Bone biology and the role of the RANK ligand pathway.

Bone biology and the molecular basis of normal bone remodeling are important for understanding bone health, particularly for medical professionals who are treating patients with skeletal complications. Key factors in bone remodeling include RANK ligand, which stimulates bone resorption, and osteoprotegerin (OPG), which inhibits bone resorption. The ratio between these two factors regulates osteoclast formation and activity. An imbalance in the expression of RANK ligand and OPG is an underlying mechanism in cancer treatment-induced bone loss, in bone metastasis in patients with solid tumors, and in osteolysis in patients with multiple myeloma. In cancer-induced bone disease, for example, RANK ligand overwhelms the effects of OPG, leading to imbalanced bone remodeling and the "vicious cycle" of metastatic disease. Experimental therapeutics that target RANK ligand are increasingly being studied and have shown promise for decreasing tumor-related bone disease.