Rabbit Anti-Human SPARC monoclonal antibody for IHC-P, WB. Secreted protein acidic and rich in cysteine (SPARC) , also known as osteonectin (ON) , or basement-membrane protein 40 (BM-40) , is a glycoprotein expressed in osteoblasts, endothelial cells, antigen presenting cells, stromal fibroblasts, spermatocytes, steroid-producing cells of the adrenal glands, and glomeruli of the kidney. It is up-regulated in many solid tumors such as astrocytoma, glioma, and osteosarcomas, and the stroma of many solid tumors from colon, lung, breast, and pancreas.