Emergence of chronic myelogenous leukemia during treatment for essential thrombocythemia

A 72-year-old male patient was initially diagnosed with essential thrombocythemia (ET), a Philadelphia chromosome-negative (Ph1−) chronic myeloproliferative disorder (CMPD), and was treated with hydroxyurea (HU). After 9 years of diagnosis of ET, his peripheral leukocytes gradually increased, while his platelet count showed a decrease. Bone marrow analysis disclosed Ph-positive chronic myelogenous leukemia (CML) in the chronic phase. Administration of imatinib mesylate (IM), a Bcr–Abl tyrosine kinase inhibitor (TKI), induced complete hematologic response in a month, but was discontinued after 4 months because of Grade 3 pleural effusion (PE). The treatment was switched to nilotinib which successfully induced a complete cytogenetic response (CCyR) after 5 months of TKI therapy and resolved the PE. Despite CCyR, however, ET recurred. Since then, the patient has been treated for 8 months with a combination of nilotinib and HU which has successfully controlled both CML and ET. This report includes a review of the characteristics of 15 reported cases with co-occurrence of CML and Bcr–Abl-negative CMPDs, including ours. Although rare, care needs to be taken since, despite the often similar clinical features of the two diseases, they require completely different treatments.