SNAI1 and head and neck squamous cell carcinoma: The association between a hypoxic environment and activation of EMT-related transcription factors (EMT-TFs), such as zinc finger transcriptional repressors Snail, Slug, Twist, and zinc finger E-box binding homebox 1/2 (ZEB1/2), is quite well studied and proven on various cancer types, such as hepatocellular carcinoma (HCC), ovarian cancer, or head and neck squamous cell carcinoma (HNSCC) [53].