CD274 and glioma: However, in a large series of human glioma samples involving 345 patients, the rate of PD-L1 expression positivity was found to be only 6.1%; specifically, positivity was found in 0/54 grade I/II, 0/47 grade III, and 21/244 grade IV gliomas (3 gliosarcoma and 18 GBM cases) [13].