Abstract
Thrombosis is the largest contributor to morbidity and mortality in patients with polycythemia vera (PV) and essential thrombocythemia (ET). Our understanding of the risk factors and pathophysiology of thrombosis in PV and ET patients is developing, including recent insights into the role of aberrant platelet-neutrophil interactions, JAK2 mutated endothelial cells and the pro-thrombotic inflammatory milieu. To date, few available therapies have demonstrated the ability to reduce the thrombotic burden in patients with these diseases. Although numerous therapeutic agents have been investigated in both PV and ET patients, few studies are designed to assess their impact on thrombotic events. In this review, we first describe the burden of thrombosis in patients with these myeloproliferative neoplasms (MPNs) and briefly explore their pathophysiologic mechanisms. We then critically assess and summarize the evidence behind currently available therapies with attention toward thrombotic endpoints. Finally, we describe a path forward for clinical research in MPNs that involves surrogate endpoint validation, biomarker development, and clinical trial design strategies in order to accurately assess reduction of thrombotic events when evaluating novel therapies.
Highlights
Polycythemia vera (PV) and essential thrombocythemia (ET) are BCR-ABL1 negative myeloproliferative neoplasms (MPNs)
The annual incidence of thrombosis after MPN diagnosis is highly dependent on age
This study developed a prognostic model which is frequently used entitled the International Prognostic Score for Thrombosis in Essential Thrombocythemia (IPSET-thrombosis), which considers age > 60, cardiovascular factors, previous thrombosis, and JAK2V617F mutation [10]
Summary
Polycythemia vera (PV) and essential thrombocythemia (ET) are BCR-ABL1 negative myeloproliferative neoplasms (MPNs). In ET, the rate of arterial and venous thrombosis after diagnosis is approximately 1.2% and 0.6% per year, respectively [6] This incidence of thrombosis is higher than the general population, as demonstrated by a population-based Swedish study where 1-year cumulative incidence was three times and the 5-year cumulative incidence was two times higher in patients with MPNs as compared with the general population. The degree of elevation of the platelet count has not been shown to be predictive of developing a thrombotic event, a higher platelet count is associated with bleeding events secondary to developing acquired von Willebrand syndrome [12] Treatment in both PV and ET involves cytoreduction for high-risk patients, with a number of therapies which will be described in detail.
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