The circulatory sPD-L1 protein levels exhibited the highest concentrations in the glioma cohort (median: 0.5594 ng/mL, range: 0–1.4235 ng/mL) compared with that in the meningioma (0.0688, 0.0454–1.4117; p < 0.001) and HC cohorts (0.1107, 0–0.5908; p < 0.001) (Table 1 and Figure 1A). Here, SPDL1 is linked to central nervous system cancer.