In support of our model that CDK4/6i treatment promotes RB1 for proteasomal degradation and CDK6 accumulation to confer breast cancer cells with acquisition of CDK4/6i resistance, compared to parental cells, the RB1 protein levels were dramatically reduced, while CDK6 protein abundance was accumulated in resistant daughter cells (Fig. 7b). Here, RB1 is linked to breast carcinoma.