Decorin, also known as PG40 and DCN, is a member of the class I family of small leucine-rich proteoglycans (SLRPs) that is expressed in the stroma of various forms of cancer and has been recently proposed to act as a guardian from the matrix. Mature human Decorin contains 12 tandem LRR and shares 80% and 78% aa sequence identity with mouse and rat Decorin, respectively. Decorin embraces numerous functions including: regulation of collagen fibrillogenesis, hepatic carcinogenesis, fetal membrane and calcium homeostasis, keratinocyte function, and suppression of angiogenesis. Most recently, soluble decorin has been shown to induce autophagy in endothelial cells and mitophagy in breast carcinoma cells.