Some women with breast cancer are treated with aromatase inhibitors. These drugs work by blocking the enzyme needed to make estrogen, a hormone that fuels the growth of many breast cancers. But in some women, the cancer continues to grow despite aromatase inhibitor therapy.
Fulvestrant is another drug used to treat breast cancer. In this study, researchers want to determine if combining fulvestrant with a PI3 kinase inhibitor is more effective than fulvestrant alone in women with advanced or metastatic breast cancer that is resistant to aromatase inhibitor therapy.
PI3 kinase is an enzyme that drives the growth of many cancers, including advanced breast cancer. This study is evaluating two investigational drugs that block the activity of PI3 kinase: GDC-0941 and GDC-0980. Women in this study will be randomly assigned to receive fulvestrant plus placebo, fulvestrant plus GDC-0941, or fulvestrant plus GDC-0980. GDC-0941 and GDC-0980 are taken orally (by mouth); fulvestrant is given via injection.