PLG and neoplasm: Astrocytes react to extravasating tumor cells by secreting plasmin, which as opposed to its advantageous use during initial tumor invasion in early metastasis, actually prevents colonization of the brain parenchyma in two ways: (1) by activating the mobilization of FasL, a proapoptotic cytokine, to induce tumor cell apoptosis; and (2) by inactivating tumor cells expressing L1 cell adhesion molecule, L1CAM to inhibit their adhesion to brain capillaries [26].