Immunohistochemical expression of somatostatin receptors in digestive endocrine tumours

Abstract

Introduction: Somatostatin receptors are expressed in a large number of human tumours. The somatostatin receptors types 1-5 expression in a series including 100 gastro-entero-pancreatic endocrine tumours were analysed.

Methods: From a prospectively built database of patients with gastro-entero-pancreatic endocrine tumours referred from three institutions, 100 cases with clinical and pathological data were selected. Somatostatin receptors expression by immunohistochemistry with somatostatin receptor types 1-5 antibodies in tissue paraffin sections were studied and correlated with the histological diagnosis according to the WHO classification, location and functional status.

Results: Of the 100 cases, 67 were gastrointestinal tumours, 25 pancreatic and 8 liver metastasis of unknown origin. Thirty-one of them were functioning tumours: 2 insulinomas, 5 gastrinomas, 1 glucagonoma and 23 carcinoids. Somatostatin receptors expression was observed in 94 tumours. The six negative cases were all non-functioning tumours. Somatostatin receptors 2a and 5 were highly expressed (86 and 62%, respectively), and surprisingly found even in poorly differentiated endocrine carcinomas. Somatostatin receptors expression was less frequent in pancreatic than in gastrointestinal tumours. Well-differentiated neoplasms had a higher density of somatostatin receptors. Only SSTR2a showed membrane staining.

Conclusions: Immunohistochemistry revealed that somatostatin receptors were highly expressed in both primary and metastatic gastro-entero-pancreatic endocrine tumours with heterogeneous staining distribution. It proved to be a reliable technique even in small tumour samples.