Somatostatin receptor subtype expression in human tumors

The presence of functional SSR in tumors has several clinical implications which include the possibility a) to control hormonal hypersecretion and rel ated symptomatology by treatment with SS-analogs, b) to detect SSR positive tumors and their metastases by in vivo SSR scintigraphy, and c) to carry o ut SSR-targeted radiotherapy using radiolabeled SS-analogs. The majority of SSR positive tumors show a differential expression of somatostatin recepto r subtypes, sst(2) receptors being the most frequently expressed SSR subtyp e. The predominant expression of sst, receptors forms the basis for the suc cessful application of sst(2) preferring agonists in the treatment of patie nts with GH-secreting pituitary adenomas, as well as in patients with carci noid or islet cell tumors. Sst(2) and sst(5) receptors appear to be differe ntially involved in the regulation of normal and tumoral pituitary hormone secretion. Additionally, sst(2) receptors are involved in the receptor-medi ated internalisation of sst, preferring radiolabeled SS-analogs. The predom inant expression of sst(2) receptors in neuroendocrine tumors probably dete rmines the successful application of radiolabeled SS-analogs for the detect ion of primary tumors and their metastases by SSR scintigraphy. In conclusion, the efficacy of treatment with SS-analogs, the visualisation of SSR-positive tumors, as well as the possibility to carry out SSR-target ed radiotherapy, may very well depend upon the density and subtype of SSR t hat is expressed by the tumors. Therefore, the characterisation of SSR subt ypes in human tumors may have important clinical consequences.