ABL1 and chronic myelogenous leukemia, BCR-ABL1 positive: The presence of residual BCR-ABL positive cells in CML patients in CMR before and after imatinib discontinuation were demonstrated by Ross et al. who used genomic DNA-based PCR, which allows to detect rearranged BCR-ABL gene at a level of around 1- to 2-log below the detection limit of conventional (mRNA) qRT-PCR.