Abstract Disclosed are Cystatin C (CysC) homologues, including CystC homologues that act as antagonists or inhibitors of transforming growth factor-p(TGF- P). Also disclosed are methods to identify CystC homologues that are antagonists or inhibitors of TGF- and compositions and therapeutic methods using CystC and homologues thereof to regulate the activity of TGF-, and TGF- mediated tumor malignancy and invasion and other TGF-P mediated fibrotic or proliferative conditions and diseases.
