Anticancer therapies and CNS relapse: overcoming blood-brain and blood-cerebrospinal fluid barrier impermeability

Prolonged survival with targeted therapies has sometimes come at the expense of an increased risk of CNS relapse; because many of these agents poorly penetrate the BBB, malignant cells may remain viable within the CNS. The ability of anticancer drugs to penetrate the BBB is a major consideration in the treatment of CNS parenchymal metastases. Optimal chemotherapy approaches for treating CNS metastases remain unclear due to a lack of evidence-based recommendations. Recent hypothesis-generating studies evaluating intra-cerebrospinal fluid administration of targeted agents indicate that these drugs may be effective in treating leptomeningeal disease and are associated with a low incidence of drug-related adverse events. Newer strategies for treating cerebrospinal fluid metastases may co-opt endogenous systems of the BBB, such as those involved in receptor-mediated transcytosis or classic carrier-mediated transporter systems to facilitate drug delivery across the BBB.