The radiolabeled version of the ligand, [11C]PK 11195 was initially used for human glioma imaging in 1989.113 The PK11195bound to TSPO, specifically in peripheral organs and hematogenous cells linked to γ-aminobutyric acid (GABA)-regulated channels, as well as the active site of microglia. Here, TSPO is linked to central nervous system cancer.