The t(9;22)/BCR-ABL1 abnormality is associated with chronic myelogenous 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.

David Viswanatha, M.D., a hematopathologist and co-director of the molecular hematology and complete genome sequencing laboratories at Mayo Clinic, provides an overview of BCR/ABL1 testing, discusses the best testing methods, NCCN/ELN criteria guidelines, why FISH testing is no longer routinely available at Mayo Clinic, and what test to order at what time for CML patients.