Human Cystatin A (CSTA) is a member of family 1 of the cystatin superfamily, which is characterized by lacking of disulphide bonds an carbohydrates. Cystatin A is an intracellular inhibitor regulating the activities of cysteine proteases of the papain family such as Cathepsins B, H and L. Cystatin A is also implicated in a number of disease states. Due to altered proteolytic state in cancer progression, Cystatin A may play a role in the proteolytic pathways.