MON-298 IGF-1 in the Early Post-operative Assessment of Acromegaly

Introduction: Transsphenoidal surgery is recommended as first line therapy in the vast majority of patients with acromegaly. Successful surgical intervention is determined by normalization of insulin like-growth factor (IGF) - 1 and adequate suppression of growth hormone (GH) during glucose GH suppression test or random GH levels <1.0 ng/mL. Given the long half-life of IGF-1, evolution of IGF-1 and GH assays and limitations of GH suppression test, clinicians remain reliant on IGF-1 results 3–6 months following surgery to assess disease remission following surgical intervention. This can lead to delayed treatment of patients with persistent disease and significantly increase patient anxiety. Aim: To determine if IGF-1 levels at 6 weeks were equally predictive of surgical outcomes when compared to IGF-1 levels at 3–6 months postoperative. Methods: Retrospective review of patients with newly diagnosed acromegaly who had surgery between 2010–2019 and had post-operative IGF-1 level measured at 6 weeks and 3–6 months. IGF-1 was measured using the Siemens Immulite assay until 2016 when it was replaced by a LC-MS/MS assay. IGF-1 measurements at 6 weeks are obtained based on clinician discretion. Results: 69 patients (mean age 49 ± 14.8, female 31/69, 44.9%) with acromegaly had surgery and IGF-1 follow-up measurements at 6 weeks and 3–6 months. Persistent acromegaly was noted in 45/69 at 3–6 months. The median IGF-1 pre-operative was 701 ng/ mL (289–1600), 6 weeks postoperative was 286 ng/ mL (109–1038) and at 3–6 months was 267 ng/ mL (77–996). The median pre-operative IGF-1 was significantly higher than the median IGF-1 level at 6 weeks and 3–6 months (P=<0.001). Although a statistically significant difference was seen between IGF-1 levels at 6 weeks and 3–6 months, the mean difference between these time points was small (20 ng/mL, P=<0.001). There was a greater percent reduction in IGF-1 at 6 weeks following surgery in those who had a normal IGF-1 at 3–6 months compared to those who did not (63% vs 35%, P=<0.01). Among patients who were deemed in remission at 3–6 months (24/69, 35%), 3/24 patients (all male with macroadenoma and no cavernous sinus invasion) had mildly elevated IGF-1 levels at 6 weeks (≤1.12 upper limit of normal) which subsequently normalized. In all of these patients, GH was <1 ng/mL post-op. In 1 male (macroadenoma and cavernous sinus invasion), IGF-1 levels increased from normal at 6 weeks to abnormal when measured at 3–6 months. Conclusion: In the vast majority of patients, 6 weeks post-operative IGF-1 can be used to assess response to surgery avoiding a delay in treatment. However, we would recommend repeating IGF-1 levels at 3–6 months in those who have marginally elevated IGF-1 above normal (≤ 1.12), without cavernous sinus invasion and a post-operative GH of <1 ng/mL prior to intervening if the IGF-1 is elevated 6 weeks as the IGF-1 may normalize.