Rare case of fatal accelerated/blast-phase myeloproliferative neoplasm arising from essential thrombocythemia

Essential thrombocythemia (ET) is a chronic myeloproliferative neoplasm (MPN) characterized by clonal thrombocytosis. Although typically indolent, rare cases progress to accelerated/blast-phase disease, often with poor outcomes. We report a fatal case of ET that transformed into an aggressive MPN, diagnosed postmortem. A 68-year-old male with a 30-year history of JAK2 V617F-positive ET presented with altered mental status, severe cytopenias, lytic bone lesions, and periportal lymphadenopathy. Initial bone marrow biopsies were inconclusive due to extensive necrosis. Despite palliative management, the patient rapidly developed metabolic derangements, multiorgan failure, and ultimately suffered fatal cardiac arrest. A limited autopsy revealed extramedullary hematopoiesis with atypical megakaryocytes and 10–20% CD34-positive blasts in lymph nodes, highly suggestive of transformation to accelerated/blast-phase MPN. This case highlights the diagnostic challenges of aggressive MPN transformation, particularly in the context of necrotic biopsies and borderline blast percentages. Concurrent COVID-19 infection may have contributed to systemic deterioration. Postmortem examination was essential in confirming transformation to accelerated/blast-phase MPN, emphasizing the diagnostic value of autopsy in unresolved hematologic malignancies. This case underscores the need for early molecular testing and vigilant surveillance for disease progression in high-risk ET patients.