The implication of somatotroph adenoma phenotype to somatostatin analog responsiveness in acromegaly

Context: Persistently elevated GH and IGF-I levels are associated with increased mortality. Their response to somatostatin analogs (SSA) is variable.

Objective: The objective of this study was to examine the significance of somatotroph adenoma type on response to SSA.

Design: This study was a retrospective examination of postoperatively treated acromegalic patients with the SSA octreotide.

Setting: The study was performed at a university-affiliated tertiary care center.

Patients: Forty patients with acromegaly were studied.

Main outcome measures: Normalization of IGF-I levels and GH responses were the main outcome measures.

Results: Univariate analysis revealed that responders were more likely to have densely granulated somatotroph adenomas (80% vs. 43.8%; P = 0.024), to be older (51.3 vs. 38.2 yr; P < 0.003), to have smaller tumors (stage < or =3; 78.6% vs. 35.7%; P = 0.022), to have lower baseline IGF-I (453 vs. 716 microg/liter; P < 0.001) and GH levels (2.7 vs. 7.8 microg/liter; P < 0.05), and to require a lower maximum dose of SSA (24 vs. 31 mg every 4 wk; P = 0.013). Multivariate analysis confirmed that a densely granulated adenoma was the strongest predictor of complete response [adjusted odds ratio (OR), 58.41; 95% confidence interval (CI), 1.24-1000.00; P = 0.04] compared with other covariates, including older age at time of diagnosis (OR, 1.15/yr; 95% CI, 1.01-1.31; P = 0.03), and tumor stage of 3 or less (OR, 29.77; 95% CI, 1.01-885.45; P < 0.05).

Conclusions: Somatotroph tumor type represents a strong clinical predictor of response to SSA treatment and will help to identify patients who warrant more vigilant management of their disease.