Brain metastases in breast cancer

Metastasis of breast cancer cells to the brain is an intricate and sophisticated process, requiring tumor cells to overcome obstacles, evolve, and adapt to unique environments in order to survive. The metastatic cascade outlines the initial mechanisms the tumor cells must adhere to in order to migrate to the brain. The cells must then penetrate through the blood-brain barrier, wherein they must quickly adapt to the unique microenvironment of the brain. In addition to utilizing and manipulating host cells, substrates and upregulating proteins, adaption and growth are achieved through other various mechanisms including tumor cell extravasation, the formation of the blood-tumor barrier, vessel co-option, and angiogenesis. Adaption is key for survival, with studies highlighting the genetic mutations associated with metastasized tumor cells, when compared to their primary breast cancer (BC) counterpart. Once diagnosed with brain metastasis (BM), prognosis is poor, especially in patients with leptomeningeal disease. Presently, treatment of BM includes surgery, radiotherapy, and systemic therapy. Choosing the appropriate treatment requires consideration of multiple factors including but not limited to the BC subtype, the progression of metastasis, and the patient's own preferences.