ABL1 and chronic myelogenous leukemia, BCR-ABL1 positive: Chronic myeloid leukemia (CML) is a myeloproliferative disorder characterized by the Philadelphia chromosome, a translocation of chromosomes 9q34 and 22q11 resulting in a fusion oncogene, BCR–ABL1 that encodes a constitutively activated tyrosine kinase (TK) mutant.