MAPK1 and head and neck squamous cell carcinoma: Notably, the MAPK1 mutation rate in HNSCC appears to be relatively higher (1.8%; 9/512 cases) than that in the TCGA pan-cancers, and such HNSCC-associated MAPK1 mutations are almost all uniformly p.E322K or p.E322* mutations (Fig. 1a).