Essential Thrombocythaemia in Young Adults: Clinical Characteristics and Outcomes – a Single Center Experience
Authors: Kam Grace , Yiu Richard , Ang Ai Leen , Loh Yvonne SM , Linn Yeh Ching , Lee Lai Heng , Goh Yeow Tee , Wong Gee Chuan 
Published: October 2019

Abstract
Abstract 5060
Less than 20% of patients with essential thrombocythemia (ET) are diagnosed below the age of 60. Patients with ET have increased risk of thrombosis and bleeding and potential for progression to myelofibrosis (MF) or acute myeloid leukaemia (AML). In limited studies of young patients, the clinical course has been relatively benign with low rates of transformation to AML or MF. Thrombohemorrhagic events are generally few, but higher than that of the general population. This study aims to characterize of a group ET patients diagnosed at age ≤40, their thrombotic and hemorrhagic events, disease progression and treatment given.
Patients were identified through a single institution MPN registry. This is an IRB approved registry that captures comprehensive information about patients with ET. Data on patient demographics, treatment, and disease-related events were obtained. Patients were diagnosed from 1975–2011, using either WHO or PVSG criteria depending on date of diagnosis. Kaplan-Meier method was used for survival analysis.
59 patients were diagnosed with ET at age ≤40. Median age of diagnosis was 31. 5years (range 16–40), with a median follow up of 7. 7years (0. 4–33. 8). All were of Asian descent: 81. 4% Chinese, 11. 9% Malay, 3. 4% Indian and 3. 4% Filipino. 40. 7% were male. JAK2 V617F mutation was screened for in 61%. Of these patients, 11 were positive, 25 negative for the mutation. Mean presenting counts were: WBC 10. 7 × 109/L (5. 9–21. 3), Hb 13. 6g/dL (9. 7–16. 4), platelets 957 × 109/L (449–2377). Splenomegaly was noted in 3 patients. 20. 3% had underlying hypertension, 16. 9% hyperlipidemia and 5. 1% diabetes mellitus. One patient had a prior stroke. Another had prior portal vein thrombosis.
At diagnosis, 23. 7% were symptomatic, with microvascular symptoms of headache (11. 9%) and giddiness (6. 8%) being most common. The remainder were diagnosed incidentally, on health screening or when seeking medical attention for unrelated conditions. One patient presented with a myocardial infarction at diagnosis, while another had a significant bleeding post hemorrhoidectomy with drop in Hb by >2g/dL (platelet 2457 × 109/L). Based on a history of prior thrombosis, 3 patients were defined as high risk for thrombotic events. 67. 8% of patients had cytoreduction, indications being platelets ≥1500 × 109/L (n=16), presence of risk factors for atherosclerotic disease (n=11) and history/onset of thrombosis (n=5). In 8, the reason for cytoreduction could not be ascertained. Hydroxyurea was most commonly used (62. 7%), followed by anagrelide in 52. 5% and interferon 25. 4%. 5. 1% received busulphan, and 1. 7% 32P. Use of antiplatelet therapy was noted in 83. 8%, most frequently aspirin (76. 5%) and ticlopidine (11. 9%). On follow up, 2 arterial thromboses occurred (stroke, TIA), giving a thrombosis rate of 0. 39%/patients/year. Neither was a recurrent thrombosis. No venous thrombosis or major bleeds occurred. 20. 4% had minor mucocutaneous bleeding; 5 had platelets ≥1500 × 109/L at that time. 3. 4% had disease progression due to MF and another 3. 4% had AML. 3. 4% of patients died due to AML. Median survival was 33. 8years (95% confidence interval 30. 3–35. 5). Initial blood counts, presence of JAK2 and high risk disease status did not correlate with thrombotic risk, risk of death or disease progression. Use of antiplatelet agents and a platelet count ≥1500 × 109/L did not correlate with bleeding risk.
Few studies have looked exclusively at young patients with ET. In this group, most patients were asymptomatic and well, ET being diagnosed incidentally. They were predominantly at low risk for thrombosis and other ET-related complications. The period of follow up was comparable to that of other studies and during that time, the rate of complications and risk of disease progression was low. The thrombosis rate of 0. 39% per patient year was less than that reported by other groups (2. 2–2. 6 thromboses/100patients/year) (Leukaemia 2007;21:1218–1223, Clin Appl Thrombosis/Hemostasis 2000;6(1):31–35) but similar to the 0. 74%/patient year reported by Barbui (Blood. Epub. June 13 2012). Overall findings generally complemented those reported by other groups. No risk factors were found to influence the occurrence of complications, but the number of events was small. Follow up of this group of patients over time is essential to see if their disease course remains benign or if complications will increase with time.
Soli Deo Gloria

Disclosures:
Kam: Shire Pharmaceuticals: Consultancy, grant to support the MPN registry Other.