Glioblastoma is the most common
primary brain tumor, highly aggressive by being proliferative, neovascularized and invasive, heavily infiltrated by immunosuppressive
glioma-associated myeloid cells (
GAMs), including
glioma-associated microglia/macrophages (GAMM) and myeloid-derived suppressor cells (MDSCs). Quantifying
GAMs by molecular imaging could support patient selection for
GAMs-targeting
immunotherapy, drug target engagement and further assessment of clinical response. Magnetic resonance imaging (MRI) and
amino acid positron emission tomography (PET) are clinically established imaging methods informing on
tumor size, localization and secondary phenomena but remain quite limited in defining
tumor heterogeneity, a key feature of
glioma resistance mechanisms. The combination of different imaging modalities improved the in vivo characterization of the
tumor mass by defining functionally distinct tissues probably linked to
tumor regression, progression and infiltration. In-depth image validation on tracer specificity, biological function and quantification is critical for clinical decision making. The current review provides a comprehensive overview of the relevant experimental and clinical data concerning the spatiotemporal relationship between
tumor cells and
GAMs using PET imaging, with a special interest in the combination of
amino acid and translocator
protein (TSPO) PET imaging to define heterogeneity and as
therapy readouts.