BCR and chronic myelogenous leukemia, BCR-ABL1 positive: Chronic myeloid leukemia is caused by the development of the Philadelphia chromosome (Ph), formed by the reciprocal translocation between chromosomes 9 and 22 that fuses the ABL gene to the breakpoint cluster region (BCR) gene; the fusion results in the dysregulated expression of the oncogenic BCR-ABL tyrosine kinase protein (Faderl et al., 1999).