In Sreekanthreddy’s study, elevated serum OPN levels were shown: in GBM, it was 31.54 ± 28.98 ng/mL, compared with 17.38 ± 7.91 ng/mL in grade III astrocytoma, 13.79 ± 4.56 ng/mL in grade II astrocytoma, and 11.70 ± 7.26 ng/mL in normal controls. Here, SPP1 is linked to glioblastoma.