PIK3CA and head and neck squamous cell carcinoma: To functionally characterize the altered genomic profiles in HNSCC, the set of commonly mutated genes was categorized into representative signaling pathways including the tumor suppressor gene (TSG), PI3 kinase (PI3K) pathway, NOTCH pathway, and receptor tyrosine kinase (RTK) pathway (Figure 4A and Supplementary Table 3).