Breast cancer subjects with multiple brain metastases are often initially treated with stereotactic radiosurgery (SRS), a non-surgical radiation technique used to treat small brain tumors or whole brain radiation therapy (WBRT). When initially managed with SRS, subjects often develop new brain metastases in the untreated brain, requiring additional SRS procedures and, eventually, WBRT, which is often associated with significant neurocognitive sequelae (headache, nausea, dizziness, confusion, memory loss and motor dysfunction).