SPDL1 and central nervous system cancer: With the increase in glioma stage, the mean level of baseline sPD-L1 tended to increase (stage I: 8.18 ± 2.70 pg/ml; stage II: 10.52 ± 18.35 pg/ml; stage III: 29.65 ± 24.23 pg/ml, and stage IV: 60.60 ± 65.95 pg/ml, Figure 1A).