A case of chronic myeloid leukemia with features of essential thrombocythemia in peripheral blood and bone marrow.

Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm characterized by overproduction of myeloid white blood cells. Philadelphia chromosome is an essential finding for CML diagnosis. Generally, a clinical diagnosis of essential thrombocythemia (ET) can be established from isolated marked thrombocytosis in peripheral blood. However, Philadelphia chromosome-positivity or bcr/abl rearrangement with isolated thrombocytosis should be diagnosed as CML, not ET, according to World Health Organization diagnostic criteria. Therefore, CML should not be excluded before confirming the presence of the Philadelphia chromosome or bcr/abl rearrangement in cases of isolated thrombocytosis in peripheral blood. We report a case of CML with clinical features of ET in a patient successfully treated with imatinib.