Abstract Disclosure: H. Shin: None. Differential gene expression and pathway analysis in growth hormone-secreting pituitary tumors according to granulation pattern. Hye Ju Shin [1], Kyung Won Kim[2], Chan Woo Kang[2], Eun Jig Lee[2], Cheol Ryong Ku[2]. [1]Department of Clinical Drug Discovery & Development, Yonsei University College of Medicine, Seoul, Republic of Korea, [2]Endocrinology, Institute of Endocrine Research, Department of Internal Medicine, Yonsei University College of Medicine, Seoul, Republic of Korea Objective: The purpose of this research is to explain clinical variations in patients with acromegaly by exploring gene expression differences according to granulation patterns in growth hormone (GH)-secreting pituitary tumors. Materials & methods: Transcriptome analysis was conducted on 6 normal pituitary tissues and 15 GH-secreting pituitary tumors, including 9 densely granulated somatotroph tumors (DGSTs) and 6 sparsely granulated somatotroph tumors (SGSTs). Results: The median age at diagnosis was 50 years, with a predominance of female patients (60%). We identified 3111 differentially expressed genes (DEGs) in tumors compared to normal pituitaries, with 1117 DEGs unique to a specific granulation within tumors. SGST showed enriched the pathways involved in neuronal development (axon development, axonogenesis, axon guidance, synapse and presynapse organization, gliogenesis, glial cell differentiation, nerve development, synaptic membrane adhesion, semaphorin-plexin signaling pathway involved in neuron projection guidance) and acute inflammatory response. No pathways were significantly downregulated in SGST compared with those in DGST. Three signaling pathways (JAK-STAT, phosphatidylinositol 3-kinase, and MAP cascade) and three neuronal development processes (generation of neurons, nerve development, and neurogenesis) were significantly enriched in both GO and GSEA analysis. The PPI networks constructed with the up- and downregulated DEGs consisted of 128 and 132 PPI pairs, respectively. There were 10 hub proteins, top highly connected DEGs: ANLN, TLE3, TLE2, DMD, ADRA1A, RBFOX1, MMP2, LMO1, RUNX1T1, and NPPA. Conclusion: The results indicate that granulation-specific gene expression may underpin diverse clinical characteristics in acromegaly. Overall, this study emphasizes the potential for further investigation into these transcriptomic variations and their roles in disease pathology, particularly the involvement of genes linked to neuronal development, inflammatory response, and JAK-STAT signaling in SGST. Presentation: 6/3/2024