BCR and chronic myelogenous leukemia, BCR-ABL1 positive: The breakpoint cluster region (BCR)-c-abl oncogene, non-receptor tyrosine kinase (ABL) fusion gene is the result of a reciprocal translocation between the q arms of chromosomes 9 and 22 (i.e., an interchromosomal translocation; Figure 1A) and occurs in more than 96% of patients with chronic myelogenous leukemia (CML) [2].