CDK6 and tongue squamous cell carcinoma: In this review, it was noted that three in vitro studies (4.4%) reported that carvacrol decreased CDK4 protein expression in human tongue squamous cell carcinoma (Tca-8113 cells) (Dai et al., 2016) and in breast cancer (MCF-7 cells) (Mari et al., 2020; Li et al., 2021) and only one (1.4%) reported a decrease in CDK6 in MCF-7 cells (Mari et al., 2020).