CTSD and breast neoplasm: Despite the fact that Cathepsin-D plays a critical role in a non-specific protein degradation in a markedly acidic environment of lysosomes, overexpression of Cathepsin-D in breast tumors is associated with the increased metastatic potential and the poor survival rate, in part by facilitaing cancer cell proliferation, fibroblast outgrowth, angiogenesis and metastasis.