The purpose of this study is to find out what effects, good and/or bad, GDC-0941 has on metastatic breast cancer when given to you in combination with another drug, called fulvestrant. GDC-0941 (Pictilisib) is a study drug that inhibits a protein called PI3‑kinase that may be involved in the growth and spread of some cancers. In animal studies and laboratory experiments, GDC-0941 (Pictilisib) has been shown to prevent or slow the growth of many different types of human cancer cells. The study drug is currently being tested in clinical studies in people with advanced cancer. Metastatic breast cancer remains an incurable disease despite a number of more effective treatments.