ABL1 and chronic myelogenous leukemia, BCR-ABL1 positive: As well as being of diagnostic importance, BCR–ABL1 also serves as a specific marker of the malignant clone, and many laboratories worldwide routinely use serial reverse-transcription quantitative PCR (RT-qPCR) analysis to monitor the response of, individual CML or acute lymphoblastic leukaemia, patients to treatment.1, 2, 3 Indeed, international recommendations for the management of CML include key time-dependent therapeutic milestones based in part on such molecular monitoring.4