Two ERs/GPER-targeting PROTACs (UI-EP001 and UI-EP002) have been designed, which effectively degrade ERα, ERβ, and GPER, inducing cytotoxicity and G2/M cell cycle arrest in MCF-7 (ERα+/ERβ+/GPER+) and SKBR3 (ERα−/ERβ−/GPER+) BC cells but not in MDA-MB-231 BC cells that do not express functional ERα/ERβ/GPER.55 This evidence concerns the gene ESR2 and breast cancer.