These three compounds inhibited proliferation and induced apoptosis of breast cancer cells in vitro (12–15), slowed the growth of MDA-MB-468 ER-negative cells in nude mice when combined with tumor necrosis factor–related apoptosis-inducing ligand (15), and reduced the tumor burden of xenografted MCF-7 cells stably transfected with HER-2/neu (ErbB2; ref. 14). Here, ESR1 is linked to breast cancer.