TNFSF11 and bone giant cell tumor: Although the low level of RANKL expression by Ewing's sarcoma-derived fibroblasts raises the question of how significant is the contribution of this RANKL-mediated mechanism, fibroblasts and bone stromal cells have been shown to play a similar role in inducing osteoclast formation in other bone tumours, such as giant cell tumour of bone and Paget's sarcoma, as well as in tumours known to metastasise to bone, such as melanoma and neuroblastoma (Michigami et al, 2001; Lau et al, 2005; Lau et al, 2006; Sun et al, 2006).