ABL1 and chronic myelogenous leukemia, BCR-ABL1 positive: Chronic myeloid leukemia (CML) is caused by the reciprocal chromosomal translocation t(9;22) that results in the gene fusion of BCR (Breakpoint Cluster Region) and ABL1 (Abelson Murine Leukemia Viral Oncogene Homolog 1).