PIK3CA and head and neck squamous cell carcinoma: The comparative analysis showed that one-third of the most frequent cancer driver mutations identified in ASCC (8 out of 25 genes) were also frequently mutated (>5% of cases) in CSCC and HNSCC (KMT2C, EP300, PIK3CA, NOTCH1, TP53, CASP8, STK11, and KDM6A) (Figure 9B).