Secreted protein acidic and rich in cysteine (SPARC), also named as osteonectin or BM-40, is an acronym for “secreted protein, acidic and rich in cysteine”. It is encoded by the SPARC gene in humans. The protein is a glycoprotein of 40 kDa, (303 amino acid residues) and consists of 17 a.a. signal sequence, an N-terminal acidic region that binds calcium, a follistatin domain containing Kazal-like sequences, and a C-terminal extracellular calcium (EC) binding domain with two EF-hand motifs. SPARC is the founding member of a family of secreted matricellular proteins with similar domain structure. It is produced by fibroblasts, capillary endothelial cells, platelets and macrophages, especially in areas of tissue morphogenesis and remodeling. SPARC is required for the collagen in bone to become calcified but is also involved in extracellular matrix synthesis and promotion of changes to cell shape. The gene product has been associated with tumor suppression but has also been correlated with metastasis based on changes to cell shape which can promote tumor cell invasion.