Palbociclib With Fulvestrant for Metastatic Breast Cancer After Treatment With Palbociclib and an Aromatase Inhibitor

Inclusion Criteria: * Women may be premenopausal or postmenopausal * Metastatic or locally advanced breast cancer, not amenable to surgery or radiation with curative intent * ER-positive and/or PR-positive, HER2-negative tumor * Prior treatment: progressed on and following at least 6 months of combined treatment with palbociclib and AI therapy; up to one (1) prior line of chemotherapy for advanced disease is allowed in addition to any number of prior lines of endocrine therapy; no prior treatment with fulvestrant, everolimus, or any agent whose mechanism of action is to inhibit the PI3K-mTOR pathway in the metastatic setting * Eastern Cooperative Oncology Group (ECOG) performance status 0-2 * Evaluable or measurable disease * Disease that is amenable to biopsy * Adequate hematologic and renal function * History of central nervous system metastasis is allowed if treated and stable * Prior radiation therapy is allowed if recovered from toxicity and disease evaluable for response outside of the radiation fields or evidence of post-radiation progression of previously irradiated sites of disease * Ability to understand and willingness to sign a written informed consent document Exclusion Criteria: * Women who are pregnant or breast-feeding * Concurrent use of inhibitors or inducers of CYP3A4, or medications which prolong the QTc interval * Major surgery, chemotherapy, radiotherapy, or other anti-cancer therapy within 2 weeks before registration; prior radiotherapy to ≥25% of bo…