Endocrine Abstracts

Background: Data on the relationship between the hormonal response to somatostatin analogues and morphological subtype of somatotroph adenomas are sparse. We have previously shown that nadir GH <1.75 μg/l on the octreotide suppression test (OST) has positive and negative predictive value 94 and 100%, respectively in predicting achievement of ‘safe’ GH levels following treatment with octreotide LAR (Karavitaki et al. 2005).

Aim: To investigate the responsiveness to OST according to somatotroph adenoma phenotype.

Patients and methods: Patients with pathologically confirmed somatotroph adenoma presenting between 2001 and 2008 were studied. Those who received medical treatment for their acromegaly prior surgery were excluded. The histological subtype was defined according to the presence of antibody Cam5.2-positive fibrous bodies (i.e. markers of sparsely granulated tumours, representing cytoplasmic filamentous globular structures).

Results: One hundred patients were identified; 44 had received medical treatment pre-operatively, 14 had no OST and 5 had no histological subtype assessment. The remaining 27 subjects were included (median age 46 years (21–80), 12 males, 7 mixed/10 densely/10 sparsely granulated). There was no difference in the GH at time 0 min (morning fasting sample) or nadir GH between the three subtypes or between densely and sparsely. There was significant difference in the percentage fall of GH on the OST between all subtypes and between densely and sparsely granulated (median: mixed 88.8% – densely 88.1% – sparsely 67.0%, P<0.05). There was no difference in the number of patients achieving nadir GH <1.75 μg/l between the subgroups. Logistic regression showed no significant effect of granularity on achieving nadir GH <1.75 μg/l after adjusting for age, sex and basal GH levels.

Conclusions: This is the first series showing that achievement of ‘safe’ GH levels following treatment with octreotide LAR, as predicted with the OST, is not associated with somatotroph adenoma subtype. Nevertheless, GH reduction is significantly less in sparsely than in densely granulated.