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Introduction: The management to reduce risk of thromboembolic complications in polycythemia vera and essential thrombocythemia are well established, but for other conditions with elevated hemoglobin, hematocrit, or platelets there are no consensus regarding treatment and follow up.

Aims: To assess frequency of elevated blood values in patients with thromboembolic event, how many of these should be investigated further regarding myeloproliferative neoplasm and if the risk of recurrent event is depending on underlying condition.

Methods: Retrospective cohort study of 3931 adult patients in the county of Norrbotten, Sweden, with thromboembolism during 2017 and 2018.

Results: Of the 3931 patients, 1195 had either elevated Hb, HCT, or platelets fulfilling the 2016 revised WHO criteria for PV and ET, and out of these 411 should be evaluated regarding underlying myeloproliferative neoplasms. Unexplained thrombocytosis and secondary erythrocytosis were associated with the highest rate of recurrent event as well as the most inferior restricted mean survival time.

Conclusion: Elevated blood values are common in patients with thromboembolic event and the high risk of recurrent event and inferior restricted mean survival time in patients with unexplained thrombocytosis and secondary erythrocytosis implicates the importance of finding and managing the underlying condition.

Thromboembolic events and bleeding are known complications in essential thrombocythaemia (ET) and polycythaemia vera (PV). Using multiple Swedish health care registers, we assessed the rate of arterial and venous events, major bleeding, all-cause stroke and all-cause mortality in ET and PV compared to matched controls. For each patient with ET (n = 3141) and PV (n = 2604), five matched controls were randomly selected. In total, 327 and 405 arterial or venous events were seen in the group of ET and PV patients respectively. Compared to corresponding controls, the rate of venous thromboembolism, major bleeding and all-cause mortality per 100 treatment years was significantly increased among both ET (0.63, 0.79 and 3.70) and PV patients (0.94, 1.20 and 4.80). The PV patients also displayed a significantly higher rate of arterial events and all-cause stroke compared to controls. When dividing the cohort into age groups, we found a significantly higher rate of arterial and venous events in all age groups of PV patients, and the rate of all-cause mortality was significantly higher in both ET and PV patients in all ages above the age of 50. This study confirms that PV and ET are diseases truly marked by thromboembolic complications and bleeding.

Bleeding and thrombotic events are known complications in myeloproliferative neoplasms (MPNs), but few studies have exclusively focused on patients with myelofibrosis (MF). In this nationwide population-based study, we assessed the frequency of major bleeding, thrombotic events, and all-cause mortality in 1079 patients diagnosed with MF and 5395 matched controls using multiple Swedish health care registers. Major bleeding, arterial, and venous events were seen at a rate of 2.55, 2.59, and 1.06 events per 100 years, respectively, in patients with MF. Compared to controls, the rates of bleedings, arterial events, venous events, and mortality were increased, with hazard ratios of 3.78 (95% confidence interval [CI], 2.98-4.79; P < .001), 1.73 (95% CI, 1.40-2.12; P < .001), 2.75 (95% CI, 1.93-3.90; P < .001), and 3.92 (95% CI, 3.50-4.40; P < .001), respectively. Patients treated with JAK inhibitors (JAKis) had higher rates of major bleeding (5.33), arterial events (4.67), and venous events (1.56) than patients with no ongoing symptom–directed therapy (rates, 2.32, 2.15, and 0.79) or hydroxyurea (rates, 2.05, 2.35, and 1.27, respectively). The use of JAKis or low-molecular-weight heparin, previous arterial or venous events, and older age were identified as independent risk factors for new arterial or venous events. A previous venous event, higher leukocyte count at diagnosis, and ongoing JAKi treatment were associated with an increased risk of major bleeding. This study shows that patients with MF have higher rates of thromboembolic events and major bleeding than described in other MPNs, and thromboembolic complications and major bleeding diverge in the different treatment groups.