CYR61, also known as CCN1, is a matricellular signaling molecule that binds to a number of cell surface proteins thereby modulating a variety of signaling pathways. CYR61 is expressed in a variety of cells and is capable of regulating cell adhesion, migration, proliferation, differentiation, apoptosis, and senescence through interaction with cell surface integrin receptors and heparan sulfate proteoglycans. CYR61 performs critical functions during embryonic development, and in adulthood CYR61 plays important roles in inflammation and tissue repair. It is associated with diseases related to chronic inflammation. Deregulated expression and signaling of CYR61 is associated with a variety of tumors exhibiting both tumorigenic and tumor suppressor properties. When up-regulated it promotes tumorigenesis, angiogenesis, and metastasis in certain cancers and when down-regulated, it suppresses tumor growth in other cancers. Increased expression correlates with the progression and estrogen independence of human breast cancers. Full-length CYR61 protein contains 381 amino acids with an N-terminal secretory signal peptide followed by four structurally distinct domains (modules); the IGF binding protein (IGFBP) domain, the von Willebrand Factor C (VWFC) domain, the Thrombospondin type-I (TSP type-1) domain, and a C-terminal cysteine knot-like domain (CTCK).