SOX9 and esophageal squamous cell carcinoma: Furthermore, immunohistochemical (IHC) staining of the tumor xenografts demonstrated that the levels of CSC markers SOX9 and CD44, as well as the mesenchymal marker vimentin, were diminished by the treatment (Fig. 2e), indicating that inhibition of YAP signaling decreases CSC-like properties in ESCC and therefore attenuates tumor growth.