Abstract

Background: Somatostatin is a tetradecapeptide exerting inhibitory action on endocrine and exocrine cell secretion and proliferation. Somatostatin receptors (SST) are widely expressed in various neoplasms including endocrine tumours. Using immunohistochemistry, the expression of SST₁, SST_2A, SST_2B, SST₃, SST₄, and SST₅ was studied in tissue microarrays (TMAs), using a series of 90 human pituitary adenomas producing growth hormone and/or prolactin, including 30 of each somatotroph, lactotroph, and mixed somatotroph/lactotroph adenoma type.

Methods: For immunohistochemistry, the standard avidin biotin complex method enhanced by tyramide was used, using polyclonal antisera for all SST types. A four point scoring system was used to assess the membranous immunopositivity.

Results: All SST types were positive in all tumour types, showing varying immunoreactivity scores. SST₅ and SST_2A were the predominant receptors, showing strong expression in high frequency in all three adenoma types. Strong expression of SST₁ was higher in lactotroph adenomas than in other tumour types.

Conclusions: The immunohistochemical results of SST expression are in agreement with most findings of previous molecular studies. The fact that SST_2A expression is predominant suggests that pharmaceutical octapeptide somatostatin analogues may act through this receptor, while the role of SST_2B may be merely synergistic.