Cartilage oligomeric matrix protein (COMP) is also known as Thrombospondin-5 (TSP5), EDM1, EPD1, MED, PSACH, THBS5, which belongs to the thrombospondin family. COMP / TSP5 contains 4 EGF-like domains, 1 TSP C-terminal (TSPC) domain, 8 TSP type-3 repeats. Abundantly expressed in the chondrocyte extracellular matrix, and is also found in bone, tendon, ligament and synovium and blood vessels. COMP may play a role in the structural integrity of cartilage via its interaction with other extracellular matrix proteins such as the collagens and fibronectin. COMP can mediate the interaction of chondrocytes with the cartilage extracellular matrix through interaction with cell surface integrin receptors. Thrombospondin-5 could play a role in the pathogenesis of osteoarthritis. COMP is a marker of cartilage turnover.