Treatment of brain metastases: chemotherapy

Although systemic therapy is the primary therapeutic modality for disseminated cancer, it plays a limited role in the treatment of brain metastases (BM). This review discusses the blood-brain barrier (BBB), interactions of systemic therapy with supportive care agents used in BM patients, the role of primary tumor sensitivity in the treatment of BM, and unique issues related to the specific primary tumor histologies. The specialized physiology of the brain vasculature that forms the BBB may preclude large and/or water-soluble systemic agents from reaching BM. Once metastases grow larger than 1-2 mm, there is preclinical and clinical evidence that the BBB is at least partially disrupted. Thus, the best treatment strategy in established BM may be to use an agent that is effective against the primary tumor regardless of its apparent BBB permeability. The use of anticonvulsants and corticosteroids must be carefully considered as they can decrease the effectiveness of systemic anti-tumor therapy. Despite the absence of level I data to routinely recommend the use of systemic therapy for solid tumor BM, these treatments should be considered in patients with good performance status and multiple, small metastases, especially if the primary tumor is chemosensitive. The systemic treatment of BM will continue to evolve as effective small-molecule inhibitors are developed and treatment regimens for each specific primary tumor are optimized.