The study of Hippo Yap pathway in head and neck squamous cell carcinoma showed that overexpression of PIK3CA (phosphatidylinositol 3-kinase catalytic subunit α) or the loss of FAT1 (fatty atypical cadherin 1) function could lead to the activation of yap [35]. Here, PIK3CA is linked to head and neck squamous cell carcinoma.