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). This evidence concerns the gene TNF and Ewing sarcoma.