Background: Essential thrombocythemia (ET) is a myeloproliferative neoplasm characterized by elevated platelet counts and proliferation of mature megakaryocytes in the bone marrow. The quantitative and qualitative platelet alterations in ET may lead to increased risks of thrombosis and bleeding. Risk factors for thrombotic complications include age >60 years, prior history of venous or arterial thrombosis, JAK2 V617F mutation, and cardiovascular risk factors. The current management of ET with cytoreductive therapy is largely directed at lowering the risk of thrombotic complications. This study aimed to characterize patients with ET treated with cytoreductive therapy in real-world clinical practice.

Methods: Data were extracted from medical charts of patients with ET who were managed with cytoreductive therapy between June 1, 2011, and September 15, 2016, at participating community oncology/hematology clinics. Physician and patient characteristics, medical history, diagnostic tests and results, and signs and symptoms at ET diagnosis were reported descriptively.

Results: 50 hematologists and oncologists participated in the study. The participating physicians had a mean (SD) of 17.5 (7.3) years of practice, and treated a mean (SD) of 31.6 (22.4) patients with ET in the past 5 years. A total of 809 patients with ET who received cytoreductive therapy from the 50 hematologists and oncologists were included. Patients were predominantly white (75.4%) with a mean (SD) age of 68.7 (11.5) years, and 48.9% were male. The majority (81.1%) of patients were referred to the participating physicians. Physicians reported that 64.5% of patients were diagnosed using World Health Organization criteria. However, less than half (48.8%) of patients had undergone a bone marrow biopsy at the time of diagnosis. Overall, 708 (87.5%) patients underwent JAK2 mutation testing; among these patients, 512 (72.3%) were positive. Physicians also noted JAK2 exon 12 mutation testing in 24 (3.0%) patients, however, none were positive. Reflex CALR and MPL molecular testing was conducted in 26.3% of patients, with 7.0% and 4.6% positive, respectively. Per physician assessment, 41.7%, and 42.5% were low and high risk, respectively; risk category was unknown in 15.8% of patients. At diagnosis, 11.4% and 19.5% of patients had a history of arterial thrombosis and venous thrombosis, respectively, and 64.4% of patients had ≥1 cardiovascular risk factor (arterial hypertension, 28.2%; smoking, 26.9%; hypercholesterolemia, 26.5%; overweight, 23.6%; diabetes, 15.3%). The most common ET signs and symptoms were fatigue (53.2%), headache (20.4%), and splenomegaly (15.1%); 90.3% of patients had platelet counts ≥600 × 109/L and 55.9% had white blood cell counts ≥10 × 109/L. For their first-line cytoreductive therapy, 755 patients (93.3%) received hydroxyurea (HU), 30 (3.7%) anagrelide, 10 (1.2%) ruxolitinib, 10 (1.2%) pegylated interferon or interferon alfa, and 4 (0.5%) other.

Conclusions: Patients with ET receiving cytoreductive therapy had substantial clinical burden of disease (eg, symptoms, elevated blood counts) at the time of diagnosis. Furthermore, a large proportion of these patients were at high risk of a thrombotic event because of age ≥60 years, prior thrombosis, ≥1 risk factor for cardiovascular event, or having a JAK2 mutation.


Yu: Incyte Corporation: Employment, Equity Ownership. Colucci: Incyte Corporation: Employment, Equity Ownership. Paranagama: Incyte Corporation: Employment, Equity Ownership. Sivaraman: Incyte Corporation: Employment, Equity Ownership. Atanasov: Incyte Corporation: Consultancy. Hanna: Incyte Corporation: Consultancy. Tang: Incyte Corporation: Consultancy. Parasuraman: Incyte Corporation: Employment, Equity Ownership.

Author notes


Asterisk with author names denotes non-ASH members.