Breast cancer cells secrete recombinant mouse receptor activator of nuclear factor-κB ligand (RANKL) to facilitate osteoclast formation.16 Both bone marrow-derived monocytes (BMMs) stimulated with RANKL (Figure 2A) and human peripheral blood mononucleated cells (hPBMCs) stimulated with conditioned medium (CM) from MDA-MB-231 human breast cancer cells (Figure 2B) were able to develop significant, multinucleated osteoclasts. The gene discussed is TNFSF11; the disease is breast cancer.