Fig. 4

TSPO-IHC correlates to TSPO-PET signal and is highest in the solid tumor core of IDH-wildtype GBMs. TSPO-PET image and TSPO-IHC (400x) of a TSPO-PET low glioblastoma case (GBM_20) (a) and a TSPO-PET high glioblastoma case (GBM_10) (b), further imaging information and full histology can be found in Suppl. Figure 4. Spearman correlation of TSPO-IHC labelling (%Area) with TSPO-PET enrichment (SUVmax) of IDH-wt GBMs showed an association with TSPO-PET enrichment in both solid tumor areas (r = 0.588, ***p < 0.001) and infiltration zones (r = 0.300, ***p < 0.001) (c). TSPO H Score and TSPO-IHC %Area (d) in solid tumor areas weighted for sample amount per patient were compared between GBM expression subtypes. A significantly higher TSPO expression was observed in patients with mesenchymal (MES) transcriptome patterns compared to patients with proneural (PRO) or classical (CL) patterns (Post hoc Games Howell, ***p < 0.001). TSPO H Score (e), TSPO-IHC %Area (f) and TSPO-PET enrichment values (g) were analyzed across different tumor cell content areas and solid tumor areas with the highest tumor cell content in all comparisons exhibited the highest TSPO signal (expression/enrichment), (Tukey multiple comparison test, ***p < 0.001, *p < 0.05). Significances are displayed as follows: p > 0.05 = n.s., p < 0.05 = *, p < 0.01 = **, p < 0.001 = ***. GBM: glioblastoma, IDH: isocitrate dehydrogenase, IDH-wt: IDH-wildtype, IHC: immunohistochemistry, PET: positron-emission tomography, SUVmax: maximum standardized uptake value