Encouraged by the approval of the in-house developed radiopharmaceutical (S)-(−)-[18F]fluspidine for clinical trials (EudraCT Numbers: 2014-005427-27, 2016-001757-41), the promising results of a collaborative pilot study in an orthotopic mouse model of GBM [40], and the establishment of orthotopic brain tumour models in our group, we decided to investigate further the relevance of sig1R in brain cancer biology and to evaluate the potential of (S)-(−)-[18F]fluspidine-PET to characterise brain tumours on a molecular level. Here, SIGMAR1 is linked to brain cancer.