Essential thrombocythemia terminating in pure erythroleukemia

Transformation into acute leukemia is a rare event in essential thrombocythemia (ET). The blasts are usually of myeloid, rarely of megakaryoblastic differentiation. We present the case of a patient with pure erythroleukemia after a nearly 10-year course of ET, which was treated with hydroxyurea. The patient, a 58-year-old male, presented with an elevated thrombocyte count (926,000/microL) and normal values of hemoglobin and leukocytes. After 10 years of therapy with hydroxyurea, the patient developed acute leukemia of solely erythroid differentiation. Chemotherapy with cytarabine and daunorubicin resulted in incomplete remission. The patient died 2 months after diagnosis of acute erythroleukemia. Transformation of ET into erythroleukemia may demonstrate the pluripotent potential of the neoplastic hemopoietic stem cell, with the ability to cause acute leukemia not only of myeloid or megakaryoblastic but also of erythroid lineage.