CDK4 and breast cancer: The effectiveness of CDK4/6 inhibitors in HR + breast cancer has been validated in clinical trials regardless of whether patients develop resistance to endocrine therapy (Finn et al., 2015; Cristofanilli et al., 2016; Sledge et al., 2017; Hortobagyi et al., 2018; Tripathy et al., 2018; Johnston et al., 2019; Rugo et al., 2019; Zhang et al., 2020; Slamon et al., 2021; Xu et al., 2022).