FASLODEX 250 mg Injection FASLODEX contains Fulvestrant, a competitive estrogen receptor (ER) antagonist with an affinity comparable to estradiol. It binds reversibly to estrogen receptors, blockading estrogen action and inducing structural changes that lead to receptor degradation via the ubiquitin-proteasome pathway. By downregulating ER levels and completely suppressing estrogen-dependent transcription without agonist properties, it halts tumor proliferation in hormone receptor-positive malignancies. It is indicated for the treatment of HR-positive, HER2-negative advanced or metastatic breast cancer in postmenopausal women.