SAT-074 Comparative Evaluation Of CGRP Expression In Pituitary Adenomas: Could It Be Linked To Clinical Course And Treatment Response In Acromegaly?

Abstract Disclosure: A. Pekmezci: None. S. Cil: None. H. Karatay: None. F.M. Dogukan: None. S. Burhan: None. M.S. Cil: None. E. Cetin: None. M. Niyazoglu: None. E. Hatipoglu: None. Background and Objective: Calcitonin gene-related peptide (CGRP) is a potent vasodilator and neuropeptide involved in neurogenic inflammation, vascular regulation, and pain mechanisms—particularly in headache—with potential relevance to endocrine and neurological processes. This study aimed to investigate CGRP expression in patients with acromegaly through immunohistochemistry and its associations with tumor features, treatment response, and symptoms. Methods: This prospective study included 49 patients followed at our center between January and October 2024: 30 with acromegaly and 19 with nonfunctioning pituitary adenomas (NFPAs). Tumor samples were evaluated for CGRP using a polyclonal anti-CGRP antibody (GeneTex, 1:100). Inclusion criteria were age 18-70, confirmed diagnosis, and informed consent; exclusion was pregnancy or no consent. Demographic and clinical data, headache status at diagnosis and follow-up (as reported by patients), radiological invasion (KNOSP/Hardy), residual tumor, and remission were recorded. Histopathology included hormone staining (GH, PRL), estrogen receptor, granularity, transcription factors (PIT-1, SF-1), Ki-67, and mitotic count. Evaluations were conducted by experienced specialists. Results: The mean age of patients with acromegaly was significantly lower than that of patients with NFPA (42.1 ± 9.6 vs. 53.1 ± 11.5 years, p=0.001). Headache prevalence at presentation was similar (63.3% vs. 63.2%, p=0.9), but chronic headache tended to be more frequent in acromegaly (26.7% vs. 10.5%, p=0.2). Hardy grade 3–4 tumors were more common in NFPAs (68.4% vs. 30.0%, p=0.008), while KNOSP grade, Ki-67, and residual tumor rates did not differ. CGRP was found in 50% of acromegaly tumors, absent in NFPAs (p<0.001). Chronic headache was more common in CGRP-positive patients (40% vs. 13%, p=0.09). Although not significant, surgical remission was higher in CGRP-negative patients (86.7%, p=0.09). Median Ki-67 index tended to be lower in CGRP-positive tumors (1.5 [IQR: 1–2.25] vs. 3 [IQR: 1–4], p=0.1), but this difference was not statistically significant. PIT-1/SF-1 co-expression occurred only in CGRP-positive tumors (20% vs. 0%, p=0.07). CGRP expression was not significantly associated with tumor size, invasion, need for surgery, residual tumor, treatment resistance, GH/PRL expression, or granularity. Conclusion: CGRP expression was found in 50% of acromegaly tumors and was completely absent in NFPAs. Although CGRP-negative tumors tended to have higher Ki-67 indices, postoperative remission rates were higher in this group. While CGRP expression was not significantly associated with chronic headache, patients with CGRP-positive tumors exhibited a higher frequency of persistent headache, suggesting a potential link between CGRP and symptom persistence in acromegaly. Presentation: Saturday, July 12, 2025