A very prolonged arrest in mitosis induced by a high concentration of a microtubule poison or ablation of Cdc20 can lead directly to cell death in some cell types [6,8,9], but such a prolonged arrest is unlikely to be sustained in patients undergoing chemotherapy, in which case the response of cancer cells to suboptimal doses of the drug and a delay (as opposed to an arrest) in mitosis are likely to be important for clinical effectiveness. The gene discussed is CDC20; the disease is cancer.