CCND1 and cancer: In the context of epigenetic alterations, can we identify DNA methylation regions representative of each key step in the well-established histological progression of head and neck cancer, including hyperplasia (CDKN2A inactivation), dysplasia (TP53 inactivation), carcinoma in situ (CCND1 amplification), and invasive carcinoma (PTEN inactivation) [19]?