Abstract
Background: In clinical practice, most patients responding to injectable somatostatin receptor ligands exhibit IGF-I variability around the upper limit of normal (ULN) during long-term follow up. These fluctuations are thought to result from various factors such as assay variability, nutrition, comorbid conditions, concomitant medications and other unknown factors. The magnitude of this variability, and the factors affecting it, is not well understood in patients with acromegaly treated with injectable SRLs. Methods: IGF-I levels of patients responding to and stably treated with injectable SRLs were measured over time in the CHIASMA OPTIMAL phase III study. Two time periods were assessed - Period 1, three assessments during screening phase before randomization to octreotide capsules (N=56), and Period 2 - multiple assessments up to week 36, in patients rescued with SRL injections for at least 12 weeks (N=21). The time from the last injection to each of the 3 assessments in period 1 [Screening visits 1 and 2 (SV1 & SV2), and Baseline (BL)], was on average 6.8 ± 10.7 (SD), 15.8 ± 2.7, and 29.0 ± 1.8 days respectively. Correlation with various demographics and Baseline characteristics, including age, gender, weight, BMI and residual tumor size to IGF-I variability was assessed. Percent change for each individual patient from Minimal to Maximal IGF-I values within each period was computed and the overall population mean was calculated (lowest value was used as the denominator and all other values were expression as a positive % above this value). Results: The overall mean within-patient percent change of IGF-I levels during Period 1 was 20.48 ± 15.56 (range: 0.6-81). Mean IGF-I levels for SV1, SV2 and BL were 0.78 ± 0.18, 0.79 ± 0.18, and 0.85 ± 0.22 x ULN respectively. The overall increase in mean IGF-I levels from SV1 to BL (longest time interval) was statistically significant (p=0.0002; paired T-test). Analysis of IGF-I levels in patients during Period 2, revealed that the overall mean within-patient percent change of IGF-I levels was 15.27 ± 12.20 (range: 0-41.5). The mean duration of follow up during this period, after patients were already treated for ≥12 weeks with injectable SRL, was 1.72 (± 1.29) months. The variability observed in Period 2 was similar to that observed in the entire sample evaluated in Period 1. No significant differences were found in the mean IGF-I percent change between any demographic or baseline characteristic subgroup examined. Conclusion: IGF-I levels fluctuate in patients with acromegaly who are responsive to injectable SRLs. These fluctuations are wide and can be up to 81% higher than the lowest (most controlled) value, with an average increase of approximately 20%. Significant IGF-I increases were observed at the end of the long acting SRL injection interval.
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The future of somatostatin receptor ligands in acromegaly