Fulvestrant is an ER antagonist with no agonist effects, which binds, blocks and degrades the ER. Fulvestrant is comparable to third-generation aromatase inhibitors in terms of efficacy and tolerability for patients who have progressed on prior tamoxifen therapy and past studies have found all three-third-generation AIs to be at least as good as tamoxifen in first-line metastatic therapy in postmenopausal women. Fulvestrant has been studied little in premenopausal women despite of its attractive mechanism of actions. The clinical effectiveness of fulvestrant as a treatment for advanced breast cancer has previously been demonstrated at the standard dose (AD; 250 mg/mo) in several phase III clinical trials in postmenopausal women. However, there is evidence to suggest that doses of fulvestrant higher than 250 mg may have greater pharmacodynamic activity against the ER pathway. Moreover, dose-dependent clinical activity has been observed for fulvestrant. The activity of a fulvestrant high-dose (HD; 500 mg/mo) regimen has been investigated in two recent studies. A pilot Japanese study showed fulvestrant HD to have clinical activity in the treatment of advanced or recurrent breast cancer, to be well tolerated, and to result in plasma levels approximately double those seen with fulvestrant low-dose. Subsequently, a neoadjuvant study comparing fulvestrant low-dose and high-dose reported that significantly greater Ki67 and ER downregulation was achieved with the high-dose compared with the low-dose regimen and that both doses were well tolerated. A recent randomized trial also showed superior outcome of high-dose fulvestrant than AI. Based on this rationale, we introduced high-dose fulvestrant with LHRH agonist as a randomized trial comparing with AI plus LHRH agonist and LHRH alone in premenopausal metastatic breast cancer patients who failed to tamoxifen treatment.

This randomized phase II trial is studying fulvestrant with goserelin for ovarian suppression by goserelin to see how well it works compared to anastrozole with goserelin and goserelin alone in recurrent or metastatic ER-positive breast cancer.