FOLH1 and neoplasm: Other limitations include the retrospective character of this study, the observation that only a subset of 100 PSMA PET-scans were re-assessed and dually assessed which may have led to larger confidence intervals in the reported observer agreement rates, and the fact that a small proportion (3.5%) of patients were excluded because of a PSMA negative primary tumour, as it is yet unknown whether this apparent absence of PSMA expression is related to imaging technical factors or whether it is due to tumour-associated factors.