Cathepsin D is synthesized as a 54 kDa precursor, which is proteolytically processed to an intermediate 44 kDa single chain, which matures into more stable 34 kDa and 14 kDa two chain form. It is an estrogen-regulated lysosomal protease that has been suggested to facilitate cancer cell migration and invasion by digesting the basement membrane, extracellular matrix, and xonnective tissue. Because of its mitogenic and proteolytic activities, it has been implicated as a prognostic marker in many tumor types. Cathepsin D is expressed in epithelial cells as well as in macrophages Synonyms: Cathepsin D, EC 3.4.23.5, CTSD, CPSD, CLN10, MGC2311