Despite significant decreases in BCR-ABL mRNA levels in the bone marrow compartment under IM long-term therapy, persistence of residual CML clones with low BCR-ABL expression and insensitivity to IM treatment makes disease eradication by TKI treatment unlikely [13, 25, 26]. This evidence concerns the gene ABL1 and chronic myelogenous leukemia, BCR-ABL1 positive.