ABL1 and chronic myelogenous leukemia, BCR-ABL1 positive: Chronic myeloid leukemia (CML) is a malignancy characterized by the appearance of the leukemogenic oncoprotein breakpoint cluster region::Abelson murine leukemia viral oncogene homolog 1 (BCR::ABL), which is a molecular product of the Ph1 (Philadelphia) chromosome in hematopoietic stem cells (HSCs).