MDM2 and head and neck squamous cell carcinoma: Close spatial coexpression of p53, MDM2, and MIB1 (an E3 ubiquitin-protein ligase) immunoreactivity was observed at the invasive front of the HNSCC and in the basal and suprabasal layers of the nontumors epithelium in all p53 positive cases (Figure 2) [8].