Because, in many cases, dysregulation of the Hippo signaling pathway and increased YAP/TAZ activity induce expansion of tissue-specific stem/progenitor cells which eventually leads to development of cancer, uncovering the physiological roles of the Hippo signaling pathway and YAP/TAZ in a tissue homeostasis and cancer stem cells would be helpful for cancer therapy. This evidence concerns the gene WWTR1 and cancer.