Enzalutamide (MDV3100) is a drug that blocks the hormone testosterone from binding to the androgen (male hormone) receptor. It is approved for the treatment of men with advanced prostate cancer. Researchers believe that blocking the androgen receptor may also slow or stop tumor growth in patients with breast cancer.
The purpose of this study is to determine the highest dose of enzalutamide that can be given safely in women with metastatic breast cancer that persists despite prior treatment. The use of enzalutamide in breast cancer patients is considered investigational. Enzalutamide is a capsule that is taken orally (by mouth).