Somatostatin and somatostatin analogues: diagnostic and therapeutic uses.

Somatostatin and its octapeptide analogues exert their effects through interaction with somatostatin receptor (sst) subtypes 1 through 5 (sst 1-5 ). Somatostatin binds with high affinity to all sst subtypes, whereas the currently commercially available octapeptide analogues bind only with a high affinity to sst 2 and sst 5. Pituitary tumors, endocrine pancreatic tumors, and carcinoid tumors express multiple sst subtypes, but sst 2 predominance is found in 90% of carcinoids and 80% of endocrine pancreatic tumors. Sst 2 and sst 5 predominance is found in growth hormone-secreting pituitary tumors. In patients harboring sst 2 - or sst 5 -positive neuroendocrine tumors, clinical symptomatology can be controlled by the chronic administration of one of the currently commercially available octapeptide somatostatin analogues. Tumors and metastases that bear sst 2 or sst 5 can be visualized in vivo after injection of radiolabeled octapeptide analogues. Radiolabeled octapeptide analogues can also be used for radiotherapy of sst 2 - and sst 5 -positive advanced or metastatic neuroendocrine tumors.