Emergence of chronic myelogenous leukemia in a patient with primary thrombocythemia and absence of BCR/ABL rearrangement.

A 65-year-old woman presented with clinical features of primary thrombocythemia (PT), and absence of the BCR/ABL fusion gene. She responded to hydroxyurea treatment, although after 1 year she required progressive increases in the dose. Six years later, she maintained a high platelet count despite hydroxyurea at 2 g/day and treatment was changed to anagrelide. After 3 weeks, both platelet and leukocyte counts increased. A karyotype study detected the Philadelphia chromosome in all of the 24 metaphases studied. Fluorescent in situ hybridization (FISH) analysis revealed the BCR/ABL rearrangement. The patient was treated with imatinib mesylate and achieved a normal platelet and leukocyte count in 3 weeks. Patients presenting clinical features of PT expressing the Ph chromosome or the BCR/ABL fusion gene have been well documented but, to our knowledge, this is the first report of evolution from typical PT to chronic myeloid leukemia.