CDK6 and head and neck squamous cell carcinoma: Dysregulated expression of CDK6 and Cyclin D1 has been reported in several cancers, including head and neck squamous cell carcinoma, non-small cell lung carcinoma, endometrial cancer, melanoma, pancreatic cancer, breast cancer, colorectal cancer, mantle cell lymphoma, multiple myeloma, prostate cancer, endometrial cancer and oesophageal cancer (Cyclin D1, [37]), and glioblastoma, myxofibrosarcoma, lymphoid malignancies and Ewing’s sarcoma cell line (CDK6, [38-42]).