PLG and neoplasm: In BrM, astrocytes exhibit both pro- and antitumor functions.78 Early after tumor cell infiltration, astrocytes are activated by gliosis and contribute to neuro-protection by inducing tumor cell death through nitric oxide production and plasmin secretion, and forming reactive astrocyte (RA) boundaries delineating the metastatic lesion from the adjacent normal brain.43,79,80 However, they also promote BrM formation and colonization at various stages.