TSPO PET, tumour grading and molecular genetics in histologically verified glioma: a correlative 18F-GE-180 PET study

Background The 18-kDa translocator protein (TSPO) is overexpressed in brain tumours and represents an interesting target for glioma imaging. 18 F-GE-180, a novel TSPO ligand, has shown improved binding affinity and a high target-to-background contrast in patients with glioblastoma. However, the association of uptake characteristics on TSPO PET using 18 F-GE-180 with the histological WHO grade and molecular genetic features so far remains unknown and was evaluated in the current study. Methods Fifty-eight patients with histologically validated glioma at initial diagnosis or recurrence were included. All patients underwent 18 F-GE-180 PET, and the maximal and mean tumour-to-background ratios (TBR max , TBR mean ) as well as the PET volume were assessed. On MRI, presence/absence of contrast enhancement was evaluated. Imaging characteristics were correlated with neuropathological parameters (i.e. WHO grade, isocitrate dehydrogenase ( IDH ) mutation, O-6-methylguanine-DNA methyltransferase (MGMT) promoter methylation and telomerase reverse transcriptase (TERT) promoter mutation). Results Six of 58 patients presented with WHO grade II, 16/58 grade III and 36/58 grade IV gliomas. An ( IDH ) mutation was found in 19/58 cases, and 39/58 were classified as IDH -wild type. High 18 F-GE-180-uptake was observed in all but 4 cases (being WHO grade II glioma, IDH -mutant). A high association of 18 F-GE-180-uptake and WHO grades was seen: WHO grade IV gliomas showed the highest uptake intensity compared with grades III and II gliomas (median TBR max 5.15 (2.59–8.95) vs. 3.63 (1.85–7.64) vs. 1.63 (1.50–3.43), p