Systemic treatment of HER2-positive breast cancer patients with brain metastases: current status and exploratory case study in a Portuguese cohort

Over the last years, the incidence of brain metastases in HER2 breast cancer patients has increased. Surgery and radiotherapy are the current standard local therapies. Nevertheless, it is unclear which and when systemic treatment should be applied in addition to local treatment. This work aims to present an updated review of current systemic treatment options for patients with HER2+ metastatic breast cancer with brain metastases and to present a case study of clinical cases that occurred in a Portuguese population. The methodology of this work included a literature search in PubMed for the impact of HER2-targeting agents, such as pertuzumab, trastuzumab emtansine (T-DM1), lapatinib, neratinib, trastuzumab deruxtecan, and tucatinib in the treatment of patients with HER2+ breast cancer with brain metastases. Then, a cohort of Portuguese patients with HER2+ breast cancer (n=44) was analyzed. In this exploratory study, considering a follow-up of 23.9 months, three patients (6.8%) developed brain metastases despite having shown a complete pathological response. The role of systemic treatment for patients with HER2 breast cancer with brain metastases has rapidly evolved following recent successes in phase II and III clinical trials. The biggest challenge is how to integrate systemic and local treatment in the management of these patients.