PIK3CA and head and neck squamous cell carcinoma: Lung SqCC also had frequent alterations in the CDKN2A/RB1, NFE2L2/KEAP1/CUL3, PI3K/AKT and SOX2/TP63/NOTCH1 pathways and shared many gene mutations in common with head and neck squamous cell carcinomas without evidence of human papilloma virus infection, including PIK3CA, PTEN, TP53, CDKN2A, NOTCH1, and HRAS [98, 99].