BCR-ABL is a fusion gene formed from the combination of two genes: BCR and ABL. This genetic alteration is commonly associated with certain types of leukemia, particularly chronic myeloid leukemia (CML). The BCR-ABL protein produced by this fusion has abnormal tyrosine kinase activity, which leads to uncontrolled cell division and growth. The presence of the BCR-ABL fusion gene can be detected through various laboratory tests, including polymerase chain reaction (PCR) and fluorescence in situ hybridization (FISH). Targeted therapies, such as imatinib, are designed to inhibit the activity of the BCR-ABL protein, providing effective treatment options for patients with CML.