In BCR-ABL+ chronic myeloid leukemia (CML), high levels of STAT5 mRNA correlate with tyrosine kinase inhibitor (TKI) resistance, regardless of the presence of tyrosine kinase domain (TKD) BCR-ABL1 mutations [18, 19]. This evidence concerns the gene STAT5A and chronic myelogenous leukemia, BCR-ABL1 positive.