PIK3CA and head and neck squamous cell carcinoma: It has been observed in these and other non-NGS studies that EGFR/ERBB2 or FGFR1/3 receptor tyrosine kinases, downstream PIK3CA and sometimes HRAS and PTEN, as well as tumor suppressors CDKN2A and TP53 are the most frequently altered genes in HNSCC.