[BCR-ABL1-positive chronic myeloid leukemia emerging in a patient with secondary myelofibrosis harboring the JAK2-V617F mutation].

A 53-year-old woman with a 27-year history of myeloproliferative neoplasms came to our hospital because of a marked white blood cell count increase and progressive anemia. Clinical examination demonstrated positivity for BCR-ABL1 and JAK2-V617F mutations. She was given a diagnosis of chronic myeloid leukemia. Using the international scale, a molecular response (MR) 4.5 was achieved after treatment with dasatinib, despite the persistence of marked splenomegaly. The pathological findings of myelofibrosis were demonstrated by bone marrow biopsy. After stopping dasatinib administration for 4 years and 5 months, treatment with ruxolitinib was started. Five months later, the size of her spleen was reduced. We speculated that translocation of BCR-ABL1 might have occurred in a sub-clone of the JAK2-V617F mutated tumor clone.