The t(9;22) translocation/BCR-ABL1 fusion gene is associated with chronic myeloid leukemia (CML ) and “Philadelphia-positive” acute lymphoblastic leukemia of B-cell lineage (Ph+ ALL). Very rarely, this abnormality has also been identified in cases of acute myeloid leukemia and T-lymphoblastic leukemia/lymphoma.

Upon initial detection of BCR/ABL1 in any of these diseases, quantitative RT-PCR (qRT-PCR) measurement of BCR/ABL1 transcript levels are recommended before treatment initiation. qRT-PCR is also used to monitor response to TKI therapy and detection of Minimal Residual Disease (MRD).