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

Abstract

Persistently elevated GH and IGF-I levels are associated with increased mortality. Their response to somatostatin analogs (SSA) is variable. The objective of this study was to examine the significance of somatotroph adenoma type on response to SSA. This study was a retrospective examination of postoperatively treated acromegalic patients with the SSA octreotide. The study was performed at a university-affiliated tertiary care center. Forty patients with acromegaly were studied. Normalization of IGF-I levels and GH responses were the main outcome measures. 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). 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.