Several molecules that are produced by breast cancer—e.g., parathyroid hormone-related protein, interleukins (IL-6, IL-8 and IL-11), cytokines (macrophage stimulating factor (M_CSF)) and prostaglandins—stimulate osteoclast active through the activation of the receptor activator of nuclear factor kB ligand (RANKL)/RANK pathway, which is the primary mediator of osteoclast-mediated bone resorption [5,6]. The gene discussed is TNFSF11; the disease is breast cancer.