Patients with advanced HER2+ breast cancer on either (1) first-line trastuzumab/pertuzumab OR (2) second-line T-DM1 in the metastatic setting OR (3) adjuvant trastuzumab-based therapy or T-DM1 with isolated intracranial recurrence will be included. Patients with de novo metastatic disease and brain metastases or isolated intracranial recurrence can enter upon initiation of maintenance trastuzumab/pertuzumab after chemotherapy if deemed necessary by treating oncologist and meeting other inclusion criteria. Patients 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 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 with extracranial disease progression while on trial with stable intracranial disease should continue tucatinib into the next line of therapy as described in protocol.
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.