Fig. 1

Summary of reported sources and effects of OPG in breast cancer. OPG is produced by bone cells, endothelial cells and breast tumor cells. OPG can exert tumor promoting effects on the primary breast tumor through blocking the action of TRAIL and through direct effects on tumor cells. OPG can promote growth of endothelial cells and tubule formation. OPG promotes formation of metastatic tumors at sites out with bone. OPG production in the bone microenvironment can block the bone destruction associated with growth of metastatic breast tumors