IGF1 and prostate carcinoma: Furthermore, prostate cancer cells express the serine proteases kallikrein and urokinase-type plasminogen activator (u-PH) which are mitogenic for osteoblasts; express the prostate-specific antigen (PSA), another serine protease, which has the capacity to stimulate osteoblast activating factors, IGF-1 and TGF-β; and also express the vasoactive peptide endothelin-1 (ET-1) that is a potent vasoconstrictor, but can also induce osteoblast growth [8,20,25,29,31,37].