Intrathecal Pertuzumab and Trastuzumab in Patients With New Untreated Asymptomatic or Low Symptomatic Brain Metastasis in HER2 Positive Breast Cancer

The purpose of this research study is to determine how well pertuzumab and trastuzumab works in treating breast cancer that has spread to the brain. Pertuzumab and trastuzumab are treatments that stop breast cancer cells from growing abnormally by inhibiting (or blocking) members of a family of proteins that include Human Epidermal Growth Factor Receptor 2 (HER2). Pertuzumab and trastuzumab have been found to be very effective for HER2-positive breast cancer and are FDA approved for treatment of metastatic breast cancer outside of the brain when given through the vein. This suggests that pertuzumab and trastuzumab may help shrink or stabilize HER2-positive breast cancer that has spread to the brain in this research study. In this research study, the investigators are looking to see whether pertuzumab and trastuzumab will work to decrease the size of or stabilize breast cancer that has spread to the brain.