PIK3CA and head and neck squamous cell carcinoma: The PI3K/AKT/mTOR signalling pathway is active in more than 90% of HNSCC cases as a result of EGFR activation (47%), mutations in the catalytic alpha subunit of PIK3CA (8.6%), PIK3CA amplifications (14.2%), PI3K overexpression (27.2%) and PTEN mutations (10–15%) [70].