Microenvironment determinants of brain metastasis

Metastasis accounts for 90% of cancer-related mortality. Brain metastases generally present during the late stages in the natural history of cancer progression. Recent advances in cancer treatment and management have resulted in better control of systemic disease metastatic to organs other than the brain and improved patient survival. However, patients who experience recurrent disease manifest an increasing number of brain metastases, which are usually refractory to therapies. To meet the new challenges of controlling brain metastasis, the research community has been tackling the problem with novel experimental models and research tools, which have led to an improved understanding of brain metastasis. The time-tested "seed-and-soil" hypothesis of metastasis indicates that successful outgrowth of deadly metastatic tumors depends on permissible interactions between the metastatic cancer cells and the site-specific microenvironment in the host organs. Consistently, recent studies indicate that the brain, the major component of the central nervous system, has unique physiological features that can determine the outcome of metastatic tumor growth. The current review summarizes recent discoveries on these tumor-brain interactions, and the potential clinical implications these novel findings could have for the better treatment of patients with brain metastasis.