To date, three different small molecule inhibitors selectively target polo-like kinase 4 with nanomolar affinity (30, 31, 32) and block cell proliferation in a number of human cancer lines, including osteosarcoma, cervical carcinoma, and breast, lung, and colon cancer cells (32, 33, 34), likely via centrosome depletion. Here, PLK4 is linked to cancer.