In cancer‐induced osteolytic bone disease, as occurs in breast cancer metastasis and multiple myeloma, tumor cells stimulate osteoclastogenesis and bone resorption, primarily in a parathyroid‐related protein (PTHrP)/receptor activator of nuclear factor kappa‐Β ligand (RANKL)‐mediated manner. The gene discussed is TNFSF11; the disease is neoplasm.