Endocrine Abstracts

Introduction: The effect of conventional somatostatin agonists (SA) on somatotroph pituitary adenomas is primarily mediated by somatostatin receptors (sstr) subtype 2. Sstr expression has been proposed as a prognostic marker for response to medical therapy. Earlier studies have shown lower sstr2a expression in SA treated adenomas, but selection bias could not be excluded.

Objective: To assess the effect of SA on the immunohistochemical expression of sstr2a, 3 and 5.

Patients and methods: Histological specimens from 78 somatotroph adenomas from patients operated for acromegaly at Oslo University Hospital, Rikshospitalet between 2000 and 2010 were evaluated. After exclusion of specimens without representative tumour tissue and from patients with pretreatment other than SA, 65 patients were included in the study. 28 of these were pretreated with SA (SA-group), 37 were operated directly (directsurgery-group; DS).

Immunohistochemical staining was performed with novel monoclonal anti-SSTR2A (UMB-1), anti-SSTR3 (UMB-5), and anti-SSTR5 (UMB-4) antibodies. The adenomas were scored into 12 categories by the IRS-score.

A subgroup of the 26 patients was earlier included in a randomised trial comparing direct surgery with surgery performed after SA treatment. Subgroup analyses were performed on this group.

Results: Immunohistochemical score for sstr2a in the pretreated patients (SA-group) was significantly lower than in patients operated directly (DS-group) (P=0.002). Subgroup analysis in the randomised patients confirmed this finding. Scores for sstr3 and sstr 5 were not significantly different between groups. There was no significant difference in sstr 3 and 5 score between the treatment groups.

Conclusion: Sstr2 is down regulated by SA treatment. Subgroup analyses in the randomised cohort excluded selection bias concerning pretreatment. There is no major effect of SA treatment on sstr3 and sstr5.