Background: Essential thrombocythemia (ET) is a chronic myeloproliferative neoplasm (MPN) characterized by clonal proliferation of megakaryocyte lineage. Natural history of ET is characterized by cardiovascular events (thrombosis) along with bleeding, transformation to myelofibrosis (MF), and acute myeloid leukemia (AML). There is paucity of data in ET patients from the Arab World. We aimed to study the risk factors for thrombosis and clinical course of ET in a cohort of 138 patients in a Middle Eastern population.

Methods: The study was approved by the institutional review board. All patients aged 16 or over, diagnosed with ET and followed at our center from January 2003 till June 2022, were included. Diagnosis was based on 2017 World Health Organization Classification diagnostic criteria. We gathered data on baseline clinical and laboratory characteristics from the electronic medical records and patients' files. Hematologic parameters (platelet counts, leukocyte counts, hemoglobin, and mean platelet volume [MPV]) at the time of diagnosis were retrieved and information on cardiovascular events and complications (arterial and venous thrombotic events) along with progression to myelofibrosis, acute myeloid leukemia, need for cytoreductive therapy, and control of platelet count were recorded. Multivariate regression model was used to determine the independent significant factor(s) for thromboembolism with corresponding odds ratio and 95% confidence intervals. A P-value of ≤0.05 was considered significant.

Results: A total of 138 patients were included in the study. Median age of the cohort was 47 (range, 16-84) years at the time of diagnosis with 73 (52.9%) females. JAK2 V617F mutation was present in 53 (38.4%) patients, CALR in 21 (15.2%), MPL in 43 (31.2%), and 21 (15.2%) patients were triple negative. All the patients with MPL mutation had Pro106Leu mutation. After a median follow up of 5 (range 1-26) years, 31 (22.5%) patients had vascular events, 16 (51.5%) had arterial events, 13 (42%) had venous thrombosis, 4 had both arterial & venous events, while 2 patients had transient ischemic attacks. Nine (6.5%) patients progressed to MF, and 5 (3.6%) to AML. Ten (7.25%) patients died, 4 due to MF or AML related and 6 due to other causes. High IPSET score was strongly associated with thrombosis (P ˂0.001). High MPV and uncontrolled (high) platelet count were associated with the risk of thrombosis in univariate analysis (P 0.006 and <0.001, respectively) and there was a trend towards increased risk of thrombosis in patients with high MPV and uncontrolled platelet count (P 0.061 and 0.09, respectively) in multivariate analysis.

Conclusions: Our ET patient population had high prevalence of MPL (Pro106Leu) mutation which may be germ line in nature as previously reported, and correspondingly lowered the prevalence of JAK2V617F and CALR mutations in our cohort. Thrombosis developed in 26.8% patients. In multivariate analysis, a high IPSET score was strongly associated with thrombosis. There was a trend towards increased risk of thrombosis with high MPV and uncontrolled (high) platelet count. This study may help better understand the biology of ET in this population.

No relevant conflicts of interest to declare.

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2023
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