Dissecting brain tumor growth and metastasis in vitro and ex vivo

Local infiltration and distal dissemination of tumor cells hamper efficacy of current treatments against central nervous system (CNS) tumors and greatly influence mortality and therapy-induced long-term morbidity in survivors. A number of in vitro and ex vivo assay systems have been established to better understand the infiltration and metastatic processes, to search for molecules that specifically block tumor cell infiltration and metastatic dissemination and to pre-clinically evaluate their efficaciousness. These systems allow analytical testing of tumor cell viability and motile and invasive capabilities in simplified and well-controlled environments. However, the urgent need for novel anti-metastatic therapies has provided an incentive for the further development of not only classical in vitro methods but also of novel, physiologically more relevant assay systems including organotypic brain slice culture. In this review, using publicly available peer-reviewed primary research and review articles, we provide an overview of a selection of in vitro and ex vivo techniques widely used to study growth and dissemination of primary metastatic brain tumors. Furthermore, we discuss how our steadily increasing knowledge of tumor biology and the tumor microenvironment could be integrated to improve current research methods for metastatic brain tumors. We believe that such rationally improved methods will ultimately increase our understanding of the biology of brain tumors and facilitate the development of more efficacious anti-metastatic treatments.