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.