TNFSF11 and cancer: Receptor activator of NF-κB ligand (TNFSF11, also known as RANKL) and its tumor necrosis factor (TNF)-family receptor RANK are essential regulators of osteoclast differentiation and thereby fundamental aspects of bone physiology, bone remodeling,13, 14 lymph node formation,15 establishment of thymic microenvironment,16 mammary gland development during pregnancy17, 18 and bone metastasis of cancer.19 Osteoprotegerin (OPG) is a decoy receptor for RANKL.