SNAI1 and head and neck squamous cell carcinoma: The classifier includes genes related to DNA repair (e.g. BRCA [18]), proliferation (e.g. STAT5 [19]), epithelial-mesenchymal-transition (EMT) (e.g. SNAI1 [20]) and hypoxia [9], which are often up-regulated in more aggressive and radioresistant tumours leading to poor prognosis (e.g. large tumours, oral cavity tumours), while HPV-positive HNSCC show higher response rates to radiotherapy due to different underlying biology.