MKI67 and neoplasm: Although the routine use of 18F-FDG PET/CT in all grades of NENs cannot be justified in view of increased costs, it might be reasonable to suggest the addition of 18F-FDG PET/CT in those particular cases (i.e., intermediate Ki-67 index, high grade lesions on biopsy, heterogeneous or low uptake on somatostatin receptor imaging, clinically aggressive disease, poor response to PRRT) where high intra- and inter-tumour heterogeneity may not be revealed on only receptor-based imaging [80,81].