CDK1 and CDK7 emerged as the most crucial genes across all five HNSCC cell lines, while other CDKs such as CDK2 or CDK5 were found to be non-essential, or showed selectivity to certain cell lines, such as CDK4, CDK6 or CDK9 (Fig. 1e). The gene discussed is CDK9; the disease is head and neck squamous cell carcinoma.