A recent clinical trial on microglia targeting in patients with brain metastases (NCT02433171) assessed the potential of positron emission tomography (PET) imaging using two different PET tracers: methionine that is sensitive to the tumor metabolic activity (with high tumor-to-normal brain contrast), and PBR28 that is sensitive to inflammatory processes (binds to translocator proteins upregulated in activated microglia). This evidence concerns the gene TSPO and neoplasm.