TP53 and head and neck squamous cell carcinoma: To study GOF mechanisms of mutant p53s, we first used HNSCC UM-SCC-1 cells that do not express endogenous p53 due to a splice-site mutation (hg19:chr17:7578370C > T) in the TP53 gene and established isogenic cell lines expressing G245D, R175H, and C238F mutant p53s.