CDKN2A and head and neck squamous cell carcinoma: Stratification of high EGFR expressors by expression levels of cyclin D1, CDK6, or the cyclin D1/CDK6-regulatory protein p16 (CDKN2A) identified groups with significant survival differences, consistent with prior studies that demonstrated improved survival in HNSCC with low levels of cyclin D1 and in those with low phosho-T356 Rb [61, 62].