ESR1 and breast cancer: Treatment of MDAMB-231 cells, a triple-negative (estrogen receptor, progesterone receptor, and HER2-negative) breast cancer cell line, with the degrader results in the efficient degradation of CDK4 and CDK6 with DC50 (the concentration at which 50% of the target protein has been degraded) values of 13 and 34 nmol/L, respectively, which subsequently decreases the level of the Rb phosphorylation in a dose-dependent manner [135].