TNFSF11 and Ewing sarcoma: Receptor activator for nuclear factor-κB ligand-independent mechanisms of osteoclast formation also exist in which cytokines, such as tumour necrosis factor (TNF)-α, a known product of Ewing's sarcoma tumour cells (Rube et al, 2003), can substitute for RANKL and induce osteoclast formation from circulating precursors (Kudo et al, 2002).