Polo-like kinase 4 (PLK4), which regulates centriole duplication and mitotic progression, is overexpressed in several cancers, including neuroblastoma as well as breast, lung and colorectal cancers, making it an attractive target. Several PLK4 inhibitors have been developed, but only one has entered clinical trials, which involve patients with acute myeloid or chronic myelomonocytic leukemia.