Secondary BRain Metastases Prevention After Isolated Intracranial Progression on Trastuzumab/Pertuzumab or T-DM1 in Patients With aDvanced Human Epidermal Growth Factor Receptor 2+ brEast Cancer With the Addition of Tucatinib

Patients with advanced HER2+ breast cancer on maintenance trastuzumab/pertuzumab or T-DM1 with 1st or 2nd intracranial disease event (brain metastases) and stable extracranial disease will be enrolled. They will receive local therapy with stereotactic radiosurgery ± surgical resection if indicated followed by enrollment. Patients will continue standard of care trastuzumab/pertuzumab or T-DM1 with the addition of tucatinib. Hormone receptor positive patients requiring endocrine therapy should continue. Study treatment will continue until disease progression or intolerable side effects. Patients on trial with extracranial disease progression with stable intracranial disease should continue tucatinib into next line of therapy.