Immunohistochemical localization of somatostatin receptor subtypes in benign and malignant adrenal tumours

Abstract

Somatostatin mediates its action through five receptor subtypes (sst1-5) that are widely distributed in various endocrine tissues and tumours. Because of the inhibitory effects of somatostatin, long-acting analogues have been synthesized. In contrast to their well-established use in neuroendocrine and pituitary tumours, little is known about their potential use in adrenal tumours. We examined somatostatin receptor protein expression in adrenal tumours of various aetiologies. Immunostaining was performed with specific polyclonal antibodies for sst1-5. Seven benign and eight malignant pheochromocytomas (PHEOs), eight aldosterone-secreting adenomas (APAs), nine cortisol-secreting adenomas (CPAs), seven nonfunctioning adrenal tumours (NFAs) and 25 adrenal carcinomas (CAs) as well as eight normal adrenal glands were investigated. Staining pattern, distribution and subcellular localization of the somatostatin receptor subtypes were evaluated. In the majority of normal cortices the expression of sst1-5 was limited to the reticular zone. The medulla was predominantly positive for sst3. Most cortical adenomas were positive for all five subtypes. However, in the majority of these tumours, less than 30% of cells were positively stained. A high expression of sst4 was found in CPAs but only very few cortical carcinomas exhibited sst immunostaining. All benign PHEOs were positive for sst3. The majority presented with more than 60% of tumour cells stained. By contrast, only six out of eight malignant PHEOs were positive for sst3. Somatostatin receptor subtypes are expressed in PHEOs as well as in tumours of the adrenal cortex with tumour-specific distribution patterns. This may offer new diagnostic and therapeutic possibilities.