Figure 2.

The primary and metastatic cell niche. Primary tumor cells reside in neural interstitial matrix composed of hyaluronan, collagen, adhesive glycoproteins, and cellular components such as microglia, macrophages, and parenchymal cells (i.e., neurons/astrocytes/oligodendrocytes). Extravasation of circulating tumor cells (CTCs) in response to cytokine secretion is mediated by cell adhesion molecules (CAMs) and integrins. The metastatic niche on the leptomeningeal (pial) surface is significantly different from neural interstitial matrix, and is composed of a dense network of collagen, laminin and fibronectin. Characterization of protein and molecular components which drive tumor cell adaptation to, and education of, the metastatic niche may uncover targets for inhibitors of leptomeningeal colonization and tumor growth.