MAPK1 and head and neck squamous cell carcinoma: In addition, FaDu cells engineered to express exogenous MAPK1E322K expressed high basal level of p-EGFR (Y1068) compared to FaDu cells exogenously expressing MAPK1WT or vector control, suggesting that the activating MAPK1 mutation likely causes a feedback activation of EGFR in HNSCC cells.