DPP4 and central nervous system cancer: The established macrophage-related gene signature includes both protective genes (SCN3A, SEMA6B) and risk-increasing genes (PXDN, CDH6, ANPEP, CCDC37, DPP4, GPNMB, FANCA, NETO2, PRRG1, TMEM26) for predicting the prognosis of glioma patients (Fig. 3).