A genus of proteolysis-targeting chimeras (PROTACs)-type compounds/antiestrogens has now been found that act as selective estrogen receptor degraders (SERDs) and estrogen receptor antagonists by degrading and antagonizing ERa in breast cancer cells. The compounds are of the following genus: The compounds described herein exhibit anti-proliferative effects, and are potentially useful, alone or in combination with other therapies, for the treatment of breast cancer. In general, these compounds combine a tight binding ERa targeting ligand tethered to a recognition motif or degron. Once bound, the degron recruits destructive cellular components and the targeted receptor (i.e., ERa) is degraded (i.e., destroyed) or antagonized.