PLK1 and breast cancer: <title>Abstract</title>  <p><bold>Background</bold>In chronic myeloid leukemia (CML), Aurora kinase A and Polo like kinase 1 (Plk1), two serine-threonine kinases involved in the maintenance of a functional G2/M checkpoint, may cooperate with the constitutive tyrosine-kinase (TK) activity of the BCR-ABL1 fusion protein increasing DNA damage, promoting the occurrence of additional genomic alterations ultimately driving resistance to TK inhibitors (TKIs) and progression from chronic phase to blast crisis (BC).