Blastic transformation in a case of essential thrombocythemia

After five years of stable disease, a 58-year-old man with essential thrombocythemia had an acute terminal illness, characterized by severe pancytopenia, micromegakaryoblasts in the peripheral blood, and bone marrow replacement by extensive fibrosis, blasts, and numerous atypical megakaryocytes. The patient died of bronchopneumonia. Autopsy showed extramedullary hemopoiesis in the liver, spleen, and lymph nodes. These features are characteristic of both acute megakaryoblastic leukemia and acute myelofibrosis, and implicate involvement of the megakaryocytes in the pathogenesis of acute myelofibrosis.