Normal insulin-like growth factor 1 during somatostatin receptor ligand treatment predicts surgical cure in acromegaly

Context: Treatment with somatostatin receptor ligands (SRLs) is often given before pituitary surgery to patients with acromegaly. Objective: To study whether the response to treatment with SRLs is predictive of surgical outcome. Design: Retrospective, observational study. Setting: Tertiary care center. Patients: We investigated 272 patients with acromegaly who had been treated with an SRL between 1990 and 2018. Intervention: All patients underwent pituitary surgery performed by a skilled neurosurgeon. Main outcome measure: Outcome of pituitary surgery in patients who had normalization of insulin-like growth factor 1 (IGF-1) levels during SRL therapy in comparison with patients who did not normalize IGF-1 levels. Results: Normalization of IGF-1 levels during SRL treatment occurred in 62 patients (22.8%) and was similar for the 3 different types of SRL (P = .88). Surgical remission occurred in 59.6% of the patients. Patients who normalized IGF-1 levels during SRL treatment had a higher probability of surgical cure than patients without IGF-1 normalization (83.9% vs 52.4%, respectively; P < .001). Multivariate analysis confirmed that lack of cavernous sinus invasion, small maximum tumor diameter, and IGF-1 normalization during SRL therapy were the only factors independently associated with a favorable surgical outcome. Conclusions: Our study demonstrates that the normalization of IGF-1 levels during treatment with SRLs is an independent predictive factor of a favorable surgical outcome. The underlying mechanisms remain unclear, but an optimal response to medical therapy may be a characteristic of less aggressive tumors that are more likely to be entirely removed at surgery. (J Clin Endocrinol Metab 105: e3339–e3347, 2020)