Tumor Volume of Growth Hormone-Secreting Pituitary Adenomas during Treatment with Pegvisomant: A Prospective Multicenter Study

Context: Clinical and biochemical remission in acromegaly can frequently be achieved with the recombinant GH receptor antagonist pegvisomant, even when other treatments fail. However, increases in tumor volume have been reported. Objective: Because previous studies suffer from inhomogenous magnetic resonance imaging (MRI) protocols, this prospective study examined the long-term course of adenoma volume during pegvisomant therapy by standardized MRI. Design: Five centers in Germany participated. High-resolution MRI was performed at baseline and 6, 12, and 24 months after enrollment. Setting/Patients: Patients were outpatients, and pegvisomant is third-line therapy in most of the cases. Main Outcome Measures: The primary end point was tumor volume at 24 month follow-up, measured by a single, double-blinded rater. Results: Forty-five of 61 patients completed 24 months' follow-up (73.8%). Tumor volume increase greater than 25% during the study was observed in three of 61 patients (4.9%), all during the first year of enrollment. All three patients had had octreotide treatment before initiation of pegvisomant; none of them had had radiotherapy. All volumetric findings were comparable with clinical radiological interpretations. ANOVA revealed no significant change in tumor volume after 24 months (n = 45). Conclusions: This study shows that pegvisomant therapy infrequently coincides with tumor growth during long-term treatment of acromegaly. Because all significant tumor volume increases occurred during the first year, these changes might correlate to the change of medication and thus be the result of a rebound from somatostatin-induced shrinkage. (J Clin Endocrinol Metab 95: 552-558, 2010)