Expression of Somatostatin Receptors in Phaeochromocytoma and Paragangliomas

N Parvizi, A Alsafi, M Vergine, R Ramachandran, NM Martin, F Palazzo, D Pinato, R Sharma, K Meeran, R Dina, TM Tan, Imperial Centre for Endocrinology.


Phaeochromocytoma and paragangliomas are neuroendocrine tumours arising from chromaffin cells. These tumours express somatostatin receptors (SSTRs), which has five different main subtypes (SSTR1, SSTR2, SSTR3, SSTR4 and SSTR5). The differential expression of the different receptor subtypes in these tumours has previously been reported with a small series of tumour samples. Our study examined the expression of SSTR subtypes in a larger series of benign and malignant phaeochromocytomas and paragangliomas.

Phaeochromocytoma and paraganglioma specimens from 77 patients were analysed in tissue microarrays, using immunohistochemical staining with SSTR1, SSTR2, SSTR3 and SSTR5. Each core was scored by two independent observers, and an immunohistochemical score of 0-300 was constructed based on the percentage and intensity of cells expressing SSTR. The results were analysed using the non-parametric Mann-Whitney test. Malignancy was defined as local tumour invasion and the presence of tumour tissue in non-chromaffin cell sites, such as in lymph nodes, bone, liver or lung.

The vast majority, 95% (73/77) of tumours expressed SSTR3. However, we found overall larger proportions of SSTR1, SSTR2 and SSTR5 expression than previously reported. There was a significantly higher expression of SSTR3 receptors in malignant tumours (n=13) compared to benign tumours (n=64) (median immunohistochemical score [interquartile ranges]: malignant score 172 [136-260] compared to benign score 117 [61-200]; p=0.03). Otherwise, no significant differences were seen in SSTR1, SSTR2 and SSTR5 expression. SSTR subtype expression was similar between phaeochromocytomas and paragangliomas.

Phaeochromocytomas and paragangliomas express SSTRs, but the pattern of SSTR subtype expression varies widely. These data suggest that somatostatin analogues targeting SSTR3 may be particularly useful in the treatment of malignant phaeochromocytomas and paragangliomas.