Brilanestrant is an orally bioavailable Selective Estrogen Receptor Degrader (SERD) that demonstrates robust activity in tamoxifen-resistant breast cancer xenografts. GDC-0810 functions by binding to the estrogen receptor, inducing a conformational change resulting in the degradation of the receptor. GDC-0810 or ARN-810 demonstrates robust activity in models of tamoxifen-sensitive and tamoxifen-resistant breast cancer, and is currently in clinical trials in women with locally advanced or metastatic estrogen receptor-positive breast cancer.