Tumour necrosis factor-α has been shown to play a role in inducing osteoclast differentiation from marrow-derived circulating monocyte precursors and inflammatory macrophages (Kudo et al, 2002; Sabokbar et al, 2003), and we found that the addition of TNF-α (with M-CSF) to cultures of Ewing's sarcoma-derived TAMs induced osteoclast formation in the absence of RANKL. The gene discussed is CSF1; the disease is Ewing sarcoma.