YAP1 and head and neck squamous cell carcinoma: YAP and TAZ are transcriptional co-activators with various upstream signals, which are mainly regulated by the Hippo signaling pathway.442 Studies have reported that both YAP and TAZ are over-expressed in head and neck squamous cell carcinoma (HNSCC).443 In HNSCC, the WNT signaling pathway and the ERBB4 ICD (erbb2 receptor tyrosine kinase 4 intracellular domain) are known to elicit YAP activation.