SOX2 and head and neck squamous cell carcinoma: For SOX2, immunohistochemical analyses revealed significantly lower expression in the metastases of HNSCC patients compared with the respective primary tumor (p < 0.0001; Figure 2D), a significantly lower expression in the metastases of CUP compared with HNSCC patients (p = 0.01; Figure 3A) and a gradual decrease in the expression level from N1 to N3 cervical lymph node status (Figure 3B).