We also analysed interrelationships between SST4 expression and the expression of the other four SST subtypes as well as the expression of other receptors of or markers for neuroendocrine tumours, such as the chemokine receptor CXCR4, CgA, and programmed cell death 1 ligand 1 (PD-L1), in BP-NEN and GEP-NEN. This evidence concerns the gene SSTR4 and neuroendocrine neoplasm.