MAPK1 and head and neck squamous cell carcinoma: Thus, we demonstrated a heightened sensitivity of MAPK1p.D321N to erlotinib in vivo, reminiscent of p.E322K we reported previously6, providing direct evidences for MAPK1 mutant-driven erlotinib sensitivity by both MAPK1p.D321N and p.E322K in HNSCC.