Fulvestrant (trade name Faslodex, by AstraZeneca) is a drug treatment of hormone receptor-positive metastatic breast cancer in postmenopausal women with disease progression following anti-estrogen therapy. It is a complete estrogen receptor antagonist with no agonist effects, which in addition, accelerates the proteasomal degradation of the estrogen receptor. The drug has poor oral bioavailability, and is administered monthly via intramuscular injection.