ABL1 and chronic myelogenous leukemia, BCR-ABL1 positive: Chronic myeloid leukemia (CML) is a myeloproliferative disorder caused by a balanced chromosomal translocation involving a fusion of the Abelson gene (ABL1) from chromosome 9q34 with the breakpoint cluster region (BCR) gene on chromosome 22q11, known as the Philadelphia chromosome, which encodes the BCR-ABL protein with protein tyrosine kinase activity (1).