Cathepsin D (CTSD), a well known lysosomal aspartyl protease and belongs to the peptidase C1 family. It is expressed in most cells and overexpressed in breast cancer cells. It is a major enzyme in protein degradation in lysosomes, and also involved in the presentation of antigenic peptides. cathepsin D is essential for proteolysis of proteins regulating cell growth and tissue homeostasis. CTSD secreted from human prostate carcinoma cells are responsible for the generation of angiostatin, a potent endogenous inhibitor of angiogenesis, suggesting its contribution to the prevention of tumor growth and angiogenesis-dependent growth of metastases.