Decorin (DCN) is a proteoglycan with critical roles in extracellular matrix (ECM) organization and tissue homeostasis. As a small leucine-rich repeat proteoglycan 1, decorin serves as an ECM structural component conferring compression resistance and regulating fibril formation. DCN is highly expressed in mesenchymal tissues including aorta, lung, skin, kidney, and smooth muscle, but not in endothelial or epithelial cells 2. Beyond structural functions, decorin modulates cellular signaling pathways including negative regulation of angiogenesis and vascular endothelial growth factor (VEGF) signaling 3. Notably, decorin expression is downregulated in lung adenocarcinoma and inversely correlates with vasculogenic mimicry formation and tumor aggressiveness; reduced DCN levels promote cancer cell migration and invasion through VEGF/TGF-β signaling 3. In cardiac pathology, circulating decorin levels are significantly elevated in wild-type transthyretin amyloidosis (ATTRwt-CM) compared to HFpEF/HFmrEF, with DCN serving as a potential diagnostic biomarker (AUC 0.74) for disease differentiation 4. Additionally, decorin-expressing fibro-adipogenic progenitors are enriched in aggressive, chemotherapy-resistant carcinomas 5. Mutations in DCN cause congenital stromal corneal dystrophy, highlighting its importance in corneal tissue integrity.