Role of cystatins in tumor neovascularization.

Cystatins form a large superfamily of proteins with diverse biologic activities. All members of the cystatin superfamily share the presence of one, two or three cystatin domains. Cystatins were initially believed to act mainly as inhibitors of lysosomal cysteine proteases. In recent years, however, there has been increased awareness of additional or alternate biologic functions for these proteins. In this review, the authors will discuss the most recent findings and hypotheses that suggest that some members of the cystatin superfamily may play important roles during tumor progression. Special emphasis is given to their potential role as novel anti-angiogenic agents.