BCR and chronic myelogenous leukemia, BCR-ABL1 positive: More than 90% of patients with chronic myeloid leukemia (CML) have the characteristic Philadelphia chromosome (translocation of chromosomes 9 and 22), forming the fusion geneBCR-ABL [encoding breakpoint cluster region protein (BCR)-Abl Oncogene 1, Receptor Tyrosine Kinase (ABL)].