CTSK and breast cancer: Among genes encoded for secreted proteins over-expressed in fibroblasts of human basal cell carcinoma [14], genes including CTSK (cathepsin K), SFRP2 (secreted frizzled-related protein 2), PDGFRL (platelet-derived growth factor receptor-like protein), and DCN (decorin) were shown to be up-regulated in non-epithelial cells of breast cancer [16].