As the CDK4/6 inhibitor palbociclib was recently shown to act synergistically with either lapatinib or afatinib (tyrosine kinase inhibitors that target EGFR and HER2) to inhibit proliferation in HNSCC cell lines [52], it may be worthwhile to test whether co-treatment of the CtxR 4 cells with palbociclib has an impact on their response to cetuximab. This evidence concerns the gene CDK4 and head and neck squamous cell carcinoma.