PIK3CA and head and neck squamous cell carcinoma: In HNSCC, frequently mutated genes detected in plasma samples included TP53 (65.7%), ATM (43.3%), DNMT3A (34.4%), CHEK2 (23.9%), PIK3CA (22.4%), ASXL1 (22.4%), CDKN2A (16.5%), and GNAS (16.4%) (Figure 1c).