FOLH1 and brain neoplasm: Examples include ligands for prostate-specific membrane antigen (PSMA), somatostatin receptors (SSTR) in neuroendocrine tumours (NETs), amino-acid tracers (e.g., for brain tumours), fibroblast activation protein (FAP) inhibitors, and emerging immuno-PET agents targeting immune checkpoints or other tumour microenvironment markers [11,12,13].