BCR and chronic myelogenous leukemia, BCR-ABL1 positive: Chronic myeloid leukemia (CML) is a myeloproliferative disease characterized by the presence of chromosomal abnormality leading to the aberrant Abelson oncogene (Abl)-breakpoint cluster region (Bcr) gene fusion, which encodes for the Bcr-Abl tyrosine kinase.