TP53 and head and neck squamous cell carcinoma: Moreover, immunohistochemical (IHC) staining of tumors from an orthotopic implantation of PCI-13 (another HNSCC cell line that does not endogenously express TP53) stable cell lines expressing different mutant p53s grown in the tongues of nude mice [6] also showed that the ratio of positive nuclear staining of FOXM1 was significantly higher in the cell lines containing the mutant p53s R175H, C238F, and G245D than in the pBabe control cell line (Fig. 2c, d), indicating that FOXM1 expression is up-regulated by these GOF mutant p53s in vivo.