BCR-ABL1 refers to a sequence found in an abnormal chromosome 22 of some people with certain forms of leukemia. The presence of the gene sequence known as BCR-ABL1 confirms the diagnosis of CML and a form of acute lymphoblastic lymphoma (ALL).
In general, if the amount of BCR-ABL1 in the blood or bone marrow decreases over time, then the person is responding to treatment. If the quantity of BCR-ABL1 drops below the test’s detection level and the person’s blood cell counts are normal, then the person is considered to be in remission.
If the BCR-ABL1 level rises, then it indicates disease progression or recurrence. It may also indicate that the person has become resistant to imatinib, the first-generation tyrosine kinase inhibitor. Additional genetic testing is often performed to detect the development of BCR-ABL1 kinase domain mutations associated with imatinib resistance.