ABL1 and chronic myelogenous leukemia, BCR-ABL1 positive: The abnormally small resulting chromosome, named the Philadelphia chromosome, was found in over 95% of patients with chronic myelogenous leukemia (CML) and consisted of the breakpoint cluster region (BCR) gene fused to the second exon of the Abelson murine leukemia viral oncogene homolog 1 (ABL1) gene [8,9].