Women with breast cancers that are fueled by the female hormone estrogen often receive treatment that blocks the effects of these hormones on cancer cells. However, in some cases, the cancer stops responding to hormonal therapy and begins growing again.
The purpose of this study is to find the highest dose of an investigational drug called ARN-810 in postmenopausal women with estrogen receptor-positive breast cancer that has returned or continued growing after hormonal therapy such as tamoxifen or aromatase inhibitors. ARN-810 works by blocking the actions of female sex hormones on cancer growth and has been shown in laboratory studies to shrink breast cancers. It works by lowering the amount of estrogen receptors on breast cancer cells (to which estrogen binds so it can exert its activity) and by causing any remaining estrogen receptors to become inactive.
ARN-810 is a tablet that is taken orally (by mouth).