SPARC, also known as ON (Osteonectin) or BM-40 (Basement-membrane protein 40), is an extracellular glycoprotein with the calculated molecular mass of 35 kDa and the apparent molecular mass of 40-43 kDa and 50 kDa (PMID: 7495300, 12365801). SPARC belongs to a group of matricellular proteins defined as secreted components that do not contribute directly to the formation of structural elements but serve to modulate cell-matrix interactions and cellular functions (PMID: 7542656; 12231357). SPARC is expressed at high levels in bone tissue, is distributed widely in many other tissues and cell types, and is associated generally with tissues undergoing morphogenesis, remodeling and wound repair (PMID: 10567433). It elicits changes in cell shape, inhibits cell-cycle progression, and influences the synthesis of extracellular matrix (PMID: 12721366). Altered expression of SPARC has been reported in a variety of cancers, which include breast, ovarian, colorectal, and pancreatic cancer as well as melanoma and glioblastomas (PMID: 18849185).