The role of somatostatin receptors in breast and pancreatic cancer

Somatostatin, a hormone which has an inhibitory influence on several physiological processes, is a small peptide consisting of 14 amino-acids, and was first isolated from the hypothalamus of the rat. Soon after, somatostatin was found in numerous other organs, such as the brain, stomach, intestines, pancreas, thyroid, thymus and bronchi, from which it could be extracted. Natural somatostatin has a very short half-life and can only be administered intravenously. The development of several longacting analogues of somatostatin facilitated diagnostic procedures and therapy involving somatostatin and its receptors. One of the first and best known effects of the hormone somatostatin is inhibition of the release of growth hormone by the pituitary gland. Other, mainly inhibitory effects of somatostatin have been described recently, including a direct inhibitory effect on the growth of tumour cells. Somatostatin receptors (SS-R's), present on tumour and pituitary celis, mediate this inhibitory effect as well as release of growth hormone. The analogue octreotide, used in this study, binds to SS-R's on normal and tumour cells. Autoradiography, using '251_ Tyr-octreotide, was utilized to localize receptors for somatostatin in vitro. These receptors were found in several neuroendocrine tumours, as well as in breast carcinomas and islet cell tumours of the pancreas. The aim of this study was to assess the possibility of visualizing SS-R's in vivo, using octreotide labelled with radioactive "'Indium and diethylene-triaminopentaacetic acid (DTPA) as a carrier (octreoscan).