Introduction: This analysis reports demographic and clinical characteristics of patients with physician-diagnosed essential thrombocythemia (ET) receiving cytoreductive therapy in US community clinical practice. Methods: Patient characteristics, medical history, diagnostic test results, signs/symptoms, treatment patterns, and physician practice settings were extracted from medical charts for patients with physician-diagnosed ET receiving cytoreductive therapy. Results: Among 809 patients (51.1% female; 75.4% White; median age, 69 years) from 50 community practices, 64.5% had physician-reported diagnosis per World Health Organization criteria. Only 48.8% underwent diagnostic bone marrow biopsies; 87.5% had JAK2 mutation testing. Among those tested, 512/708 (72.3%), 57/213 (26.8%), and 37/213 (17.4%) had JAK2, CALR, and MPLmutations, respectively. Of physician-assigned risk assessments, 41.8% were misclassifications based on data-derived risk assessment. Most patients (93.3%) received first-line hydroxyurea (HU) cytoreductive therapy. Discontinuations were primarily for intolerance (35.4%) and resistance (23.8%). Of those who discontinued, 65.9% received no subsequent therapy and had higher ET symptom rates at last visit versus patients continuing HU (48.8% vs. 25.0%). Conclusion: This study shows notable gaps in ET diagnosis and management. Half of patients were diagnosed without bone marrow biopsy, many received incorrect risk assignment, and the majority who discontinued HU received no subsequent therapy despite continued need.

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