TNFSF11 and neoplasm: In addition to their function in suppressing the activity of T-cell cytotoxicity, which in part may also be due to secretion of TGF-β [188,189,190,191], Tregs also secrete high levels of RANKL which facilitate the tumor-induced process of osteoclast activation, and promotes a favorable pre-metastatic niche in bone by inducing osteolysis and release of bone matrix bound growth factors prior to tumor cell arrival [192,193].