Prior to the current standard of care utilizing estrogen deprivation or antiestrogen therapy to treat hormonally sensitive breast cancers, treatment with pharmacologic doses of estrogen was a common technique used to treat post-menopausal women with hormone sensitive metastatic disease that resulted in durable responses with regression of disease. A randomized trial comparing tamoxifen and pharmacologic doses of estrogen demonstrated similar rates of response with long-term follow-up data confirming a survival benefit for those treated with the estrogen preparation. Additional data has shown that post-menopausal women with hormonally sensitive tumors that have progressed on prior endocrine therapies responded to treatment with pharmacologic doses of estrogen. These data, coupled with pre-clinical data that postmenopausal levels of estrogen can be used to cause apoptosis (programmed cell death within the tumor) and tumor regression in exhaustively treated endocrine resistant disease form the rationale for the proposed clinical trial. This trial seeks to confirm the response rate for estrace treatment in a patient population heavily pre-treated with modern endocrine therapies.