.6% vs. 0.1% patients/year; RR=5.2, p=0.001). Cumulative leukemic transformation rate at 10 and 15 years was 0.7% and 2.1% in true ET versus 5.8% and 11.7% in PMF Similarly, survival was significantly worse in patients with early PMF (mortality rate: 2.7% vs. 1.3% patients/year; RR=2.1, p=0.002).The 10 and 15-years overall survival rates were: 89% and 80% in true ET versus 76% and 59% in PMF. On multivariable analysis, other risk factors for poor survival were age > 60 years (HR=6.3, p<0.0001), a leukocyte count of > 11×109/L (HR=2.13, p<0.0001) and history of thrombosis (HR=3.0, p<0.0001). Conclusions- The current study validates the clinical relevance of strict adherence to WHO criteria in the diagnosis of ET and provides seminal information on the survival and risk of leukemic transformation in strictly WHO-defined ET, which appears to be substantially better than previously assumed. Disclosures: No relevant conflicts of interest to declare.