Emergence of Philadelphia positive chronic myeloid leukaemia during treatment with hydroxyurea for Philadelphia negative essential thrombocythaemia

A 58-yr-old male patient with essential thrombocythaemia (ET) developed chronic myeloid leukaemia (CML) after continuous uneventful treatment with hydroxyurea for 18 yr. G-banding analyses of bone marrow cells had repeatedly demonstrated normal male karyotype before this event, but t(9;22)(q34;q11) was demonstrated after the event. An unrelated allogeneic stem cell transplantation was performed. Blood and bone marrow morphology, and the karyotype were normalised and the patient is in good health 1 yr post-transplant. There are no previous reports in the literature about the emergence of CML during treatment with hydroxyurea.