Atezolizumab + Pertuzumab + Trastuzumab In CNS Mets In BC

This research study is a Phase II clinical trial. Phase II clinical trials test the safety and effectiveness of an investigational intervention to learn whether the intervention works in treating a specific disease. "Investigational" means that the intervention is being studied. It also means that the FDA (U.S. Food and Drug Administration) has not approved the combination of atezolizumab, trastuzumab, and pertuzumab for use in humans. The FDA has not approved atezolizumab for this specific disease but it has been approved for other uses. * Atezolizumab is a protein that affects the immune system by blocking the PD-L1 pathway. The PD-L1 pathway controls the body's natural immune response, but for some types of cancer the immune system does not work as it should and is prevented from attacking tumors. Atezolizumab works by blocking the PD-L1 pathway, which may help the immune system identify and catch tumor cells. * Pertuzumab and trastuzumab are targeted therapies approved by the FDA to be used alone or in combination with a chemotherapy drug to treat HER2-positive metastatic breast cancer that hasn't been treated with either trastuzumab or chemotherapy yet. * Pertuzumab and trastuzumab are called "targeted therapies" because they work by attaching themselves to specific receptors on the surface of breast cancer cells, known as HER2 receptors. When these targeted therapies attach to HER2 receptors, the signals that tell the cells to grow are blocked and the cancer cell may be marked for destruction by your immune system. This process allows pertuzumab and trastuzumab to help slow or stop the growth of the breast cancer. Pertuzumab and trastuzumab target different areas of the HER2 cell, so they are believed to work together more effectively. In this research study, investigators are looking to see how well the cancer responds to the combination of atezolizumab in combination with pertuzumab and trastuzumab.