EGFR and head and neck squamous cell carcinoma: Furthermore, while EGFR TKI treatment leads to only a modest reduction in EGFR/PI3K signaling in PIK3CA-MT HNSCC cells, p-EGFR (Y1068), p-AKT (S473), and p-S6 were markedly reduced in PIK3CA-WT cells following erlotinib or lapatinib treatment (Figure 1e).