PPM1D and neoplasm: WIP1 inhibitors, including GSK2830371, are now under development as anticancer drugs based on their ability to inhibit tumor growth and sensitize cancer cells to chemotherapy by reactivating p53.27–29 However, neither WIP1 nor the therapeutic effect of WIP1 inhibitors has previously been linked to the properties of CSCs, which are the major source of cancer initiation, progression, relapse, and drug resistance.