Expression of PD-L1/2 has been analysed in some NEN subgroups, including poorly-differentiated (grade 3) neuroendocrine carcinomas (NECs)[35, 36], with reported PD-L1 expression rates which vary between 20-50%, however there is very limited data describing PD-L1/2 expression in well-differentiated NETs, including Si-NETs [37, 38]. This evidence concerns the gene CD274 and neuroendocrine carcinoma.