Long-term treatment of acromegalic patients resistant to somatostatin analogues with the GH receptor antagonist pegvisomant: its efficacy in relation to gender and previous radiotherapy

Context: Pegvisomant is an effective treatment for somatostatin analogue-resistant acromegaly, but the determinants defining the response to this treatment are largely unknown. Objective: To investigate the efficacy of pegvisomant treatment in resistant acromegalic patients (e.g. serum IGF1 at least 1.25 x upper normal limit) in a clinical setting and the factors conditioning this response. Design and setting: A retrospective cross-sectional study performed in six Spanish University hospitals from 2004 to 2007. Patients: Forty-four acromegalic patients (61.4% female, mean age: 49 +/- 14). 95% of whom had undergone pituitary surgery and 61% having received pituitary radiotherapy. The mean follow-up was 22.7 +/- 11.2 months. Main outcome measures: IGF1 levels reflected treatment efficacy, and the influence of gender, age, weight, previous radiotherapy and duration of treatment was assessed. Results: IGF1 normalisation was achieved in 84% of the patients. Male gender (P < 0.05), previous irradiation (P < 0.05) and the treatment duration (r = 0.364. P < 0.02) were associated with a better response to pegvisomant therapy, There was a significant decrease in HbA1c (P < 0.001) and in the mean insulin dose (P < 0.01) in acromegalic diabetic patients. Although 25% of patients experienced mild adverse events, pegvisomant was only withdrawn in four patients due to side effects (two cases of tumour growth, one liver dysfunction and one headache). Conclusions: Long-term pegvisomant is a very effective therapy in resistant acromegaly. Male gender and prior radiotherapy influence the therapeutic response rate.