Aromatase inhibitors are drugs used in postmenopausal women to treat breast cancers that are fueled by estrogen. They interfere with the production of estrogen in the body. However, in some women, the breast cancer stops responding to these drugs. Exemestane is an example of an aromatase inhibitor.
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 assess the safety and effectiveness of giving enzalutamide in combination with exemestane in women with advanced breast cancer. Women will be randomly assigned to receive exemestane with either enzalutamide or a placebo. All drugs used in this study are taken orally (by mouth).