The combination of CDK4/6i and ET has reshaped treatment for HR+/HER2– breast cancer (Johnston et al., 2019; Finn et al., 2015; Finn et al., 2016; Turner et al., 2018; Dickler et al., 2017; Hortobagyi et al., 2022; Slamon et al., 2020; Im et al., 2019). This evidence concerns the gene CDK4 and breast cancer.