Besides, a recent study found that BMP4 could induce transition of endothelial cells to OBs at PCa metastatic sites, and thus another possible mechanism whereby PSA promotes PCa osteoblastic bone metastasis could be inferred: PSA upregulates BMP4 expression and secretion of OBs, thereby facilitating endothelial-OB transition at PCa metastatic sites (37). The gene discussed is BMP4; the disease is posterior cortical atrophy.