The BCR(22q11.23) probe is located on chromosome 22. The ABL1(9q34.12) probe and the ASS1(9q34.12) are located on chromosome 9. A 600 Kb probe covering the BCR gene region is labeled with a green dye. A 700 Kb probe covering the ABL1 gene region is labeled with an aqua dye. A 350 Kb probe covering the ASS1 gene region is labeled with an orange dye.

BCR/ABL fusion gene is a hallmark of CML and is also present in 30% of adult ALL, approximately 10% of pediatric ALL, and a small percentage of AML; it indicates extremely poor prognosis in ALL. Detects BCR-ABL1 fusion in chronic myelogenous leukemia (CML) for diagnosis and monitors minimal residual disease during therapy. Highly sensitive in identifying derivative chromosome 9 deletions and distinguishes true fusion signals from random overlaps in imatinib-resistant CML patients, enabling accurate treatment response assessment.