SSTR5 and digestive system neuroendocrine tumor, grade 1/2: Among the five SST subtypes (SST1-SST5), SST5 is concomitantly expressed at high density in 70–100% of gastroenteropancreatic neuroendocrine tumors (GEP-NETs), breast cancer and in growth hormone (GH)-secreting pituitary adenomas [7–9].