TSPO and central nervous system cancer: We further demonstrate the background-free detection of syngeneic PBR/TSPO-expressing glioma cells growing in the brains of Tspo−/− animals in vitro and in vivo using the selective PBR/TSPO ligands, [3H]PK11195 and [18F]PBR111, as well as antibody staining against the PBR/TSPO.