The metastatic microenvironment

Tumor cells making up the primary tumor and those in metastatic lesions are genetically and phenotypically different. It is safe to assume that the phenotype and functions of non-tumor cells such as endothelial cells, fibroblasts or macrophages residing in the microenvironment of primary tumors differ from those of similar non-tumor cells residing in metastatic microenvironments. It is therefore to be expected that the patho-biologic consequences of interactions between tumor cells and the microenvironments of the primary tumor or of the metastatic lesions will also be different. Tumor-microenvironment interactions should, thus, be studied in the context of the site. This short review summarizes state of the art with respect to interactions between the brain microenvironment with brain-metastasizing tumor cells.