YAP1 and osteosarcoma: It has been reported that the Hippo pathway effector YAP1 is a direct transcriptional target of SOX2 in mesenchymal stem cells and osteoprogenitors22; WWC1 and NF2, two Hippo activators, appear to be directly repressed at the transcriptional level by SOX2 in human osteosarcomas.23 Moreover, ACTL6A and p63 could physically interact, cooperatively suppressing WWC1 transcription to activate the Hippo‐YAP1 pathway and thus promoting tumorigenesis in HNSCC.14 However, whether and how SOX2, ACTL6A, or TP63 interacts with the Hippo‐YAP1 pathway in ESCC remain to be determined.