PTEN and cancer: In fact, astrocyte-derived exosomes mediate the intercellular transfer of miRNAs that target the PTEN tumor suppressor gene to metastatic cancer cells, promoting invasion and brain metastasis.81 This, in turn, leads to the increased secretion of chemokine ligand 2 (CCL2), which recruits myeloid cells, enhancing the outgrowth of brain metastatic cells and reducing the effect of apoptotic signaling.81 Inhibition of astrocytic exosomal release prevents PTEN loss and suppresses brain metastasis.81