DENOSUMAB BINDS TO RANKL, A TRANSMEMBRANE OR SOLUBLE PROTEIN ESSENTIAL FOR THE FORMATION, FUNCTION, AND SURVIVAL OF OSTEOCLASTS, THE CELLS RESPONSIBLE FOR BONE RESORPTION. INCREASED OSTEOCLAST ACTIVITY, STIMULATED BY RANKL, IS A MEDIATOR OF BONE PATHOLOGY IN SOLID TUMORS WITH OSSEOUS METASTASES. SIMILARLY, GIANT CELL TUMORS OF BONE CONSIST OF STROMAL CELLS EXPRESSING RANKL AND OSTEOCLAST-LIKE GIANT CELLS EXPRESSING RANK RECEPTOR, AND SIGNALING THROUGH THE RANK RECEPTOR CONTRIBUTES TO OSTEOLYSIS AND TUMOR GROWTH. DENOSUMAB PREVENTS RANKL FROM ACTIVATING ITS RECEPTOR, RANK, ON THE SURFACE OF OSTEOCLASTS, THEIR PRECURSORS, AND OSTEOCLAST-LIKE GIANT CELLS.