Cyclin-dependent kinase 4/6 inhibitors (CDK4/6is), such as palbociclib, ribociclib, and abemaciclib, have been approved for treating patients with hormone receptor-positive and human epidermal growth factor receptor 2-negative breast cancer (Finn et al., 2015; Cristofanilli et al., 2016; Finn et al., 2016; Hortobagyi et al., 2016; Dickler et al., 2017; Goetz et al., 2017; Sledge et al., 2017; Slamon et al., 2018; Tripathy et al., 2018; Turner et al., 2018; Johnston et al., 2020; Royce et al., 2022). Here, CDK4 is linked to breast cancer.