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Long-term GH blocker safe, effective in acromegaly

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October 30, 2018

An analysis of 12 years of real-world patient data suggests that the growth hormone blocker pegvisomant is a safe and effective treatment for acromegaly, with a low occurrence of pituitary tumor enlargement and no reports of treatment-related liver failure, according to findings published in the European Journal of Endocrinology.

Pegvisomant (Somavert, Pfizer), a pegylated GH analogue, enhances affinity for the GH receptor and prevents functional GH-receptor signaling, Michael Buchfelder, MD, PhD, professor in the department of neurosurgery at the University of Erlangen-Nurnberg, Germany, and colleagues wrote in the study background. Initial studies in approximately 200 patients suggested that the therapy was effective in relief of symptoms and normalization of insulin-like growth factor I levels in up to 97% of patients; however, researchers initiated the ACROSTUDY in 2004 to investigate the long-term effects of the drug in a real-world, international cohort.

Buchfelder and colleagues analyzed data from 2,090 patients with acromegaly from 14 European countries and the United States enrolled in the ACROSTUDY as of May 12, 2016, including descriptive analyses of safety, pituitary imaging and outcomes with pegvisomant therapy for up to 12 years (49% women; 93% white; mean follow-up time, 6.3 years; mean pegvisomant treatment duration, 7.6 years). Mean age at diagnosis of acromegaly was 42 years, and the mean age at start of pegvisomant therapy was 50 years, with men slightly younger at diagnosis vs. women (mean, 41 years vs. 43 years). Within the cohort, 466 (22.3%) were still ongoing participants at the time of data freeze, and 1,624 had concluded their participation or died (n = 78). Researchers assessed laboratory data for 2,080 patients and pituitary imaging data for 2,045 patients. Before initiating pegvisomant therapy, 96% of patients reported undergoing surgery, radiation, medical therapy or a combination of the three interventions.

Researchers found that, over 10 years, the percentage of patients with normal IGF-I levels increased from 53% in year 1 to 73% at year 10, corresponding with an average pegvisomant daily dose increase from 12.8 mg in year 1 to 18.9 mg in year 10. There were 570 treatment-related adverse events in 337 patients (16.1%), with the most common being liver test elevations (n = 71) and injection-site conditions (n = 71), followed by gastrointestinal disorders (n = 26), asthenia (n = 9), pituitary tumor recurrence (n = 9), headache (n = 7) and fatigue (n = 6).

Most patients (72.2%) experienced no change in tumor size relative to a prior scan, whereas 16.8% experienced a decrease, 6.8% experienced an increase and 4.3% experienced both, according to researchers.

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Among the 1,094 patients with normal baseline liver function tests, 62% continued to have normal values during follow-up. Among the 89 participants entering the study with mildly elevated liver function values, 30 (34%) shifted to normal liver function levels during follow-up.

“This second interim analysis, after more than a decade of ACROSTUDY enrollment, performed on 2,090 patients, confirms that long-term use of [pegvisomant] can be an effective and safe treatment in patients with acromegaly,” the researchers wrote. “The low occurrence of pituitary tumor enlargement, new liver test elevations and site administration reactions was reassuring.”

The researchers noted that the larger number of ACROSTUDY participants, including those who may not have been eligible for enrollment in clinical trials, and the longer duration of follow-up, allowed a better understanding of the safety profile of the drug. – by Regina Schaffer

Disclosures: Pfizer sponsored this study. Five of the authors report they are employees of Pfizer.

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