Prostate cancer cells secrete BMP1, IGF, PDGF, vascular endothelial growth factor (VEGF), endothelin 1 (EDN1), plasminogen activator urokinase (PLAU) and kallikrein-related peptidase 3 (KLK3; also known as PSA), which regulate osteoblast proliferation or differentiation [56, 58]. Here, KLK3 is linked to prostate cancer.