PLK1 and cancer: Polo-like kinase 1 (Plk1) is a key regulator of mitosis, and its overexpression has been linked with poor prognosis in human cancer.6 Inhibition of Plk1 in vitro was found to block proliferation of leukemic cell lines, and to reduce the clonogenic potential of cell lines derived from patients with leukemia.7 Volasertib is a low-molecular-weight, adenosine triphosphate-competitive kinase inhibitor that potently inhibits Plk1, as well as the 2 closely related kinases, Plk2 and Plk3.