In a study conducted by Shi and colleagues in 2017 [97], it was reported that GAMs secrete abundant pleiotrophin (PTN), which stimulates glioma stem cells (GSCs) through its receptor PTPRZ1, thereby promoting malignant growth of glioblastoma (GBM) through PTN–PTPRZ1 paracrine signaling. Here, PTN is linked to central nervous system cancer.