The development, over the past two decades, of small-molecule tyrosine kinase inhibitors (TKIs) targeting the fusion protein BCR-ABL1 expressed by the Philadelphia chromosome (Ph) has considerably advanced the treatment of chronic myeloid leukemia (CML) and Ph+ acute lymphoblastic leukemia (ALL). This evidence concerns the gene BCR and chronic myelogenous leukemia, BCR-ABL1 positive.