CDK4 and oral cavity squamous cell carcinoma: Previous research has revealed that the negative regulation of cyclin D1 and CDK4 is consistent with the downregulation of CENPN (Molenaar et al., 2008), and recent reports in oral squamous cell carcinoma (OSCC) suggest that downregulation of CENPN can reduce the expression of cyclin D1 and CDK4 with corresponding increases in the expression of p21 and p27 (Oka et al., 2019).