Bone-derived RANK-L and several tumour-derived factors including parathyroid hormone related-protein, interleukins 6, 8, and 11, and prostaglandins are involved in the development of breast cancer osteolytic lesions by promoting both osteoclastogenesis and osteoclast activity (Guise et al, 2005; Yin et al, 2005). The gene discussed is TNFSF11; the disease is breast cancer.