Background Current risk stratification in Polycythemia Vera (PV), is designed to estimate the likelihood of thrombotic complications. In ECLAP large prospective study of 1638 PV cases diagnosed by Polycythemia Vera Study Group (PVSG) criteria, risk factors were age over 65 years and prior thrombotic events. After the JAK2V617F discovery, diagnosis has undergone substantial revision by the World Health Organization (WHO). Consequently, current risk factors determination should be described in patients diagnosed by the most recent recommendations and requires a large sample size with reliable and sufficiently long clinical course documentation. Accordingly, the current study includes 1545 patients with strictly WHO-defined PV diagnosed and followed-up in seven centers from Italy, Austria and the United States, belonging to the International Working Group for Myeloproliferative Neoplasm (MPN) Research and Treatment (IWG-MRT). Objective and design 1) Describe the rate of thrombosis in this population; 2) Report the sites and frequency of recurrences after a first arterial or venous event; 3) Identify separately risk factors for arterial versus venous thrombosis and develop practically useful prognostic models. Results 1. Presenting features The characteristics of the cohort recruited reflected well the heterogeneity of epidemiologic and clinical features that are found in the routine clinical practice of PV. Arterial and venous thrombosis history before or at diagnosis was documented in 246 (16%) and 114 (7.4%) patients, respectively. The frequencies of arterial and venous thrombosis were lower than those recorded in the ECLAP4 (27% and 11% respectively) but comparable to those reported in the recent Cyto-PV2 (arterial 17%, venous 12%) studies. The discrepancy might be partly related to earlier diagnosis in the post-ECLAP JAK2mutation era. 2. Thrombotic events after diagnosis Median follow-up was 6.9 years and treatment included aspirin (84%) and cytoreductive agents (73%), in addition to phlebotomy. Post-diagnosis total major thrombosis rate was 2.62% pt/yr, lower than reported in the ECLAP trial (4.4% pt/yr) but comparable to the Cyto-PV study (2.7% pt/yr) where management of cardiovascular risk factors was more intensive than in ECLAP. Arterial or venous thrombosis occurred in 184 (12%, rate: 1.59 % pts/yr) and 137 (9%, rate: 1.05 % pts/yr) patients, respectively. In addition, prior arterial events were associated in 75% of cases with subsequent arterial events and in the remaining 25% with venous thrombosis including splanchnic vein events. Moreover, patients with prior venous events had recurrences in venous district in 61% of cases and in the arterial district in 39%. 3. Risk factors for arterial versus venous thrombosis and prognostic models In multivariable analysis, arterial thrombosis was predicted by previous arterial event (HR 1.7, 95% CI 1.2-2.4), and hypertension (HR 1.6, 95% CI 1.2-2.2) while predictors of venous events were previous venous thrombosis (HR 2.6, 95% CI 1.5-4.4), and age ≥ 65 years (HR 1.7, 95% CI 1.2-2.5). We used the above-mentioned risk factors in order to develop prognostic models allowing to identify patients at different probability to develop arterial or venous thrombosis. For arterial thrombosis, the absence of previous arterial thrombosis and hypertension defined lower-risk (rate 1.27 % pts/yr) while the presence of one or both identified higher-risk patients (rate 2.04 % pts/yr). Previous venous event and/or age ≥ 65 years identified patients at higher risk of venous (rate 1.62 % pts/yr) thrombosis and, if absent, patients at lower risk (rate 0.78 % pts/yr). Conclusion The overall rate of thrombosis was half than in ECLAP and should be considered in future clinical trials. Of note, patients with a prior venous thrombosis had a more frequent subsequent recurrence in the venous district but a proportion of them (40%) had also arterial events; conversely, recurrences after previous arterial event were also registered in the leg and non-leg veins in 30 % of cases, indicating that in PV, venous and arterial thrombosis may share some common pathogenetic mechanisms. These findings may have practical implications and suggests antiplatelet therapy and anticoagulant therapy as the favorite choice to prevent arterial and venous thrombosis, respectively, but also suggests studies of antithrombotic drug combination. Disclosures No relevant conflicts of interest to declare.
Polycythemia vera (PV) is a chronic myeloproliferative disorder with a propensity to develop myelofibrosis, a condition named post polycythemia vera myelofibrosis (post-PV MF). Survival and prognostic factors after transition to MF remain to be defined. We studied 68 patients with post-PV MF to define survival and prognostic factors for survival at diagnosis of post-PV MF. We also developed a dynamic prognostic model to predict survival at any time from diagnosis of post-PV MF. The median interval between the diagnosis of PV and that of post-PV MF was 13 years (range, 4–29.6 years). Patients with post-PV MF were observed for 181 person-years of follow-up. At diagnosis of post-PV MF, 43 (63%) of 68 patients had less than 65 years. During the follow-up, the incidence of thrombosis was 42 × 1000 person-years (95% CI: 19–93.5) and the incidence of leukemia was 50.3 × 1000 person-years (95% CI: 26–115). The median survival was 5.7 years. Multivariable Cox proportional hazard regression including age, hemoglobin value, platelet count, leukocyte count, and spleen size, showed that hemoglobin < 10 g/dL (P < .001) and platelet count < 100 × 109/L (P= .026) were independent risk factors for survival. We stratified patients at diagnosis of post-PV MF, according to these factors, obtaining two risk groups with significantly different survival (P = .003): low risk (Hb > 10 g/dL and platelet count > 100 × 109/L) with a median survival of 7 years, and high risk (Hb < 10 g/dL or platelet count < 100 × 109/L) with a median survival of 2 years. The prognostic model retained significance after adjustment for age in a multivariable Cox proportional hazard regression (HR: 4.3, 95% CI: 1.6–11.4; P= .003). To assess whether this prognostic model may predict survival at any time from diagnosis of post-PV MF, we evaluated in a time-dependent analysis 64 patients who had longitudinal blood cell counts during follow-up. As first step, we evaluated univariate survival analysis with hemoglobin value < 10 g/dL and platelet count < 100 ×109/L as time-dependent covariates. Both time-dependent parameters affected survival (HR for hemoglobin 5.8, 95% CI: 2.2–15.2, P < 0.001; HR for platelets 4.5, 95% CI: 1.67-12, P=.002). As second step, we evaluated the prognostic model assessed at diagnosis as time-dependent covariate, to define whether the acquisition of one risk factor during follow-up may affect survival. The HR was 7.5 (95% CI: 2.4-23.4; P < .001). The time-dependent prognostic model retained statistical significance after adjustment for age (P < .001). In conclusion, in patients developing post-PV myelofibrosis, a prognostic model based on hemoglobin level < 10 g/dL and platelet count < 100 × 109/L may predict survival at diagnosis of post-PV MF and at any time thereafter.
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