CTSD and breast cancer: Overexpression of RAB27A has been shown to enhance tumor invasion and metastasis in breast cancer cell lines through secretion of insulin-like factor-II (IGF-II), which in turn modulates many important tumor progression markers including p16, vascular endothelial growth factor, cathepsin D, cyclin D1, matrix metalloproteinase-9, and urokinase-type plasminogen activator [25].