TNFSF11 and neoplasm: Focusing on bone metastasis, there is a vicious cycle between bone resorption and tumor proliferation in which osteoprotegerin (OPG), receptor (R) activator of nuclear factor kappa B (RANK), RANK ligand (RANKL) and tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) play a pivotal role [8-10].