CDKN2A and head and neck squamous cell carcinoma: CIN HNSCC subtype is marked by cell cycle activation (higher Cyclin-dependent kinases (CDK) 4/6 activity), recurrent genetic alterations (increased cyclin D1 (CCND1) and cyclin-dependent kinase inhibitor 2a (CDKN2A) expression), and the worst prognosis [11, 13].