Study of Physiological and High Dose Estradiol in the Treatment of Hormone Receptor Positive Metastatic Breast Cancer

The purpose of this study is to compare the effects of two doses (6 mg and 30 mg) of Estradiol, a type of estrogen. This and other forms of estrogen used at doses much higher than those used for postmenopausal hormone replacement therapy have been shown to cause tumor growth stabilization or shrinkage in patients with breast cancer.