PIK3CA and head and neck squamous cell carcinoma: There were 103 HNSCC samples that had mutations (n = 165) in the PIK3CA gene, 19% of them harboring E542K mutation (19%; 20/103); 3 LSCC cases (3%; 3/117) and 17 non-LSCC HNSCC (4%; 17/413).