Maspin (mammary serine protease inhibitor) is a non-inhibitory serpin that is expressed predominantly in normal mammary epithelial cells but at significantly reduced levels or absent in most breast carcinomas. It has the ability to block the growth, invasiveness, and metastatic potential of breast and lung tumors. This anti-tumor activity is achieved, in part, by the ability of Maspin to inhibit angiogenesis and to preferentially promote apoptosis of tumor cells. Recombinant human Maspin is a 42.1 kDa non-glycosylated protein containing 375 amino acid residues.