MAPK1 and head and neck squamous cell carcinoma: The study was later extended to additional MAPK1 mutations in HNSCC, and led to the finding that MAPK1 p.D321N (also hyperactivates MAPK and p-EGFR) could also confer heightened sensitivity to erlotinib in HNSCC in vivo, while MAPK1 p.R135K mutation (moderately activating p-EGFR) conferred moderate level of erlotinib sensitivity12.