YAP1 and cancer: As the main effector of Hippo pathway, YAP1 responds to a wide range of extracellular and intracellular signals, including cell–cell contact,20 cell polarity,25 mechanical cues,26 ligands of G‐protein‐coupled receptors27 and cellular energy status.28 Regulation of YAP1 by cell density suggests a critical role for the Hippo pathway in contact inhibition, tissue growth, and tumorigenesis.7 Meanwhile, many established cancer cell lines exhibit growth in vitro that is impervious to contact inhibition, implying dysfunction of Hippo/YAP signaling.