Fulvestrant

Fulvestrant is both an antagonist and a degrader of the estrogen receptors in the breast. It is considered both a SERM (selective estrogen receptor modulator) and a SERD (selective estrogen receptor downregulator) due to this action.

The medication inhibits estradiol binding in the breast at a much higher level than tamoxifen, is a complete (not partial) ER antagonist due to disrupting AF1 and AF2 sites that fuel breast and breast cancer growth, and also destroys ER receptors.